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6 INTEGRATED HEALTH EFFECTS OF SHORT-TERM 

OZONE EXPOSURE 

6.1 Introduction

1 This chapter reviews, summarizes, and integrates the evidence for various health 

2 outcomes associated with short-term (i.e., hours, days, or weeks) exposures to O3. 

3 Numerous controlled human exposure, epidemiologic, and toxicological studies have 

4 permitted evaluation of the relationships between short-term O3 exposure and a range of 

5 endpoints related to respiratory effects (Section 6.2), cardiovascular effects (Section 6.3), 

6 and mortality (Section 6.2, Section 6.3, and Section 6.6). A smaller number of studies 

7 were available to assess the effects of O3 exposure on other physiological systems such as 

8 the central nervous system (Section 6.4), liver and metabolism (Section 6.5.1), and 

9 cutaneous and ocular tissues (Section 6.5.2). This chapter evaluates the majority of recent 

10 (i.e., published since the completion of the 2006 O3 AQCD) short-term exposure studies; 

11 however, those for birth outcomes and infant mortality are evaluated in Chapter 7

12 (Section 7.4), because they compare associations among overlapping short- and long13 term exposure windows that are difficult to distinguish. 

14 Within each individual section of this chapter, a brief summary of conclusions from the 

15 2006 O3 AQCD is included along with an evaluation of recent evidence that is intended 

16 to build upon the body of evidence from previous reviews. The studies evaluated are 

17 organized by health endpoint (e.g., lung function, pulmonary inflammation) then by 

18 scientific discipline (e.g., controlled human exposure, epidemiology, and toxicology). 

19 Each major section (e.g., respiratory, cardiovascular, mortality) concludes with an 

20 integrated summary of the findings and a conclusion regarding causality based upon the 

21 framework described in the Preamble to this ISA. The causal determinations are 

22 presented for a broad health effect category, such as respiratory effects, with coherence 

23 and plausibility based on the total evidence available across disciplines and across the 

24 suite of related health endpoints, including cause-specific mortality. 

6.2 Respiratory Effects

25 Based on evidence integrated across controlled human exposure, epidemiologic, and 

26 toxicological studies, the 2006 O3 AQCD concluded “that acute O3 exposure is causally 

27 associated with respiratory system effects” (U.S. EPA, 2006b). Contributing to this 

28 conclusion were the consistency and coherence across scientific disciplines for the effects 
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1 of short-term O3 exposure on a variety of respiratory outcomes including “pulmonary 

2 function decrements, respiratory symptoms, lung inflammation, and increased lung 

3 permeability, airway hyperresponsiveness.” Collectively, these findings provided 

4 biological plausibility for associations in epidemiologic studies observed between short5 term increases in ambient O3 concentration and increases in respiratory symptoms and 

6 respiratory-related hospitalizations and emergency department (ED) visits.

7 Controlled human exposure studies have provided strong and quantifiable exposure8 response data on the human health effects of O3. The most salient observations from 

9 studies reviewed in the 1996 and 2006 O3 AQCDs (U.S. EPA, 2006b, 1996a) included: 

10 (1) young healthy adults exposed to O3 concentrations ≥ 80 ppb develop significant 

11 reversible, transient decrements in pulmonary function and symptoms of breathing 

discomfort if minute ventilation (V̇ 12 E) or duration of exposure is increased sufficiently; 

13 (2) relative to young adults, children experience similar spirometric responses but lower 

14 incidence of symptoms from O3 exposure; (3) relative to young adults, O3-induced 

15 spirometric responses are decreased in older individuals; (4) there is a large degree of 

16 intersubject variability in physiologic and symptomatic responses to O3, but responses 

17 tend to be reproducible within a given individual over a period of several months; (5) 

18 subjects exposed repeatedly to O3 for several days experience an attenuation of 

19 spirometric and symptomatic responses on successive exposures, which is lost after about 

20 a week without exposure; and (6) acute O3 exposure initiates an inflammatory response 

21 that may persist for at least 18 to 24 hours postexposure.

22 Substantial evidence for biologically plausible O3-induced respiratory morbidity has been 

23 derived from the coherence between toxicological and controlled human exposure study 

24 findings for parallel endpoints. For example, O3-induced lung function decrements and 

25 increased airway hyperresponsiveness have been observed in both animals and humans. 

26 Airway hyperresponsiveness could be an important consequence of exposure to ambient 

27 O3 because the airways are then predisposed to narrowing upon inhalation of a variety of 

28 ambient stimuli. Additional airway hyperresponsiveness tends to resolve more slowly and 

29 appears less subject to attenuation with repeated exposures than lung function 

30 decrements. Increased permeability and inflammation have been observed in the airways 

31 of humans and animals alike after O3 exposure, although these processes are not 

32 necessarily associated with immediate changes in lung function or hyperresponsiveness. 

33 Furthermore, the potential relationship between repetitive bouts of acute inflammation 

34 and the development of chronic respiratory disease is unknown. Another feature of 

35 O3-related respiratory morbidity is impaired host defense and reduced resistance to lung 

36 infection, which has been strongly supported by toxicological evidence and, to a limited 

37 extent, by evidence from controlled human exposure studies. Recurrent respiratory 

38 infection in early life is associated with increased incidence of asthma in humans.
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1 In concordance with experimental studies, epidemiologic studies have provided clear 

2 evidence for decrements in lung function related to short-term ambient O3 exposure. 

3 These effects were demonstrated in healthy children attending camps, adults exercising or 

4 working outdoors, and children with and without asthma (U.S. EPA, 2006b, 1996a). In 

5 addition to lung function decrements, short-term increases in ambient O3 concentration 

6 were associated with increases in respiratory symptoms (e.g., cough, wheeze, shortness of 

7 breath), notably in large U.S. panel studies of children with asthma (Gent et al., 2003; 

8 Mortimer et al., 2000). The evidence across disciplines for O3 effects on a range of 

9 respiratory endpoints collectively provides support for epidemiologic studies that have 

10 demonstrated consistent associations between short-term increases in ambient O3

11 concentration and increases in respiratory hospital admissions and ED visits, specifically 

12 during the summer or warm months. In contrast with other respiratory health endpoints, 

13 epidemiologic evidence did not clearly support a relationship between short-term O3

14 exposure and respiratory mortality. Although O3 was consistently associated with 

15 nonaccidental and cardiopulmonary mortality, the contribution of respiratory causes to 

16 these findings was uncertain as the few studies that examined mortality specifically from 

17 respiratory causes reported inconsistent associations with ambient O3 concentrations. 

18 As will be discussed throughout this section, consistent with the strong body of evidence 

19 presented in the 2006 O3 AQCD, recent studies continue to support associations between 

20 short-term O3 exposure and respiratory effects, in particular, lung function decrements in 

21 controlled human exposure studies, airway inflammatory responses in toxicological 

22 studies, and respiratory-related hospitalizations and ED visits. Recent epidemiologic 

23 studies contribute new evidence for potentially at-risk populations and associations 

24 linking ambient O3 concentrations with biological markers of airway inflammation and 

25 oxidative stress, which is consistent with the extensive evidence from controlled human 

26 exposure and toxicological studies. Furthermore, extending the potential range of 

27 well-established O3-associated respiratory effects, recent multicity studies and a 

28 multicontinent study demonstrate associations between short-term increases in ambient 

29 O3 concentration and respiratory-related mortality.

6.2.1 Lung Function

6.2.1.1 Controlled Human Exposure

30 This section focuses on studies examining O3 effects on lung function and respiratory 

31 symptoms in volunteers exposed, for periods of up to 8 hours, to O3 concentrations 

32 ranging from 40 to 500 ppb, while at rest or during exercise of varying intensity. 
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1 Responses to acute O3 exposures in the range of ambient concentrations include

2 decreased inspiratory capacity; mild bronchoconstriction; rapid, shallow breathing 

3 patterns during exercise; and symptoms of cough and pain on deep inspiration (PDI). 

4 Reflex inhibition of inspiration results in a decrease in forced vital capacity (FVC) and 

5 total lung capacity (TLC) and, in combination with mild bronchoconstriction, contributes 

6 to a decrease in the forced expiratory volume in 1 second (FEV1). 

7 In studies that have exposed subjects during exercise, the majority of shorter duration 

8 (≤ 4-hour exposures) studies utilized an intermittent exercise protocol in which subjects 

9 rotated between 15-minute periods of exercise and rest. A limited number of 1- to 2-hour 

10 studies, mainly focusing on exercise performance, have utilized a continuous exercise 

11 regime. A quasi continuous exercise protocol is common to prolonged exposure studies 

12 where subjects complete 50-minute periods of exercise followed by 10-minute rest 

13 periods. 

14 The majority of controlled human exposure studies have been conducted within exposure 

15 chambers, although a smaller number of studies used a facemask to expose subjects to 

16 O3. Little effort has been made herein to differentiate between facemask and chamber 

17 exposures since FEV1 and respiratory symptom responses appear minimally affected by 

18 these exposure modalities. Similar responses between facemask and chamber exposures 

19 have been reported for exposures to 80 and 120 ppb O3 (6.6-hour, moderate quasi 

20 continuous exercise, 40 L/min) and 300 ppb O3 (2 h, heavy intermittent exercise, 70 

21 L/min) (Adams, 2003a, b, 2002). 

22 The majority of controlled human exposure studies investigating the effects O3 are of a 

23 randomized, controlled, crossover design in which subjects were exposed, without 

24 knowledge of the exposure condition and in random order to clean filtered air (FA; the 

25 control) and, depending on the study, to one or more O3 concentrations. The FA control 

26 exposure provides an unbiased estimate of the effects of the experimental procedures on 

27 the outcome(s) of interest. Comparison of responses following this FA exposure to those 

28 following an O3 exposure allows for estimation of the effects of O3 itself on an outcome 

29 measurement while controlling for independent effects of the experimental procedures. 

30 As individuals may experience small changes in various health endpoints from exercise, 

31 diurnal variation, or other effects in addition to those of O3 during the course of an 

32 exposure, the term “O3-induced” is used herein to designate effects that have been 

33 corrected or adjusted for such extraneous responses as measured during FA exposures. 

34 Spirometry, viz., FEV1, is a common health endpoint used to assess effects of O3 on 

35 respiratory health in controlled human exposure studies. In considering 6.6-hour 

36 exposures to FA, group mean FEV1 changes have ranged from -0.7% (McDonnell et al., 

37 1991) to 2.7% (Adams, 2006a). On average, across ten 6.6-hour exposure studies, there 
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1 has been a 1.0% (n = 279) increase in FEV1 (Kim et al., 2011; Schelegle et al., 2009; 

2 Adams, 2006a, 2003a, 2002; Adams and Ollison, 1997; Folinsbee et al., 1994; 

3 McDonnell et al., 1991; Horstman et al., 1990; Folinsbee et al., 1988). Regardless of the 

4 reason for small changes in FEV1 over the course of FA exposures, whether biologically 

5 based or a systematic effect of the experimental procedures, the use of FA responses as a 

6 control for the assessment of responses following O3 exposure in randomized exposure 

7 studies serves to eliminate alternative explanations other than those of O3 itself in causing 

8 the measured responses. 

9 Considering FEV1 responses in young healthy adults, an O3-induced change in FEV1 is 

10 typically the difference between the decrement observed with O3 exposure and the 

11 improvement observed with FA exposure. Noting that some healthy individuals 

12 experience small improvements while others have small decrements in FEV1 following 

13 FA exposure, investigators have used the randomized, crossover design with each subject 

14 serving as their own control (exposure to FA) to discern relatively small effects with 

15 certainty since alternative explanations for these effects are controlled for by the nature of 

16 the experimental design. The utility of intraindividual FA control exposures becomes 

17 more apparent when considering individuals with respiratory disease. The occurrence of 

18 exercise-induced bronchospasm is well recognized in patients with asthma and COPD 

19 and may be experienced during both FA and O3 exposures. Absent correction for FA 

20 responses, exercise-induced changes in FEV1 could be mistaken for responses due to O3. 

21 This biological phenomenon serves as an example to emphasize the need for a proper 

22 control exposure in assessing the effects of O3 as well as the role of this control in 

23 eliminating the influence of other factors on the outcomes of interest. 

Pulmonary Function Effects of Ozone Exposure in Healthy Subjects

Acute Exposure of Healthy Subjects

24 The majority of controlled human exposure studies have investigated the effects of 

25 exposure to O3 in young healthy nonsmoking adults (18-35 years of age). These studies 

26 typically use fixed concentrations of O3 under carefully regulated environmental 

27 conditions and subject activity levels. The magnitude of respiratory effects (decrements 

28 in spirometry measurements and increases in symptomatic response) in these individuals 

is a function of O3 concentration (C), minute ventilation (V̇ 29 E), and exposure duration 

30 (time). Any physical activity will increase minute ventilation and therefore the dose of 

31 inhaled O3. Dose of inhaled O3 to the lower airways is also increased due to a shift from 

32 nasal to oronasal breathing with a consequential decrease in O3 scrubbing by the upper 

33 airways. Thus, the intensity of physiological response following an acute exposure will 

34 be strongly associated with minute ventilation. 
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The product of C × V̇ 1 E × time is commonly used as a surrogate for O3 dose to the 

2 respiratory tract in controlled human exposure studies. A large body of data regarding the 

interdependent effects of C, V̇ 3 E, and time on pulmonary responses was assessed in the 

4 1986 and 1996 O3 AQCDs (U.S. EPA, 1996a, 1986). Acute responses were modeled as a 

function of total inhaled dose (C × V̇ 5 E × time) which was found to be a better predictor of 

response to O3 than C, V̇ 6 E, or time of exposure, alone, or as a combination of any two of 

these factors. However, intake dose (C × V̇ 7 E × time) did not adequately capture the 

8 temporal dynamics of pulmonary responses in a comparison between a constant (square9 wave) and a variable (triangular) O3 exposure (average 120 ppb O3; moderate exercise, 

V̇ 10 E = 40 L/min; 8 hour duration) conducted by Hazucha et al. (1992). Recent nonlinear 

11 statistical models clearly describe the temporal dynamics of FEV1 responses as a function 

of C, V̇ 12 E, time, and age of the exposed subject (McDonnell et al., 2010, 2007). 

13 For healthy young adults exposed at rest for 2 hours, 500 ppb is the lowest O3

14 concentration reported to produce a statistically significant O3-induced group mean FEV1

15 decrement of 6.4% (n = 10) (Folinsbee et al., 1978) to 6.7% (n = 13) (Horvath et al., 

16 1979). Airway resistance was not clearly affected during at-rest exposure to these 

17 O3 concentrations. For exposures of 1-2 hours to ≥ 120 ppb O3, statistically significant 

symptomatic responses and effects on FEV1 are observed when V̇ 18 E is sufficiently 

19 increased by exercise (McDonnell et al., 1999b). For instance, 5% of young healthy 

20 adults exposed to 400 ppb O3 for 2 hours during rest experienced pain on deep 

21 inspiration. Respiratory symptoms were not observed at lower exposure concentrations 

22 (120-300 ppb) or with only 1 hour of exposure even at 400 ppb. However, when exposed 

to 120 ppb O3 for 2 hours during light-to-moderate intermittent exercise (V̇ 23 E of 22 -

24 35 L/min), 9% of individuals experienced pain on deep inspiration, 5% experienced 

25 cough, and 4% experienced shortness of breath. With very heavy continuous exercise 

(V̇ 26 E = 89 L/min), an O3-induced group mean decrement of 9.7% in FEV1 has been reported 

27 for healthy young adults exposed for 1 hour to 120 ppb O3 (Gong et al., 1986). Symptoms 

28 are present and decrements in forced expiratory volumes and flows occur at 160-240 ppb 

O3 following 1 hour of continuous heavy exercise (V̇ 29 E ≈ 55 to 90 L/min (Gong et al., 

30 1986; Avol et al., 1984; Folinsbee et al., 1984; Adams and Schelegle, 1983) and 

following 2 hours of intermittent heavy exercise (V̇ 31 E ≈ 65-68 L/min) (Linn et al., 1986; 

32 Kulle et al., 1985; McDonnell et al., 1983). With heavy intermittent exercise (15-min 

intervals of rest and exercise [V̇ 33 E = 68 L/min]), symptoms of breathing discomfort and a 

34 group mean O3-induced decrement of 3.4% in FEV1 occurred in young healthy adults 

exposed for 2 hours to 120 ppb O3 (McDonnell et al., 1983).

1 35 Table 6-1 provides 

36 examples of typical exercise protocols utilized in controlled human exposures to O3. The 

 1 In total, subjects were exposed to O3 for 2.5 hours. Intermittent exercise periods, however, were only conducted for the first 2 

hours of exposure and FEV1 was determined 5 minutes after the exercise was completed. 
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V̇

E rates in this table are per body surface area (BSA) which is, on average, about 1.7 m2 1

and 2.0 m2 2 for young healthy adult females and males, respectively, who participated in 

3 controlled O3 exposure studies. 

Table 6-1 Activity levels used in controlled exposures of healthy young 

adults to ozone.

Activitya,b Study

Duration

(hours)

V̇

E

(L/min per 

m2 BSA)

Heart 

Rate

(bpm)

Treadmill

Speed (mph)

Treadmill

Grade (%)

Cycle 

(watts)

Rest 2 4 70 n.a. n.a. n.a.

Light quasi-continuous 

exercise

6.6-7.6 15 110 3.5-4.4 0 42

Moderate quasicontinuous exercise6.6 17-23 115-130 3.3-3.5 4-5 72

Heavy intermittent 

exercise

1-2 27-33 160 3.5-5 10 100

Very heavy continuous 

exercise

1 45 160 n.a. n.a. 260

a

Based on group mean exercise specific data provided in the individual studies. On average, subjects were 23 years of age. For 

exercise protocols, the minute ventilation and heart rate are for the exercise periods. Quasi-continuous exercise consists of 50 

minutes of exercise periods followed by 10 minutes of rest. Intermittent exercise consists of alternating periods of 15 minutes of 

exercise and 15 minutes of rest.

b

References: Horvath et al. (1979) for rest; Adams (2000) and Horstman et al. (1995) for light quasi-continuous exercise, 2006a); 

(2002, 2000), Folinsbee et al. (1988), Horstman et al. (1990), and McDonnell et al. (1991) for moderate quasi-continuous exercise; 

Kehrl et al. (1987), Kreit et al. (1989), and McDonnell et al. (1983) for heavy intermittent exercise, and Gong et al. (1986) for very 

heavy continuous exercise.
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A 

Source: Brown et al. (2008).

B

Top, panel A: All studies exposed subjects to a constant (square-wave) concentration in a chamber, except Adams (2002) where a 

facemask was used. All responses at and above 0.06 ppm were statistically significant. The McDonnell et al. (2007) curve illustrates 

the predicted FEV1 decrement at 6.6 hours as a function of O3 concentration for a 23 year-old (the average age of subjects that 

participated in the illustrated studies). Note that this curve was not “fitted” to the plotted data. Error bars (where available) are the 

standard error of responses. 

Bottom, panel B: All studies used constant (square-wave) exposures in a chamber unless designated as triangular (t) and/or 

facemask (m) exposures. All responses at and above 0.07 ppm were statistically significant. At 0.06 ppm, Adams (2006a) and Kim 

et al. (2011) responses to square-wave chamber exposures were statistically significant. During each hour of the exposures, 

subjects were engaged in moderate quasi continuous exercise (40 L/min) for 50 minutes and rest for 10 minutes. Following the third 

hour, subjects had an additional 35-minute rest period for lunch. The data at 0.06, 0.08 and 0.12 ppm have been offset for 

illustrative purposes.

Studies appearing in the figure legends: Adams (2006a); (2003a, 2002), Folinsbee et al. (1988), Horstman et al. (1990), (Kim et al., 

2011), 2007); (1991), and Schelegle et al. (2009).

Figure 6-1 Cross-study comparison of mean ozone-induced FEV1 decrements 

following 6.6 hours of exposure to ozone.

0%

2%

4%

6%

8%

0.03 0.04 0.05 0.06 0.07 0.08 0.09

Ozone-induced

FEV1 decrement (%)

Ozone (ppm)

Adams (2006)

Adams (2003)

Adams (2002)

Horstman et al. (1990)

Kim et al. (2011)

McDonnell et al. (1991)

Schelegle et al. (2009)

(t)

(t)

(t,m)

(m) (m)

(m) 

(m)

(t)

(t)

(t)

(t)

(t)
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1 For prolonged (6.6 hours) exposures relative to shorter exposures, significant pulmonary 

2 function responses and symptoms have been observed at lower O3 concentrations and at a 

moderate level of exercise (V̇ 3 E = 40 L/min). The 6.6-hour experimental protocol was 

4 intended to simulate the performance of heavy physical labor for a full workday 

5 (Folinsbee et al., 1988). The results from studies using 6.6 hours of constant or square6 wave exposures to between 40 and 120 ppb O3 are illustrated in Figure 6-1(A). 

7 Figure 6-1(B) focuses on the range from 40 to 80 ppb and includes triangular exposure 

8 protocols as well as facemask exposures. Exposure to 40 ppb O3 for 6.6 hours produces 

9 small, statistically nonsignificant changes in FEV1 that are relatively similar to responses 

10 from FA exposure (Adams, 2002). Volunteers exposed to 60 ppb O3 experience group 

11 mean O3-induced FEV1 decrements of about 3% (Kim et al., 2011; Brown et al., 2008; 

Adams, 2006a)

1 12 ; those exposed to 80 ppb have group mean decrements that range from 6 

13 to 8% (Adams, 2006a, 2003a; McDonnell et al., 1991; Horstman et al., 1990); at 100 ppb, 

14 group mean decrements range from 8 to 14% (McDonnell et al., 1991; Horstman et al., 

15 1990); and at 120 ppb, group mean decrements of 13 to 16% are observed (Adams, 2002; 

16 Horstman et al., 1990; Folinsbee et al., 1988). As illustrated in Figure 6-1, there is a 

17 smooth intake dose-response curve without evidence of a threshold for exposures 

18 between 40 and 120 ppb O3. This is consistent with Hazucha and Lefohn (2007), who 

19 suggested that a randomly selected group of healthy individuals of sufficient size would 

20 include hypo-, normo-, and hyper-responsive individuals such that the average response 

21 would show no threshold for any spirometric endpoint. Taken together, these data 

22 indicate that mean FEV1 is clearly decreased by 6.6-hour exposures to 60 ppb O3 and 

23 higher concentrations in subjects performing moderate exercise. 

24 The time course of responses during prolonged (6.6 hours) square-wave O3 exposures 

with moderate exercise (V̇ 25 E = 40 L/min) depends on O3 concentration. At 120 ppb O3, 

26 Folinsbee et al. (1988) observed that somewhat small FEV1 decrements and symptoms of 

27 breathing discomfort become apparent in healthy subjects following the second hour of 

28 exposure with a more rapid change in responses between the 3rd and 5th hour of 

29 exposure and a diminishing response or plateau in responses over the last hour of 

30 exposure. Relative to FA, the change in FEV1 at 120 ppb O3 became statistically 

31 significant after 4.6 hours. Following the same exposure protocol, Horstman et al. (1990)

32 observed a linear increase in FEV1 responses with time following 2 hours of exposure to 

33 120 ppb O3 that was statistically different from FA responses after 3 h. At 100 ppb O3, 

34 FEV1 responses diverged from FA after 3 hours and were statistically different at 4.6 

35 hours (Horstman et al., 1990). At 80 ppb O3, FEV1 responses diverged from FA after 4.6 

 1 Adams (2006b) did not find effects on FEV1 at 60 ppb to be statistically significant. In an analysis of the Adams (2006b) data, 

even after removal of potential outliers, Brown et al. (2008) found the average effect on FEV1 at 60 ppb to be small, but highly 

statistically significant (p < 0.002) using several common statistical tests.
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1 hours and were statistically different from FA at 5.6 hours (Horstman et al., 1990). 

2 Subsequently, Adams (2006a) observed FEV1 decrements and total respiratory symptoms 

3 at 80 ppb O3 to diverge from FA responses after 3 h, but did not become statistically 

4 different until 6.6 hours. At 60 ppb O3, FEV1 responses generally tracked responses in FA 

5 for the first 4.6 hours of exposure and diverged after 5.6 hours (Adams, 2006a). FEV1

6 responses, but not symptomatic responses, become statistically different between 60 ppb 

7 O3 and FA at 6.6 hours (Kim et al., 2011; Brown et al., 2008). At 40 ppb, FEV1 and 

8 symptomatic responses track FA for 5.6 hours of exposure and may begin to diverge after 

9 6.6 hours (Adams, 2002). In prolonged (6.6 hours) square-wave O3 exposures between 40 

and 120 ppb with moderate exercise (V̇ 10 E = 40 L/min), the time required for group mean 

11 responses to differ between O3 and FA exposures increases with decreasing O3

12 concentration. 

13 As opposed to constant (i.e., square-wave) concentration patterns used in the studies 

14 described above, many studies conducted at the levels of 40-80 ppb have used variable 

15 O3 concentration patterns. It has been suggested that a triangular (variable concentration) 

16 exposure profile can potentially lead to higher FEV1 responses than square-wave profiles 

17 despite having the same average O3 concentration over the exposure period. Hazucha et 

18 al. (1992) were the first to investigate the effects of variable versus constant 

19 concentration exposures on responsiveness to O3. In their study, volunteers were 

20 randomly exposed to a triangular concentration profile (averaging 120 ppb over the 

21 8-hour exposure) that increased linearly from 0-240 ppb for the first 4 hours of the 8-hour 

22 exposure, then decreased linearly from 240 to 0 ppb over the next 4 hours of the 8-hour 

23 exposure, and to an square-wave exposure of 120 ppb O3 for 8 hours. While the total 

24 inhaled O3 doses at 4 hours and 8 hours for the square-wave and the triangular 

25 concentration profile were almost identical, the FEV1 responses were dissimilar. For the 

26 square-wave exposure, FEV1 declined ~5% by the fifth hour and then remained at that 

27 level. With the triangular O3 profile, there was minimal FEV1 response over the first 

28 3 hours followed by a rapid decrease in FEV1 to a decrement of 10.3% over the next 3 

29 hours. During the seventh and eighth hours, mean FEV1 decrement improved to 6.3% as 

30 the O3 concentration decreased from 120 to 0 ppb (mean = 60 ppb). These findings 

31 illustrate that the severity of symptoms and the magnitude of spirometric responses are 

32 time-dependent functions of O3 delivery rate with periods of both effect development and 

33 recovery during the course of an exposure. 

34 Subsequently, others have also demonstrated that variable concentration exposures can 

35 elicit greater FEV1 and symptomatic responses than do square-wave exposures (Adams, 

36 2006a, b, 2003a). Adams (2006b) reproduced the findings of Hazucha et al. (1992) at 

37 120 ppb. However, Adams (2006a); (2003a) found that responses from an 80 ppb O3

38 (average) triangular exposure did not differ significantly from those observed in the 
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1 80 ppb O3 square-wave exposure at 6.6 hours. Nevertheless, FEV1 and symptoms were 

2 significantly different from pre-exposure at 4.6 hours (when the O3 concentration was 

3 150 ppb) in the triangular exposure, but not until 6.6 hours in the square-wave exposure. 

4 At the lower O3 concentration of 60 ppb, no temporal pattern differences in FEV1

5 responses between square-wave and triangular exposure profiles could be discerned 

6 (Adams, 2006a). However, both total symptom scores and pain on deep inspiration 

7 tended to be greater following the 60 ppb triangular than the 60 ppb square-wave 

8 exposure. At 80 ppb, respiratory symptoms tended to increase more rapidly during the 

9 triangular than square-wave exposure protocol, but then decreased during the last hour of 

10 exposure to be less than that observed with the square-wave exposure at 6.6 hours. Both 

11 total symptom scores and pain on deep inspiration were significantly increased following 

12 exposures to 80 ppb relative to all other exposure protocols, i.e., FA, 40, and 60 ppb 

13 exposures. Following the 6.6-hour exposures, respiratory symptoms at 80 ppb were 

14 roughly 2-3 times greater than those observed at 60 ppb. At 40 ppb, triangular and 

15 square-wave patterns produced spirometric and subjective symptom responses similar to 

16 FA exposure (Adams, 2006a, 2002).

17 For O3 exposures of 60 ppb and greater, studies (Adams, 2006a, b, 2003a; Hazucha et al., 

18 1992) demonstrate that during triangular exposure protocols, volunteers exposed during 

moderate exercise (V̇ 19 E = 40 L/min) may develop greater spirometric and/or symptomatic 

20 responses during and following peak O3 concentrations as compared to responses over 

21 the same time interval of square-wave exposures. This observation is not unexpected 

22 since the inhaled dose rate during peaks of the triangular protocols approached twice that 

23 of the square-wave protocols, e.g., 150 ppb versus 80 ppb peak concentration. At time 

24 intervals toward the end of an exposure, O3 delivery rates for the triangular protocols 

25 were less than those of square-wave. At these later time intervals, there is some recovery 

26 of responses during triangular exposure protocols, whereas there is a continued 

27 development of or a plateau of responses in the square-wave exposure protocols. Thus, 

28 responses during triangular protocols relative to square-wave protocols may be expected 

29 to diverge and be greater following peak exposures and then converge toward the end of 

30 an exposure. Subsequent discussion will focus on exposures between 40 and 80 ppb 

31 where FEV1 pre-to-post responses are similar (although not identical) between triangular 

32 and square-wave protocols having equivalent average exposure concentrations.

33 Schelegle et al. (2009) recently investigated the effects of 6.6-hour variable O3 exposure 

34 protocols at mean concentrations of 60, 70, 80, and 87 ppb on respiratory symptoms and 

35 pulmonary function in young healthy adults (16 F, 15 M; 21.4 ± 0.6 years) exposed 

during moderate quasi continuous exercise (V̇ 36 E = 40 L/min). The mean FEV1 (± standard 

37 error) decrements at 6.6 hours (end of exposure relative to pre-exposure) were -

38 0.80 ± 0.90%, 2.72 ± 1.48%, 5.34 ± 1.42%, 7.02 ± 1.60%, and 11.42 ± 2.20% for 
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1 exposure to FA, 60, 70, 80, and 87 ppb O3, respectively. Statistically significant 

2 decrements in FEV1 and increases in total subjective symptom scores (p <0.05) were 

3 found following exposure to mean concentrations of 70, 80, and 87 ppb O3 relative to FA. 

4 Statistically significant effects were not found at 60 ppb. One of the expressed purposes 

5 of the Schelegle et al. (2009) study was to determine the minimal mean O3 concentration 

6 that produces a statistically significant decrement in FEV1 and respiratory symptoms in 

7 healthy individuals completing 6.6-hour exposure protocols. At 70 ppb, Schelegle et al. 

8 (2009) observed a statistically significant O3-induced FEV1 decrement of 6.1% at 

9 6.6 hours and a significant increase in total subjective symptoms at 5.6 and 6.6 hours. A 

10 re analysis found the FEV1 responses at 70 ppb to be significantly different from FA 

11 responses beginning at 4.6 hours of exposure (Lefohn et al., 2010a). At 60 ppb, an 

12 O3-induced 3.5% FEV1 decrement was not found to be statistically significant. However, 

13 this effect is similar in magnitude to the 2.9% FEV1 decrement at 60 ppb observed by 

14 Adams (2006a), which was found to be statistically significant by Brown et al. (2008).

15 More recently, Kim et al. (2011) investigated the effects of a 6.6-hour exposure to 60 ppb 

O3 during moderate quasi continuous exercise (V̇ 16 E = 40 L/min) on pulmonary function 

17 and respiratory symptoms in young healthy adults (32 F, 27 M; 25.0 ± 0.5 year) who 

18 were roughly half GSTM1-null and half GSTM1-positive. Sputum neutrophil levels were 

19 also measured in a subset of the subjects (13 F, 11 M). The mean FEV1 (± standard error) 

20 decrements at 6.6 hours (end of exposure relative to pre-exposure) were significantly 

21 different (p = 0.008) between the FA (0.002 ± 0.46%) and O3 (1.76 ± 0.50%) exposures. 

22 The inflammatory response following O3 exposure was also significantly (p <0.001) 

23 increased relative to the FA exposure. Respiratory symptoms were not affected by O3

24 exposure. There was also no significant effect of GSTM1 genotype on FEV1 or 

25 inflammatory responses to O3.

26 Consideration of the minimal O3 concentration producing statistically significant effects 

27 on FEV1 and respiratory symptoms (e.g., cough and pain on deep inspiration) following 

28 6.6-hour exposures warrants additional discussion. As discussed above, numerous studies 

29 have demonstrated statistically significant O3-induced group mean FEV1 decrements of 

30 6-8% and an increase in respiratory symptoms at 80 ppb. Schelegle et al. (2009) have 

31 now reported a statistically significant O3-induced group mean FEV1 decrement of 6%, as 

32 well as increased respiratory symptoms, at 70 ppb. At 60 ppb, there is information 

33 available from 4 separate studies (Kim et al., 2011; Schelegle et al., 2009; Adams, 2006a, 
Draft – Do Not Cite or Quote 6-13 June 2012

2002).

1 1 The group mean O3-induced FEV1 decrements observed in these studies were 

3.6% (facemask, square-wave) by Adams (2006a); (2002)

2 2 , 2.8% (triangular exposure) 

3 and 2.9% (square-wave exposure) by Adams (2006a), 3.5% (triangular exposure) by 

4 Schelegle et al. (2009), and 1.8% (square-wave exposure) by Kim et al. (2011). Based on 

5 data from these studies, at 60 ppb, the weighted-average group mean O3-induced FEV1

6 decrement (i.e., adjusted for FA responses) is 2.7% (n = 150). Although not consistently 

7 statistically significant, these group mean changes in FEV1 at 60 ppb are consistent 

8 among studies, i.e., none observed an average improvement in lung function following a 

9 6.6-hour exposure to 60 ppb O3. Indeed, as was illustrated in Figure 6-1, the group mean 

10 FEV1 responses at 60 ppb fall on a smooth intake dose-response curve for exposures 

11 between 40 and 120 ppb O3. Furthermore, in a re-analysis of the 60 ppb square-wave data 

12 from Adams (2006a), Brown et al. (2008) found the mean effects on FEV1 to be highly 

13 statistically significant (p <0.002) using several common statistical tests even after 

14 removal of 3 potential outliers. A statistically significant increase in total respiratory 

15 symptoms at 60 ppb has only been reported by Adams (2006a) for a triangular exposure 

16 protocol at 5.6 hours and 6.6 hours relative to baseline (not FA). Although not 

17 statistically significant, there was a tendency for an increase in total symptoms and pain 

18 on deep inspiration following the 60 ppb exposures (triangular and square-wave) relative 

19 to those following both FA and 40 ppb exposures. The time-course and magnitude of 

20 FEV1 responses at 40 ppb resemble those occurring during FA exposures (Adams, 2006a, 

21 2002). In both of these studies, there was a tendency (not statistically significant) for a 

22 small increase in total symptoms and pain on deep inspiration following the 40 ppb 

23 exposures relative to those following FA. Taken together, the available evidence shows 

24 that detectable effects of O3 on group mean FEV1 persist down to 60 ppb, but not 40 ppb 

25 in young healthy adults exposed for 6.6 hours during moderate exercise. Although group 

26 mean FEV1 responses at 60 ppb are relatively small (2-3% mean FEV1 decrement), it 

27 should be emphasized that there is considerable intersubject variability, with some 

28 responsive individuals consistently experiencing larger than average FEV1 responses.

29 In addition to overt effects of O3 exposure on the large airways indicated by spirometric 

30 responses, O3 exposure also affects the function of the small airways and parenchymal 

31 lung. Foster et al. (1997); (1993) examined the effect of O3 on ventilation distribution. In 

32 healthy adult males (n = 6; 26.7 ± 7 years old) exposed to O3 (330 ppb with light 

33 intermittent exercise for 2 h), there was a significant reduction in ventilation to the lower 

 1 Adams (2006a); (2002) both provide data for an additional group of 30 healthy subjects that were exposed via facemask to 

60 ppb (square-wave) O3 for 6.6 hours with moderate exercise (V̇

E = 23 L/min per m2 BSA). These subjects are described on page 

133 of Adams (2006a) and pages 747 and 761 of Adams (2002). The FEV1 decrement may be somewhat increased due to a target

V̇

E of 23 L/min per m2 BSA relative to other studies with which it is listed having the target V̇E of 20 L/min per m2 BSA. Based on 

Adams (2003a, b, 2002)the facemask exposure is not expect to affect the FEV1 responses relative to a chamber exposure.

2 This group average FEV1 response is for a set of subjects exposed via facemask to 60 ppb O3, see page 133 of Adams (2006a).
Draft – Do Not Cite or Quote 6-14 June 2012

1 lung (31% of lung volume) and significant increases in ventilation to the upper- and 

2 middle-lung regions (Foster et al., 1993). In a subsequent study of healthy males (n = 15; 

3 25.4 ± 2 years old) exposed to O3 (350 ppb with moderate intermittent exercise for 2.2 h), 

4 O3 exposure caused a delayed gas washout in addition to a 14% FEV1 decrement (Foster 

5 et al., 1997). The pronounced slow phase of gas washout following O3 exposure 

6 represented a 24% decrease in the washout rate. A day following O3 exposure, 50% of 

7 the subjects still had (or developed) a delayed washout relative to the pre-O3 maneuver. 

8 These studies suggest a prolonged O3 effect on the small airways and ventilation 

9 distribution in healthy young individuals.

10 There is a rapid recovery of O3-induced spirometric responses and symptoms; 40 to 65% 

11 recovery appears to occur within about 2 hours following exposure (Folinsbee and 

12 Hazucha, 1989). For example, following a 2-hour exposure to 400 ppb O3 with 

13 intermittent exercise, Nightingale et al. (2000) observed a 13.5% mean decrement in 

14 FEV1. By 3 hours postexposure, however, only a 2.7% FEV1 decrement persisted. Partial 

15 recovery also occurs following cessation of exercise despite continued exposure to O3

16 (Folinsbee et al., 1977) and at low O3 concentrations during exposure (Hazucha et al., 

17 1992). A slower recovery phase, especially after exposure to higher O3 concentrations, 

18 may take at least 24 hours to complete (Folinsbee and Hazucha, 2000; Folinsbee et al., 

19 1993). Repeated daily exposure studies at higher concentrations typically show that FEV1

20 response to O3 is enhanced on the second day of exposure. This enhanced response 

21 suggests a residual effect of the previous exposure, about 22 hours earlier, even though 

22 the pre-exposure spirometry may be the same as on the previous day. The absence of the 

23 enhanced response with repeated exposure at lower O3 concentrations may be the result 

24 of a more complete recovery or less damage to pulmonary tissues (Folinsbee et al., 1994). 

Predicted Responses in Healthy Subjects

25 Studies analyzing large data sets (hundreds of subjects) provide better predictive ability 

of acute changes in FEV1 at low levels of O3 and V̇ 26 E than is possible via comparisons 

27 between smaller studies. A few such studies described in the 2006 O3 AQCD (U.S. EPA, 

28 2006b) analyzed FEV1 responses in healthy young adults (18-35 years of age) recruited 

29 from the area around Chapel Hill, NC and exposed for 2 hours to O3 concentrations of up 

30 to 400 ppb at rest or with intermittent exercise (McDonnell et al., 1997; Seal et al., 1996; 

31 Seal et al., 1993). McDonnell et al. (1999b) examined changes in respiratory symptoms 

32 with O3 exposure in a subset of the Chapel Hill data. In general, these studies showed that 

33 FEV1 and respiratory symptom responses increase with increasing O3 concentration and 

V̇ 34 E and decrease with increasing subject age. More recent studies expand upon these 

35 analyses of FEV1 responses to also include longer duration (up to 8 h) studies and periods 

36 of recovery following exposure. 
Draft – Do Not Cite or Quote 6-15 June 2012

1 McDonnell et al. (2007) provided a nonlinear empirical model for predicting group 

average FEV1 responses as a function of O3 concentration, exposure time, V̇ 2 E, and age of 

3 the exposed individual. The model predicts temporal dynamics of FEV1 change in 

4 response to any set of O3 exposure conditions that might reasonably be experienced in the 

5 ambient environment. The model substantially differs from earlier statistical models in 

6 that it effectively considers the concurrent processes of damage and repair, i.e., the model 

7 allows effects on FEV1 to accumulate during exposure at the same time they are reduced 

8 due to the reversible nature of the effects. The model was based on response data of 

9 healthy, nonsmoking, white males (n = 541), 18-35 years old, from 15 studies conducted 

10 at the U.S. EPA Human Studies Facility in Chapel Hill, NC. 

11 McDonnell et al. (2010) tested the predictive ability of the model (McDonnell et al., 

12 2007) against independent data (i.e., data that were not used to fit the model) of Adams 

13 (2006a); (2006b, 2003a, 2002, 2000), Hazucha et al. (1992), and Schelegle et al. (2009). 

14 The model generally captured the dynamics of group average FEV1 responses within 

15 about a one percentage point of the experimental data. Consistent with Bennett et al. 

16 (2007), an increased body mass index (BMI) was found to be associated with enhanced 

17 FEV1 responses to O3 by McDonnell et al. (2010). The BMI effect is of the same order of 

18 magnitude but in the opposite direction of the age effect where by FEV1 responses 

19 diminish with increasing age. Although the effects of age and BMI are relatively strong, 

20 these characteristics account for only a small amount of the observed variability in 

21 individual responses.

22 Alternatively, Lefohn et al. (2010a) proposed that FEV1 responses to O3 exposure might 

23 be described by a cumulative integrated exposure index with a sigmoidal weighting 

24 function similar to the W126 used for predicting vegetation effects (see Section 9.5). The 

25 integrated exposure index is the sum of the hourly average O3 concentrations times their 

26 respective weighing factors. Based on a limited number of studies, the authors assumed 

27 weighting factors ranged from near zero at 50 ppb up to approximately 1.0 for 

28 concentrations at ≥ 125 ppb. The concentrations of 60, 70 and 80 ppb correspond to the 

29 weights of 0.14, 0.28, and 0.50, respectively. These weighting factors apply only to the 

case of exposure during moderate exercise (V̇

E = 20 L/min per m2 30 BSA). Lefohn et al. 

31 (2010a) calculated the cumulative exposure index for the protocols used by Adams 

32 (2006a); (2003a) and Schelegle et al. (2009). They found statistically significant O3

33 effects after 4 hours on FEV1 at 105 ppb-hour based on Schelegle et al. (2009) and at 

34 235 ppb-hour based on Adams (2006a); (2003a). Based on this analysis, the authors 

35 recommended a 5-hour accumulation period to protect against O3 effects on lung 

36 function. 
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Intersubject Variability in Response of Healthy Subjects

1 Consideration of group mean changes is important in discerning if observed effects are 

2 due to O3 exposure rather than chance alone. Inter-individual variability in responses is, 

3 however, considerable and pertinent to assessing the fraction of the population that might 

4 actually be affected during an O3 exposure. Hackney et al. (1975) first recognized a wide 

5 range in the sensitivity of subjects to O3. The range in the subjects’ ages (29 to 49 years) 

6 and smoking status (0 to 50 pack years) in the Hackney et al. (1975) study are now 

7 understood to affect the spirometric and symptomatic responses to O3. Subsequently, 

8 DeLucia and Adams (1977) examined responses to O3 in six healthy non-smokers and 

9 found that two exhibited notably greater sensitivity to O3. Since that time, numerous 

10 studies have documented considerable variability in responsiveness to O3 even in subjects 

11 recruited to assure homogeneity in factors recognized or presumed to affect responses. 

12 An individual’s FEV1 response to a 2 hour O3 exposure is generally reproducible over 

13 several months and presumably reflects the intrinsic responsiveness of the individual to 

14 O3 (Hazucha et al., 2003; McDonnell et al., 1985b). The frequency distribution of 

15 individual FEV1 responses following these relatively short exposures becomes skewed as 

16 the group mean response increases, with some individuals experiencing large reductions 

17 in FEV1 (Weinmann et al., 1995a; Kulle et al., 1985). For 2-hour exposures with 

18 intermittent exercise causing a predicted average FEV1 decrement of 10%, individual 

19 decrements ranged from approximately 0 to 40% in white males aged 18-36 years 

20 (McDonnell et al., 1997). For an average FEV1 decrement of 13%, Ultman et al. (2004)

21 reported FEV1 responses ranging from a 4% improvement to a 56% decrement in young 

22 healthy adults (32 M, 28 F) exposed for 1 hour to 250 ppb O3. One-third of the subjects 

23 had FEV1 decrements of >15%, and 7% of the subjects had decrements of >40%. The 

24 differences in FEV1 responses did not appear to be explained by intersubject differences 

25 in the fraction of inhaled O3 retained in the lung (Ultman et al., 2004).
Draft – Do Not Cite or Quote 6-17 June 2012

Note: During each hour of the exposures, subjects were engaged in moderate quasi continuous exercise (40 L/min) for 50 minutes 

and rest for 10 minutes. Following the third hour, subjects had an additional 35 minute rest period for lunch. Subjects were exposed 

to a triangular O3 concentration profile having the average O3 concentration provided in each panel. As average ozone 

concentration increased, the distribution of responses became asymmetric with a few individuals exhibiting large FEV1 decrements. 

The percentage indicated in each panel is the portion of subjects having a FEV1 decrement in excess of 10%. 

Source: Adapted with permission of American Thoracic Society (Schelegle et al., 2009).

Figure 6-2 Frequency distributions of FEV1 decrements observed by Schelegle 

et al. (2009) in young healthy adults (16 F, 15 M) following 6.6-hour 

exposures to ozone or filtered air.

1 Consistent with the 1- to 2-hour studies, the distribution of individual responses 

2 following 6.6-hour exposures becomes skewed with increasing exposure concentration 

3 and magnitude of the group mean FEV1 response (McDonnell, 1996). Figure 6-2

4 illustrates frequency distributions of individual FEV1 responses observed in 31 young 

5 healthy adults following 6.6-hour exposures between 0 and 80 ppb. Schelegle et al. 

6 (2009) found >10% FEV1 decrements in 16, 19, 29, and 42% of individuals exposed for 

7 6.6 hours to 60, 70, 80, and 87 ppb, respectively. Just as there are differences in mean 

8 decrements between studies having similar exposure scenarios (Figure 6-1 at 80 and

9 120 ppb), there are differences in the proportion of individuals affected with >10% FEV1

10 decrements. At 80 ppb, the proportion affected with >10% FEV1 decrements was 17% 

(n = 30) by Adams (2006a)

1 11 , 26% (n = 60) by McDonnell (1996), and 29%(n = 31) by 

12 Schelegle et al. (2009). At 60 ppb, the proportion with >10% FEV1 decrements was 20% 

(n = 30) by Adams (2002)

2

, 3% (n = 30) by Adams (2006a)

1 13 , 16% (n = 31) by Schelegle 

14 et al. (2009), and 5% (n = 59) by Kim et al. (2011). Based on these studies, the weighted

15 average proportion of individuals with >10% FEV1 decrements is 10% following 

16 exposure to 60 ppb. Due to limited data within the published papers, these proportions 

17 were not corrected for responses to FA exposure where lung function typically improves 

18 in healthy adults. For example, uncorrected versus O3-induced (i.e., adjusted for response 

 1 Not assessed by Adams (2006a), the proportion was provided in Figure 8-1B of the 2006 O3 AQCD (U.S. EPA, 2006b).

2 This information is from page 761 of Adams (2002). Adams (2006a, 2002) both provide data for a group of 30 healthy subjects 

that were exposed via facemask to 60 ppb (square-wave) O3 for 6.6 hours with moderate exercise (V̇

E = 23 L/min per m2 BSA). 

These subjects are described on page 133 of Adams (2006a) and pages 747 and 761 of Adams (2002). The FEV1 decrement may 

be somewhat increased due to a target V̇

E of 23 L/min per m2 BSA relative to other studies with which it is listed having the target V̇E

of 20 L/min per m2 BSA. Based on Adams (2003a, b, 2002), similar FEV1 responses are expected between facemask and chamber 

exposures.
Draft – Do Not Cite or Quote 6-18 June 2012

1 during FA exposure) proportions of individuals having >10% FEV1 decrements in the 

Adams (2006a)

1 2 study were, respectively, 3% versus 7% at 60 ppb and 17% versus 23% 

3 at 80 ppb. Thus, uncorrected proportions underestimate the actual fraction of healthy 

4 individuals affected. 

5 Given considerable inter-individual variability in responses, the interpretation of 

6 biologically small group mean decrements requires careful consideration. Following 

7 prolonged 6.6-hour exposures to an average level of 60 ppb O3, data available from four 

8 studies yield a weighted-average group mean O3-induced FEV1 decrement (i.e., adjusted 

9 for FA responses) of 2.7% (n = 150) (Kim et al., 2011; Schelegle et al., 2009; Adams, 

10 2006a, 1998). The data from these studies also yield a weighted-average proportion 

11 (uncorrected for FA responses) of subjects with >10% FEV1 decrements of 10% 

12 (n = 150) (Kim et al., 2011; Schelegle et al., 2009; Adams, 2006a, 1998). In an individual 

13 with relatively “normal” lung function, with recognition of the technical and biological 

14 variability in measurements, confidence can be given that within-day changes in FEV1 of 

15 ≥ 5% are clinically meaningful (Pellegrino et al., 2005; ATS, 1991). Here focus is given 

16 to individuals with >10% decrements in FEV1 since some individuals in the Schelegle et 

17 al. (2009) study experienced 5-10% FEV1 decrements following exposure to FA. A 10% 

18 FEV1 decrement is also generally accepted as an abnormal response and a reasonable 

19 criterion for assessing exercise-induced bronchoconstriction (Dryden et al., 2010; ATS, 

20 2000a). The data are not available in the published papers to determine the O3-induced 

21 proportion for either the Adams (1998) or Schelegle et al. (2009) studies. As already 

22 stated, however, this uncorrected proportion likely underestimates the actual proportion 

23 of healthy individuals experiencing O3-induced FEV1 decrements in excess of 10%. 

24 Therefore, by considering uncorrected responses and those individuals having >10% 

25 decrements, 10% is an underestimate of the proportion of healthy individuals that are 

26 likely to experience clinically meaningful changes in lung function following exposure 

27 for 6.6 hours to 60 ppb O3 during moderate exercise. Of the studies conducted at 60 ppb, 

28 only Kim et al. (2011) reported FEV1 decrements at 60 ppb to be statistically significant. 

29 However, Brown et al. (2008) found those from Adams (2006a) to be highly statistically 

30 significant. Though group mean decrements are biologically small and generally do not 

31 attain statistical significance, a considerable fraction of exposed individuals experience 

32 clinically meaningful decrements in lung function.

 1 Not assessed by Adams (2006a), uncorrected and O3-induced proportions are from Figures 8-1B and 8-2, respectively, of the 

2006 O3 AQCD (2006b).
Draft – Do Not Cite or Quote 6-19 June 2012

Factors Modifying Responsiveness to Ozone

Physical activity increases V̇ 1 E and therefore the dose of inhaled O3. Consequently, the 

2 intensity of physiological response during and following an acute O3 exposure will be 

3 strongly associated with minute ventilation. Apart from inhaled O3 dose and related 

4 environmental factors (e.g., repeated daily exposures), individual-level factors, such as 

5 health status, age, gender, ethnicity, race, smoking habit, diet, and socioeconomic status 

6 (SES) have been considered as potential modulators of a physiologic response to such 

7 exposures. 

Responses in Individuals with Pre-existing Disease

8 Individuals with respiratory disease are of primary concern in evaluating the health 

9 effects of O3 because a given change in function is likely to have more impact on a 

10 person with preexisting function impairment and reduced reserve. 

11 Possibly due to the age of subjects studied, patients with COPD performing light to 

12 moderate exercise do not generally experience statistically significant pulmonary 

13 function decrements following 1- and 2-hour exposures to ≤ 300 ppb O3 (Kehrl et al., 

14 1985; Linn et al., 1983; Linn et al., 1982a; Solic et al., 1982). Following a 4-hour 

15 exposure to 240 ppb O3 during exercise, Gong et al. (1997b) found an O3-induced FEV1

16 decrement of 8% in COPD patients which was not statistically different from the 

17 decrement of 3% in healthy subjects. Demonstrating the need for control exposures and 

18 presumably due to exercise, four of the patients in the Gong et al. (1997b) study had 

19 FEV1 decrements of >14% following both the FA and O3 exposures. Although the 

20 clinical significance is uncertain, small transient decreases in arterial blood oxygen 

21 saturation have also been observed in some of these studies. 

22 Based on studies reviewed in the 1996 and 2006 O3 AQCDs, asthmatic subjects appear to 

23 be at least as sensitive to acute effects of O3 as healthy nonasthmatic subjects. Horstman 

24 et al. (1995) found the O3-induced FEV1 decrement in 17 mild-to-moderate asthmatics to 

25 be significantly larger than that in 13 healthy subjects (19% versus 10%, respectively) 

exposed to 160 ppb O3 during light exercise (V̇

E of 15 L/min per m2 26 BSA) for 7.6-hour 

27 exposure. In asthmatics, a significant positive correlation between O3-induced 

28 spirometric responses and baseline lung function was observed, i.e., responses increased 

29 with severity of disease. In the shorter duration study by Kreit et al. (1989), 9 asthmatics 

30 also showed a considerable larger average O3-induced FEV1 decrement than 9 healthy 

31 controls (25% vs. 16%, respectively) following exposure to 400 ppb O3 for 2 hours with 

moderate-heavy exercise (V̇ 32 E = 54 L/min). Alexis et al. (2000) [400 ppb; 2 h; exercise, 

V̇

E = 30 L/min] and Jorres et al. (1996) [250 ppb; 3 h; exercise, V̇ 33 E = 30 L/min] reported a 

34 tendency for slightly greater FEV1 decrements in asthmatics than healthy subjects. 
Draft – Do Not Cite or Quote 6-20 June 2012

1 Several studies reported similar responses between asthmatics and healthy individuals 

2 (Scannell et al., 1996; Hiltermann et al., 1995; Basha et al., 1994). The lack of differences 

in the Hiltermann et al. (1995) [400 ppb; 2 h; exercise, V̇ 3 E = 20 L/min] and Basha et al. 

(1994) [200 ppb; 6 h; exercise, V̇ 4 E = 25 L/min] studies was not surprising, however, given 

5 extremely small sample sizes (5-6 subjects per group) and corresponding lack of 

6 statistical power. Power was not likely problematic for Scannell et al. (1996) [200 ppb; 

4 h; exercise, V̇ 7 E ≈ 44 L/min] with 18 mild asthmatics and 81 age-matched healthy 

8 controls from companion studies (Balmes et al., 1996; Aris et al., 1995). Of note, 

9 Mudway et al. (2001) reported a tendency for asthmatics to have smaller O3-induced 

10 FEV1 decrements than healthy subjects (3% versus 8%, respectively) when exposed to 

11 200 ppb O3 for 2 hours during exercise. However, the asthmatics in (Mudway et al., 

12 2001) also tended to be older than the healthy subjects, which could partially explain 

13 their smaller response since FEV1 responses to O3 diminish with age. 

14 In a study published since the 2006 O3 AQCD, Stenfors et al. (2010) exposed persistent 

15 asthmatics (n = 13; aged 33 years) receiving chronic inhaled corticosteroid therapy to 

16 200 ppb O3 for 2 hours with moderate exercise. An average O3-induced FEV1 decrement 

17 of 8.4% was observed, whereas, only a 3.0% FEV1 decrement is predicted for similarly 

18 exposed age-matched healthy controls (McDonnell et al., 2007). Vagaggini et al. (2010)

19 exposed mild-to-moderate asthmatics (n = 23; 33 ± 11 years) to 300 ppb O3 for 2 hours 

20 with moderate exercise. Although the group mean O3-induced FEV1 decrement was only 

21 4%, eight subjects were categorized as “responders” with >10% FEV1 decrements. 

22 Baseline lung function did not differ between the responders and nonresponders 

23 suggesting that, in contrast to Horstman et al. (1995), O3-induced FEV1 responses were 

24 not associated with disease severity.

Lifestage

25 Children, adolescents, and young adults (<18 years of age) appear, on average, to have 

26 nearly equivalent spirometric responses to O3, but have greater responses than middle27 aged and older adults when similarly exposed to O3 (U.S. EPA, 1996a). Symptomatic 

28 responses to O3 exposure, however, appear to increase with age until early adulthood and 

29 then gradually decrease with increasing age (U.S. EPA, 1996a). For example, healthy 

30 children (aged 8-11 y) exposed to 120 ppb O3 (2.5 h; heavy intermittent exercise) 

31 experienced similar spirometric responses, but lesser symptoms than similarly exposed 

32 young healthy adults (McDonnell et al., 1985a). For subjects aged 18-36 years, 

33 McDonnell et al. (1999b) reported that symptom responses from O3 exposure also 

34 decrease with increasing age. Diminished symptomatic responses in children and the 

35 elderly might put these groups at increased risk for continued O3 exposure, i.e., a lack of 

36 symptoms may result in their not avoiding or ceasing exposure. Once lung growth and 
Draft – Do Not Cite or Quote 6-21 June 2012

1 development reaches the peak (18-20 years of age in females and early twenties in 

2 males), pulmonary function, which is at its maximum as well, begins to decline 

3 progressively with age as does O3 sensitivity. 

4 In healthy individuals, the fastest rate of decline in O3 responsiveness appears between 

5 the ages of 18 and 35 years (Passannante et al., 1998; Seal et al., 1996), more so for 

6 females then males (Hazucha et al., 2003). During the middle age period (35-55 years), 

7 O3 sensitivity continues to decline, but at a much lower rate. Beyond this age (>55 years), 

8 acute O3 exposure elicits minimal spirometric changes. Whether the same age-dependent 

9 pattern of O3 sensitivity decline also holds for nonspirometric pulmonary function, 

10 airway reactivity or inflammatory endpoints has not been determined. Although there is 

11 considerable evidence that spirometric and symptomatic responses to O3 exposure 

12 decrease with age beyond young adulthood, this evidence comes from cross-sectional 

13 analyses and has not been confirmed by longitudinal studies of the same individuals. 

Sex

14 Several studies have suggested that physiological differences between sexes may 

15 predispose females to greater O3-induced health effects. In females, lower plasma and 

16 nasal lavage fluid (NLF) levels of uric acid (the most prevalent antioxidant), the initial 

17 defense mechanism of O3 neutralization in airway surface liquid, may be a contributing 

18 factor (Housley et al., 1996). Consequently, reduced absorption of O3 in the upper 

19 airways may promote its deeper penetration. Dosimetric measurements have shown that 

20 the absorption distribution of O3 is independent of sex when absorption is normalized to 

21 anatomical dead space (Bush et al., 1996). Thus, a sex-related differential removal of O3

22 by uric acid seems to be minimal. In general, the physiologic response of young healthy 

23 females to O3 exposure appears comparable to the response of young males (Hazucha et 

24 al., 2003). Several studies have investigated the effects of the menstrual cycle on 

25 responses to O3 in healthy young women. In a study of 9 women exposed during exercise 

26 to 300 ppb O3 for an hour, Fox et al. (1993) found lung function responses to O3

27 significantly enhanced during the follicular phase relative to the luteal phase. However, 

28 Weinmann et al. (1995c) found no difference in responses between the follicular and 

29 luteal phases as well as no significant differences between 12 males and 12 females 

30 exposed during exercise to 350 ppb O3 for 2.15 hours. Seal et al. (1996) also reported no 

31 effect of menstrual cycle phase in their analysis of responses of 150 women (n = 25 per 

32 exposure group; 0, 120, 240, 300, and 400 ppb O3). Seal et al. (1996) conceded that the 

33 methods used by Fox et al. (1993) more precisely defined menstrual cycle phase.
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Ethnicity

1 Only two controlled human exposure studies have assessed differences in lung function 

2 responses between races. Seal et al. (1993) compared lung function responses of whites 

3 (93 M, 94 F) and blacks (undefined ancestry; 92 M, 93 F) exposed to a range of O3

4 concentrations (0-400 ppb). The main effects of the sex-race group and O3 concentration 

5 were statistically significant (both at p <0.001), although the interaction between sex-race 

6 group and O3 concentration was not significant (p = 0.13). These findings indicate some 

7 overall difference between the sex-race groups that is independent of O3 concentration, 

8 i.e., the concentration-response (C-R) curves for the four sex-race groups are parallel. In 

9 a multiple comparison procedure on data collapsed across all O3 concentrations for each 

10 sex-race group, both black men and black women had significantly larger decrements in 

11 FEV1 than did white men. The authors noted that the O3 dose per unit of lung tissue 

12 would be greater in blacks and females than whites and males, respectively. It cannot be 

13 ruled out that this difference in tissue dose might have affected responses to O3. The 

14 college students recruited for the Seal et al. (1993) study were noted by the authors as 

15 probably being from better educated and SES advantaged families, thus reducing the 

16 potential influence of these variables on results. In a follow-up analysis, Seal et al. (1996)

17 reported that, of three SES categories, individuals in the middle SES category showed 

18 greater concentration-dependent decline in percent-predicted FEV1 (4-5% at 400 ppb O3) 

19 than low and high SES groups. The authors did not have an “immediately clear” 

20 explanation for this finding. 

21 More recently, Que et al. (2011) assessed pulmonary responses in blacks of African 

22 American ancestry (22 M, 24 F) and Caucasians (55 M, 28 F) exposed to 220 ppb O3 for 

23 2.25 hours (alternating 15 min periods of rest and brisk treadmill walking). On average, 

24 the black males experienced a 16.8% decrement in FEV1 following O3 exposure which 

25 was significantly larger than mean FEV1 decrements of 6.2, 7.9, and 8.3% in black 

26 females and Caucasian males and Caucasian females, respectively. In the study by Seal et 

27 al. (1993), there was potential that the increased FEV1 decrements in blacks relative to 

28 whites were due to increased O3 tissue doses since exercise rates were normalized to 

29 BSA. Differences in O3 tissue doses between the races should not have occurred in the 

30 Que et al. (2011) study because exercise rates were normalized to lung volume (viz., 

31 6-8 times FVC). Thus, the increased mean FEV1 decrement in black males is not likely 

32 attributable to systematically larger O3 tissue doses in blacks relative to whites.

Smoking

33 Smokers are less responsive to O3 for some (but not all) health endpoints than 

34 nonsmokers. Spirometric and plethysmographic pulmonary function decline, respiratory 

35 symptoms, and nonspecific airway hyperreactivity of smokers to O3 were all weaker than 
Draft – Do Not Cite or Quote 6-23 June 2012

1 data reported for nonsmokers. However, the time course of development and recovery of 

2 these effects as well their reproducibility in smokers was not different from nonsmokers 

3 (Frampton et al., 1997a). Another similarity between smokers and nonsmokers is that, the 

4 inflammatory response to O3 does not appear to depend on smoking status nor the 

5 responsiveness of individuals to changes in lung function (Torres et al., 1997). Chronic 

6 airway inflammation with desensitization of bronchial nerve endings and an increased 

7 production of mucus may plausibly explain the reduced responses to O3 in smokers 

8 relative to nonsmokers (Frampton et al., 1997a; Torres et al., 1997). 

Antioxidant supplementation

9 The first line of defense against oxidative stress is antioxidants-rich ELF which 

10 scavenges free radicals and limits lipid peroxidation. Exposure to O3 depletes the 

11 antioxidant level in nasal ELF probably due to scrubbing of O3 (Mudway et al., 1999a), 

12 however, the concentration and the activity of antioxidant enzymes either in ELF or 

13 plasma do not appear to be related to O3 responsiveness (Samet et al., 2001; Avissar et 

14 al., 2000; Blomberg et al., 1999). Carefully controlled studies of dietary antioxidant 

15 supplementation have demonstrated some protective effects of α-tocopherol and 

16 ascorbate on spirometric lung function from O3 but not on the intensity of subjective 

17 symptoms and inflammatory response including cell recruitment, activation and a release 

18 of mediators (Samet et al., 2001; Trenga et al., 2001). Dietary antioxidants have also been 

19 reported to attenuate O3-induced bronchial hyperresponsiveness in asthmatics (Trenga et 

20 al., 2001). 

Genetic polymorphisms

21 Some studies (e.g., Corradi et al., 2002; Bergamaschi et al., 2001) reviewed in the 2006 

22 O3 AQCD reported that genetic polymorphisms of antioxidant enzymes may modulate 

23 pulmonary function and inflammatory response to O3 challenge. It was suggested that 

24 healthy carriers of NAD(P)H:quinone oxidoreductase wild type (NQO1wt) in 

25 combination with glutathione S-transferase μ-1 genetic deficiency (GSTM1null) were 

26 more responsive to O3. Bergamaschi et al. (2001) reported that subjects having NQO1wt 

27 and GSTM1null genotypes had increased O3 responsiveness (FEV1 decrements and 

28 epithelial permeasbility), whereas subjects with other combinations of these genotypes 

29 were less affected. A subsequent study from the same laboratory reported a positive 

30 association between O3 responsiveness, as characterized by the level of oxidative stress 

31 and inflammatory mediators (8-isoprostane, LTB4 and TBARS) in exhaled breath 

32 condensate and the NQO1wt and GSTM1null genotypes (Corradi et al., 2002). However, 

33 none of the spirometric endpoints (e.g., FEV1) were affected by O3 exposure. 
Draft – Do Not Cite or Quote 6-24 June 2012

1 In a controlled exposure of mild-to-moderate asthmatics (n = 23; 33 ± 11 years) to 

2 300 ppb O3 for 2 hours with moderate exercise, Vagaggini et al. (2010) found that six of 

3 the subjects had a NQO1wt and GSTM1 null, but this genotype was not associated with 

4 the changes in lung function or inflammatory responses to O3. Kim et al. (2011) also 

5 recently reported that GSTM1 genotype was not predictive of FEV1 responses in young 

6 healthy adults (32 F, 27 M; 25.0 ± 0.5 year) who were roughly half GSTM1-null and half 

7 GSTM1-sufficient. Sputum neutrophil levels, measured in a subset of the subjects (13 F, 

8 11 M), were also not significantly associated with GSTM1 genotype.

9 In a study of healthy volunteers with GSTM1 sufficient (n = 19; 24 ± 3) and GSTM1 null 

10 (n = 16; 25 ± 5) genotypes exposed to 400 ppb O3 for 2 hours with exercise, Alexis et al. 

11 (2009) found that inflammatory responses but not lung function responses to O3 were 

12 dependent on genotype. At 4 hours post-O3 exposure, both GSTM1 genotype groups had 

13 significant increases in sputum neutrophils with a tendency for a greater increase in 

14 GSTM1 sufficient than nulls. At 24 hours postexposure, sputum neutrophils had returned 

15 to baseline levels in the GSTM1 sufficient individuals. In the GSTM1 null subjects, 

16 however, sputum neutrophil levels increased from 4 hours to 24 hours and were 

17 significantly greater than both baseline levels and levels at 24 hours in the GSTM1 

18 sufficient individuals. Since there was no FA control in the Alexis et al. (2009) study, 

19 effects of the exposure other than O3 itself cannot be ruled out. In general, the findings 

20 between studies are inconsistent. 

Body Mass Index

21 In a retrospective analysis of data from 541 healthy, nonsmoking, white males between 

22 the ages of 18-35 years from 15 studies conducted at the U.S. EPA Human Studies 

23 Facility in Chapel Hill, NC, McDonnell et al. (2010) found that increased BMI was 

24 associated with enhanced FEV1 responses to O3. The BMI effect was of the same order of 

25 magnitude but in the opposite direction of the age effect where by FEV1 responses 

26 diminish with increasing age. In a similar retrospective analysis, Bennett et al. (2007)

27 found enhanced FEV1 decrements following O3 exposure with increasing BMI in a group 

28 of 75 healthy, nonsmoking, women (age 24 ± 4 years; BMI range 15.7 to 33.4), but not 

29 122 healthy, nonsmoking, men (age 25 ± 4 years; BMI range 19.1 to 32.9). In the women, 

30 greater O3-induced FEV1 decrements were seen in overweight (BMI >25) than in normal 

31 weight (BMI from 18.5 to 25), and in normal weight than in underweight (BMI <18.5) 

32 (P trend ≤ 0.022). Together, these results indicate that higher BMI may be a risk factor 

33 for pulmonary effects associated with O3 exposure.
Draft – Do Not Cite or Quote 6-25 June 2012

Repeated Ozone Exposure Effects

1 The attenuation of responses observed after repeated consecutive O3 exposures in 

2 controlled human exposure studies has also been referred to in the literature as 

3 “adaptation” or “tolerance” (e.g., Linn et al., 1988). In animal toxicology studies, 

4 however, the term tolerance has more classically been used to describe the phenomenon 

5 wherein a prior exposure to a low, nonlethal concentration of O3 provides some 

6 protection against death and lung edema at a higher, normally lethal exposure 

7 concentration (see Section 9.3.5 of U.S. EPA, 1986). The term “attenuation” will be used 

8 herein to refer to the reduction in responses to O3 observed with repeated O3 exposures in 

9 controlled human exposure studies. Neither tolerance nor attenuation should be presumed 

10 to imply complete protection from the biological effects of inhaled O3, because 

11 continuing injury still occurs despite the desensitization to some responses. 

12 The attenuation of responses due to ambient O3 exposure was first investigated by 

13 Hackney et al. (1976); (1977a). Experiencing frequent ambient O3 exposures, Los 

14 Angeles residents were compared to groups having less ambient O3 exposure. Following 

15 a controlled laboratory exposure to 370-400 ppb O3 for 2 hours with light intermittent 

exercise (2-2.5 times resting V̇ 16 E), the Los Angeles residents exhibited minimal FEV1

17 responses relative to groups having less ambient O3 exposure. Subsequently, Linn et al. 

18 (1988) examined the seasonal variation in Los Angeles residents’ responses to O3

19 exposure. A group of 8 responders (3M, 5F) and 9 nonresponders (4M, 5F) were exposed 

to 180 ppb O3 for 2 hours with heavy intermittent exercise (V̇

E = 35 L/min per m2 20 BSA) 

21 on four occasions (spring, fall, winter, and the following spring). In responders, relative 

22 to the first spring exposures, FEV1 responses were attenuated in the fall and winter, but 

23 returned to similar decrements the following spring. By comparison, the nonresponders, 

24 on average, showed no FEV1 decrements on any of the four occasions. In subjects 

25 recruited regardless of FEV1 responsiveness to O3 from the area around Chapel Hill, NC, 

26 no seasonal effect of ambient O3 exposure on FEV1 responses following chamber 

27 exposures to O3 has been observed (Hazucha et al., 2003; McDonnell et al., 1985b).

28 Based on studies reviewed in previous O3 AQCDs, several conclusions can be drawn 

29 about repeated 1- to 2-h O3 exposures. Repeated exposures to O3 causes enhanced 

30 (i.e., greater decrements) FVC and FEV1 responses on the second day of exposure. The 

31 enhanced response appears to depend to some extent on the magnitude of the initial 

32 response (Horvath et al., 1981). Small responses to the first O3 exposure are less likely to 

33 result in an enhanced response on the second day of O3 exposure (Folinsbee et al., 1994). 

34 With continued daily exposures (i.e., beyond the second day) there is a substantial (or 

35 even total) attenuation of pulmonary function responses, typically on the third to 

36 fifth days of repeated O3 exposure. This attenuation of responses is lost in 1 week (Kulle 
Draft – Do Not Cite or Quote 6-26 June 2012

1 et al., 1982; Linn et al., 1982b) or perhaps 2 weeks (Horvath et al., 1981) without O3

2 exposure. In temporal conjunction with pulmonary function changes, symptoms induced 

3 by O3 (e.g., cough, pain on deep inspiration, and chest discomfort), are also increased on 

4 the second exposure day but are attenuated with repeated O3 exposure thereafter (U.S. 

5 EPA, 1998b; Foxcroft and Adams, 1986; Linn et al., 1982b; Folinsbee et al., 1980). In 

6 longer-duration (4-6.6 hours), lower-concentration studies that do not cause an enhanced 

7 second-day response, the attenuation of response to O3 appears to proceed more rapidly 

8 (Folinsbee et al., 1994). 

9 Consistent with other investigators, Frank et al. (2001) found FVC and FEV1 decrements 

10 to be significantly attenuated following four consecutive days of exposure to O3

11 (250 ppb, 2 h). However, the effects of O3 on the small airways (assessed by a combined 

12 index of isovolumetric forced expiratory flow between 25 and 75% of vital capacity 

13 [FEF25-75] and flows at 50% and 75% of FVC) showed a persistent functional reduction 

14 from Day 2 through Day 4. Notably, in contrast to FVC and FEV1 which exhibited a 

15 recovery of function between days, there was a persistent effect of O3 on small airways 

16 function such that the baseline function on Day 2 through Day 4 was depressed relative to 

17 Day 1. Frank et al. (2001) also found neutrophil (PMN) numbers in BAL remained 

18 significantly higher following O3 (24 hours after last O3 exposure) compared to FA. 

19 Markers from bronchioalveolar lavage fluid (BALF) following 4 consecutive days of 

20 both 2-hour (Devlin et al., 1997) and 4-hour (Jorres et al., 2000; Christian et al., 1998)

21 exposures have indicated ongoing cellular damage irrespective of the attenuation of some 

22 cellular inflammatory responses of the airways, lung function and symptoms response. 

23 These data suggest that the persistent small airways dysfunction assessed by Frank et al. 

24 (2001) is likely induced by both neurogenic and inflammatory mediators, since the 

25 density of bronchial C-fibers is much lower in the small than large airways. 

Summary of Controlled Human Exposure Studies on Lung Function 

26 Responses in humans exposed to ambient O3 concentrations include: decreased 

27 inspiratory capacity; mild bronchoconstriction; rapid, shallow breathing pattern during 

28 exercise; and symptoms of cough and pain on deep inspiration (U.S. EPA, 2006b, 1996a). 

29 Discussed in subsequent Section 6.2.2.1 and Section 6.2.3.1, exposure to O3 also results 

30 in airway hyperresponsiveness, pulmonary inflammation, immune system activation, and 

31 epithelial injury (Que et al., 2011; Mudway and Kelly, 2004a). Reflex inhibition of 

32 inspiration results in a decrease in forced vital capacity and, in combination with mild 

33 bronchoconstriction, contributes to a decrease in the FEV1. Healthy young adults exposed 

34 to O3 concentrations ≥ 60 ppb develop statistically significant reversible, transient 

35 decrements in lung function and symptoms of breathing discomfort if minute ventilation 

36 or duration of exposure is increased sufficiently (Kim et al., 2011; McDonnell et al., 
Draft – Do Not Cite or Quote 6-27 June 2012

1 2010; Schelegle et al., 2009; Brown et al., 2008; Adams, 2006a). With repeated O3

2 exposures over several days, FEV1 and symptom responses become attenuated in both 

3 healthy individuals and asthmatics, but this attenuation of responses is lost after about 

4 a week without exposure (Gong et al., 1997a; Folinsbee et al., 1994; Kulle et al., 1982). 

5 In contrast to the attenuation of FEV1 responses, there appear to be persistent O3 effects 

6 on small airways function as well as ongoing cellular damage during repeated exposures. 

7 There is a large degree of intersubject variability in lung function decrements 

8 (McDonnell, 1996). However, these lung function responses tend to be reproducible 

9 within a given individual over a period of several months indicating differences in the 

10 intrinsic responsiveness of individuals (Hazucha et al., 2003; McDonnell et al., 1985b). 

11 In healthy young adults, O3-induced decrements in FEV1 do not appear to depend on 

12 gender (Hazucha et al., 2003), body surface area or height (McDonnell et al., 1997), lung 

13 size or baseline FVC (Messineo and Adams, 1990). There is limited evidence that blacks 

14 may experience greater O3-induced decrements in FEV1 than age-matched whites (Que et 

15 al., 2011; Seal et al., 1993). Healthy children experience similar spirometric responses 

16 but lesser symptoms from O3 exposure relative to young adults (McDonnell et al., 

17 1985a). On average, spirometric and symptom responses to O3 exposure appear to decline 

18 with increasing age beyond about 18 years of age (McDonnell et al., 1999b; Seal et al., 

19 1996). There is a tendency for slightly increased spirometric responses in individuals 

20 with mild asthma and allergic rhinitis relative to healthy young adults (Jorres et al., 

21 1996). Spirometric responses in asthmatics appear to be affected by baseline lung 

22 function, i.e., responses increase with disease severity (Horstman et al., 1995). 

23 Available information on recovery of lung function following O3 exposure indicates that 

24 an initial phase of recovery in healthy individuals proceeds relatively rapidly, with acute 

25 spirometric and symptom responses resolving within about 2 to 4 hours (Folinsbee and 

26 Hazucha, 1989). Small residual lung function effects are almost completely resolved 

27 within 24 h. One day following O3 exposure, persistent effects on the small airways 

28 assessed by decrements in FEF25-75 and altered ventilation distribution have been reported 

29 (Frank et al., 2001; Foster et al., 1997). 

6.2.1.2 Epidemiology

30 The O3-induced lung function decrements consistently demonstrated in controlled human 

31 exposure studies (Section 6.2.1.1) provide biological plausibility for the epidemiologic 

32 evidence consistently linking short-term increases in ambient O3 concentration with lung 

33 function decrements in diverse populations. In the 1996 and 2006 O3 AQCDs, coherence 

34 with controlled human exposure study results was found not only for epidemiologic 
Draft – Do Not Cite or Quote 6-28 June 2012

1 associations observed in groups with expected higher ambient O3 exposures and higher 

2 exertion levels, including children attending summer camps and adults exercising or 

3 working outdoors, but also for associations observed in children and individuals with 

4 asthma (U.S. EPA, 2006b, 1996a). Recent epidemiologic studies focused more on 

5 children with asthma rather than groups with increased outdoor exposures or other 

6 healthy populations. Whereas recent studies contributed less consistent evidence, the 

7 cumulative body of evidence indicates decreases in lung function in association with 

8 increases in ambient O3 concentration in children with asthma. Collectively, studies in 

9 adults with asthma and individuals without asthma found both O3-associated decreases 

10 and increases in lung function. Recent studies did provide additional data to assess 

11 whether particular lags of O3 exposure were more strongly associated with decrements in 

12 lung function; whether O3 associations were confounded by copollutant exposures; and 

13 whether associations were modified by factors such as corticosteroid (CS) use, genetic 

14 polymorphisms, and elevated BMI. 

Populations with Increased Outdoor Exposures

15 Epidemiologic studies primarily use ambient O3 concentrations to represent exposure; 

16 however, few studies have accounted for time spent outdoors, which has been shown to 

17 influence the relationship between ambient concentrations and individual exposures to O3 

18 (Section 4.3.3). Epidemiologic studies of individuals engaged in outdoor recreation, 

19 exercise, or work are noteworthy for the likely greater extent to which ambient O3

20 concentrations represent ambient O3 exposures. Ambient O3 concentrations, locations, 

21 and time periods for epidemiologic studies of populations with increased outdoor 

22 exposures are presented in Table 6-2. Most of these studies measured ambient O3 at the 

23 site of subjects’ outdoor activity and related lung function changes to the O3

24 concentrations measured during outdoor activity, which have contributed to higher O3

25 personal exposure-ambient concentration correlations and ratios (Section 4.3.3). Because 

26 of improved O3 exposure estimates, measurement of lung function before and after 

27 discrete periods of outdoor activity, and examination of O3 effects during exertion when 

28 the dose of O3 reaching the lungs may be higher due to higher ventilation and inhalation 

29 of larger volumes of air, epidemiologic studies of populations with increased outdoor 

30 exposures are more comparable to controlled human exposure studies. Further, these 

31 epidemiologic studies provide strong evidence for respiratory effects in children and 

32 adults related to ambient O3 exposure. Similar to findings from controlled human 

33 exposure studies, the collective body of epidemiologic evidence clearly demonstrates 

34 decrements in lung function in association with increases in ambient O3 exposure during 

35 periods of outdoor activity (Figure 6-3 to Figure 6-5 and Table 6-3 to Table 6-5). 
Draft – Do Not Cite or Quote 6-29 June 2012

Table 6-2 Mean and upper percentile ozone concentrations in epidemiologic 

studies of lung function in populations with increased outdoor 

exposures.

Study* Location Study Period O3 Averaging Time Mean/Median 

Concentration 

(ppb)

Upper Percentile 

Concentrations (ppb)

Thurston et al. 

(1997)

Connecticut River 

Valley, CT

June 1991-1993 1-h max 83.6 Max: 160

Berry et al. 

(1991)

Mercer County, 

NJ

July 1988 1-h maxa NR Max: 204

Spektor and 

Lippmann 

(1991)

Fairview Lake, NJ July-August 

1988 

1-h avgb 69 Max: 137

Avol et al. 

(1990)

Idyllwild, CA June-August 

1988 

1-h avgb 94 Max: 161

Burnett et al. 

(1990)

Lake 

Couchiching, 

Ontario, Canada

June-July 1983 1-h avgb 59 Max: 95

Higgins et al. 

(1990)

San Bernardino, 

CA

June-July 1987 1-h avgb 123 Max: 245

Raizenne et al. 

(1989)

Lake Erie, 

Ontario, Canada

July-August 

1986 

1-h avgb 71 Max: 143

Spektor et al. 

(1988a)

Fairview Lake, NJ July-August 

1984 

1-h avgb 53 Max: 113

Neas et al. 

(1999)

Philadelphia, PA July-September 

1993 

12-h avga

(9 a.m. - 9 p.m.)

57.5 (near Camp 

1) 55.9 (near 

Camp 2)

Max (near Camp 1): 106

Nickmilder et 

al. (2007)

Southern Belgium July-August 

2002 

1-h max

8-h max

NR Max (across 6 camps):

24.5-112.7c

Max (across 6 camps): 

18.9-81.1c

Girardot et al.

(2006)

Great Smoky 

Mountain NP, TN

August-October 

2002 JuneAugust 2003

Hike-time avg

(2-9 h)d

48.1 Max: 74.2

Korrick et al. 

(1998)

Mt. Washington, 

NH

Summers 1991, 

1992 

Hike-time avg 

(2-12 h)d

40 Max: 74

Hoppe et al. 

(2003)

Munich, Germany Summers 1992-

1995

30-min max (1-4 

p.m.)

High O3 days: 65.9 

Control O3 days: 

27.2

Max (high O3 days): 86

Spektor et al. 

(1988b)

Tuxedo, NY June-August 

1985 

Exercise-time avg 

(15 - 55 min)

NR Max: 124

Selwyn et al. 

(1985)

Houston, TX May-October 

1981 

Exercise-time 15-

min max (4-7 p.m.)

47 Max: 135

Brunekreef et 

al. (1994)

Eastern 

Netherlands

June-August 

1981 

Exercise-time avga

(10-145 min)

42.8c Max: 99.5c

BraunFahrlander et 

al. (1994)

Southern 

Switzerland

May-October 

1989 

Exercise-time 

30-min avg

NR Max: 80c

Castillejos et 

al. (1995)

Mexico City, 

Mexico

June 1990-

October 1991

1-h maxa 179 Max: 365

Hoek et al. 

(1993)

Wageningen, 

Netherlands

May-July 1989 1-h maxa NR Max: 122c
Draft – Do Not Cite or Quote 6-30 June 2012

Study* Location Study Period O3 Averaging Time Mean/Median 

Concentration 

(ppb)

Upper Percentile 

Concentrations (ppb)

Hoppe et al. 

(1995)

Munich, Germany Summers 1992-

1995

30-min max (1-4 

p.m.)

High O3 days: 64 

Control O3 days: 

32

Max (high O3 days): 77

Chan and Wu 

(2005)

Taichung City, 

Taiwan

NovemberDecember 2001 8-h avg (9 a.m.-

5 p.m.)

1-h max

35.6

52.6

Max: 65.1

95.5

Brauer et al. 

(1996)

British Columbia, 

Canada

June-August 

1993 

1-h maxa 40 Max: 84

Romieu et al. 

(1998b)

Mexico City, 

Mexico

March-August 

1996 

Work-shift avg 

(6 - 12 h)a

67.3 95th: 105.8

Thaller et al. 

(2008)

Galveston, TX Summer 2002-

2004

1-h max 35 (median) Max: 118

* Note: Studies presented in order of first appearance in the text of this section.

NR = not reported. 

a

Some or all measurements obtained from monitors located off site of outdoor activity.

b

1-h avg, preceding lung function measurement, as reported in the pooled analysis by Kinney et al. (1996).

c

Concentrations converted from μg/m3 to ppb using the conversion factor of 0.51 assuming standard temperature (25°C) and 

pressure (1 atm).

d

Individual-level estimates calculated from concentrations measured in different segments of hiking trail.

Children Attending Summer Camps

1 Studies of children attending summer camps, most of which were discussed in the 1996 

2 O3 AQCD, have provided important evidence of the impact of ambient O3 exposure on 

3 respiratory effects in young, healthy children. In addition to the improved exposure 

4 assessment as described above, these studies were noted for their daily assessment of 

5 lung function by trained staff over 1- to 2-week periods in the mornings and late 

6 afternoons before and after hours of outdoor activity (Thurston et al., 1997; Berry et al., 

7 1991; Spektor and Lippmann, 1991; Avol et al., 1990; Burnett et al., 1990; Higgins et al., 

8 1990; Raizenne et al., 1989; Spektor et al., 1988a). 

9 In groups mostly comprising healthy children (ages 7-17 years), decrements in FEV1

10 were associated consistently with increases in ambient O3 concentration averaged over 

11 the 1-12 hours preceding lung function measurement (Figure 6-3 and Table 6-3). Kinney 

12 et al. (1996) corroborated this association in a re-analysis combining 5,367 lung function 

13 measurements collected from 616 healthy children from six studies (Spektor and 

14 Lippmann, 1991; Avol et al., 1990; Burnett et al., 1990; Higgins et al., 1990; Raizenne et 

15 al., 1989; Spektor et al., 1988a). Based on uniform statistical methods, a -20 ml (95% CI: 

16 -25, -14) change in afternoon FEV1 was estimated for a 40-ppb increase in O3

17 concentration averaged over the 1 hour before lung function measurement (Kinney et al., 

18 1996) (all effect estimates are standardized to increments specific to the O3 averaging 

19 time as detailed in Section 2.1). All of the studies in the pooled analysis were conducted 
Draft – Do Not Cite or Quote 6-31 June 2012

1 during summer months but were diverse in locations examined (i.e., Northeast U.S., 

2 Canada, California), range in ambient concentrations of O3 (presented within Table 6-2) 

3 and other pollutants measured, and magnitudes of association observed. Study-specific 

4 effect estimates ranged between a 0.76 and 48 mL decrease or a 0.3% to 2.2% decrease in 

5 study mean FEV1 per 40-ppb increase in 1-h avg O3.

6 Among camp studies included the pooled analysis plus others, associations for peak 

7 expiratory flow (PEF) were more variable than were those for FEV1, as indicated by the 

8 wider range in effect estimates and wider 95% CIs (Figure 6-3 and Table 6-3). 

9 Nonetheless, in most cases, increases in ambient O3 concentration were associated with 

10 decreases in PEF. The largest O3-associated decrease in PEF (mean 2.8% decline per 

11 40-ppb increase in 1-h max O3) was found in a group of campers with asthma, in whom 

12 an increase in ambient O3 concentration also was associated with increases in chest 

13 symptoms and bronchodilator use (Thurston et al., 1997).

14 For both FEV1 and PEF, the magnitude of association was not related to the study mean 

15 ambient 1-h avg or max O3 concentration. With exclusion of results from Spektor and 

16 Lippmann (1991), larger O3-associated FEV1 decrements were found in populations with 

17 lower mean FEV1. No trend was found with mean PEF. Sufficient data were not provided 

18 to assess whether the temporal variability in O3 concentrations, activity levels of subjects, 

19 or associations with other pollutants contributed to between-study heterogeneity in O3 

20 effect estimates.
Draft – Do Not Cite or Quote 6-32 June 2012

Note: Results generally are presented in order of increasing mean ambient O3 concentration. Effect estimates are from singlepollutant models and are standardized to a 40-ppb increase for 1-h avg or 1-h max O3 concentration and a 30-ppb increase for 

12-h avg O3 concentration.

Figure 6-3 Changes in FEV1 (mL) or PEF (mL/sec) in association with ambient 

ozone concentrations among children attending summer camp.

Study

FEV1 (ml)

Spektor et al. (1988a)

Spektor and Lippmann 

(1991)

Raizenne et al. (1989)

Burnett et al. (1990)

Higgins et al. (1990)

Avol et al. (1990)

Kinney et al. (1996)

Berry et al. (1991)

Population

Campers without asthma

Campers without asthma

Campers without asthma

Campers without asthma

Campers without asthma

Campers without asthma

Pooled estimate

Campers without asthma

-160 -120 -80 -40 0 40 80

Change in FEV1 (ml) per unit increase in ambient O3 (95% CI)

PEF (ml/sec)

Spektor et al. (1988a)

Raizenne et al. (1989)

Burnett et al. (1990)

Higgins et al. (1990)

Avol et al. (1990)

Kinney et al. (1996)

Berry et al. (1991)

Neas et al. (1999)

Thurston et al. (1997)

Campers without asthma

Campers without asthma

Campers without asthma

Campers without asthma

Campers without asthma

Pooled estimate

Campers without asthma

Campers without asthma

Campers with asthma

◄

◄

►

-160 -120 -80 -40 0 40 80

Change in PEF (ml/sec) per unit increase in ambient O3 (95% CI)
Draft – Do Not Cite or Quote 6-33 June 2012

Table 6-3 Additional characteristics and quantitative data for studies 

represented in Figure 6-3.

Study Location Population, Mean FEV1

(mL) 

or PEF (mL/sec)

Standardized 

Percent Change 

(95% CI)a

Standardized Effect 

Estimate (95% CI)a

FEV1 (mL)

Spektor et al. 

(1988a)

Fairview Lake, NJ 91 campers without asthma 

ages 8-15 yr, 2,140

-0.93 (-1.5, -0.35)b -20.0 (-32.5, -7.5)b

Spektor and 

Lippmann (1991)

Fairview Lake, NJ 46 campers without asthma 

ages 8-14 yr, 2,390

-2.2 (-3.0, -1.3)b -51.6 (-72.8, -30.4)b

Burnett et al. 

(1990)

Lake Couchiching, 

Ontario, Canada

29 campers without asthma 

ages 7-15 yr, 2,410

-0.32 (-1.7, 1.1)b -7.6 (-42.1, 26.9)b

Raizenne et al. 

(1989)

Lake Erie, Ontario, 

Canada

112 campers without asthma 

mean age 11.6 yr, 2,340

-0.50 (-0.83, -0.16)b -11.6 (-19.4, -3.8)b

Avol et al. (1990) Pine Springs, CA 295 campers without asthma 

ages 8-17 yr, 2,190

-0.58 (-1.0, -0.12)b -12.8 (-23.0, -2.6)b

Higgins et al. 

(1990)

San Bernardino, CA 43 campers without asthma 

ages 7-13 yr, 2,060

-1.6 (-2.4, -0.87)b -33.6 (-49.3, -17.9)b

Kinney et al. 

(1996)

Pooled analysis of 

preceding 6 studies

616 campers without asthma 

ages 7-17 yr, 2,300

-0.87 (-1.1, -0.63) -20.0 (-25.5, -14.5)b

Berry et al. (1991) Hamilton, NJ 14 campers without asthma 

58% age <14 yr, NA

NA 32.8 (6.9, 58.7)

PEF (mL/sec)

Spektor et al. 

(1988a)

Fairview Lake, NJ 91 campers without asthma 

ages 8-15 yr, 4,360

-1.8 (-3.3, -0.40) -80.0 (-142.7, -17.3)b

Burnett et al. 

(1990)

Lake Couchiching, 

Ontario, Canada

29 campers without asthma 

ages 7-15 yr, 5,480

-1.9 (-3.8, -0.05) -106.4 (-209.9, -2.9)b

Raizenne et al. 

(1989)

Lake Erie, Ontario, 

Canada

112 campers without asthma 

mean age 11.6 yr, 5,510

-0.07 (-0.56, 0.41) -4.0 (-30.7, 22.7)b

Avol et al. (1990) Pine Springs, CA 295 campers without asthma 

ages 8-17 yr, 4,520

1.9 (0.71, 3.1) 86.8 (31.9, 142)b

Higgins et al. 

(1990)

San Bernardino, CA 43 campers without asthma 

ages 7-13 yr, 5,070

-0.87 (-2.1, 0.34) -44.0 (-105, 17.2)b

Kinney et al. 

(1996)

Pooled analysis of 

preceding 6 studies

616 campers without asthma 

ages 7-17 yr, 4,222

0.31 (-0.88, 1.5) 6.8 (-19.1, 32.7)b

Thurston et al. 

(1997)

CT River Valley, CT 166 campers with asthma 

ages 7-13 yr, 5,333

-2.8 (-4.9, -0.59) -146.7 (-261.7, -31.7)

Neas et al. (1999) Philadelphia, PA 156 campers without asthma 

ages 6-11 yr, 4,717

-0.58 (-1.5, 0.33) -27.5 (-70.8, 15.8)

Berry et al. (1991) Hamilton, NJ 14 campers without asthma 

58% age <14 yr, NA

NA -40.4 (-132.1, 51.3)

*Includes studies form Figure 6-3.

NA = Data not available.

a

All results are standardized to a 40-ppb increase in 1-h avg or 1-h max O3, except that from Neas et al. (1999), which is 

standardized to a 30-ppb increase in 12-h avg (9 a.m.-9 p.m.) O3.

b

Effect estimates were reported in the pooled analysis by Kinney et al. (1996).
Draft – Do Not Cite or Quote 6-34 June 2012

1 Similar to controlled human exposure studies, camp studies found interindividual 

2 variability in the magnitude of O3-associated changes in lung function. Based on separate 

3 regression analyses of data from individual subjects, increases in ambient O3

4 concentration were associated with a wide range of changes in lung function across 

5 subjects (Berry et al., 1991; Higgins et al., 1990; Spektor et al., 1988a). For example, 

6 among children attending camp in Fairview Lake, NJ, 36% of subjects had statistically 

7 significant O3-associated decreases in FEV1, and the 90th percentile of response was a 

8 6.3% decrease in FEV1 per a 40-pbb increase in 1-h avg O3 (Spektor et al., 1988a).

9 In contrast with previous studies, a recent study of children attending six different 

10 summer camps in Belgium did not find an association between ambient O3 concentration 

11 and lung function (Nickmilder et al., 2007). This study examined similar ambient O3

12 concentrations as did previous studies (Table 6-2) but used a less rigorous methodology. 

13 Lung function was measured only once in each subject, and mean lung function was 

14 compared among camps. Children at camps with higher daily 1-h max or 8-h max O3 

15 concentrations did not consistently have larger decreases in mean intraday FEV1 or 

16 FEV1/FVC (Nickmilder et al., 2007).

Populations Exercising Outdoors

17 As discussed in the 1996 and 2006 O3 AQCDs, epidemiologic studies of adults exercising 

18 outdoors have provided evidence for lung function decrements in healthy adults 

19 associated with increases in ambient O3 exposure during exercise with durations (10 min 

20 to 12 h) and intensities (heart rates 121-190 beats per min) in the range of those examined 

21 in controlled human exposure studies (Table 6-1). As in the camp studies, lung function 

22 was measured before and after exercise by trained staff. Collectively, studies of adults 

found FEV1 decrements of 1.3 to 1.5% per unit increase in O3

1 23 (Figure 6-4 and 

24 Table 6-4). The magnitude of association did not appear to be related to study mean 

25 ambient O3 concentrations (Table 6-2), exercise duration, or the mean heart rate 

26 measured during exercise (Figure 6-4 and Table 6-4). Increases in ambient O3 

27 concentration also were associated with decreases in lung function in children exercising 

28 outdoors (Table 6-4). 

 1

Effect estimates were standardized to a 40-ppb increase in O3 averaged over 15 min to 1 h and a 30-ppb increase for O3

averaged over 2 to 12 h.
Draft – Do Not Cite or Quote 6-35 June 2012

Note: Studies generally are presented in order of increasing duration of outdoor exercise. Data refer to the maximum or mean 

measured during exercise or in different groups or conditions as described in Table 6-4. 

a

bpm = beats per minute. NR = Not reported. Effect estimates are from single-pollutant models and are standardized to a 40-ppb 

increase for O3 concentrations averaged over 15 minutes to 1 hour and a 30-ppb increase for O3 concentrations averaged over 2 to 

12 hours.

Figure 6-4 Percent change in FEV1 in association with ambient ozone 

concentrations among adults exercising outdoors.

Study

Korrick et al. (1998)

Girardot et al. (2006)

Hoppe et al. (2003)

Spektor et al. (1988b)

Brunekreef et al. (1994)

Population

Adults hiking

Adults hiking

Adults exercising

Adults exercising

Adults exercising

Exercise

duration

2-12 h

2-9 h

2 h

15-55 min

10 min-1 h

Mean heart

rate (bpm)a

max: 122

max: 121

NR

162, 145

161, 176

-4 -3 -2 -1 0 1 2

Percent change in FEV1 per unit increase

in O3 (95% CI)
Draft – Do Not Cite or Quote 6-36 June 2012

Table 6-4 Additional characteristics and quantitative data for studies 

represented in Figure 6-4 plus results from studies in children 

exercising outdoors.

Study* Location Population Exercise 

Duration, Mean 

Heart Rate

O3 Averaging 

Time

Parameter Standardized

Percent 

Change 

(95% CI)a

Studies of adults

Brunekreef et 

al. (1994)

Netherlands 29 adults 

exercising, 

ages 18-37 yr

10 min - 2.4 h,

HR: 161 bpm 

(training), 176 bpm 

(races)

Exercise 

duration

FEV1

PEF

-1.3 (-2.2, -0.37)

-2.5 (-3.8, -1.2)

Spektor et al. 

(1988b)

Tuxedo, NY 30 adults 

exercising, 

ages 21-44 yr

15 - 55 min, 

HR:162 bpm if V̇

E

>100 L, 145 bpm if 

V̇

E 60-100 L

30-min avg FEV1 -1.31 (-2.0, -0.65)

Hoppe et al. 

(2003)

Munich, 

Germany

43 adults and 

children exercising, 

ages 13-38 yr

2 h, HR: NR 30-min max 

(1-4 p.m.)

FEV1

PEF

-1.3 (-2.6, 0.10)

-2.8 (-5.9, 0.31)

Girardot et al. 

(2006)

Great Smoky 

Mt, TN

354 adult day 

hikers, ages 18-

82 yr

2-9 h, max HR:121 

bpm

Hike duration FEV1

PEF

0.72 (-0.46, 1.90)

3.5 (-0.11, 7.2)

Korrick et al. 

(1998)

Mt. 

Washington, 

NH

530 adult day 

hikers, ages 18-

64 yr

2-12 h, max HR: 

122 bpm

Hike duration FEV1

PEF

-1.5 (-2.8, -0.24)

-0.54 (-4.0, 2.9)

Selwyn et al. 

(1985)

Houston, TX 24 adults 

exercising, 

ages 29-47 yr

Duration: NR, 

max HR: 

179 bpm in males, 

183 bpm in females

15-min max FEV1 -16 mL (-28.8, 

-3.2)b

Studies of children not included in Figure 6-4

BraunFahrlander et 

al. (1994)

Switzerland 128 children 

exercising, 

ages 9-11 yr

10 min, max 

HR: 180 bpm

30-min avg PEF -3.8 (-6.7, -0.96)

Castillejos et 

al. (1995)

Mexico City, 

Mexico

40 children 

exercising, ages 7-

11 yr

2 15 min with 

15 min rest periods, 

max HR: <190 bpm

1-h avg over full 

exercise-rest 

period

FEV1 -0.48 (-0.72, -0.24)

Hoek et al. 

(1993)

Wageningen, 

Netherlands

65 children 

exercising, ages 7-

12 yr

25 min-1.5 h, 

HR: NR

1-h max PEF -2.2 (-4.9, 0.54)

*Includes studies from Figure 6-4, plus others.

HR = heart rate, bpm = beats per minute, V̇

E = minute ventilation, NR = Not reported.

a

Effect estimates are standardized to a 40-ppb increase for O3 concentrations averaged over 15 minutes to 1 hour and a 30-ppb 

increase for O3 concentrations averaged over 2 to 12 hours.

b

Results not included in the figure because data were not provided to calculate percent change in lung function.

1 Compared with the studies of individuals exercising outdoors described above, analyses 

2 of day-hikers assessed lung function only on one day per subjects but examined longer 

3 periods of outdoor activity and included much larger sample sizes. Studies of adult day4 hikers had similar design but produced contrasting results (Girardot et al., 2006; Korrick 

5 et al., 1998). Among 530 hikers on Mt. Washington, NH, Korrick et al. (1998) reported 
Draft – Do Not Cite or Quote 6-37 June 2012

1 posthike declines in FEV1 and FVC of 1.5% and 1.3%, respectively, per a 30-ppb 

2 increase in 2- to 12-h avg O3. Associations with FEV1/FVC, FEF25-75%, and PEF were 

3 weaker. In contrast, among 354 hikers on Great Smoky Mt, TN, Girardot et al. (2006)

4 found that higher O3 concentrations were associated with posthike increases in many of 

5 the same lung function indices (Figure 6-4 and Table 6-4). These studies were similar in 

6 the examination of a mostly white, healthy population and of changes in lung function 

7 associated with ambient O3 concentrations measured on site during multihour (2-12 h) 

8 periods of outdoor exercise. Mean O3 concentrations were similar as were the population 

9 mean and variability in lung function. However, Girardot et al. (2006) differed from 

10 Korrick et al. (1998) in several aspects, including a shorter hike time (maximum: 9 versus 

11 12 h), older age of subjects (maximum: 82 versus 64 yr), and measurement of lung 

12 function by a larger number of less well-trained technicians. The impact of these 

13 differences on the heterogeneity in results between the studies was not examined. 

14 Similar to the camp studies, some studies of outdoor exercise examined and found 

15 interindividual variability in the magnitude of O3-associated decreases in lung function. 

16 In Korrick et al. (1998), although a 30-ppb increase in 2- to 12-h avg ambient O3

17 concentration was associated with a group mean decrement in FEF25-75% of -0.81% 

18 (95% CI: -4.9, 3.3), some individuals experienced a >10% decline. The odds of >10% 

19 decline in FEF25-75% increased with increasing ambient O3 concentration (OR: 2.3 

20 [95% CI: 1.2, 6.7] per 30-ppb increase in 2- to 12-h avg O3). Likewise, Hoppe et al. 

21 (2003) found that compared with days with 30-min max (1-4 p.m.) ambient O3

22 concentrations <40 ppb, on days with O3 >50 ppb, 14% of athletes had at least a 10% 

23 decrease in lung function or 20% increase in airway resistance.

Outdoor Workers

24 Consistent findings in outdoor workers add to the evidence that short-term increases in 

25 ambient O3 exposure decrease lung function in healthy adults (Figure 6-5 and Table 6-5). 

26 Except for Hoppe et al. (1995), studies used central site ambient O3 concentrations. 

27 However, in outdoor workers, ambient concentrations have been more highly correlated 

28 with and similar in magnitude to personal exposures (Section 4.3.3) likely because 

29 workers spend long periods of time outdoors (6-14 hours across studies) and the O3

30 averaging times examined correspond to periods of outdoor work. For example, in a 

31 subset of berry pickers, the correlation and ratio of personal to ambient 24-h avg O3

32 concentrations (15 km from work site) were 0.64 and 0.96, respectively (Brauer and 

33 Brook, 1997). The 6-h avg personal-ambient ratio in a population of shoe cleaners in 

34 Mexico City was 0.56 (O'Neill et al., 2003). Many studies of outdoor workers found that 

35 in addition to same-day concentrations, O3 concentrations lagged 1 or 2 days (Chan and 
Draft – Do Not Cite or Quote 6-38 June 2012

1 Wu, 2005; Brauer et al., 1996) or averaged over 2 days (Romieu et al., 1998b) were 

2 associated with equal or larger decrements in lung function (Figure 6-5 and Table 6-5).

3 Similar to other populations with increased outdoor exposure, most of the magnitudes of 

4 O3-associated lung function decrements in outdoor workers were small, i.e., <1% to 3.4% 

per unit increase in O3 concentration1 5 . The magnitude of decrease was not found to 

6 depend strongly on duration of outdoor work or ambient O3 concentration. The largest 

7 decrease (6.4% per 40-ppb increase in 1-h max O3) was observed in berry pickers in 

8 British Columbia who were examined during a period of relatively low ambient O3

9 concentrations (work shift mean: 26.0 ppb [SD: 11.8]) but had longer daily periods of 

10 outdoor work (8-14 hours) (Brauer et al., 1996) (Figure 6-5 and Table 6-5). However, a 

11 much smaller O3-associated decrease in FEV1 was found in shoe cleaners in Mexico City 

12 who were examined during a period of higher O3 concentrations (work shift mean: 

13 67.3 ppb [SD: 24]) but had period of outdoor work that was as long as that of the berry 

14 pickers. The smallest magnitude of decrease (-0.4% [95% CI: -0.8, 0] in afternoon 

15 FEV1/FVC per 40-ppb increase in 1-h max O3) was observed in lifeguards in Galveston, 

16 TX (Thaller et al., 2008) whose outdoor work periods were shorter than those of the berry 

17 pickers but characterized by a similar range of ambient O3 concentrations. Not all studies 

18 provided information on ventilation rate or pulse rate, thus it was not possible to ascertain 

19 whether differences in the magnitude of O3-associated lung function decrement across 

20 studies were related to differences in the level of exertion of workers.

 1

Effect estimates were standardized to a 40-ppb increase for O3 averaged over 30 min to 1 h and a 30-ppb increase for O3

averaged over 8 or 12 h.
Draft – Do Not Cite or Quote 6-39 June 2012

Note: Studies generally are presented in order of increasing mean ambient O3 concentration. Effect estimates are from singlepollutant models and are standardized to a 40-ppb increase for 30-min, 1-h avg, or 1-h max O3 concentrations.

Figure 6-5 Percent change in FEV1 or FEV1/FVC in association with ambient 

ozone concentrations among outdoor workers.

Study

Thaller et al. (2008)

Brauer et al. (1996)

Hoppe et al. (1995)

Romieu et al. (1998)

Population

Lifeguards

Berry pickers

Forestry workers

Shoe Cleaners

Parameter

FVC

FEV1/FVC

FEV1

FEV1

FEV1

O3 Lag

0

0

1

0

0

0-1 avg

Subgroup

Placebo

Antioxidant supplement

Placebo

Antioxidant supplement

-8 -7 -6 -5 -4 -3 -2 -1 0 1 2

Percent change in lung function per unit

increase in O3 (95% CI)
Draft – Do Not Cite or Quote 6-40 June 2012

Table 6-5 Additional characteristics and quantitative data for studies 

represented in Figure 6-5.

Study* Location Population Parameter Duration 

of 

Outdoor 

Work

O3 Averaging 

Time

O3

Lag

Subgroup Standardized 

Percent 

Change 

(95% CI)a

Thaller 

et al. 

(2008)

Galveston, 

TX

142 lifeguards, 

ages 16-27 yr

FVC 6-8 h 1-h max

12-h avg

0 0.24 (-0.28, 

0.72)

0.15 (-0.06, 

0.36)

FEV1/FVC 1-h max

12-h avg

-0.40 (-0.80, 0)

-0.60 (-1.2, 0)

Brauer 

et al.

(1996)

British 

Columbia, 

Canada

58 berry 

pickers, ages 

10-69 yr

FEV1 8-14 h 1-h max 0

1

-5.4 (-6.5, -4.3)

-6.4 (-8.0, -4.7)

Hoppe et 

al. 

(1995)

Munich, 

Germany

41 forestry 

workers, ages 

20-60 yr

FEV1 Not 

reported

30-min max 

(1 - 4 p.m.)

0 -1.4 (-3.0, 0.16)

Romieu 

et al. 

(1998b)

Mexico City, 

Mexico

47 male shoe 

cleaners, mean 

(SD) age: 38.9 

(10) yr

FEV1 Mean (SD): 

9 h (1)

1-h avg before 

lung function 

measurement

0 Placebo

Antioxidant

-2.1 (-3.3, -0.85)

-0.52 (-2.0, 0.97)

0-1 

avg

Placebo

Antioxidant

-3.4 (-6.0, -0.78)

-1.2 (-4.2, 1.8)

Chan 

and Wu 

(2005)

b

Taichung 

City, Taiwan

43 mail carriers. 

Mean (SD) age: 

39 (8) yr

PEF 8 h 1-h max 0

1

-1.3 (-1.7, -0.92)

-1.4 (-1.7, -1.2)

8-h avg 

(9 a.m. - 5 p.m.)

0

1

-1.6 (-2.2, -1.1)

-1.9 (-2.5, -1.3)

*Includes studies from Figure 6-5, plus others.

a

Effect estimates are standardized to a 40-ppb increase for 30-min, 1-h avg, or 1-h max O3 and a 30-ppb increase for 8-h avg or 

12-h avg O3.

b

PEF results not included in figure.

Associations at Lower Ozone Concentrations

1 In some studies of populations with increased outdoor exposures, O3-associated lung 

2 function decrements were observed when maximum or average ambient O3

3 concentrations over 30 minutes to 12 hours did not exceed 80 ppb (Chan and Wu, 2005; 

4 Korrick et al., 1998; Hoppe et al., 1995; Braun-Fahrlander et al., 1994) (presented within 

5 Table 6-2). Korrick et al. (1998) found associations between hike-time average (2-12 h) 

6 O3 concentrations and lung function between concentrations 40 and 74 ppb but not 

7 <40 ppb. Several other studies that included higher maximum ambient O3 concentrations 

8 restricted analyses to observations with 10-min to 1-hour average O3 concentrations 

9 <80 ppb (Table 6-6). Higgins et al. (1990) found that O3-associated lung function 

10 decrements in children attending camp were limited largely to 1-h avg ambient 

11 concentrations >120 ppb; however, many other studies found associations in the lower 

12 range of O3 concentrations (Table 6-6). Among adults exercising outdoors, Spektor et al. 
Draft – Do Not Cite or Quote 6-41 June 2012

1 (1988b) found that for most lung function parameters, effect estimates in analyses 

2 restricted to 30-min max ambient O3 concentrations <80 ppb were similar to those 

3 obtained for the full range of O3 concentrations (Table 6-6). In a study of children 

4 attending summer camp, similar effects were estimated for the full range of 1-h avg O3

5 concentrations and those <60 ppb (Spektor et al., 1988a). Brunekreef et al. (1994) found 

6 increases in ambient O3 concentration (10-min to 1-h) during outdoor exercise to be 

7 associated with decreases in FEV1 in analyses restricted to concentrations <61 

8 (Table 6-6) and <51 ppb (quantitative results not reported). Whereas Brunekreef et al. 

9 (1994) found that effect estimates were near zero with O3 concentrations <41 ppb 

10 (Brunekreef et al., 1994), Brauer et al. (1996) found that associations persisted with 

11 1-h max O3 concentrations <40 ppb (quantitative results not provided).

Table 6-6 Associations between ambient ozone concentration and FEV1

decrements in different ranges of ambient ozone concentrations.

Study Location Population O3 Averaging Time O3 Concentration 

Range

Standardized

Percent Change 

(95% CI)a

Brunekreef et al. 

(1994)

Netherlands 29 adults exercising, 

ages 18-37 yr

10-min to 1-hour 

average during 

exercise

Full range

O3 <61 ppb

-1.3 (-2.2, -0.37)

-2.1 (-4.5, 0.32)

Spektor et al. 

(1988a)

Fairview Lake, 

NJ

91 children without 

asthma at camp, 

ages 8-15 yr

1-hour average 

before afternoon 

FEV1 measurement

Full range

O3 <60 ppb

O3 <80 ppb

-2.7 (-3.3, -2.0)

-2.2 (-3.7, -0.80)

-1.4 (-2.5, -0.34)

Spektor et al. 

(1988b)

Tuxedo, NY 30 adults exercising, 

ages 21-44 yr

30-min average 

during exercise

Full range

O3 <80 ppb

-1.3 (-2.0, -0.64)

-1.3 (-2.4, -0.08)

1998) Mt. 

Washington, 

NH

53 adult day hikers, 

ages 18-64 yr

Hike duration (2-12 h) Full range

O3 40-74 ppb

-1.5 (-2.8, -0.24)

-2.6 (-4.9, -0.32)

Higgins et al. 

(1990)

San 

Bernardino, CA

43 children without 

asthma at camp, 

ages 7-13 yr

1-hour average in the 

6-hours before FEV1

measurement

>120 ppb

<120 ppb

-1.4 (-2.8, 0.03)

0.34 (-1.3, 2.0)

a

Results are presented in order of increasing maximum O3 concentration included in models. Effect estimates are standardized to a 

40-ppb increase for O3 concentrations averaged over 10 min to 1 h and a 30-ppb increase for O3 concentrations averaged over 

2 to 12 h.

Children with Asthma

12 Increases in ambient O3 concentration are associated with lung function decrements in 

13 children with asthma in epidemiologic studies conducted across diverse geographical 

14 locations and a range of ambient O3 concentrations (Table 6-7). Whereas most studies of 

15 populations with increased outdoor exposures monitored O3 concentrations at the site of 

16 subjects’ outdoor activities and used trained staff to measure lung function, studies of 
Draft – Do Not Cite or Quote 6-42 June 2012

1 children with asthma relied more on O3 measured at central monitoring sites and lung 

2 function measured by subjects. Nonetheless, compared with the camp studies, studies of 

3 children with asthma have provided an understanding of the changes in lung function 

4 associated with patterns of outdoor activity and ambient O3 exposure that likely better 

5 represent those of children in the general population. Further, these studies have provided 

6 more information on factors that potentially may increase the risk of O3-associated 

7 respiratory effects and on potential confounding by copollutant exposure or meteorology.

Table 6-7 Mean and upper percentile concentrations of ozone in 

epidemiologic studies of lung function in children with asthma.

Study* Location Study Period O3 

Averaging 

Time

Mean/Median 

Concentration 

(ppb)

Upper Percentile 

Concentrations 

(ppb)

Jalaludin et al. 

(2000)

Sydney, Australia FebruaryDecember 199415-h avg 

(6 a.m.-

9 p.m.)

12 Max: 43

1-h max 26 91

Lewis et al. 

(2005)

Detroit, MI February 2001-

May 2002

24-h avg

8-h max

27.6, 26.5a

40.4, 41.4a

Overall max: 66.3a

Overall max: 92.0a

Just et al. (2002) Paris, France April-June 1996 24-h avg 30.0b Max: 61.7b

Hoppe et al. 

(2003)

Munich, Germany Summers 1992-

1995

30-min max 

(1-4 p.m.)

High O3 days: 66.9c

Control O3 days: 

32.5c

Max: 91 (high O3

days)c

39 (control O3 days)c

Thurston et al. 

(1997)

CT River Valley, CT June 1991-1993 1-h max 83.6c Max: 160c

Romieu et al. 

(2006); (2004b; 

2002)

Mexico City, Mexico October 1998-

April 2000

8-h max

1-h max

69

102

Max: 184

Max: 309

Romieu et al. 

(1997)

Southern Mexico City, Mexico April-July 1991; 

November 

1991-February 

1992

1-h max 196 Max: 390

Romieu et al. 

(1996)

Northern Mexico City, Mexico April-July 1991; 

November 

1991-February 

1992

1-h max 190 Max: 370

O'Connor et al. 

(2008)

Boston, MA; Bronx, 

Manhattan NY; Chicago, IL; 

Dallas, TX, Seattle, WA; 

Tucson, AZ (ICAS)

August 1998-

July 2001

24-h avg NR NR

Mortimer et al. 

(2002)

(2000)

Bronx, East Harlem, NY; 

Baltimore, MD; Washington, 

DC; Detroit, MI, 

Cleveland, OH; Chicago, IL; 

St. Louis, MO (NCICAS)

June-August 

1993

8-h avg

(10 a.m.-6 

p.m.)

48 NR

Gielen et al. 

(1997)

Amsterdam, Netherlands April-July 1995 8-h max 34.2b Max: 56.5b
Draft – Do Not Cite or Quote 6-43 June 2012

Study* Location Study Period O3 

Averaging 

Time

Mean/Median 

Concentration 

(ppb)

Upper Percentile 

Concentrations 

(ppb)

Dales et al. 

(2009)

(2009a)

Windsor, ON, Canada OctoberDecember 200524-h avg

1-h max

13.0

27.2

75th: 26.0

75th: 32.8

Rabinovitch et al. 

(2004)

Denver, CO NovemberMarch 1999-

2002

1-h max 28.2 75th: 36.0, Max 70.0

Barraza-Villarreal 

et al. (2008)

Mexico City, Mexico June 2003-June 

2005

8-h moving 

avg

31.6 Max: 86.3

Wiwatanadate 

and 

Trakultivakorn 

(2010)

Chiang Mai, Thailand August 2005-

June 2006

24-h avg 17.5 90th: 26.82, Max: 

34.65

Delfino et al. 

(2004)

Alpine, CA SeptemberOctober 1999; 

April-June 2000

8-h max 62.9 90th: 83.9, Max: 105.9

HernándezCadena et al. 

(2009)

Mexico City, Mexico May-September 

2005

24-h avg

1-h max

26.3

74.5

75th: 35.3; Max: 62.8

75th: 92.5; Max: 165

*Note: Studies presented in order of first appearance in the text of this section.

ICAS = Inner City Asthma Study, NR = Not Reported, NCICAS = National Cooperative Inner-City Asthma Study.

a

Measurements at two sites established by investigators and located within 5 km of most subjects’ residences.

b

Concentrations converted from μg/m3 to ppb using the conversion factor of 0.51 assuming standard temperature (25°C) and 

pressure (1 atm).

c

Measured where subjects spent daytime hours.

1 In a majority of studies, including large U.S. multicity studies and several smaller studies 

2 conducted in the U.S., Mexico City, and Europe, an increase in ambient O3 concentration 

3 (various averaging times and lags) was associated with a decrement in FEV1 (Figure 6-6

4 and Table 6-8) or PEF (Figure 6-7 and Table 6-9) in children with asthma. Results were 

5 more variable for FEV1, which typically was measured on nonconsecutive days, than for 

6 PEF, which was measured daily. Further, associations with FEV1 were found in specific 

7 subgroups. Some studies found that increases in ambient O3 concentration were 

8 associated with greater lung function variability, i.e., a deviation from a baseline level. 

9 These results pointed to associations of O3 with poorer lung function, as indicated by a 

10 decrease from the individual’s mean lung function over the study period (Jalaludin et al., 

11 2000), a decrease in lung function over the course of the day (Lewis et al., 2005), or a 

12 decrease in the lowest daily measurement (Just et al., 2002). Within many studies, 

13 increases in O3 concentration were associated concurrently (at the same or similar lag) 

14 with decreases in lung function and increases in respiratory symptoms (Just et al., 2002; 

15 Mortimer et al., 2002; Gielen et al., 1997; Romieu et al., 1997; Thurston et al., 1997; 

16 Romieu et al., 1996) (see Figure 6-11 and Table 6-20 for symptom results).
Draft – Do Not Cite or Quote 6-44 June 2012

Note: Results generally are presented in order of increasing mean ambient O3 concentration. CS = Corticosteroid, URI = Upper 

respiratory inf ection. Effect estimates are from single-pollutant models and are standardized to a 40-ppb increase for 30-min or 

1-h max O3 concentrations, a 30-ppb increase for 8-h max or 8-h avg O3 concentrations, and a 20-ppb increase for 24-h avg O3

concentrations.

Figure 6-6 Percent change in FEV1 in association with ambient ozone 

concentrations among children with asthma.

Study

Liu et al. (2009)

Lewis et al. (2005)

Hoppe et al. (2003)

Barraza-Villarreal et al. 

(2008)

Romieu et al. (2002)

Romieu et al. (2006)

O3 Lag

0

1

1

1

0-4 avg

1

1

Subgroup

CS user

With URI

Without asthma

With asthma

Without asthma

With asthma

Placebo

Antioxidant

Placebo

Antioxidant

GSTP1 Ile/Ile or Ile/Val

GSTP1 Val/Val

, moderate/severe

, moderate/severe

asthma

asthma

◄ ►

-10 -8 -6 -4 -2 0 2 4

Percent change in FEV1 per unit increase in O3 (95% CI)
Draft – Do Not Cite or Quote 6-45 June 2012

Table 6-8 Characteristics and quantitative data for studies represented in 

Figure 6-6, of FEV1 or FVC in children with asthma.

Study* Location/Population O3

Averaging 

Time

O3

Lag

Parameter Subgroup Standardized

Percent Change 

(95% CI)a

Liu et al. 

(2009a)

Windsor, ON, Canada

182 children with asthma, 

ages 9-14 yr

24-h avg 0

1

FEV1 -0.89 (-3.5, 1.8)

-0.44 (-2.4, 1.6)

Lewis et al. 

(2005)

Detroit, MI

86 children with asthma, 

mean (SD) age 9.1 (1.4) yr

8-h max 1 Lowest daily 

FEV1

CS user

With URI

-2.1 (-11.4, 8.3)

-6.1 (-10.4, -1.6)

2 CS user

With URI

-8.0 (-13.5, -2.1)

-5.4 (-11.3, 1.0)

Hoppe et 

al. (2003)

Munich, Germany

43 children, ages 12-23 yr

30-min max 

(1-4 p.m.)

1 Afternoon 

FEV1

Without asthma

With asthma

0.93 (-0.80, 2.7)

-0.56 (-4.6, 3.7)

Afternoon 

FVC

Without asthma

With asthma

-0.09 (-1.7, 1.6)

-3.5 (-5.9, -1.0)

BarrazaVillarreal et 

al. (2008)

Mexico City, Mexico

208 children, ages 6-14 yr

8-h avg 0-4 

avg

FEV1 50 without asthma

158 with asthma

-1.5 (-4.7, 1.7)

-0.12 (-2.0, 1.8)

Romieu et 

al. (2002)

Mexico City, Mexico

158 children with asthma, 

ages 6-17 yr

1-h max 1 FEV1 Placebo -0.21 (-0.77, 0.36)

Antioxidant supplement 0.05 (-0.60, 0.69)

Placebo, 

moderate/severe asthma

-1.1 (-2.0, -0.19)

Antioxidant supplement,

moderate/severe asthma

-0.04 (-0.92, 0.83)

Romieu et 

al. (2006)

Mexico City, Mexico

151 children with asthma, 

mean age 9 yr

1-h max 1 FEV1 GSTP1 Ile/Ile or Ile/Val

GSTP1 Val/Val

-0.51 (-1.1, 0.05)

0.50 (-0.25, 1.3)

Studies not included in Figure 6-6b

Dales et al. 

(2009)

Windsor, ON, Canada

182 children with asthma, 

ages 9-14 yr

1-h max 0 Evening 

percent 

predicted 

FEV1

-0.47 (-1.9, 0.95)

Rabinovitch 

et al. (2004)

Denver, CO

86 children with asthma, 

ages 6-12 yr

1-h max 0-2 

avg

Morning 

FEV1 (mL)

55 (-2.4, 108)

O'Connor 

et al. (2008)

Boston, MA; 

Bronx, Manhattan NY; 

Chicago, IL; Dallas, TX, 

Seattle, WA; Tucson, AZ 

861 children with asthma, 

mean (SD) age 7.7 (2.0) yr

24-h avg 1-5 

avg

Change in 

percent 

predicted 

FEV1

-0.41 (-1.0, 0.21)

*Includes studies in Figure 6-6, plus others

CS = corticosteroid, URI = Upper respiratory infection. 

a

Effect estimates are standardized to a 40-ppb increase for 30-min or 1-h max O3, a 30-ppb increase for 8-h max or 8-h avg O3, and 

a 20-ppb increase for 24-h avg O3.

b

Results not presented in Figure 6-6 because a different form of FEV1 with a different scale was examined or because sufficient data 

were not provided to calculate percent change in FEV1.
Draft – Do Not Cite or Quote 6-46 June 2012

Note: Results generally are presented in order of increasing mean ambient O3 concentration. BW = birth weight, 

CS = Corticosteroid. Effect estimates are from single pollutant models and are standardized to a 40-ppb increase for 1-h max O3

concentrations and a 30-ppb increase for 8-h max or 8-h avg O3 concentrations.

Figure 6-7 Percent change in PEF or FEF25-75% in association with ambient 

ozone concentrations among children with asthma.

Study

Gielen et al. (1997)

Mortimer et al. (2002)

Mortimer et al. (2000)

Thurston et al. (1997)

Romieu et al. (2004a)

Romieu et al. (1996)

Romieu et al. (1997)

Parameter

Evening PEF

Morning PEF

Morning PEF

Morning PEF

PEF

FEF25-75%

Evening PEF

Evening PEF

O3 Lag

0

2

2

1

3

1-5 avg

0

1

0

2

0

2

Subgroup

All subjects

Normal BW

Low BW

No asthma medication

CS user

Placebo, GSTM1 null

Placebo, GSTM1 positive

Antioxidant, GSTM1 null

Antioxidant, GSTM1positive

-10 -8 -6 -4 -2 0 2 4

Percent change in PEF or FEF25-75%

per unit increase in O3 (95% CI)
Draft – Do Not Cite or Quote 6-47 June 2012

Table 6-9 Characteristics and quantitative data for studies represented in 

Figure 6-7, of PEF or FEF25-75% in children with asthma.

Study* Location/Population O3

Averaging 

Time

O3

Lag

Parameter Subgroup Standardized

Percent 

Change 

(95% CI)a

Gielen et al. 

(1997)

Amsterdam, Netherlands

61 children with asthma, ages 7-

13 yr

8-h max 0

2

2

Evening PEF

Evening PEF

Morning PEF

-1.3 (-0.25, 2.9)

-1.3 (-2.8, 0.16)

-1.3 (-2.6, -0.08)

Mortimer et al. 

(2002)

Bronx, East Harlem, NY; 

Baltimore, MD; Washington, DC; 

Detroit, MI, Cleveland, OH; 

Chicago, IL; St. Louis, MO 

846 children with asthma, ages 4-

9 yr

8-h avg

(10 a.m.-

6 p.m.)

1

3

1-5 

avg

Morning PEF All subjects -0.12 (-0.76, 

0.52)

-0.64 (-1.2, 

-0.10)

-1.2 (-2.1, -0.26)

Mortimer et al. 

(2000)

Bronx, East Harlem, NY; 

Baltimore, MD; Washington, DC; 

Detroit, MI, Cleveland, OH; 

Chicago, IL; St. Louis, MO

846 children with asthma, ages 4-

9 yr

8-h avg

(10 a.m.-6 

p.m.)

1-5 

avg

Morning PEF Normal BW

Low BW (<5.5 lbs.)

No medication

CS user

-0.60 (-1.6, 0.39)

-3.6 (-5.2, -2.0)

-1.1 (-3.0, 0.84)

-1.2 (-2.5, 0.11)

Thurston et al. 

(1997)

CT River Valley, CT

166 children with asthma, ages 7-

13 yr

1-h max 0 Intraday 

change PEF

-2.8 (-4.9, -0.59)

Romieu et al. 

(2004b)

Mexico City, Mexico

158 children with asthma, 

mean age 9 yr

1-h max 1 FEF25-75% Placebo, GSTM1 

null

Placebo, GSTM1 

positive

Antioxidant, 

GSTM1 null

Antioxidant, GSTM1 

positive

-2.3 (-4.2, -0.44)

-0.48 (-1.7, 0.74)

-0.16 (-1.8, 1.6)

0.24 (-1.3, 1.8)

Romieu et al. 

(1996)

Northern Mexico City, Mexico

71 children with asthma, ages 5-

7 yr

1-h max 0

2

Evening PEF -0.17 (-0.79, 

0.46)

-0.55 (-1.3, 0.19)

Romieu et al. 

(1997)

Southern Mexico City, Mexico

65 children with asthma, ages 5-

13 yr

1-h max 0

2

Evening PEF -0.52 (-1.0, 

-0.01)

-0.06 (-0.70, 

0.58)
Draft – Do Not Cite or Quote 6-48 June 2012

Study* Location/Population O3

Averaging 

Time

O3

Lag

Parameter Subgroup Standardized

Percent 

Change 

(95% CI)a

Studies not included in Figure 6-7b

Jalaludin et al. 

(2000)

Sydney, Australia

20 children with asthma and AHR, 

mean (SD) age 9.6 (0.9) yr

24-h avg

1-h max

0 Daily 

deviation 

from mean 

PEF

-2.4 (-5.1, 0.28)c

-1.3 (-2.8, 0.17)c

Wiwatanadate 

and 

Trakultivakorn 

(2010)

Chiang Mai, Thailand

31 children with asthma, ages 4-

11 yr

24-h avg 0

5

Daily avg 

PEF (L/min)

1.0 (-1.6, 3.6)

-2.6 (-5.2, 0)

O'Connor et al. 

(2008)

Boston, MA; Bronx, Manhattan 

NY; Chicago, IL; Dallas, TX, 

Seattle, WA; Tucson, AZ

861 Children with asthma, 

mean (SD) age 7.7 (2.0) yr

24-h avg 1-5 

avg

Change in 

percent 

predicted 

PEF

-0.22 (-0.86, 

0.43)

Just et al. 

(2002)

Paris, France

82 children with asthma, 

mean (SD) age 10.9 (2.5) yr

8-h avg 0-2 

avg

Percent 

variability 

PEF

15.6 (0, 31.2)

*Includes studies in Figure 6-7, plus others

BW = birth weight, CS = corticosteroid, AHR = Airway hyperresponsiveness. 

a

Effect estimates are standardized to a 40-ppb increase for 1-h max O3, a 30-ppb increase for 8-h max or avg O3, and a 20-ppb 

increase for 24-h avg O3.

b

Results are not presented in Figure 6-7 because a different form of PEF with a different scale was examined or because sufficient 

data were not provided to calculate percent change in PEF. 

c

Outcome defined as the normalized percent deviation from individual mean PEF during the study period. Quantitative results from 

generalized estimating equations were provided only for models that included PM10 and NO2.

1 The most geographically representative data were provided by the large, multi-U.S. city 

2 National Cooperative Inner City Asthma Study (NCICAS) (Mortimer et al., 2002; 2000)

3 and Inner-City Asthma Study (ICAS) (O'Connor et al., 2008). Although the two studies 

4 differed in the cities, seasons, racial distribution of subjects, and lung function indices 

5 examined, results were fairly similar. In ICAS, which included children with asthma and 

6 atopy (i.e., allergic sensitization) and year-round examinations of lung function, a 20-ppb 

7 increase in the lag 1-5 average of 24-h avg O3 was associated with a 0.41-point decrease 

8 in percent predicted FEV1 (95% CI: -1.0, 0.21) and a 0.22-point decrease in percent 

9 predicted PEF (95% CI: -0.86, 0.43) (O'Connor et al., 2008).

10 Increases in lag 1-5 avg O3 (8-h avg, 10 a.m.-6 p.m.) also were associated with declines 

11 in PEF in NCICAS, which included different U.S. cities, summer-only measurements, 

12 larger proportions of Black and Hispanic children, and fewer subjects with atopy (79%) 

13 (Mortimer et al., 2002). Ozone concentrations lagged 3 to 5 days were associated with 

14 larger PEF decrements than were O3 concentrations lagged 1 to 2 days (Figure 6-7 and 

15 Table 6-9). NCICAS additionally identified groups potentially at increased risk of 

16 O3-associated PEF decrements, namely, males, children of Hispanic ethnicity, children 

17 living in crowded housing, and as indicated in Figure 6-7 and Table 6-9, children with 
Draft – Do Not Cite or Quote 6-49 June 2012

1 birth weight <5.5 lbs (Mortimer et al., 2000). Somewhat paradoxically, O3 was associated 

2 with a larger decrease in PEF among subjects taking cromolyn, medication typically used 

3 to treat asthma due to allergy, but a smaller decrease among subjects with positive atopy 

4 (as determined by skin prick test). NCICAS also indicated robust associations with 

5 consideration of other sources of heterogeneity. Except for Baltimore, MD, effect 

6 estimates were similar across the study cities (1.1 to 1.7% decrease in PEF per 30-ppb 

7 increase in lag 1-5 avg of 8-h avg O3). Results were similar with O3 averaged from all 

8 available city monitors and concentrations averaged from the three monitors closest to 

9 subject ZIP code centroid (1.2% and 1.0%, respectively, per 30-ppb increase in O3). At 

10 concentrations <80 ppb, a 30-ppb increase in lag 1-5 of 8-h avg O3 was associated with a 

11 1.4% decrease (95% CI: -2.6, -0.21) in PEF, which was similar to the effect estimated for 

12 the full range of O3 concentrations (Figure 6-7 and Table 6-9). In a study of children with 

13 asthma in the Netherlands, Gielen et al. (1997) estimated similar effects for the full range 

14 of 8-h max O3 concentrations and concentrations <51 ppb.

15 Several but not all controlled human exposure studies have reported slightly larger 

16 O3-induced FEV1 decrements in adults with asthma (Section 6.2.1.1). However, in the 

17 few epidemiologic studies that compared children with and without asthma, evidence did 

18 not conclusively indicate that children with asthma were at increased risk of 

19 O3-associated lung function decrements. Hoppe et al. (2003) and Jalaludin et al. (2000)

20 generally found larger O3-associated lung function decrements in children with asthma; 

21 whereas Raizenne et al. (1989) did not consistently demonstrate differences between 

22 campers with and without asthma. In their study of children in Mexico City, Barraza23 Villarreal et al. (2008) estimated larger O3-associated decreases in children without 

24 asthma; however, 72% of these children had atopy. These findings indicate that children 

25 with atopy, who also have airway inflammation and similar respiratory symptoms, may 

26 experience respiratory effects from short-term ambient O3 exposure.

27 As shown in Figure 6-6 and Figure 6-7 and Table 6-8 and Table 6-9, lung function 

28 decrements in children with asthma mostly ranged from <1% to 2% per unit increase in 

ambient O3 concentration1 29 . Larger magnitudes of decrease, were found in children with 

30 asthma who were using CS, had a concurrent upper respiratory infection (URI), were 

31 GSTM1 null, had airway hyperresponsiveness, or had increased outdoor exposure 

32 (Romieu et al., 2006; Lewis et al., 2005; Romieu et al., 2004b; Jalaludin et al., 2000) than 

33 among children with asthma overall (Barraza-Villarreal et al., 2008; Lewis et al., 2005; 

34 Delfino et al., 2004; Romieu et al., 2002). For example, Jalaludin et al. (2000) estimated a 

35 -5.2% deviation from mean FEV1 per a 20-ppb increase in 24-h avg O3 concentration 

36 among children with asthma and airway hyperresponsiveness and a much smaller -0.71% 

 1

Effect estimates were standardized to a 40-, 30-, and 20-ppb increase for 1-h max, 8-h max or avg, and 24-h avg O3.
Draft – Do Not Cite or Quote 6-50 June 2012

1 deviation among children with asthma without airway hyperresponsiveness. In a group of 

2 86 children with asthma in Detroit, MI, Lewis et al. (2005) reported that associations 

3 between ambient O3 concentration and FEV1 were confined largely to children with 

4 asthma who used CS or had a concurrent URI, 8.0% and 5.4% decreases, respectively, in 

5 the mean of lowest daily FEV1 per 30-ppb increase in 8-h max ambient O3 concentration.

6 Heterogeneity in response to O3 exposure also was demonstrated by observations that 

7 some individuals experienced larger O3-associated lung function decrements than the 

8 population mean effect estimate. Similar observations were made in controlled human 

9 exposure studies (Section 6.2.1.1). Mortimer et al. (2002) found that for a 30-ppb 

10 increase in lag 1-5 avg of 8-h avg O3, there was a 30% (95% CI: 4, 61) higher incidence 

11 of >10% decline in PEF. Likewise, Hoppe et al. (2003) found that while the percentages 

12 of lung function decrements were variable and small, 47% of children with asthma 

13 experienced >10% decline in FEV1, FVC, or PEF or 20% increase in airway resistance on 

14 days with 30-min (1-4 p.m.) max ambient O3 concentrations >50 ppb relative to days 

15 with <40 ppb O3.

Effect modification by corticosteroid use

16 In controlled human exposure studies, CS treatment of subjects with asthma generally has 

17 not prevented O3-induced FEV1 decrements (Section 6.2.1.1). Epidemiologic evidence is 

18 equivocal, with findings that use of inhaled CS attenuated (Hernández-Cadena et al., 

19 2009), increased (Lewis et al., 2005), and did not affect (Mortimer et al., 2000), ambient 

20 O3-associated lung function decrements. In winter-only studies, consideration of CS use 

21 largely did not influence associations between ambient O3 and various lung function 

22 indices (Liu et al., 2009a; Rabinovitch et al., 2004). Similarly equivocal evidence was 

23 found for modification of associations with respiratory symptoms (Section 6.2.4.1). The 

24 assessment of effect modification by CS use has been hampered by differences in the 

25 severity of asthma among CS users and the definition of CS use. Additionally, 

26 investigators did not assess adherence to reported CS regimen, and misclassification of 

27 CS use may bias findings. For example, Mortimer et al. (2000) classified children by no 

28 or any CS use at baseline but did not measure daily use during the study period. Lewis et 

29 al. (2005) defined CS use as use for at least 50% of study days and estimated larger 

30 O3-associated FEV1 decrements among CS users (Figure 6-6 and Table 6-8) than among 

31 CS nonusers (quantitative results not reported). In this study, most children with 

32 moderate to severe asthma (91%) were classified as CS users. However, CS users had a 

33 higher percent predicted FEV1. In contrast, Hernández-Cadena et al. (2009) observed 

34 larger O3-related decrements in FEV1 among the 60 CS nonusers than among the 25 CS 

35 users. A definition for CS use was not provided; however, children with persistent asthma 
Draft – Do Not Cite or Quote 6-51 June 2012

1 were included among the group of CS nonusers. Thus, across studies, both CS use and 

2 nonuse have been used to indicate more severe, uncontrolled asthma. 

Effect modification by antioxidant capacity

3 Ozone is a powerful oxidant whose secondary oxidation products have been described to 

4 initiate the key modes of action that mediate decreases in lung function, including the 

5 activation of neural reflexes (Section 5.3.2). Additionally, O3 exposure of humans and 

6 animals has induced changes in the levels of antioxidants in the ELF (Section 5.3.3). 

7 These observations provide biological plausibility for diminished antioxidant capacity to 

8 increase the risk of O3-associated respiratory effects and for augmented antioxidant 

9 capacity to decrease risk. Controlled human exposure studies have demonstrated the 

10 protective effects of α-tocopherol (vitamin E) and ascorbate (vitamin C) supplementation 

11 on O3-induced lung function decrements (Section 6.2.1.1), and epidemiologic studies of 

12 children with asthma conducted in Mexico City produced similar findings. Particularly 

13 among children with moderate to severe asthma, increases in ambient O3 concentration 

14 were associated with a smaller decrease in FEV1 in the group supplemented with vitamin 

15 C and E as compared with the placebo group (Romieu et al., 2002) (Figure 6-6 and 

16 Table 6-8). Romieu et al. (2009) also demonstrated an interaction between dietary 

17 antioxidant intake and ambient O3 concentrations by finding that the main effect of diet 

18 was modified by ambient O3 concentrations. Diets high in antioxidant vitamins and/or 

19 omega-3 fatty acids protected against FEV1 decrements at 8-h max O3 concentrations 

20 ≥ 38 ppb. Results for the main effect of O3 on FEV1 or effect modification by diet were 

21 not presented. 

22 Antioxidant capacity also can be characterized by variants in genes encoding xenobiotic 

23 metabolizing enzymes with altered enzymatic activity. Ambient O3-associated FEF25-75% 

24 decrements were larger among children with asthma with the GSTM1 null genotype, 

25 which is associated with lack of oxidant metabolizing activity (Romieu et al., 2004b). 

26 The difference in association between GSTM1 null and positive subjects was minimal in 

27 children supplemented with antioxidant vitamins (Figure 6-7 and Table 6-9). Although 

28 these findings are biologically plausible given the well-characterized evidence for the 

29 secondary oxidation products of O3 mediating effects, it is important to note that a larger 

30 body of controlled human exposure studies has not consistently found larger O3-induced 

31 lung function decrements in GSTM1 null subjects (Section 6.2.1.1). Effect modification 

32 by GSTP1 variants is less clear. Romieu et al. (2006) observed larger O3-associated 

33 decreases in FEV1 in children with asthma with the GSTP1 Ile/Ile or Ile/Val variant, 

34 which are associated with relatively higher oxidative metabolism activity (Figure 6-6 and 

35 Table 6-8). An increase in ambient O3 concentration was associated with an increase in 

36 FEV1 among children with the GSTP1 Val/Val variant, which is associated with reduced 
Draft – Do Not Cite or Quote 6-52 June 2012

1 oxidative metabolism. Rather than reflecting effect modification by the GSTP1 variant, 

2 these results may reflect effect modification by asthma severity, as 77% of subjects with 

3 the GSTP1 Ile/Ile genotype had moderate to severe asthma. In support of this alternate 

4 hypothesis, another analysis of the same cohort indicated a larger O3-associated 

5 decrement in FEV1 among children with moderate to severe asthma than among all 

6 subjects with asthma (Romieu et al., 2002).

Exposure Measurement Error

7 Across the studies of children with asthma, lung function decrements were associated 

8 with ambient O3 concentrations assigned to subjects using various exposure assessment 

9 methods. As described in Section 4.3.3, exposure measurement error due to use of 

10 ambient concentrations measured at central sites has varied, depending on the population 

11 and season examined. Because there are a limited number of studies of each method, it is 

12 difficult to conclude that a particular method of exposure assessment produced stronger 

13 results. 

14 Seasonal differences have been observed in the personal-ambient O3 relationship 

15 (Section 4.3.3); however, in children with asthma, O3-associated lung function 

16 decrements were found in studies conducted in summer months and over multiple 

17 seasons. Lung function was associated with O3 measured on site of subjects’ daytime 

18 hours in summer months (Hoppe et al., 2003; Thurston et al., 1997), factors that have 

19 contributed to higher personal-ambient O3 ratios and correlations. Many year-round 

20 studies in Mexico City (Romieu et al., 2006; 2004b; 2002; 1997; 1996) and a study in 

21 Detroit, MI (Lewis et al., 2005) found associations with O3 measured at sites within 5 km 

22 of children’s home or school. Children with asthma examined by Romieu et al. (2006); 

23 (2004b; 2002) had a personal-ambient ratio and correlation for 48- to 72-h avg O3

24 concentrations were 0.17 and 0.35, respectively (Ramírez-Aguilar et al., 2008). These 

25 findings indicate that the effects of personal O3 exposure on lung function decrements 

26 may have been underestimated in the children in Mexico City. Associations were found 

27 with O3 concentrations averaged across multiple community monitoring sites (O'Connor 

28 et al., 2008; Just et al., 2002; Mortimer et al., 2002; Jalaludin et al., 2000) and measured 

29 at a single site (Gielen et al., 1997), O3 measured at multiple sites within a region have 

30 shown high temporal correlation (Darrow et al., 2011a; Gent et al., 2003).

31 Studies of children with asthma restricted to winter months provided little evidence of an 

32 association between various single- and multi-day lags of ambient O3 concentration and 

33 lung function decrements with several studies reporting O3-associated increases in lung 

34 function (Dales et al., 2009; Liu et al., 2009a; Rabinovitch et al., 2004). One explanation 

35 for these results may be lower indoor than outdoor O3 concentrations, variable indoor to 
Draft – Do Not Cite or Quote 6-53 June 2012

1 outdoor ratios, and lower correlations between personal and ambient O3 concentrations in 

2 non-summer months (Section 4.3.2 and Section 4.3.3). As noted for other respiratory 

3 endpoints such as respiratory hospital admissions, ED visits, and mortality, associations 

4 with O3 generally are lower in colder seasons.

Adults with Respiratory Disease

5 Relative to studies in children with asthma, studies of adults with asthma or COPD have 

6 been limited in number. Details from these studies regarding location, time period, and 

7 ambient O3 concentrations are presented in Table 6-10. Increases in ambient O3

8 concentration were not consistently associated with lung function decrements in adults 

9 with respiratory disease. Several different exposure assessment methods were used, 

10 including monitoring personal exposures (Delfino et al., 1997), monitoring on site of 

11 outdoor activity (Girardot et al., 2006; Korrick et al., 1998), and using measurements 

12 from one (Peacock et al., 2011; Wiwatanadate and Liwsrisakun, 2011; Thaller et al., 

13 2008; Ross et al., 2002) to several central monitors (Khatri et al., 2009; Lagorio et al., 

14 2006; Park et al., 2005a). There was not a clear indication that differences in exposure 

15 assessment methodology contributed to inconsistencies in findings.
Draft – Do Not Cite or Quote 6-54 June 2012

Table 6-10 Mean and upper percentile concentrations of ozone in 

epidemiologic studies of lung function in adults with respiratory 

disease.

Study* Location Study Period O3 Averaging 

Time

Mean/Median 

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

Delfino et al. 

(1997)

Alpine, CA May-July 1994 12-h avg 

personal

(8 a.m.-8 p.m.)

18 90th: 38

Max: 80

Girardot et al. 

(2006)

Great Smoky 

Mountain NP, 

TN

August-October 

2002 June-August 

2003

Hike-time avg

(2-9 h)

48.1 Max: 74.2

Korrick et al. 

(1998)

Mt. 

Washington, 

NH

Summer 1991, 1992 Hike-time avg

(2-12 h)

40 Max: 74

Peacock et al. 

(2011)

London, 

England

All-year 1995-1997 8-h max 15.5 Autumn/Winter Max: 32

Spring/Summer Max: 74

Wiwatanadate and 

Liwsrisakun 

(2011)

Chiang Mai, 

Thailand

August 2005-June 

2006

24-h avg 17.5 90th: 26.82

Max: 34.65

Thaller et al. 

(2008); Brooks 

(2010)

Galveston, TX Summer 2002-2004 1-h max 35 (median) Max: 118

Ross et al. (2002) East Moline, IL April-October 1994 8-h avg 41.5 Max: 78.3

Khatri et al. (2009) Atlanta, GA May-September 

2003, 2005, 2006

8-h max With asthma: 

61(median)a

No asthma: 56 

(median)a

75th (all subjects): 74a

Lagorio et al. 

(2006)

Rome, Italy May-June, 

NovemberDecember 1999

24-h avg Spring: 36.2b

Winter: 8.0b

Overall max: 48.6b

Park et al. (2005a) Incheon, Korea March-June 2002 24-h avg Dust event days: 23.6

Control days: 25.1

NR

* Note: Studies presented in order of first appearance in the text of this section.

NR = Not reported.

a

Individual-level estimates were calculated based on time spent in the vicinity of various O3 monitors. b

Concentrations converted from μg/m3 to ppb using the conversion factor of 0.51 assuming standard temperature (25°C) and 

pressure (1 atm).

1 Comparisons of adults with asthma (8-18% of study population) and without asthma did 

2 not conclusively demonstrate that adults with asthma had larger ambient O3-associated 

3 lung function decrements. Several studies examined on-site or central-site ambient O3

4 concentrations measured while subjects were outdoors, and ambient O3 measured during 

5 time spent outdoors has been closer in magnitude and more correlated with personal 

6 exposures (Section 4.3.3). In a panel study of lifeguards (ages 16-27 years) in Galveston, 

7 TX, a larger O3-associated decrement in FEV1/FVC was found among the 16 lifeguards 

8 with asthma (-1.6% [95% CI: -2.8, -0.4] per 40 ppb increase in 1-h max O3) than among 

9 the 126 lifeguards without asthma (-0.40% [95% CI: -0.80, 0] per 40-ppb increase in 
Draft – Do Not Cite or Quote 6-55 June 2012

1 1-h max O3) Brooks (2010). In Korrick et al. (1998), hikers with a history of asthma or 

2 wheeze had larger O3-associated lung function decrements (e.g.-4.4% [95% CI: -7.5, 

3 -1.2] in FEV1 per 30-ppb increase in 2-12 h avg O3). In contrast, Girardot et al. (2006)

4 generally did not find O3-associated lung function decrements in hikers with or without 

5 respiratory disease history. In a cross-sectional study of 38 adults with asthma and 

6 13 adults without asthma, Khatri et al. (2009) used central site O3 measurements but 

7 aimed to account for spatial variability by calculating an average of concentrations 

8 measured at sites closest to each subject’s location during each hour. Investigators 

9 reported a larger O3-associated decrease in percent predicted FEV1/FVC in the 38 

10 subjects with atopy (with or without asthma) (-12 points [95% CI: -21, -3] per 30-ppb

11 increase in 8-h max O3) than in subjects with asthma (-4.7 points [95% CI: -11, 2.3]). 

12 Among adults with asthma, O3 was associated with an increase in FEV1.

13 In panel studies that exclusively examined adults with asthma, increases in ambient O3

14 concentrations, across the multiple lags examined, generally were associated with 

15 increases in lung function (Wiwatanadate and Liwsrisakun, 2011; Lagorio et al., 2006; 

16 Park et al., 2005a). These studies were conducted in Europe and Asia during periods of 

17 low ambient O3 concentrations, including one conducted in Korea during a period of dust 

18 storms (Park et al., 2005a)

19 Some studies included children and adults with asthma. Among subjects ages 9-46 years 

20 (41% adults) in Alpine, CA with low personal 12-h avg O3 exposures (55% samples 

21 below limit of detection) and a majority of sampling hours spent indoors (mean 71%), 

22 Delfino et al. (1997) reported that neither 12-h avg personal exposure nor ambient O3

23 concentration was associated with a decrease in PEF. Ross et al. (2002) examined 

24 subjects ages 5-49 years (proportion of adults not reported) in East Moline, IL and found 

25 that a 20-ppb increase in lag 0 of 24-h avg O3 was associated with a 2.6 L/min decrease 

26 (95% CI: -4.3, -0.90) in evening PEF. In this population with asthma, an increase in lag 0 

27 O3 also was associated with an increase in symptom score.

28 Controlled human exposure studies have found diminished, statistically nonsignificant 

29 O3-induced lung function responses in older adults with COPD (Section 6.2.1.1). 

30 Similarly, epidemiologic studies do not provide strong evidence that short-term increases 

31 in ambient O3 exposure result in lung function decrements in adults with COPD. 

32 Inconsistent associations were reported for PEF, FEV1, and FVC in a study that followed 

33 94 adults with COPD (ages 40-83 years) in London, England daily over two years 

34 (Peacock et al., 2011). For example, a 30-ppb increase in 8-h max O3 was associated with 

35 a 1.7 L/min decrease (95% CI: -3.1, -0.39) in PEF in an analysis of summer 1996 but not 

36 summer 1997 (-0.21 L/min [95% CI: -2.4, 2.0]). Further, in this study, an increase in 

37 ambient O3 concentration was associated with lower odds of a large PEF decrement (OR 
Draft – Do Not Cite or Quote 6-56 June 2012

1 for a >20% drop from an individual’s median value: 0.89 [95% CI: 0.72, 1.10] per 

2 30-ppb increase in lag 1 of 8-h max O3) and was not consistently associated with 

3 increases in respiratory symptoms (Peacock et al., 2011). Inconsistent associations also 

4 were reported in a small panel study of 11 adults with COPD (mean age 67 years) in 

5 Rome, Italy (Lagorio et al., 2006).

Populations Not Restricted to Individuals with Asthma

6 Several studies have examined associations between ambient O3 concentrations and lung 

7 function in groups that included children with and without asthma; however, a limited 

8 number of studies have examined groups of children or adults restricted to healthy 

9 individuals. Details from studies not restricted to individuals with asthma regarding 

10 location, time period, and ambient O3 concentrations are presented in Table 6-11.

Table 6-11 Mean and upper percentile concentrations of ozone in 

epidemiologic studies of lung function in populations not restricted 

to individuals with asthma.

Study* Location Study Period O3 Averaging Time Mean/Median 

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

Avol et al. (1998b) 6 southern CA 

communities 

Spring and 

summer 1994

24-h avg personal NR NR

Hoppe et al. (2003) Munich, 

Germany

Summers 

1992-

1995

30-min max (1-4 

p.m.)

High O3 days: 70.4a

Control O3 days: 29.8a

Max (high O3 days): 99a

Max (control O3 days): 

39a

Chen et al. (1999) 3 Taiwan 

communities

May-January, 

1995-1996

1-h max (8 a.m.-6 

p.m.)

NR Max: 110.3a

Gold et al. (1999) Mexico City, 

Mexico

JanuaryNovember 199124-h avg 52.0a Max: 103a

Ward et al. (2002) Birmingham and 

Sandwell, 

England

January-March 

and May-July 

1997

24-h avg Winter median: 13.0

Summer median: 22.0

Winter Max: 33

Summer Max: 41

Ulmer et al. (1997) Freudenstadt 

and Villingen, 

Germany

March-October 

1994

30-min avg Freudenstadt median: 

50.6

Villingen median: 32.1

Freudenstadt 95th: 89.8

Villingen 95th: 70.1

Linn et al. (1996) Rubidoux, 

Upland, 

Torrence, CA

September-June 

1992-1994

24-h avg personal

24-h avg ambient

5

23

Max: 16

Max: 53

Scarlett et al. 

(1996)

Surrey, England June-July 1994 8-h max 50.7a Max: 128a

Neuberger et al. 

(2004)

Vienna, Austria June-October 

1999, JanuaryApril 2000

NR NR NR

Alexeeff et al. 

(2008); (2007)

Greater Boston, 

MA; NAS

January 1995-

June 2005

48-h avg 24.4b NR
Draft – Do Not Cite or Quote 6-57 June 2012

Study* Location Study Period O3 Averaging Time Mean/Median 

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

Steinvil et al. (2009) Tel Aviv, Israel September 2002-

November 2007

8-h avg 

(10 a.m.-6 p.m.)

41.1 75th: 48.7

Max: 72.8

Naeher et al. (1999) Multiple 

communities, VA

May-September 

1995-1996

8-h max 53.7 Max: 87.6

Son et al. (2010) Ulsan, Korea All-year, 2003-

2007

8-h max 35.86 

(avg of 13 monitors)

Max: 59.53

* Note: Studies presented in order of first appearance in the text of this section.

NAS = Normative Aging Study, NR = Not Reported.

a

Measured at subjects’ schools where lung function was measured.

b

Measured at central monitoring sites established by investigators. Concentrations were averaged across four monitors.

Children

1 Based on studies available at the time of the 2006 O3 AQCD, evidence consistently links 

2 increases in ambient O3 concentration with decrements in FEV1 and PEF in children 

3 (U.S. EPA, 2006b) (Figure 6-8 and Table 6-12). These associations were found with 

4 personal O3 exposures (Avol et al., 1998b), ambient O3 measured at children’s schools 

5 where lung function was measured (Hoppe et al., 2003; Chen et al., 1999; Gold et al., 

6 1999), and ambient O3 measured at sites within the community (Ward et al., 2002; Ulmer 

7 et al., 1997; Linn et al., 1996). Among children in California who spent a mean 2-3 hours 

8 outdoors per day and whose personal-ambient O3 correlation was 0.28 across multiple 

9 seasons, Avol et al. (1998b) found slightly larger O3-associated decrements in FEV1 and 

10 FVC for 24-h avg personal exposures than for 1-h max ambient measurements 

11 (Figure 6-8 and Table 6-12). The effect estimates for personal exposures were similar in 

12 magnitude to those found in other studies for ambient O3 measured at schools (Hoppe et 

13 al., 2003; Chen et al., 1999). In another study of children in California, Linn et al. (1996)

14 did not present results for personal O3 exposures but found FEV1 decrements in 

15 association with increases in ambient O3 concentrations in children who spent 1-2 hours 

16 per day outdoors and whose personal-ambient correlations were 0.61. Because of 

17 between-study heterogeneity in populations and ambient O3 concentrations examined, it 

18 is difficult to assess how the method of exposure assessment may have influenced 

19 findings. 
Draft – Do Not Cite or Quote 6-58 June 2012

Note: The 95% CI was constructed using a standard error that was estimated from the p-value. Results generally are presented in 

order of increasing mean ambient O3 concentration. Effect estimates are from single-pollutant models and are standardized to a 40-, 

30-, and 20-ppb increase for a 1-hour (or 30-min) max, 8-h max, and 24-h avg O3 concentrations, respectively.

Figure 6-8 Percent change in FEV1 or FVC in association with ambient ozone 

concentrations in studies of children in the general population.

Study

Linn et al. (1996)

Hoppe et al. (2003)

Scarlett et al. (1996)

Chen et al. (1999)

Avol et al. (1998)a

Parameter

Intraday change FEV1

Intraday change FVC

Afternoon FEV1

Afternoon FVC

FEV0.75

FVC

FEV1

FVC

Intraday change FEV1

Intraday change FVC

O3 Lag

0

0

0

1

1

0 Personal

0 Ambient

0 Personal

0 Ambient

-10 -8 -6 -4 -2 0 2

Percent change in FEV1 or FVC per unit

increase in O3 (95% CI)
Draft – Do Not Cite or Quote 6-59 June 2012

Table 6-12 Characteristics and quantitative data for studies represented in 

Figure 6-8, of lung function in children.

Study* Location/ Population O3 Averaging 

Time

O3 Lag Parameter Standardized

Percent Change 

(95% CI)a

Linn et al. (1996) 3 southern CA communities

269 children, 4th and 5th grades

24-h avg 0 Intraday change 

FEV1

Intraday change 

FVC

-0.58 (-1.0, -0.13)

-0.21 (-0.62, 0.20)

Hoppe et al. 

(2003)

Munich, Germany

44 children, ages 6-8 yr

30-min max 

(1 - 4 p.m.)

0 Afternoon FEV1

Afternoon FVC

-0.14 (-2.7, 2.5)

-1.4 (-3.9, -1.2)

Scarlett et al. 

(1996)

Surrey, England

154 children, ages 7-11 yr

8-h max 1 FEV0.75

FVC

-0.04 (-0.32, 0.23)

0.07 (-0.25, 0.39)

Chen et al. (1999) 3 Taiwan communities

941 children, 

mean (SD) age 9.8 (1.6) yr

1-h max 1 FEV1

FVC

-1.5 (-2.8, -0.12)

-1.6 (-2.9, -0.33)

Avol et al. (1998b) 3 southern CA communities

195 children, ages 10-12 yr

24-h avg 

personal

1-h max ambient

24-h avg 

personal

1-h max ambient

0 Intraday change 

FEV1

Intraday change 

FEV1

Intraday change 

FVC

Intraday change 

FVC

-0.85 (-2.2, 0.53)b

-0.49 (-1.5, 0.57)b

-1.0 (-2.0, 0)b

-0.50 (-1.3, 0.35)b

Studies of children not included in Figure 6-8c

Ulmer et al. (1997) Freudenstadt and Villingen, 

Germany

135 children, ages 8-10 yr

30-min max 1 FEV1 (mL) -59 (-103, 14)b

Ward et al. (2002) Birmingham and Sandwell, England

162 children, age 9 yr

24-h avg 0

2

Daily deviation from 

mean PEF (L/min)

-3.2 (-8.3, 2.0)d

-6.7 (-12, -1.4)d

Gold et al. (1999) Mexico City, Mexico

40 children, ages 8-11 yr

24-h avg 0

1-10 

avg

Intraday change 

PEF (% change)

-0.47 (-1.1, 0.11)

-3.4 (-5.4, -1.5)

*

Includes studies in Figure 6-8 plus others.

a

Effect estimates are standardized to a 40-, 30-, and 20-ppb increase for 1-h (or 30-min) max, 8-h max, and 24-h avg O3, 

respectively.

b

The 95% CI was constructed using a standard error that was estimated from the p-value.

c

Results are not presented in Figure 6-8 because sufficient data were not provided to calculate percent change in FEV1 or PEF was 

analyzed.

d

Effect estimates are from analyses restricted to summer months.

1 In the limited number of studies that examined only healthy children, increases in 

2 ambient O3 concentration were associated with decreases (Hoppe et al., 2003) or no 

3 change in lung function (Neuberger et al., 2004). Several studies that included small 

4 proportions (4-10%) of children with history of respiratory disease or symptoms found 

5 associations between increases in ambient O3 concentration and lung function decrements 

6 (Chen et al., 1999; Ulmer et al., 1997; Scarlett et al., 1996). Based on analysis of 

7 interaction terms for O3 concentration and asthma/wheeze history, Avol et al. (1998b)
Draft – Do Not Cite or Quote 6-60 June 2012

1 and Ward et al. (2002) did not find differences in O3-associated lung function decrements 

2 between children with history of asthma or wheeze and healthy children. Combined, 

3 these lines of evidence indicate that the ambient O3-associated lung function decrements 

4 in children were not solely due to effects in children with asthma, and that increases in 

5 ambient O3 exposure may decrease lung function in healthy children.

6 Among the studies of children, the magnitudes of decrease in lung function per unit 

increase in ambient O3 concentration1 7 ranged from <1 to 4%, a range similar to that 

8 estimated in children with asthma. Comparable data were not adequately available to 

9 assess whether mean lung function differed between groups of children with asthma and 

10 healthy children. In contrast with children with asthma, O3-associated decreases in lung 

11 function were not consistently accompanied by O3-associated increases in respiratory 

12 symptoms in children in the general population. For example, Gold et al. (1999) found 

13 O3-associated decreases in PEF and increases in phlegm; however, the increase in phlegm 

14 was associated with lag 1 O3 concentrations whereas the PEF decrement was found with 

15 single-day lags 2 to 4 of O3. Also, O3 was weakly associated with cough and shortness of 

16 breath among children in England (Ward et al., 2002) and was associated with a decrease 

17 in respiratory symptom score among children in California (Linn et al., 1996).

Adults

18 Compared with children, in a more limited body of studies, O3 was less consistently 

19 associated with lung function decrements in populations of adults not restricted to healthy 

20 subjects (Table 6-13). In studies that included only healthy adults, increases in ambient 

21 O3 concentration were associated with decreases (Naeher et al., 1999) and increases in 

22 lung function (Steinvil et al., 2009). Contrasting results also were found in studies of 

23 older adults (Alexeeff et al., 2008; Alexeeff et al., 2007; Hoppe et al., 2003). 

 1

Effect estimates were standardized to a 40-, 30-, and 20-ppb increase for 1-h max (or 30-min max), 8-h max, and 24-h avg O3.
Draft – Do Not Cite or Quote 6-61 June 2012

Table 6-13 Associations between ambient ozone concentration and lung 

function in studies of adults.

Studya Location/Population O3

Averaging 

Time

O3 Lag Parameter O3 Assessment 

Method/Subgroup

Standardized 

Effect 

Estimate 

(95% CI)b

Son et al. 

(2010)

Ulsan, Korea

2,102 children and adults, 

ages 7-97 yr

8-h max 0-2 avg Change in 

percent 

predicted FEV1

All monitor avg

Nearest monitor

IDW

Kriging

-1.4 (-2.7, 

-0.08)

-0.76 (-1.8, 

0.25)

-1.1 (-2.2, 0.05)

-1.4 (-2.6, 

-0.11)

Steinvil et 

al. (2009)

Tel Aviv, Israel

2,380 healthy adults, 

mean age 43 yr, 

75th percentile: 52 yr

8-h avg

(10 a.m 

- 6 p.m.)

0

0-6 avg

FEV1 (mL) 60 (0, 120)

141 (33, 234)

Naeher et 

al. (1999)

Multiple communities, VA

473 healthy women, 

ages 19 - 43 yr

24-h avg 0

0-2 avg

Evening PEF 

(L/min)

-1.7 (-3.4, 0.03)

-3.0 (-4.4, -1.7)

Hoppe et 

al. (2003)

Munich, Germany

61 older adults, ages 69-95 yr

30-min max 

(1-4 p.m.)

0

1

% change in 

afternoon FEV1

0.75 (-2.1, 3.7)

1.2 (-1.3, 3.6)

Alexeeff et 

al. (2008)

Greater Boston, MA

1,015 older adults, 

mean (SD) age: 68.8 (7.2) yr 

at baseline

24-h avg 0-1 avg % change in 

FEV1

GSTP1 Ile/Ile

GSTP1 Ile/Val or 

Val/Val

-1.0 (-2.2, 0.20)

-2.3 (-3.5, -1.0)

Alexeeff et 

al. (2007)

Greater Boston, MA

904 older adults, 

mean (SD) age: 68.8 (7.3) yr 

at baseline

24-h avg 0-1 avg % change in 

FEV1

BMI <30

BMI ≥ 30

No AHR

AHR

BMI ≥ 30 and AHR 

-1.5 (-2.5, 

-0.51)

-3.5 (-5.1, -1.9)

-1.7 (-2.7, 

-0.73)

-4.0 (-6.2, -1.8)

-5.3 (-8.2, -2.3)

a

Results generally are presented in order of increasing mean ambient O3 concentration.

IDW = Inverse distance weighting, BMI = Body mass index, AHR = airway hyperresponsiveness. b

Effect estimates are standardized to a 40-ppb increase for 30-min max O3, 30-ppb increase for 8-h max or 8-h avg O3, and 20-ppb 

increase for 24-h avg O3.

1 Despite mixed results overall, lung function decrements in adults were associated with 

2 increases in ambient O3 concentrations assigned to subjects using various methods with 

3 potentially varying degrees of measurement error. These methods included the average of 

4 multiple intra-city monitors, nearest monitor, estimates from spatial interpolation (Son et 

5 al., 2010), average of monitors in multiple towns (Alexeeff et al., 2008; 2007), and one 

6 site for multiple towns (Naeher et al., 1999). In a large cross-sectional study, conducted 

7 in 2,102 children and adults (mean age: 45 years) living near a petrochemical plant in 

8 Ulsan, Korea, Son et al. (2010) did not find a consistent difference in the magnitude of 

9 association with lung function among ambient O3 concentrations averaged across 13 city 

10 monitors, concentrations from the nearest monitor, inverse distance-weighted 
Draft – Do Not Cite or Quote 6-62 June 2012

1 concentrations, and estimates from kriging across the various lags examined 

2 (Table 6-13). Ozone concentrations were similar (<10% difference) and highly correlated 

3 (r = 0.84-96) among the methods. Although the health status of subjects was not reported, 

4 the study population mean percent predicted FEV1 was 82.85%, indicating a large 

5 proportion of subjects with underlying airway obstruction. Results from this study were 

6 not adjusted for meteorological factors and thus, confounding cannot be ruled out. 

7 Importantly, the similarities among exposure assessment methods in Son et al. (2010)

8 may apply mostly to populations living within the same region of a city. The majority of 

9 women examined by Naeher et al. (1999) lived >60 miles from the single available 

10 central site monitor. However, in the nonurban (southwest Virginia) study area, O3

11 concentrations may be more spatially homogeneous (Section 4.6.2.1), and the 

12 concentrations measured at the single site may capture temporal variability in ambient 

13 exposures.

14 The inconsistent findings for older adults parallel observations from controlled human 

15 exposure studies (Section 6.2.1.1). In a study that followed adults ages 69-95 years over a 

16 summer in Germany, Hoppe et al. (2003) did not find decreases in lung function in 

17 association with ambient O3 measured at subjects’ retirement home. However, recently, 

18 the Normative Aging Study found decrements in FEV1 and FVC in a group of older men 

19 (mean [SD] age = 68.9 [7.2] years) in association with ambient O3 concentrations 

20 averaged from four town-specific monitors (Alexeeff et al., 2008), which may less well 

21 represent spatial heterogeneity in ambient O3 exposures. Among all subjects, who were 

22 examined once every three years for ten years, associations were found with several lags 

23 of 24-h avg O3 concentration, i.e., 1- to 7-day avg (Alexeeff et al., 2008). Additionally, 

24 larger effects were estimated in adults with airway hyperresponsiveness, higher BMI (≥ 

25 30), and GSTP1 Ile/Val or Val/Val genetic variants (Val/Val variant produces enzyme 

26 with reduced oxidative metabolism activity) (Alexeeff et al., 2008; Alexeeff et al., 2007)

27 (Table 6-13). Larger O3-related decrements in FEV1 and FVC also were observed in 

28 subjects with long GT dinucleotide repeats in the promoter region of the gene for the 

29 antioxidant enzyme heme oxygenase-1 (Alexeeff et al., 2008), which has been associated 

30 with reduced inducibility (Hiltermann et al., 1998). In this cohort, O3 also was associated 

31 with decreases in lung function in adults without airway hyperresponsiveness and those 

32 with BMI <30, indicating effects of O3 on lung function in healthy older adults. However, 

33 the findings may be generalizable only to this study population of older, predominately 

34 white men.

Confounding in epidemiologic studies of lung function

35 The 1996 O3 AQCD noted uncertainty regarding confounding by temperature and pollen 

36 (U.S. EPA, 1996a); however, collective evidence does not indicate that these factors fully 
Draft – Do Not Cite or Quote 6-63 June 2012

1 account for the associations observed between increases in ambient O3 concentration and 

2 lung function decrements. Across the populations examined, most studies that found 

3 ambient O3-associated lung function decrements, whether conducted in multiple seasons 

4 or only in summer, included temperature in statistical analyses. Some summer camp 

5 studies conducted detailed analysis of temperature. In most of these studies, temperature 

6 and O3 were measured at the camps. In two Northeast U.S. studies, an increase in 

7 temperature was associated with an increase in lung function (Thurston et al., 1997; 

8 Berry et al., 1991). This positive association likely accounted for the nearly 2-fold greater 

9 decrease in O3-associated PEF found by Thurston et al. (1997) with temperature in the 

10 model than with O3 alone. In another Northeast U.S. camp study, Spektor et al. (1988a)

11 estimated similar effects for O3 in a model with and without a temperature-humidity 

12 index. In the re analysis of six camp studies, investigators did not include temperature in 

13 models because temperature within the normal ambient range had not been shown to 

14 affect O3-induced lung function responses in controlled human exposure studies (Kinney 

15 et al., 1996).

16 Pollen was evaluated in far fewer studies. Camp studies that examined pollen found that 

17 pollen independently was not associated with lung function decrements (Thurston et al., 

18 1997; Avol et al., 1990). Many studies of children with asthma with follow-up over 

19 multiple seasons found O3-associated decrements in lung function in models that adjusted 

20 for pollen counts (Just et al., 2002; Ross et al., 2002; Jalaludin et al., 2000; Gielen et al., 

21 1997). In these studies, large proportions of subjects had atopy (22-98%), with some 

22 studies examining large proportions of subjects specifically with pollen allergy and thus 

23 would be more responsive to pollen exposure (Ross et al., 2002; Gielen et al., 1997).

24 A relatively larger number of studies provided information on potential confounding by 

25 copollutants such as PM2.5, PM10, NO2, or SO2. While studies were varied in how they 

26 evaluated confounding, most indicated that O3-associated lung function decrements were 

27 not solely due to copollutant confounding. Some studies of subjects exercising outdoors 

28 indicated that ambient concentrations of copollutants such as NO2, SO2, or acid aerosol 

29 were low and thus, not likely to confound associations observed for O3 (Hoppe et al., 

30 2003; Brunekreef et al., 1994; Hoek et al., 1993). In other studies of children with 

31 increased outdoor exposures, O3 was consistently associated with decreases in lung 

32 function, whereas other pollutants such as PM2.5, sulfate, and acid aerosol individually 

33 showed variable associations across studies (Thurston et al., 1997; Castillejos et al., 1995; 

34 Berry et al., 1991; Avol et al., 1990; Spektor et al., 1988a). Most of these studies 

35 measured ambient pollutants on site of subjects’ outdoor activity and related lung 

36 function changes to the pollutant concentrations measured during outdoor activity. Thus, 

37 the degree of exposure measurement error likely is comparable for O3 and copollutants.
Draft – Do Not Cite or Quote 6-64 June 2012

1 Studies that conducted copollutant modeling generally found O3-associated lung function 

2 decrements to be robust; most copollutant-adjusted effect estimates fell within the 

3 95% CI of the single-pollutant effect estimates (Figure 6-9 and Table 6-14). These studies 

4 used central site measurements for both O3 and copollutants. There may be residual 

5 confounding because of differential exposure measurement error for O3 and copollutants 

6 due to differing spatial heterogeneity and indoor-outdoor ratios; however, the limited 

7 available evidence indicates that personal O3 exposures are weakly correlated with 

8 personal PM2.5 and NO2 exposures (Section 4.3.4.1). Whereas a few studies used the same 

9 averaging time for copollutants (Lewis et al., 2005; Jalaludin et al., 2000), more 

10 examined 1-h max or 8-h max O3 and 24-h avg copollutant concentrations (Son et al., 

11 2010; Chen et al., 1999; Romieu et al., 1997; Romieu et al., 1996). In a Philadelphia-area 

12 summer camp study, Neas et al. (1999) was among the few studies to find that the effect 

13 estimate for O3 was attenuated to near zero in a copollutant model (24-h avg sulfate in 

14 this study) (Figure 6-9 and Table 6-14).

15 Ambient O3 concentrations showed a wide range of correlations with copollutant 

16 concentrations (r = -0.31 to 0.74). In Sydney, Australia, Jalaludin et al. (2000) found low 

17 correlations of O3 with PM10 (r = 0.13) and NO2 (r = -0.31), all averaged over 24 hours. 

18 In two-pollutant models, PM10 and NO2 remained associated with increases in PEF, and 

19 O3 remained associated with decreases in PEF in children with asthma. In Detroit, MI, O3

20 was moderately correlated with PM2.5 (Pearson r = 0.57) and PM10 (Pearson r = 0.59), all 

21 averaged over 24 hours (Lewis et al., 2005). Adjustment for PM10 or PM2.5 resulted in a 

22 large change in the O3-associated FEV1 decrement in children with asthma, but only in 

23 CS users and not in children with concurrent URI (Figure 6-9 and Table 6-14). Studies 

24 conducted in Mexico City found small changes in O3-associated PEF decrements with 

25 copollutant adjustment although different averaging times were used for copollutants 

26 (Romieu et al., 1997; Romieu et al., 1996) (Figure 6-9 and Table 6-14). In these studies, 

27 O3 was moderately correlated with copollutants such as NO2 and PM10 (range of Pearson 

28 r = 0.38-0.58). Studies conducted in Asia also found that associations between O3 and 

29 lung function were robust to adjustment for weakly- to moderately-correlated 

30 copollutants; effect estimates for copollutants generally were attenuated, indicating that 

31 O3 may confound associations of copollutants (Son et al., 2010; Chen et al., 1999).

32 In a summer camp study conducted in Connecticut, Thurston et al. (1997) found ambient 

33 concentrations of 1-h max O3 and 12-h avg sulfate to be highly correlated (r = 0.74), 

34 making it difficult to separate their independent effects. With sulfate in the model, a 

35 larger decrease in PEF was estimated for O3; however, the 95% CI was much wider 

36 (Figure 6-9 and Table 6-14). Investigators found that the association for sulfate was due 

37 to one day when the ambient concentrations of both pollutants were at their peak. With 

38 the removal of this peak day, the sulfate effect was attenuated, whereas O3 effects 
Draft – Do Not Cite or Quote 6-65 June 2012

1 remained robust (Thurston et al., 1997). Among children with asthma in Thailand, the 

2 O3-associated decrease in PEF was robust to adjustment of SO2; however, different lags 

3 were examined for O3 (lag 5) and SO2 (lag 4) (Wiwatanadate and Trakultivakorn, 2010). 

Note: Results are presented first for FEV1 then for PEF and then in order of increasing mean ambient O3 concentration. aInformation 

was not available to calculate 95% CI of the copollutant model. CS = corticosteroid, URI = Upper respiratory infection. Effect 

estimates are standardized to a 40-, 30-, and 20-ppb increase for 1-h max, 12-h avg, and 24-h avg O3, respectively. Black circles 

represent O3 effect estimates from single pollutant models, and open circles represent O3 effect estimates from copollutant models.

Figure 6-9 Comparison of ozone-associated changes in lung function in 

single- and co-pollutant models.

PEF

Neas et al. (1999)a

Children attending camp

Thurston et al. (1997)

Children with asthma 

Romieu et al. (1996)

Children with asthma

Romieu et al. (1997)

Children with asthma

attending camp

12-h avg, Lag 1

12-h avg, Lag 1

1-h max, Lag 0

1-h max, Lag 0

1-h max, Lag 0

1-h max, Lag 0

1-h max, Lag 0

1-h max, Lag 0

None

24-h avg, Lag 1 sulfate

None

12-h avg, Lag 0 sulfate

None

24-h avg, Lag 2 PM2.5

None

24-h avg, Lag 2 PM10

◄ ►

-15 -13 -11 -9 -7 -5 -3 -1 1 3

Percent change in PEF per unit increase in O3 (95% CI)

Study

FEV1

Lewis et al. (2005)

Children with asthma

Children with asthma

Chen et al. (1999)

Children

using CS

with URI

O3 metrics

24-h avg, Lag 2

24-h avg, Lag 2

24-h avg, Lag 2

24-h avg, Lag 2

24-h avg, Lag 2

24-h avg, Lag 2

1-h max, Lag 1

1-h max, Lag 1

O3 with copollutant

None

24-h avg, Lag 2 PM2.5

24-h avg, Lag 2 PM10

None

24-h avg, Lag 2 PM2.5

24-h avg, Lag 2 PM10

None

24-h avg, Lag 1 NO2

◄

►

►

-15 -13 -11 -9 -7 -5 -3 -1 1 3

Percent change in FEV1 per unit increase in O3 (95% CI)
Draft – Do Not Cite or Quote 6-66 June 2012

Table 6-14 Additional characteristics and quantitative data for studies 

represented in Figure 6-9.

Study* Location/Population Parameter O3-associated 

Percent Change in 

Single-Pollutant 

Model (95% CI)a

O3-associated 

Percent Change in 

Copollutant Model 

(95% CI)a

PEF

Neas et al. 

(1999)

Philadelphia, PA

156 Children at summer camp, 

ages 6 - 11 yr

Morning PEF For 12-h avg, Lag 1

-0.94 (-2.0, 0.08)

With 24-h avg, Lag 1 

sulfate

-0.10b

Thurston et al. 

(1997)

CT River Valley

166 Children with asthma at summer 

camp, ages 7-13 yr

Intraday 

change PEF

For 1-h max, Lag 0

-2.8 (-4.9, -0.59)

With 12-h avg, Lag 0 

sulfate

-11.8 (-31.6, 8.1)

Romieu et al. 

(1996)

Mexico City, Mexico

71 children with asthma, ages 5-7 yr

Evening PEF For 1-h max, Lag 2

-0.55 (-1.3, 0.19)

With 24-h avg, Lag 2 

PM2.5

-0.24 (-1.2, 0.68)

Romieu et al. 

(1997)

Mexico City, Mexico

65 children with asthma, ages 5-13 yr

Evening PEF For 1-h max, Lag 0

-0.52 (-1.0, -0.01)

With 24-h avg, Lag 0 

PM10

-0.79 (-1.4, -0.16)

FEV1

Lewis et al. 

(2005)

Detroit, MI

Children with asthma using CS

393 person-days

Lowest daily 

FEV1

For 24-h avg, Lag 2

0.29 (-4.2, 5.0)

With 24-h avg, Lag 2 

PM2.5

-0.18 (-11.0, 11.9)

With 24-h avg, Lag 2 

PM10

-13.4 (-17.8, -8.8)

Children with asthma with URI

231 person-days

Overall mean (SD) age 9.1 (1.4 yr)

For 24-h avg, Lag 2

-6.0 (-11.2, -0.41)

With 24-h avg, Lag 2 

PM2.5

-5.5 (-10.3, -0.42)

With 24-h avg, Lag 2 

PM10

-7.1 (-11.3, -2.8)

Chen et al. 

(1999)

3 Taiwan communities

941 children, mean (SD) age 9.8 

(1.6) yr

FEV1 For 1-h max, Lag 1

-1.5 (-2.8, -0.12)

With 24-h avg, Lag 1 

NO2

-2.0 (-3.5, -0.43)
Draft – Do Not Cite or Quote 6-67 June 2012

Study* Location/Population Parameter O3-associated 

Percent Change in 

Single-Pollutant 

Model (95% CI)a

O3-associated 

Percent Change in 

Copollutant Model 

(95% CI)a

Results not included in Figure 6-9c

Jalaludin et al. 

(2000)

Sydney, Australia

125 children with asthma or wheeze, 

mean (SD) age 9.6 (1.0) yr

Daily 

deviation 

from mean 

PEF

For 24-h avg, Lag 0

-1.8 (-3.5, -0.19)

With 24-h avg, Lag 0 

PM10,

-1.8 (-3.5, -0.19)

With 24-h avg, Lag 0 

NO2

-1.8 (-3.4, -0.11)

Wiwatanadate 

and 

Trakultivakorn 

(2010)

Chiang Mai, Thailand

31 children with asthma, ages 4-11 yr

Evening PEF 

(L/min)

For 24-h avg, Lag 5

-2.6 (-5.2, 0)

With 24-h avg, Lag 4 

SO2

-3.2 (-6.2, -0.2)

Son et al. 

(2010)

Ulsan, Korea

2,102 children and adults, ages 7-97 yr

Change in 

percent 

predicted 

FEV1

For 8-h max, Lag 0-2 avg 

(kriging)

-1.4 (-2.6, -0.11)

With 24-h avg, Lag 2 

PM10 (kriging)

-1.8 (-3.4, -0.25)

*Includes studies in Figure 6-9 plus others.

CS = Corticosteroid, URI = Upper respiratory infection.

a

Effect estimates are standardized to a 40-ppb increase for 1-h max O3, 30-ppb increase for 8-h max or 12-h avg O3, and 20-ppb 

increase for 24-h avg O3.

b

Information was not available to calculate 95% CI.

c

Results are not presented in Figure 6-9 because sufficient data were not provided to calculate percent change in lung function.

1 Some studies did not provide quantitative results but reported that O3-associated lung 

2 function decrements remained statistically significant in models that included 

3 copollutants such as PM10, NO2, sulfate, nitrate, or ammonium (Romieu et al., 1998b; 

4 Brauer et al., 1996; Linn et al., 1996; Spektor et al., 1988b). 

5 Several studies estimated robust O3-associated lung function decrements in multipollutant 

6 models that most often included O3, NO2, and either PM2.5 or PM10 (O'Connor et al., 

7 2008; Thaller et al., 2008; Chan and Wu, 2005; Romieu et al., 2002; Korrick et al., 1998; 

8 Higgins et al., 1990). However, the independent effects of O3 are more difficult to assess 

9 in relation to incremental changes in more than one copollutant.

Summary of Epidemiologic Studies of Lung Function

10 The cumulative body of epidemiologic evidence indicates that short-term increases in 

11 ambient O3 concentration are associated with decrements in lung function in children 

12 with asthma (Figure 6-6 and Figure 6-7 and Table 6-8 and Table 6-9) and without 

13 asthma. In contrast with results from controlled human exposure studies, within-study 

14 epidemiologic comparisons did not consistently indicate larger ambient O3-associated 

15 lung function decrements in groups with asthma (children or adults) than in groups 

16 without asthma. Notably, most epidemiologic studies were not designed to assess 
Draft – Do Not Cite or Quote 6-68 June 2012

1 between-group differences. Based on comparisons between studies, differences were 

2 noted between children with and without asthma in so far as in studies of children with 

3 asthma, an increase in ambient O3 concentration was associated concurrently with lung 

4 function decrements and increases in respiratory symptoms (Just et al., 2002; Mortimer et 

5 al., 2002; Ross et al., 2002; Gielen et al., 1997; Romieu et al., 1997; Thurston et al., 

6 1997; Romieu et al., 1996). In studies of children in the general population, O3-associated 

7 decreases in lung function were not accompanied by O3-associated increases in 

8 respiratory symptoms (Ward et al., 2002; Gold et al., 1999; Linn et al., 1996).

9 Across studies of children, there was no clear indication that a particular exposure 

10 assessment method using central site measurements produced stronger findings, despite 

11 potential differences in exposure measurement error. In children, lung function was 

12 associated with ambient O3 concentrations measured on site of children’s daytime hours 

13 (Hoppe et al., 2003; Thurston et al., 1997), at children’s schools (Chen et al., 1999; Gold 

14 et al., 1999), at the closest site (Romieu et al., 2006; Lewis et al., 2005; Romieu et al., 

15 2004b; 2002; 1997; 1996), at multiple community sites then averaged (O'Connor et al., 

16 2008; Just et al., 2002; Mortimer et al., 2002; Jalaludin et al., 2000), and at a single site 

17 (Ward et al., 2002; Gielen et al., 1997; Ulmer et al., 1997; Linn et al., 1996). Among 

18 children in California, \ found slightly larger O3-associated lung function decrements for 

19 24-h avg personal exposures than for 1-h max ambient concentrations.

20 As noted in the 1996 and 2006 O3 AQCDs, evidence clearly demonstrates ambient 

21 O3-associated lung function decrements in children and adults engaged in outdoor 

22 recreation, exercise, or work. Moreover, several results indicated associations with 10-

23 min to 12-h avg O3 concentrations <80 ppb. These studies are noteworthy for their 

24 measurement of ambient O3 on site of and at the time of subjects’ outdoor activity, 

25 factors that have contributed to higher O3 personal exposure-ambient concentration 

26 correlations and ratios (Section 4.3.3). These epidemiologic results are well supported by 

27 observations from controlled human exposure studies of lung function decrements 

28 induced by O3 exposure during exercise (Section 6.2.1.1). Although investigation was 

29 relatively limited, increases in ambient O3 concentration were not consistently associated 

30 with lung function decrements in adults with respiratory disease, healthy adults, or older 

31 adults.

32 Across the diverse populations examined, most effect estimates ranged from a <1 to 2% 

decrease in lung function per unit increase in O3 concentration1 33 . Heterogeneity in 

34 O3-associated respiratory effects within populations was indicated by observations of 

35 larger decreases (3-8%) in children with asthma with CS use or concurrent URI (Lewis et 

36 al., 2005) and older adults with airway hyperresponsiveness and/or BMI >30 (Alexeeff et 

 1 Effect estimates were standardized to a 40-, 30-, and 20-ppb increase for 1-h max, 8-h max, and 24-h avg O3.
Draft – Do Not Cite or Quote 6-69 June 2012

1 al., 2007). Among children in Mexico City, high dietary antioxidant intake attenuated 

2 O3-associated lung function decrements (Romieu et al., 2004b; 2002), similar to results 

3 from controlled human exposure studies. Each of these potential effect modifiers was 

4 examined in one to two populations; thus, firm conclusions about their influences are not 

5 warranted. Adding to the evidence for heterogeneity in response, Hoppe et al. (2003) and 

6 Mortimer et al. (2002) found that increases in ambient O3 concentration were associated 

7 with increased incidence of >10% decline in lung function in children with asthma. 

8 Collectively, epidemiologic studies examined and found lung function decrements in 

9 association with single-day O3 concentrations lagged from 0 to 7 days and concentrations 

10 averaged over 2-10 days. More studies found associations with O3 concentrations lagged 

11 0 or 1 day (Son et al., 2010; Alexeeff et al., 2008; Lewis et al., 2005; Ross et al., 2002; 

12 Jalaludin et al., 2000; Chen et al., 1999; Romieu et al., 1997; Brauer et al., 1996; Romieu 

13 et al., 1996; Spektor et al., 1988b) than those lagged 5-7 days (Wiwatanadate and 

14 Trakultivakorn, 2010; Hernández-Cadena et al., 2009; Steinvil et al., 2009). Associations 

15 with multiday average concentrations (Son et al., 2010; Liu et al., 2009a; Barraza16 Villarreal et al., 2008; O'Connor et al., 2008; Alexeeff et al., 2007; Mortimer et al., 2002; 

17 Ward et al., 2002; Gold et al., 1999; Naeher et al., 1999; Neas et al., 1999) indicate that 

18 elevated exposures over several days may be important. Within studies, O3

19 concentrations for multiple lag periods were associated with lung function decrements, 

20 possibly indicating that multiple modes of action may be involved in the responses. 

21 Activation of bronchial C-fibers (Section 5.3.2) may lead to decreases in lung function as 

22 an immediate response to O3 exposure, and increased airway hyperresponsiveness to 

23 antigens resulting from sensitization of airways by O3 (Section 5.3.5) may mediate lung 

24 function responses associated with lagged or multiday O3 exposures (Peden, 2011).

25 For single- and multi-day average O3 concentrations, lung function decrements were 

26 associated with 1-h max, 8-h max, and 24-h avg O3, with no strong difference in the 

27 consistency or magnitude of association among the averaging times. For example, among 

28 studies that examined multiple averaging times, Spektor and Lippmann (1991) found a 

29 larger magnitude of association for 1-h max O3 than for 24-h avg O3. However, other 

30 studies found larger magnitudes of association for longer averaging times [8-h max in 

31 Chan and Wu (2005) and 12-h avg in Thaller et al. (2008)] than for 1-h max O3. Other 

32 studies found no clear difference among O3 averaging times (Jalaludin et al., 2000; Chen 

33 et al., 1999; Scarlett et al., 1996; Berry et al., 1991).

34 Several studies found that associations with lung function decrements persisted at lower 

35 ambient O3 concentrations. For O3 concentrations averaged up to 1 hour during outdoor 

36 recreation or exercise, associations were found in analyses restricted to O3 concentrations 

37 <80 ppb (Spektor et al., 1988a; Spektor et al., 1988b), 60 ppb (Brunekreef et al., 1994; 
Draft – Do Not Cite or Quote 6-70 June 2012

1 Spektor et al., 1988a), and 50 ppb (Brunekreef et al., 1994). Among outdoor workers, 

2 Brauer et al. (1996) found a robust association using daily 1-h max O3 concentrations 

3 <40 ppb. Ulmer et al. (1997) found a robust association in schoolchildren using 30-min 

4 max O3 concentrations <60 ppb. For 8-hour avg O3 concentrations, associations with lung 

5 function decrements in children with asthma were found to persist at concentrations 

6 <80 ppb in a U.S. multicity study (for lag 1-5 avg) (Mortimer et al., 2002) and <51 ppb in 

7 a study conducted in the Netherlands (for lag 2) (Gielen et al., 1997).

8 Evidence did not demonstrate strong confounding by meteorological factors and 

9 copollutant exposures. Most O3 effect estimates for lung function were robust to 

10 adjustment for temperature, humidity, and copollutants such as PM2.5, PM10, NO2, or SO2. 

11 Although examined in few epidemiologic studies, O3 was associated with decreases in 

12 lung function with adjustment for pollen or acid aerosols. The consistency of association 

13 in the collective body of evidence with and without adjustment for ambient copollutant 

14 concentrations and meteorological factors combined with evidence from controlled 

15 human exposure studies for the direct effects of O3 exposure provide strong support for 

16 the independent effects of short-term ambient O3 exposure on lung function decrements.

6.2.1.3 Toxicology: Lung Function

17 The 2006 O3 AQCD concluded that pulmonary function decrements occur in a number of 

18 species with acute exposures (≤ 1 week), ranging from 0.25 to 0.4 ppm O3 (U.S. EPA, 

19 2006b). Early work has demonstrated that during acute exposure of ~0.2 ppm O3 in rats, 

20 the most commonly observed alterations are increased frequency of breathing and 

21 decreased tidal volume (i.e., rapid, shallow breathing). Decreased lung volumes are 

22 observed in rats with acute exposures to 0.5 ppm O3. At concentrations of ≥ 1 ppm, 

23 breathing mechanics (compliance and resistance) are also affected. Exposures of 6 h/day 

24 for 5 days create a pattern of attenuation of pulmonary function decrements in both rats 

25 and humans without concurrent attenuation of lung injury and morphological changes, 

26 indicating that the attenuation did not result in protection against all the effects of O3

27 (Tepper et al., 1989). A number of studies examining the effects of O3 on pulmonary 

28 function in rats, mice, and dogs are described in Table 6-13 on page 6-91 (U.S. EPA, 

29 1996m) of the 1996 O3 AQCD, and Table AX5-11 on page AX5-34 (U.S. EPA, 2006f) of 

30 the 2006 O3 AQCD (U.S. EPA, 2006b, 1996a). Lung imaging studies using 

hyperpolarized 3 31 He provide evidence of ventilation abnormalities in rats following 

32 exposure to 0.5 ppm O3 (Crémillieux et al., 2008). Rats were exposed to 0.5 ppm O3 for 2 

33 or 6 days, either continuously (22 h/day) or alternatingly (12 h/day). Dynamic imaging of 

34 lung filling (2 mL/sec) revealed delayed and incomplete filling of lung segments and 

35 lobes. Abnormalities were mainly found in the upper regions of the lungs and proposed to 
Draft – Do Not Cite or Quote 6-71 June 2012

1 be due to the spatial distribution of O3 exposure within the lung. Although the small 

2 number of animals used in the study (n = 3 to 7/group) makes definitive conclusions 

3 difficult, the authors suggest that the delayed filling of lung lobes or segments is likely a 

4 result of an increase in airway resistance brought about by narrowing of the peripheral 

5 small airways. 

6.2.2 Airway Hyperresponsiveness

6 Airway hyperresponsiveness refers to a condition in which the conducting airways 

7 undergo enhanced bronchoconstriction in response to a variety of stimuli. Airway 

8 responsiveness is typically quantified by measuring changes in pulmonary function 

9 (e.g., FEV1 or specific airway resistance [sRaw]) following the inhalation of an 

10 aerosolized specific (allergen) or nonspecific (e.g., methacholine) bronchoconstricting 

11 agent or another stimulus such as exercise or cold air. Asthmatics are generally more 

12 sensitive to bronchoconstricting agents than nonasthmatics, and the use of an airway 

13 challenge to inhaled bronchoconstricting agents is a diagnostic test in asthma. Standards 

14 for airway responsiveness testing have been developed for the clinical laboratory (ATS, 

15 2000a), although variation in methodology for administering the bronchoconstricting 

16 agent may affect the results (Cockcroft et al., 2005). There is a wide range of airway 

17 responsiveness in nonasthmatic people, and responsiveness is influenced by a wide range 

18 of factors, including cigarette smoke, pollutant exposures, respiratory infections, 

19 occupational exposures, and respiratory irritants. Airways hyperresponsiveness in 

20 response to O3 exposure has not been examined widely in epidemiologic studies; such 

21 evidence is derived primarily from controlled human exposure and toxicological studies.

6.2.2.1 Controlled Human Exposures

22 Beyond its direct effect on lung function, O3 exposure causes an increase in airway 

23 responsiveness in human subjects. Increased airway responsiveness is an important 

24 consequence of exposure to ambient O3, because the airways are then predisposed to 

25 narrowing upon inhalation of a variety of ambient stimuli.

26 Increases in airway responsiveness have been reported for exposures to 80 ppb O3 and 

27 above. Horstman et al. (1990) evaluated airway responsiveness to methacholine in young 

28 healthy adults (22 M) exposed to 80, 100, and 120 ppb O3 (6.6 hours, quasi continuous 

29 moderate exercise, 39 L/min). Dose-dependent decreases of 33, 47, and 55% in the 

30 cumulative dose of methacholine required to produce a 100% increase in sRaw after 

31 exposure to O3 at 80, 100, and 120 ppb, respectively, were reported. Molfino et al. (1991)
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1 reported increased allergen-specific airway responsiveness in mild asthmatics exposed to 

2 120 ppb O3 (1 hour resting exposure). Due to safety concerns, however, the exposures in 

3 the Molfino et al. (1991) study were not randomized with FA conducted first and O3

4 exposure second. Attempts to reproduce the findings of Molfino et al. (1991) using a 

5 randomized exposure design have not found statistically significant changes in airway 

6 responsiveness at such low levels of O3 exposure. At a considerably higher exposure to 

7 250 ppb O3 (3 h, light-to-moderate intermittent exercise, 30 L/min), Jorres et al. (1996)

8 found significant increases in specific and non-specific airway responsiveness of mild 

9 asthmatics 3 hours following O3 exposure. Kehrl et al. (1999) found increased reactivity 

10 to house dust mite antigen in mild atopic asthmatics 16-18 hours after exposure to 

11 160 ppb O3 (7.6 hours, light quasi continuous exercise, 25 L/min). Holz et al. (2002)

12 demonstrated that repeated daily exposure to lower concentrations of 125 ppb O3 (3 hours 

13 for four consecutive days; intermittent exercise, 30 L/min) causes an increased response 

14 to allergen challenge at 20 hours postexposure in allergic airway disease. 

15 Ozone exposure of asthmatic subjects, who characteristically have increased airway 

16 responsiveness at baseline relative to healthy controls (by nearly two orders of 

17 magnitude), can cause further increases in responsiveness (Kreit et al., 1989). Similar 

18 relative changes in airway responsiveness are seen in asthmatics and healthy control 

19 subject exposed to O3 despite their markedly different baseline airway responsiveness. 

20 Several studies (Kehrl et al., 1999; Jorres et al., 1996; Molfino et al., 1991) have 

21 suggested an increase in specific (i.e., allergen-induced) airway reactivity. An important 

22 aspect of increased airway responsiveness after O3 exposure is that this may provide 

23 biological plausibility for associations observed between increases in ambient O3

24 concentrations and increased respiratory symptoms in children with asthma 

25 (Section 6.2.4.1) and increased hospital admissions and ED visits for asthma 

26 (Section 6.2.7). 

27 Changes in airway responsiveness after O3 exposure appear to resolve more slowly than 

28 changes in FEV1 or respiratory symptoms (Folinsbee and Hazucha, 2000). Studies 

29 suggest that O3-induced increases in airway responsiveness usually resolve 18 to 24 hours 

30 after exposure, but may persist in some individuals for longer periods (Folinsbee and 

31 Hazucha, 1989). Furthermore, in studies of repeated exposure to O3, changes in airway 

32 responsiveness tend to be somewhat less susceptible to attenuation with consecutive 

33 exposures than changes in FEV1 (Gong et al., 1997a; Folinsbee et al., 1994; Kulle et al., 

34 1982; Dimeo et al., 1981). Increases in airway responsiveness do not appear to be 

35 strongly associated with decrements in lung function or increases in symptoms (Aris et 

36 al., 1995). Recently, Que et al. (2011) assessed methacholine responsiveness in healthy 

37 young adults (83M, 55 F) one day after exposure to 220 ppb O3 and FA for 2.25 hours 

38 (alternating 15 min periods of rest and brisk treadmill walking). Increases in airways 
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1 responsiveness at 1 day post-O3 exposure were not correlated with FEV1 responses 

2 immediately following the O3 exposure nor with changes in epithelial permeability 

3 assessed 1 day post-O3 exposure.

6.2.2.2 Toxicology: Airway Hyperresponsiveness

4 In addition to human subjects, a number of species, including nonhuman primates, dogs, 

5 cats, rabbits, and rodents, have been used to examine the effect of O3 exposure on airway 

6 hyperresponsiveness (see Table 6-14 on page 6-93 (U.S. EPA, 1996n) of the 1996 O3

7 AQCD and Table AX5-12 on page AX5-36 (U.S. EPA, 2006g) of the 2006 O3 AQCD). 

8 With a few exceptions, commonly used animal models have been guinea pigs, rats, or 

9 mice acutely exposed to O3 concentrations of 1 to 3 ppm to induce airway 

10 hyperresponsiveness. These animal models are helpful for determining underlying 

11 mechanisms of general airway hyperresponsiveness and are relevant for understanding 

12 airway responses in humans. Although 1-3 ppm may seem like a high exposure 

concentration, based on 18 13 O3 (oxygen-18-labeled O3) in the BALF of humans and rats, an 

14 exposure of 0.4 ppm O3 in exercising humans appears roughly equivalent to an exposure 

15 of 2 ppm in resting rats (Hatch et al., 1994).

16 A limited number of studies have observed airway hyperresponsiveness in rodents and 

17 guinea pigs after exposure to less than 0.3 ppm O3. As previously reported in the 2006 O3

18 AQCD, one study demonstrated that a very low concentration of O3 (0.05 ppm for 4 h) 

19 induced airway hyperresponsiveness in some of the nine strains of rats tested (Depuydt et 

20 al., 1999). This effect occurred at a concentration of O3 that was much lower than has 

21 been reported to induce airway hyperresponsiveness in any other species. Similar to the 

22 effects of O3 on other endpoints, these observations suggest a genetic component plays an 

23 important role in O3-induced airway hyperresponsiveness in this species and warrants 

24 verification in other species. More recently, Chhabra et al. (2010) demonstrated that 

25 exposure of ovalbumin (OVA)-sensitized guinea pigs to 0.12 ppm for 2 h/day for 

26 4 weeks produced specific airway hyperresponsiveness to an inhaled OVA challenge. 

27 Interestingly, in this study, dietary supplementation of the guinea pigs with vitamins C 

28 and E ameliorated a portion of the airway hyperresponsiveness as well as indices of 

29 inflammation and oxidative stress. Larsen and colleagues conducted an O3 C-R study in 

30 mice sensitized by 10 daily inhalation treatments with an OVA aerosol (Larsen et al., 

31 2010). Although airway responsiveness to methacholine was increased in non-sensitized 

32 animals exposed to a single 3-hour exposure to 0.5, but not 0.1 or 0.25 ppm O3, airway 

33 hyperresponsiveness was observed after exposure to 0.1 and 0.25 ppm O3 in OVA34 sensitized mice. 
Draft – Do Not Cite or Quote 6-74 June 2012

1 In order to evaluate the ability of O3 to enhance specific and non-specific airway 

2 responsiveness, it is important to take into account the phenomenon of attenuation in the 

3 effects of O3. Several studies have clearly demonstrated that some effects caused by acute 

4 exposure are absent after repeated or prolonged exposures to O3. The ability of the 

5 pulmonary system to adapt to repeated insults to O3 is complex, however, and 

6 experimental findings for attenuation to O3-induced airway hyperresponsiveness are 

7 inconsistent. Airway hyperresponsiveness was observed in mice after a 3-hour exposure 

8 but not in mice exposed continuously for 72 hours to 0.3 ppm (Johnston et al., 2005b). 

9 However, the Chhabra study demonstrated O3-induced airway hyperresponsiveness in 

10 guinea pigs exposed for 2 h/day for 10 days (Chhabra et al., 2010). Besides the obvious 

11 species disparity, these studies differ in that the mice were exposed continuously for 

12 72 hours, whereas the guinea pigs were exposed intermittently over 10 days, suggesting 

13 that attenuation might be lost with periods of rest in between O3 exposures. 

14 Overall, numerous toxicological studies have demonstrated that O3-induced airway 

15 hyperresponsiveness occurs in guinea pigs, rats, and mice after either acute or repeated 

16 exposure to relevant concentrations of O3. The mechanisms by which O3 enhances the 

17 airway responsiveness to either specific (e.g., OVA) or non-specific (e.g., methacholine) 

18 bronchoprovocation are not clear, but appear to be associated with complex cellular and 

19 biochemical changes in the conducting airways. A number of potential mediators and 

20 cells may play a role in O3-induced airway hyperresponsiveness; mechanistic studies are 

21 discussed in greater detail in Section 5.3.

6.2.3 Pulmonary Inflammation, Injury and Oxidative Stress 

22 In addition to physiological pulmonary responses, respiratory symptoms, and airway 

23 hyperresponsiveness, O3 exposure has been shown to result in increased epithelial 

24 permeability and respiratory tract inflammation. In general, inflammation can be 

25 considered as the host response to injury and the induction of inflammation as evidence 

26 that injury has occurred. Inflammation induced by exposure of humans to O3 can have 

27 several potential outcomes: (1) inflammation induced by a single exposure (or several 

28 exposures over the course of a summer) can resolve entirely; (2) continued acute 

29 inflammation can evolve into a chronic inflammatory state; (3) continued inflammation 

30 can alter the structure and function of other pulmonary tissue, leading to diseases such as 

31 fibrosis; (4) inflammation can alter the body’s host defense response to inhaled 

32 microorganisms, particularly in potentially at-risk populations such as the very young and 

33 old; and (5) inflammation can alter the lung’s response to other agents such as allergens 

34 or toxins. Except for outcome (1), the possible chronic responses have only been directly 

35 observed in animals exposed to O3. It is also possible that the profile of response can be 
Draft – Do Not Cite or Quote 6-75 June 2012

1 altered in persons with preexisting pulmonary disease (e.g., asthma, COPD) or smokers. 

2 Oxidative stress has been shown to play a key role in initiating and sustaining O3-induced 

3 inflammation. Secondary oxidation products formed as a result of reactions between O3

4 and components of the ELF can increase the expression of cytokines, chemokines, and 

5 adhesion molecules and enhance airway epithelium permeability (Section 5.3.3. and 

6 Section 5.3.4).

6.2.3.1 Controlled Human Exposures

7 As reported in studies reviewed in the 1996 and 2006 O3 AQCDs, acute O3 exposure 

8 initiates an acute inflammatory response throughout the respiratory tract that has been 

9 observed to persist for at least 18-24 hours postexposure. A meta-analysis of 21 studies 

10 (Mudway and Kelly, 2004a) for varied experimental protocols (80-600 ppb O3; 

11 1-6.6 hours duration; light to heavy exercise; bronchoscopy at 0-24 hours post-O3

12 exposure) showed that neutrophils (PMN) influx in healthy subjects was linearly 

13 associated (p <0.01) with total O3 dose (i.e., the product of O3 concentration, exposure 

duration, and V̇ 14 E). As with FEV1 responses to O3, within individual inflammatory 

15 responses to O3 are generally reproducible and correlated between repeat exposures (Holz 

16 et al., 1999). Some individuals also appear to be intrinsically more susceptible to 

17 increased inflammatory responses to O3 exposure (Holz et al., 2005). 

18 The presence of PMNs in the lung has long been accepted as a hallmark of inflammation 

19 and is an important indicator that O3 causes inflammation in the lungs. Neutrophilic 

20 inflammation of tissues indicates activation of the innate immune system and requires a 

21 complex series of events that are normally followed by processes that clear the evidence 

22 of acute inflammation. Inflammatory effects have been assessed in vivo by lavage 

23 (proximal airway and bronchoalveolar), bronchial biopsy, and more recently, induced 

24 sputum. A single acute exposure (1-4 hours) of humans to moderate concentrations of O3

25 (200-600 ppb) while exercising at moderate to heavy intensities results in a number of 

26 cellular and biochemical changes in the lung, including an inflammatory response 

27 characterized by increased numbers of PMNs, increased permeability of the epithelial 

28 lining of the respiratory tract, cell damage, and production of proinflammatory cytokines 

29 and prostaglandins (U.S. EPA, 2006b). These changes also occur in humans exposed to 

30 80 and 100 ppb O3 for 6-8 hours (Alexis et al., 2010; Peden et al., 1997; Devlin et al., 

31 1991). Significant (p = 0.002) increases in sputum PMN (16-18 hours postexposure) 

32 relative to FA responses have been recently reported for 60 ppb O3 which is the lowest 

33 exposure concentration that has been investigated in young healthy adults (Kim et al., 

34 2011). Soluble mediators of inflammation such as the cytokines (e.g., IL-6, IL-8) and 

35 arachidonic acid metabolites (e.g., prostaglandin [PG]E2, PGF2α, thromboxane, and 
Draft – Do Not Cite or Quote 6-76 June 2012

1 leukotrienes [LTs] such as LTB4) have been measured in the BALF of humans exposed 

2 to O3. In addition to their role in inflammation, many of these compounds have 

3 bronchoconstrictive properties and may be involved in increased airway responsiveness 

4 following O3 exposure. The possible relationship between repetitive bouts of acute 

5 inflammation in humans caused by O3 and the development of chronic respiratory disease 

6 is unknown. 

Asthma

7 Inflammatory responses to O3 exposure have also been studied in asthmatic subjects. 

8 Asthmatics exposed to 200 ppb O3 for 4-6 hours with exercise show significantly more 

9 neutrophils in BALF (18 hours postexposure) than similarly exposed healthy individuals 

10 (Scannell et al., 1996; Basha et al., 1994). In allergic asthmatics who tested positive for 

11 Dermatophagoides farinae antigen, there was an eosinophilic inflammation (2-fold 

12 increase), as well as neutrophilic inflammation (3-fold increase) 18 hours after exposure 

13 to 160 ppb O3 for 7.6 hours with exercise (Peden et al., 1997). In a study of subjects with 

14 intermittent asthma exposed to 400 ppb O3 for 2 hours, increases in eosinophil cationic 

15 protein, neutrophil elastase and IL-8 were found to be significantly increased 16 hours 

16 postexposure and comparable in induced sputum and BALF (Hiltermann et al., 1999). At 

17 18 hours post-O3 exposure (200 ppb, 4 hours with exercise) and corrected for FA 

18 responses, Scannell et al. (1996) found significantly increased neutrophils in 18 

19 asthmatics (12%) compared to 20 healthy subjects (4.5%). This difference in 

20 inflammatory response was observed despite no group differences in spirometric 

21 responses to O3. Scannell et al. (1996) also reported that IL-8 tends to be higher in the 

22 BALF of asthmatics compared to nonasthmatics following O3 exposure, suggesting a 

23 possible mediator for the significantly increased neutrophilic inflammation in those 

24 subjects. Bosson et al. (2003) found significantly greater epithelial expression of IL-5, 

25 IL-8, granulocyte-macrophage colony-stimulating factor and epithelial cell-derived 

26 neutrophil-activating peptide-78 in asthmatics compared to healthy subjects following 

27 exposure to 200 ppb O3 for 2 h. In contrast, Stenfors et al. (2002) did not detect a 

28 difference in the O3-induced increases in neutrophil numbers between 15 mild asthmatic 

29 and 15 healthy subjects by bronchial wash at the 6 hours postexposure time point. 

30 However, the asthmatics were on average 5 years older than the healthy subjects in this 

31 study, and it is not yet known how age affects inflammatory responses. It is also possible 

32 that the time course of neutrophil influx differs between healthy and asthmatic 

33 individuals. Differences between asthmatics and healthy subjects in O3-mediated 

34 activation of innate and adaptive immune responses have been observed in two studies 

35 (Hernandez et al., 2010; Bosson et al., 2003), as discussed in Section 6.2.5.4 and 

36 Section 5.4.2.2. 
Draft – Do Not Cite or Quote 6-77 June 2012

1 Vagaggini et al. (2002) investigated the effect of prior allergen challenge on responses in 

2 mild asthmatics exposed for 2 hours to 270 ppb O3 or filtered air. At 6 hours 

3 postexposure, eosinophil numbers in induced sputum were found to be significantly 

4 greater after O3 than after air exposures. Studies such as this suggest that the time course 

5 of eosinophil and neutrophil influx following O3 exposure can occur at levels detectable 

6 within the airway lumen by as early as 6 h. They also suggest that the previous or 

7 concurrent activation of proinflammatory pathways within the airway epithelium may 

8 enhance the inflammatory effects of O3. For example, in an in vitro study of primary 

9 human nasal epithelial cells and BEAS-2B cell line, cytokine production induced by 

10 rhinovirus infection was enhanced synergistically by concurrent exposure to O3 at 

11 200 ppb for 3 hours (Spannhake et al., 2002). 

12 A few studies have evaluated the effects of corticosteroid usage on the response of 

13 asthmatics to O3. Vagaggini et al. (2007) evaluated whether corticosteroid usage would 

14 prevent O3-induced lung function decrements and inflammatory responses in a group of 

15 subjects with mild persistent asthma (n = 9; 25 ± 7 years). In this study, asthmatics were 

16 randomly exposed on four occasions to 270 ppb O3 or FA for 2 hours with moderate 

17 exercise. Exposures were preceded by four days of treatment with prednisone or placebo. 

18 Pretreatment with corticosteroids prevented an inflammatory response in induced sputum 

19 at 6 hours postexposure. FEV1 responses were, however, not prevented by corticosteroid 

20 treatment and were roughly equivalent to those observed following placebo. Vagaggini et 

21 al. (2001) also found budesonide to decrease airway neutrophil influx in asthmatics 

22 following O3 exposure. In contrast, inhalation of corticosteroid budesonide failed to 

23 prevent or attenuate O3-induced responses in healthy subjects as assessed by 

24 measurements of lung function, bronchial reactivity and airway inflammation 

25 (Nightingale et al., 2000). High doses of inhaled fluticasone and oral prednisolone have 

26 each been reported to reduce inflammatory responses to O3 in healthy individuals (Holz 

27 et al., 2005).

28 Stenfors et al. (2010) exposed persistent asthmatics (n = 13; aged 33 years) receiving 

29 chronic inhaled corticosteroid therapy to 200 ppb O3 for 2 hours with moderate exercise. 

30 At 18 hours postexposure, there was a significant O3-induced increase in 

31 bronchioalveolar lavage (BAL) neutrophils, but not eosinophils. Bronchial biopsy also 

32 showed a significant O3-induced increase in mast cells. This study suggests that the 

33 protective effect of acute corticosteroid therapy against inflammatory responses to O3 in 

34 asthmatics demonstrated by Vagaggini et al. (2007) may be lost with continued treatment 

35 regimes.
Draft – Do Not Cite or Quote 6-78 June 2012

Associations between Inflammation and FEV1 responses

1 Studies reviewed in the 2006 O3 AQCD reported that inflammatory responses do not 

2 appear to be correlated with lung function responses in either asthmatic or healthy 

3 subjects. In healthy adults (14 M, 6 F) and asthmatic (12 M, 6 F) volunteers exposed to 

200 ppb O3 (4 hours with moderate quasi continuous exercise, V̇ 4 E = 44 L/min), percent

5 PMN and total protein in BAL fluids were significantly increased in the asthmatics 

6 relative to the healthy controls. Spirometric measures of lung function were significantly 

7 decreased following the O3 exposure in both groups, but were not significantly different 

8 between the asthmatic and healthy subjects. Effects of O3 on PMN and total protein were 

9 not correlated with changes in FEV1 or FVC (Balmes et al., 1997; Balmes et al., 1996). 

10 Devlin et al. (1991) exposed healthy adults (18 M) to 80 and 100 ppb O3 (6.6-hours with 

11 moderate quasi continuous exercise, 40 L/min). In BAL fluid collected 18 hours after 

12 exposure to 100 ppb O3, significant increases in PMNs, protein, PGE2, fibronectin, IL-6, 

13 lactate dehydrogenase, and α-1 antitrypsin compared to FA. Similar but smaller increases 

14 in all mediators were found after exposure to 80 ppb O3 except for protein and 

15 fibronectin. Changes in BAL markers were not correlated with changes in FEV1. Holz et 

16 al. (1999) examined inflammatory responses in healthy (n = 21) and asthmatic (n = 15) 

17 subjects exposed to 125 and 250 ppb O3 (3 h, light intermittent exercise, 26 L/min). 

18 Significantly increased percent PMN in sputum due to O3 exposure was observed in both 

19 asthmatics and healthy subjects following the 250 ppb exposure. At the lower 125 ppb 

20 exposure, only the asthmatic group experienced statistically significant increases in the 

21 percent PMN. Significant decrements in FEV1 were only found following exposure to 

22 250 ppb; these changes in FEV1 did not differ significantly between the asthmatic and 

23 healthy groups and were not correlated with changes in PMN levels. Peden et al. (1997)

24 also found no correlation between PMN and FEV1 responses in 8 individuals with asthma 

exposed to 160 ppb O3 for 7.6 hours with light-to-moderate exercise (V̇ 25 E = 25 L/min). 

26 However, a marginally significant correlation (r = -0.69, two-tailed p = 0.08, n = 7) was 

27 observed between increases in the percentage of eosinophils and FEV1 responses 

28 following O3 exposure.

29 In contrast to these earlier findings, Vagaggini et al. (2010) recently reported a significant 

30 (r = 0.61, p = 0.015) correlation between changes in FEV1 and changes in sputum 

31 neutrophils in mild-to-moderate asthmatics (n = 23; 33 ± 11 years) exposed to 300 ppb 

32 O3 for 2 hours with moderate exercise. Eight subjects were categorized as “responders” 

33 based on >10% FEV1 decrements. There were no baseline differences between 

34 responders and nonresponders. However, at 6 hours post-O3 exposure, sputum 

35 neutrophils were significantly increased by 15% relative to FA in responders. The 

36 neutrophil increase in responders was also significantly greater than the 0.2% increase in 

37 nonresponders. Interestingly, the nonresponders in the Vagaggini et al. (2010) study 
Draft – Do Not Cite or Quote 6-79 June 2012

1 experienced a significant O3-induced 11.3% increase in sputum eosinophils, while 

2 responders had an nonsignificant 2.6% decrease.

Time Course of the Inflammatory Response

3 The time course of the inflammatory response to O3 in humans has not been fully 

4 characterized. Different markers exhibit peak responses at different times. Studies in 

5 which lavages were performed 1 hour after O3 exposure (1 hours at 400 ppb or 4 hours at 

6 200 ppb) have demonstrated that the inflammatory responses are quickly initiated (Torres 

7 et al., 1997; Devlin et al., 1996; Schelegle et al., 1991). Inflammatory mediators and 

8 cytokines such as IL-8, IL-6, and PGE2 are greater at 1 hours than at 18 hours post-O3

9 exposure (Torres et al., 1997; Devlin et al., 1996). However, IL-8 still remained elevated 

10 at 18 hours post-O3 exposure (4 hours at 200 ppb O3 versus FA) in healthy subjects 

11 (Balmes et al., 1996). Schelegle et al. (1991) found increased PMNs in the “proximal 

12 airway” lavage at 1, 6, and 24 hours after O3 exposure (4 hours at 200 ppb O3), with a 

13 peak response at 6 hours. However, at 18-24 hours after O3 exposure, PMNs remain 

14 elevated relative to 1 hour postexposure (Torres et al., 1997; Schelegle et al., 1991). 

Genetic Polymorphisms

15 Alexis et al. (2010) recently reported that a 6.6-hour exposure with moderate exercise to 

16 80 ppb O3 caused increased sputum neutrophil levels at 18 hours postexposure in young 

17 healthy adults (n = 15; 24 ± 1 years). In a prior study, Alexis et al. (2009) found genotype 

18 effects on inflammatory responses to O3, but not lung function responses following a 

19 2-hour exposure to 400 ppb O3. At 4 hours post-O3 exposure, both GSTM1 genotypes 

20 had significant increases in sputum neutrophils with a tendency for a greater increase in 

21 GSTM1-sufficient than null individuals. At 24 hours postexposure, neutrophils had 

22 returned to baseline levels in the GSTM1-sufficient individuals. In the GSTM1-null 

23 subjects, however, neutrophil levels increased further from 4 hours to 24 hours and were 

24 significantly greater than both baseline levels and 24 hours levels in GSTM1-sufficient 

25 individuals. Alexis et al. (2009) found that GSTM1-sufficient individuals (n = 19; 

26 24 ± 3 years) had a decrease in macrophage levels at 4-24 hours postexposure to 400 ppb 

27 O3 for 2 hours with exercise. These studies also provide evidence for activation of innate 

28 immunity and antigen presentation, as discussed in Section 5.3.6. Effects of the exposure 

29 apart from O3 cannot be ruled out in the Alexis et al. (2010); (2009) studies, however, 

30 since no FA exposure was conducted. 

31 Vagaggini et al. (2010) examined FEV1 and sputum neutrophils in mild-to-moderate 

32 asthmatics (n = 23; 33 ± 11 years) exposed to 300 ppb O3 for 2 hours with moderate 

33 exercise. Six of the subjects were NQO1 wild type and GSTM1 null, but this genotype 

34 was not found to be associated with O3-induced changes in lung function or inflammatory 
Draft – Do Not Cite or Quote 6-80 June 2012

1 responses to O3. Kim et al. (2011) showed a significant (p = 0.002) increase in sputum 

2 neutrophil levels following a 6.6-hour exposure to 60 ppb O3 relative to FA in young 

3 healthy adults (13 F, 11 M; 25.0 ± 0.5 years). There was no significant effect of GSTM1 

4 genotype (half GSTM1-null) on the inflammatory responses observed in these 

5 individuals. Previously, inflammatory responses had only been evaluated down to a level 

6 of 80 ppb O3. 

Repeated Exposures

7 Markers from BALF following both 2 hours (Devlin et al., 1997) and 4 hours (Jorres et 

8 al., 2000; Christian et al., 1998) repeated O3 exposures (up to 5 days) indicate that there is 

9 ongoing cellular damage irrespective of the attenuation of some cellular inflammatory 

10 responses of the airways, pulmonary function, and symptom responses. Devlin et al. 

11 (1997) found that several indicators of inflammation (e.g., PMN, IL-6, PGE2, fibronectin) 

12 were attenuated after 5 days of exposure (i.e., values were not different from FA). 

13 However, other markers (LDH, IL-8, total protein, epithelial cells) did not show 

14 attenuation, suggesting that tissue damage probably continues to occur during repeated 

15 exposure. Some cellular responses did not return to baseline levels for more than 10-

16 20 days following O3 exposure. Christian et al. (1998) showed decreased numbers of 

17 neutrophils and a decrease in IL-6 levels in healthy adults after 4 days of exposure versus 

18 the single exposure to 200 ppb O3 for 4 h. Jorres et al. (2000) also found both functional 

19 and BALF cellular responses to O3 were abolished at 24 hours postexposure following 

20 the fourth exposure day. However, levels of total protein, IL-6, IL-8, reduced glutathione 

21 and ortho-tyrosine were still increased significantly. In addition, visual scores 

22 (bronchoscopy) for bronchitis and erythema and the numbers of neutrophils in bronchial 

23 mucosal biopsies were increased. Results indicate that, despite an attenuation of some 

24 markers of inflammation in BALF and pulmonary function decrements, inflammation 

25 within the airways persists following repeated exposure to O3. The continued presence of 

26 cellular injury markers indicates a persistent effect that may not necessarily be recognized 

27 due to the attenuation of spirometric and symptom responses. 

Epithelial Permeability

28 A number of studies show that O3 exposures increase epithelial cell permeability through 

direct (technetium-99m labeled diethylene triamine pentaacetic acid, 99m 29 Tc-DTPA, 

30 clearance) and indirect (e.g., increased BALF albumin, protein) techniques. Kehrl et al. 

(1987) showed increased 99m 31 Tc-DTPA clearance in healthy young adults (age 20-30 yrs) 

32 at 75 minutes postexposure to 400 ppb O3 for 2 hours. Also in healthy young adults (age 

26±2 yrs), Foster and Stetkiewicz (1996) have shown that increased 99m 33 Tc-DTPA 

34 clearance persists for at least 18-20 hours post-O3 exposure (130 minutes to average O3

35 concentration of 240 ppb), and the effect is greater at the lung apices than at the base. In a 
Draft – Do Not Cite or Quote 6-81 June 2012

1 older group of healthy adults (mean age = 35 yrs), Morrison et al. (2006) observed 

99m 2 Tc-DTPA clearance at 1 hours and 6 hours postexposure to O3 (100 and 400 ppb; 1 

hour; moderate intermittent exercise, V̇ 3 E = 40 L/min) to be similar and not statistically 

different from 99mTc-DTPA clearance at 1 hours postexposure to FA (1 h; V̇ 4 E = 40 

5 L/min). 

6 Increased BALF protein, suggesting O3-induced changes in epithelial permeability, have 

7 also been reported at 1 hour and 18 hours postexposure (Devlin et al., 1997; Balmes et 

8 al., 1996). Meta-analysis of results from 21 publications (Mudway and Kelly, 2004a) for 

9 varied experimental protocols (80-600 ppb O3; 1-6.6 hours duration; light to heavy 

10 exercise; bronchoscopy at 0-24 hours post-O3 exposure), showed that increased BALF 

11 protein is associated with total inhaled O3 dose (i.e., the product of O3 concentration, 

exposure duration, and V̇ 12 E). 

13 It has been postulated that changes in permeability associated with acute inflammation 

14 may provide increased access of inhaled antigens, particles, and other inhaled substances 

15 deposited on lung surfaces to the smooth muscle, interstitial cells, and the blood. Hence, 

16 increases in epithelial permeability following O3 exposure might lead to increases in 

17 airway responsiveness to specific and nonspecific agents. Que et al. (2011) investigated 

18 this hypothesis in healthy young adults (83M, 55 F) exposed to 220 ppb O3 for 2.25 hours 

19 (alternating 15 min periods of rest and brisk treadmill walking). As has been observed by 

20 others for FEV1 responses, within individual changes in permeability were correlated 

21 between sequential O3 exposures. This indicates intrinsic differences in susceptibility to 

22 epithelial damage from O3 exposure among individuals. Increases in epithelial 

23 permeability at 1 day post-O3 exposure were not correlated with FEV1 responses 

24 immediately following O3 exposure nor with changes in airway responsiveness to 

25 methacholine assessed 1 day post-O3 exposure. The authors concluded that changes in 

26 FEV1, permeability, and airway responsiveness following O3 exposure were relatively 

27 constant over time in young healthy adults; although, these responses appear to be 

28 mediated by differing physiologic pathways. 

6.2.3.2 Epidemiology

29 In the 2006 O3 AQCD, epidemiologic evidence of associations between short-term 

30 increases in ambient O3 concentration (30-min or 1-h max) and changes in pulmonary 

31 inflammation was limited to a few observations of increases in nasal lavage levels of 

32 inflammatory cell counts, eosinophilic cationic protein, and myeloperoxidases (U.S. 

33 EPA, 2006b). In recent years, there has been a large increase in the number of studies 

34 assessing ambient O3-related changes in pulmonary inflammation and oxidative stress, 
Draft – Do Not Cite or Quote 6-82 June 2012

1 types of biological samples collected (i.e., lower airway), and types of indicators 

2 examined. Most studies collected samples every 1 to 3 weeks resulting in a total of 3 to 8 

3 samples per subject. These recent studies form a larger base to establish coherence with 

4 findings from controlled human exposure and animal studies that have measured the 

5 same or related biological markers. Additionally, these studies provide further biological

6 plausibility for the associations observed between ambient O3 concentrations and 

7 respiratory symptoms and asthma exacerbations. 

8 Despite the strengths of studies of inflammation, it is important to note that research in 

9 this field continues to develop, and several uncertainties are recognized that may limit 

10 inferences of the effects of ambient O3 exposure. Current areas of development include 

11 examination of the clinical relevance of the observed magnitudes of changes in biological 

12 markers of pulmonary inflammation (Murugan et al., 2009; Duramad et al., 2007), 

13 characterization of the time course of changes between biomarker levels and other 

14 endpoints of respiratory morbidity, development of standardized methodologies for 

15 collection, improvement of the sensitivity and specificity of assay methods, and 

16 characterization of subject factors (e.g., asthma severity and recent medication use) that 

17 contribute to inter-individual variability. These sources of uncertainty may contribute to 

18 differences in findings among studies.

19 Although most of the biomarkers examined in epidemiologic studies were not specific to 

20 the lung, most studies collected exhaled breath, exhaled breath condensate (EBC), nasal 

21 lavage fluid, or induced sputum with the aim of monitoring inflammatory responses in 

22 airways, as opposed to monitoring systemic responses in blood. The biomarker most 

23 frequently measured was exhaled nitric oxide (eNO), likely related to its ease of 

24 collection in the field and automated measurement. Other biological markers were 

25 examined in EBC, induced sputum, and nasal lavage fluid, which are hypothesized to 

26 represent the fluid lining the lower or upper airways and contain cytokines, cells, and/or 

27 markers of oxidative stress that mediate inflammatory responses (Balbi et al., 2007; 

28 Howarth et al., 2005; Hunt, 2002). Table 6-15 presents the locations, time periods, and 

29 ambient O3 concentrations for studies examining associations with biological markers of 

30 pulmonary inflammation and oxidative stress. Many studies found that short-term 

31 increases in ambient O3 concentration were associated with increases in pulmonary 

32 inflammation and oxidative stress, in particular, studies of children with asthma 

33 conducted in Mexico City (Figure 6-10 and Table 6-16 and 

34 Table 6-17).
Draft – Do Not Cite or Quote 6-83 June 2012

Table 6-15 Mean and upper percentile ozone concentrations in studies of 

biological markers of pulmonary inflammation and oxidative stress.

Study* Location Study 

Period

O3

Averaging 

Time

Mean/Median

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

BarrazaVillarreal et al. 

(2008)

Mexico City, Mexico June 2003-

June 2005

8-h moving 

avg

31.6 Max: 86.3

Berhane et al. 

(2011)

13 Southern California 

Communities

September 

2004- June 

2005

8-h avg

(10 a.m.-6 

p.m.)

NR NR

Liu et al. 

(2009a)

Windsor, ON, Canada OctoberDecember 

2005

24-h avg 13.0 95th: 26.5

Khatri et al. 

(2009)

Atlanta, GA MaySeptember 

2003, 2005, 

2006

8-h max With asthma: 61 

(median)a

No asthma: 56 (median)a

75th (all subjects): 74a

Qian et al. 

(2009)

Boston, MA; New York, 

NY; Denver, CO; 

Philadelphia, PA; San 

Francisco, CA; 

Madison, WI (SOCS)

February 

1997-January 

1999

8-h max 33.6 75th: 44.4, Max: 91.5

Romieu et al. 

(2008)

Mexico City, Mexico JanuaryOctober 20048-h max 31.1 75th: 38.3, Max: 60.7

Sienra-Monge 

et al. (2004)

Mexico City, Mexico All-year 1999-

2000

8-h max 66.2 Max: 142.5

Ferdinands et 

al. (2008)

Suburb of Atlanta, GA August 2004 1-h max 61 (median) 75th: 67

Chimenti et al. 

(2009)

Sicily, Italy November, 

February, 

July, year NR

8-h avg 

(7 a.m. –

3 p.m.)

November: 32.7 (prerace), 35.1 (race)b

February: 37.0 (pre-race), 

30.8 (race)b

July: 51.2 (pre-race), 

46.1 (race)b

NR

Nickmilder et 

al. (2007)

Southern Belgium July-August 

2002

1-h max NR Max (across 6 camps):

24.5-112.7b

8-h max NR Max (across 6 camps):

18.9-81.1b

Delfino et al. 

(2010a)

Los Angeles, CA Warm and 

cold season 

2005-2007

24-h avg Warm season: 32.1 

(median)c

Cool season: 19.1 

(median)c

Max: 76.4c

Max: 44.9c

Adamkiewicz 

et al. (2004)

Steubenville, OH SeptemberDecember 

2000

24-h avg

1-h avgd

15.3

19.8

75th: 20.2, Max: 32.2

75th: 27.5, Max: 61.6

* Note: Studies presented in order of first appearance in the text of this section.

NR = Not Reported, SOCS = Salmeterol Off Corticosteroids Study.

a

Individual-level estimates were calculated based on time spent in the vicinity of various O3 monitors.

b

Concentrations converted from μg/m3 to ppb using the conversion factor of 0.51 assuming standard temperature (25°C) and 

pressure (1 atm).

c

Measurements outside subject’s residence (retirement home).

d

Average O3 concentration in the 1 hour preceding eNO collection.
Draft – Do Not Cite or Quote 6-84 June 2012

Note: Results are presented first for children with asthma then for adults with asthma and older adults. Effect estimates are from 

single-pollutant models and are standardized to a 40-ppb increase for 1-h avg O3 concentrations, a 30-ppb increase for 8-h max or 

8-h avg O3 concentrations, and a 20-ppb increase for 24-h avg O3 concentrations.

Figure 6-10 Percent change in exhaled nitric oxide (eNO) in association with 

ambient ozone concentrations in populations with and without 

asthma.

O3 Lag

0

1

0

0

0-3 avg

1-23 cum avg

2

0, 24-h avg

0, 1-h avg

0-4 avg

Study

Individuals with

Liu et al. (2009)

Children with

Barraza-Villarreal et 

al. (2008)

Children

Qian et al. (2009)

Children and adults 

with asthma

Berhane et al. 

(2011)

Children

Khatri et al. (2009)

Older adults

Adamkiewicz et al. 

(2004)

Delfino et al. (2010)

Subgroup

Without asthma

With asthma

Without asthma

With asthma

Without allergy

With allergy

Cool season

Warm season

asthma

asthma

►

►

►

►

►

◄

◄

◄

-30 -20 -10 0 10 20 30 40 50

Percent change in eNO per unit increase in O3 (95% CI)
Draft – Do Not Cite or Quote 6-85 June 2012

Table 6-16 Additional characteristics and quantitative data for studies 

represented in Figure 6-10.

Study* Location/Population O3 Averaging 

Time

O3 Lag Subgroup Standardized 

% Change 

(95% CI)a

Studies in individuals with asthma

Liu et al. (2009a) Windsor, ON, Canada

182 children with asthma, ages 9-

14 yr

24-h avg 0

1

-25.1 (-42.9, -1.7)

-17.5 (-32.1, -0.24)

Barraza-Villarreal et 

al. (2008)

Mexico City, Mexico

208 children, ages 6-14 yr

8-h max 0 Without 

asthma

With asthma

13.5 (11.2, 15.8)

6.2 (6.0, 6.5)

Berhane et al. 

(2011)

13 Southern California communities

2,240 children, ages 6-10 yr

8-h avg

(10 a.m.-6 p.m.)

1-23 

cummulative 

avg

Without 

asthma

With asthma

Without 

allergy

With allergy

30.1 (10.6, 53.2)

26.0 (-1.4, 60.9)

25.5 (5.3, 49.6)

32.1 (12.0, 55.9)

Qian et al. (2009) Boston, MA; New York, NY; Denver, 

CO;

Philadelphia, PA; San Francisco, 

CA; Madison, WI

119 children and adults with 

asthma, ages 12-65 yr

8-h max 0

0-3 avg

-1.2 (-1.7, -0.64)

-1.0 (-1.8, -0.26)

Khatri et al. (2009) Atlanta, GA

38 adults with asthma, ages 31-

50 yr

8-h max 2 36.6 (1.2, 71.9)

Studies in older adults

Adamkiewicz et al. 

(2004)

Steubenville, Ohio

29 older adults, ages 53-90 yr

24-h avg

1-h avgb

0 -5.7 (-25.9, 14.5)

-19.7 (-41.3, 1.9)

Delfino et al. 

(2010a)

Los Angeles, CA

60 older adults, ages ≥ 65 yr

24-h avg 0-4 avg Cool season

Warm 

season

35.2 (10.9, 59.5)

-0.60 (-14.0, 12.8)

*Includes studies in Figure 6-10.

a

Effect estimates are standardized to a 40-ppb, 30-ppb, and 20-ppb increase for 1-h avg, 8-h max or avg, and 24-h avg O3, 

respectively.

b

Average O3 concentration in the 1 hour preceding eNO collection.
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Table 6-17 Associations between short-term ambient ozone exposure and 

biological markers of pulmonary inflammation and oxidative stress.

Study Location/Population O3

Averaging 

Time

O3

Lag

Biological Marker Subgroup Standardized 

Effect Estimate 

(95% CI)a

Liu et al. 

(2009a)

Windsor, ON, Canada

182 children with asthma, 

ages 9 - 14 yr

24-h avg 0 EBC 8-isoprostane 

(% change)

EBC TBARS (% 

change)

16.2 (-14.9, 56.8)

11.5 (-27.0, 70.1)

Romieu et al. 

(2008)

Mexico City, Mexico

107 children with asthma, 

mean (SD) age 9.5 (2.1) yr

8-h max 0 EBC 

Malondialdehydeb

1.9 (1.1, 3.5)

BarrazaVillarreal et al. 

(2008)

Mexico City, Mexico

208 children, ages 6-14 yr

8-h max 0 Nasal lavage IL-8 

(pg/mL)

Without 

asthma

With asthma

1.6 (1.4, 1.8)

1.6 (1.4, 1.9)

EBC pH Without 

asthma

With asthma

-0.10 (-0.27, 0.08)c

-0.10 (-0.20, 0.01)c

Sienra-Monge 

et al. (2004)

Mexico City, Mexico

117 children with asthma, 

mean age 9 yr

8-h max 0-2 

avg

Nasal lavage IL-8b Placebo

Antioxidant

2.2 (1.1, 4.7)

1.0 (0.44, 2.3)

Nasal lavage IL-6b Placebo

Antioxidant

2.7 (1.4, 5.1)

1.1 (0.53, 2.2)

Nasal lavage Uric 

acidb Placebo

Antioxidant

0.75 (0.44, 1.3)

1.3 (0.68, 2.4)

Nasal lavage 

Glutathioneb Placebo

Antioxidant

0.79 (0.63, 0.98)

0.80 (0.66, 0.96)

Khatri et al. 

(2009)

Atlanta, GA

38 adults with asthma, 

ages 31 - 50 yr

8-h max 2 Blood eosinophils (% 

change)

2.4 (0.62, 4.2)

Ferdinands et 

al. (2008)

Atlanta, GA

16 children exercising 

outdoors, ages 14 - 17 yr

1-h max 0 EBC pH (normalized 

score)

0.80 (-0.20, 1.8)c

Results generally are presented in order of increasing mean ambient O3 concentration. EBC = exhaled breath condensate, 

TBARS = thiobarbituric acid reactive substances, IL-8 = interleukin 8, IL-6 = interleukin 6, Antioxidant = group supplemented with 

vitamins C and E. 

a

Effect estimates are standardized to a 40-, 30- and 20-ppb increase for 1-h max, 8-h max, and 24-h avg O3, respectively. 

b

Effect estimates represent the ratio of the geometric means of biological marker per unit increase in O3 concentration. A ratio <1 

indicates a decrease in marker, and a ratio >1 indicates an increase in marker for an increase in O3.

c

Model analyzed log-transformed O3. Decreases and increases in pH indicate increases and decreases in pulmonary inflammation, 

respectively.
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Populations with Asthma

Exhaled Nitric Oxide

1 Neither NO nor eNO has been examined in controlled human exposure or toxicological 

2 studies of O3 exposure. However, several lines of evidence support its analysis as an 

3 indicator of pulmonary inflammation. Inducible NO synthase can be activated by 

4 pro-inflammatory cytokines, and NO can be produced by cells such as neutrophils, 

5 eosinophils, and epithelial cells in the lung during an inflammatory response (Barnes and 

6 Liew, 1995). Further, eNO commonly is higher in individuals with asthma and increases 

7 during acute exacerbations (Jones et al., 2001; Kharitonov and Barnes, 2000).

8 As indicated in Figure 6-10 and Table 6-16, short-term increases in ambient O3

9 concentration (8-h max or avg) were associated with increases in eNO in children with 

10 asthma. These studies used different methods to assign exposures using central site O3

11 measurements: the site closest (within 5 km) to home or school (Barraza-Villarreal et al., 

12 2008) and a single site per community (Berhane et al., 2011). Because information on 

13 spatial homogeneity of ambient O3 concentrations and time spent outdoors was not 

14 provided, it is not possible to assess whether these two methods differed in personal15 ambient O3 ratios and correlations. Liu et al. (2009a) (described in Section 6.2.1.2) 

16 reported O3-associated decreases in eNO; however, this study was restricted to winter. 

17 Results for EBC markers of oxidative stress and lung function collectively provided weak 

18 evidence of O3-associated respiratory effects in this study. As described in Section 4.3.3, 

19 in non-summer months, indoor to outdoor O3 ratios are lower as are personal-ambient 

20 ratios, making it more difficult to detect associations with ambient O3 concentrations.

21 In contrast with controlled human exposure studies (Section 6.2.3.1), epidemiologic 

22 studies did not find larger O3-associated increases in pulmonary inflammation in groups 

23 with asthma than in groups without asthma (Figure 6-10 and Table 6-16). Among 

24 children in Southern California, Berhane et al. (2011) estimated similar associations for a 

25 1-23 day cumulative average of 8-h avg (10 a.m.-6 p.m.) O3 in children with and without 

26 asthma. Among children in Mexico City, Barraza-Villarreal et al. (2008) found a larger 

27 association (for lag 0 of 8-max O3) in children without asthma, most of whom had atopy. 

28 Studies that included adults with asthma produced contrasting results (Khatri et al., 2009; 

29 Qian et al., 2009). The multicity salmeterol (β-2 agonist) trial (Boston, MA; New York, 

30 NY; Denver, CO; Philadelphia, PA; San Francisco, CA; and Madison, WI) involved 

31 serial collection of eNO from 119 subjects with asthma, 87% of whom were 20-65 years 

32 of age (Qian et al., 2009). Ambient O3 concentrations were averaged from all sites within 

33 20 miles of subjects’ zipcode centroids, which in a repeated measures study, may capture 

34 the temporal variation in O3 reasonably well (Darrow et al., 2011a; Gent et al., 2003). 
Draft – Do Not Cite or Quote 6-88 June 2012

1 Among all subjects, increases in 8-h max O3 at multiple lags (0 to 3 single-day and 

2 0-4 avg) were associated with decreases in eNO. Results did not vary among the 

3 salmeterol-, CS-, and placebo-treated groups, indicating that the counterintuitive findings 

4 for O3 were not only due to the reduction of inflammation by medication. Qian et al. 

5 (2009) suggested that at higher concentrations, O3 may transform NO in airways to 

6 reactive nitrogen species. However, this hypothesis was not supported by results from 

7 Khatri et al. (2009), who in Atlanta, GA examined overall higher 8-h max O3 ambient 

8 concentrations than did Qian et al. (2009) and found that an increase in O3 was associated 

9 with an increase in eNO in adults with asthma (36.6% [95% CI: 1.2, 71.9] per 30-ppb 

10 increase in lag 2 of 8-h max O3). Although Khatri et al. (2009) was cross-sectional and 

11 did not adjust for any meteorological factors, it may have better characterized O3

12 exposures because subjects were examined during warm months, and an 8-h max O3

13 concentration was calculated for each subject using measurements at the site closest to 

14 his/her location each hour.

Other biological markers of pulmonary inflammation and oxidative 

stress

15 Short-term increases in ambient O3 concentration were associated with changes in the 

16 levels of pro-inflammatory cytokines and cells, indicators of oxidative stress, and 

17 antioxidants (

18 Table 6-17). Importantly, any particular biomarker was examined in only one to two 

19 studies, and the evidence in individuals with asthma is derived primarily from studies 

20 conducted in Mexico City (Barraza-Villarreal et al., 2008; Romieu et al., 2008; Sienra21 Monge et al., 2004). These studies measured ambient O3 concentrations at sites within 5 

22 km of subjects’ schools or homes. In a Mexico City cohort of children with asthma, 

23 school ambient O3 concentrations averaged over 48 to 72 hours had a ratio and 

24 correlation with personal exposures (48- to 72-h avg) of 0.17 and 0.35, respectively 

25 (Ramírez-Aguilar et al., 2008). These observations suggest that the effects of personal O3

26 exposure on inflammation may have been underestimated in the Mexico City studies. 

27 Despite the limited evidence, the epidemiologic findings are well supported by controlled 

28 human exposure and toxicological studies that measured the same or related endpoints. 

29 Several of the modes of action of O3 are mediated by reactive oxygen species (ROS) 

30 produced in the airways by O3 (Section 5.3.3). These ROS are important mediators of 

31 inflammation as they regulate cytokine expression and inflammatory cell activity in 

32 airways (Heidenfelder et al., 2009). Controlled human exposure and toxicological studies, 

33 frequently have found O3-induced increases in oxidative stress as shown by increases in 

34 prostaglandins (Section 5.3.3 and Section 6.2.3.1), which are produced by the 

35 peroxidation of cell membrane phospholipids (Morrow et al., 1990). Romieu et al. (2008)
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1 analyzed EBC malondialdehyde (MDA), a thiobarbituric acid reactive substance, which 

2 like prostaglandins, is derived from lipid peroxidation (Janero, 1990). For a 30-ppb 

3 increase in lag 0 of 8-h max O3, the ratio of the geometric means of MDA was 1.3 

4 (95% CI: 1.0, 1.7). Similar results were reported for lags 1 and 0-1 avg O3. A limitation 

5 of the study was that 25% of EBC samples had nondetectable levels of MDA, and the 

6 random assignment of concentrations between 0 and 4.1 nmol to these samples may have 

7 contributed random measurement error to the estimated O3 effects. Because MDA 

8 represents less than 1% of lipid peroxides and is present at low concentrations, its 

9 biological relevance has been questioned. However, Romieu et al. (2008) pointed to their 

10 observations of statistically significant associations of EBC MDA levels with nasal 

11 lavage IL-8 levels to demonstrate its relationship with pulmonary inflammation.

12 Uric acid and glutathione are ROS scavengers that are present in the airway ELF. While 

13 the roles of these markers in the inflammatory cascade of asthma are not well defined, 

14 they have been observed to be consumed in response to short-term O3 exposure as part of 

15 an antioxidant response in controlled human exposure and animal studies (Section 5.3.3). 

16 Results from an epidemiologic study also indicate that a similar antioxidant response may 

17 be induced by increases in ambient O3 exposure.2004) Sienra-Monge et al. (2004) found 

18 O3-associated decreases in nasal lavage levels of uric acid and glutathione in children 

19 with asthma not supplemented with antioxidant vitamins (

20 Table 6-17). The magnitudes of decrease were similar for O3 concentrations lagged 2 or 

21 3 days and averaged over 3 days.

22 Both controlled human exposure and toxicological studies have found O3-induced 

23 increases in the cytokines IL-6 and IL-8 (Section 5.3.3, Section 6.2.3.1, and 

24 Section 6.2.3.3), which are involved in initiating an influx of neutrophils, a hallmark of 

25 O3-induced inflammation (Section 6.2.3.1). Epidemiologic studies conducted in Mexico 

26 City had similar findings. Sienra-Monge et al. (2004) found that 8-h max O3 was 

27 associated with increases in nasal lavage levels of IL-6 and IL-8 (placebo group), with 

28 larger effects estimated for lag 0-2 avg than for lag 2 or 3 O3 (

29 Table 6-17). In another cohort of children with asthma, a 30-ppb increase in lag 0 of 

30 8-h max O3 was associated with a 1.61 pg/mL increase (95% CI: 1.4, 1.8) in nasal lavage 

31 levels of IL-8 (Barraza-Villarreal et al., 2008). This study also reported a small 

32 O3-associated decrease in EBC pH (

33 Table 6-17). EBC pH, which is thought to reflect the proton-buffering capacity of 

34 ammonium in airways, decreases upon asthma exacerbation, and is negatively correlated 

35 with airway levels of pro-inflammatory cytokines (Carpagnano et al., 2005; Kostikas et 

36 al., 2002; Hunt et al., 2000).
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1 Albeit with limited investigation, controlled human exposure studies have found 

2 O3-induced increases in eosinophils in adults with asthma (Section 6.2.3.1). Eosinophils 

3 are believed to be the main effector cells that initiate and sustain inflammation in asthma 

4 and allergy (Schmekel et al., 2001). Consistent with these findings, in a cross-sectional 

5 study of adults with asthma in Atlanta, GA, a 30-ppb increase in lag 2 of 8-h max O3 was 

6 associated with a 2.4% increase (95% CI: 0.62, 4.2) in blood eosinophils (Khatri et al., 

7 2009). Potential confounding by weather was not evaluated in models.

8 The prominent influences demonstrated for ROS and antioxidants in mediating the 

9 respiratory effects of O3 provide biological plausibility for effect modification by 

10 antioxidant capacity. Effect modification by antioxidant capacity has been described for 

11 O3-associated lung function in controlled human exposure and epidemiologic studies 

12 (Section 6.2.1.1 and Section 6.2.1.2). An epidemiologic study conducted in Mexico City 

13 also found that vitamin C and E supplements, which potentially increase antioxidant 

14 capacity, attenuated O3-associated inflammation and oxidative stress. Among children 

15 with asthma supplemented daily with vitamin C and E, the ratios of the geometric means 

16 of nasal lavage IL-6 and IL-8 per 30-ppb increases in lag 0-2 avg of 8-h max O3 were 1.0, 

17 reflecting no change with increases in O3 concentration (

18 Table 6-17) (Sienra-Monge et al., 2004). The results did not clearly delineate interactions 

19 among O3 concentrations, endogenous antioxidants, and dietary antioxidants (

20 Table 6-17). Ozone was associated with increases in uric acid in the antioxidant group 

21 but decreases in the placebo group across the O3 lags examined. Associations with 

22 glutathione were similar in the two groups. In another cohort, 8-h max O3 concentrations 

23 ≥ 38 ppb enhanced the effects of diets high in antioxidant vitamins and/or omega-3 fatty 

24 acids on protecting against O3-related increases in nasal lavage IL-8 (Romieu et al., 

25 2009). Information on the main effects of O3 or effect modification by diet was not 

26 presented.

27 The levels of several biological markers such as eNO, EBC pH, and MDA consistently 

28 differ between groups with and without asthma and change during an asthma 

29 exacerbation (Corradi et al., 2003; Hunt et al., 2000); however, the magnitudes of change 

30 associated with these overt effects are not well defined. Ozone-associated increases in 

31 interleukins and indicators of oxidative stress were small: 1-2% increase for each 30-ppb 

32 increase in 8-h max O3 concentration (

33 Table 6-17). Ozone-associated increases in eNO were larger: 6-36% increase per 30-ppb 

34 increase in 8-h max ambient O3 concentration (Berhane et al., 2011; Delfino et al., 2010a; 

35 Khatri et al., 2009; Barraza-Villarreal et al., 2008). Some studies in populations with 

36 asthma found O3-associated increases in pulmonary inflammation concurrently (at the 
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1 same lag) with O3-associated in respiratory symptoms. For example, among adults with 

2 asthma in Atlanta, an increase in ambient O3 concentration was associated with increases 

3 in eNO, blood eosinophils, and a decrease in quality of life score, which incorporates 

4 indices for symptoms and activity limitations (Khatri et al., 2009). Also, among children 

5 with asthma in Mexico City, O3 was associated with increases in eNO and nasal lavage 

6 IL-8 and concurrently assessed cough but not wheeze (Barraza-Villarreal et al., 2008). 

Children without Asthma

7 In the limited investigation, short-term increases in ambient O3 concentration (8-h max or 

8 avg) were associated with increases in pulmonary inflammation in children without 

9 asthma (Berhane et al., 2011; Barraza-Villarreal et al., 2008) (Figure 6-10 and Table 6-16

10 and

11 Table 6-17). The study of children in Mexico City found a larger O3-associated increase 

12 in eNO in the children without asthma than with asthma (13.5% versus 6.2% increase per 

13 30-ppb increase in lag 0 of 8-h max O3) (Barraza-Villarreal et al., 2008). Ozone was 

14 associated with similar magnitudes of change in IL-8 and EBC pH in children with and 

15 without asthma. A distinguishing feature of this study was that 72% of children without 

16 asthma had allergies. A study conducted in 13 Southern California communities also 

17 found that increases in ambient O3 concentration (8-h avg, 10 a.m.-6 p.m.) were 

18 associated with increases in eNO in children with respiratory allergy (Berhane et al., 

19 2011). Coherence for these epidemiologic findings is provided by observations of 

20 O3-induced allergic inflammation in animal models of allergy (Section 6.2.3.3 and 

21 Section 6.2.6).

22 Berhane et al. (2011) found O3-associated increases in eNO in children without asthma 

23 and children without respiratory allergy, providing evidence for effects on pulmonary 

24 inflammation in healthy children. This study provided detailed information on differences 

25 in association among various lags of 8-h avg (10 a.m.-6 p.m.) O3. Ozone concentrations 

26 averaged over the several hours preceding eNO collection were not significantly 

27 associated with eNO. Consistent with other studies examining pulmonary inflammation 

28 and oxidative stress, Berhane et al. (2011) found that relatively short lags of O3, i.e., 1 to 

29 5 days, were associated with increases in eNO. However, among several types of lag30 based models, including unconstrained lag models, polynomial distributed lag models, 

31 spline-based distributed lag models, and cumulative lag models, a 23-day cumulative lag 

32 of O3 best fit the data. Among the studies evaluated in this ISA, Berhane et al. (2011) was 

33 unique in evaluating and finding larger respiratory effects for multi-week (e.g., 13-

34 30 days) average O3 concentrations. The mechanism for the effects of O3 peaking with a 
Draft – Do Not Cite or Quote 6-92 June 2012

1 23-day cumulative lag of exposure has not been delineated. Further, with examination of 

2 such long lag periods, there is greater potential for residual confounding by weather.

Populations with Increased Outdoor Exposures

3 With limited investigation, increases in ambient O3 concentration were not consistently 

4 associated with pulmonary inflammation in populations engaged in outdoor activity or 

5 exercise. Common limitations of these studies were the small numbers of subjects and 

6 lack of consideration for potential confounding factors. A study in 16 adolescent long7 distance runners near Atlanta, GA was noted for the daily collection of EBC and the 

8 likely greater extent to which ambient O3 concentrations represented ambient exposures 

9 because of the analysis of O3 concentrations measured during outdoor running at a site 

10 less than 1 mile from the exercise track (Ferdinands et al., 2008). Increases in 1-h max O3

11 (lags 0 to 2) were associated with increases in EBC pH, indicating O3-associated 

12 decreases in pulmonary inflammation. Among 9 adult male runners in Sicily, Italy 

13 examined 3 days before and 20 hours after 3 races in fall, winter, and summer, weekly 

14 average O3 concentrations (8-h avg, 7 a.m.-3 p.m.) were positively correlated with 

15 apoptosis of neutrophils (Spearman’s r = 0.70, p <0.005) and bronchial epithelial cell 

16 differential counts (Spearman’s r = 0.47, p <0.05) but not with neutrophil or macrophage 

17 cell counts or levels of the pro-inflammatory cytokines TNF-α and IL-8 (Chimenti et al., 

18 2009). Associations with O3 concentrations measured during the races (mean 35 to 89 

19 minutes) were not examined. This study provides evidence for new endpoints; however, 

20 the implications of findings are limited due to the lack of a rigorous statistical analysis.

21 In a cross-sectional study of children at camps in south Belgium, although lung function 

22 was not associated with O3 measured at camps during outdoor activity, an association 

23 was found for eNO (Nickmilder et al., 2007). Children at camps with lag 0 1-h max O3

24 concentrations >85.2 ppb had greater increases in intraday eNO compared with children 

25 at camps with O3 concentrations <51 ppb. A benchmark dose analysis indicated that the 

26 threshold for an O3-associated increase of 4.3 ppb eNO (their definition of increased 

27 pulmonary inflammation) was 68.6 ppb for 1-h max O3 and 56.3 ppb for 8-h max O3. 

28 While these results provide additional evidence for O3-associated increases in pulmonary 

29 inflammation in healthy children, they should be interpreted with caution since they were 

30 unadjusted for any potential confounding factors and based on camp-level comparisons. 

Older Adults

31 The panel studies examining O3-associated changes in eNO in older adults produced 

32 contrasting findings (Figure 6-10 and Table 6-16). The studies differed with respect to 

33 geographic location, inclusion of healthy subjects, exposure assessment method, and lags 
Draft – Do Not Cite or Quote 6-93 June 2012

1 of O3 examined. Delfino et al. (2010a) followed 60 older adults with coronary artery 

2 disease in the Los Angeles, CA area for 6 weeks each during a warm and cool season; the 

3 specific months were not specified. Ambient O3 was measured at subjects’ retirement 

4 homes, possibly reducing some exposure measurement error due to spatial variability. 

5 Multiday averages of O3 (3- to 9-day) were associated with increases in eNO, with effect 

6 estimates increasing with increasing number of averaging days. In contrast with most 

7 other studies, an association was found in the cool season but not warm season (increase 

8 in eNO per 20-ppb increase in lag 0-4 avg of 24-h avg O3: 4.1 ppb [95% CI: 1.3, 6.9] in 

9 cool season, -0.01 ppb [95% CI: -2.3, 2.1] in warm season). Despite these unusual 

10 findings for the cool season, they were similar to findings from another study of 

11 Los Angeles area adults with asthma, which indicated an O3-associated decrease in 

12 indoor activity during the fall season (Eiswerth et al., 2005).

13 In a cool season (September-December) study conducted in older adults (ages 54-

14 91 years) in Steubenville, OH, Adamkiewicz et al. (2004) found that increases in O3

15 (1-h avg and 24-h avg before eNO collection) were associated with decreases in eNO, 

16 reflecting decreases in pulmonary inflammation (Figure 6-10 and 

17 Table 6-17). The study included healthy adults and those with asthma or COPD. A study 

18 in a subset of these adults illustrated why it is difficult to detect effects with central site 

19 O3 concentrations in the cool season by showing that subjects spent ≥ 90% of time 

20 indoors and >77% at home and had a mean 24-h avg O3 personal-ambient ratio of 0.27 

21 (Sarnat et al., 2006a).

Confounding in Epidemiologic Studies of Pulmonary Inflammation and 

Oxidative Stress

22 Except where noted in the preceding text; epidemiologic studies of pulmonary 

23 inflammation and oxidative stress accounted for potential confounding by meteorological 

24 factors. Increases in ambient O3 concentration were associated with pulmonary 

25 inflammation or oxidative stress in models that adjusted for temperature and/or humidity 

26 (Delfino et al., 2010a; Barraza-Villarreal et al., 2008; Romieu et al., 2008). Final results 

27 from Sienra-Monge et al. (2004) and Berhane et al. (2011) were not adjusted for 

28 temperature because associations were not altered by adjustment for temperature. Most 

29 studies conducted over multiple seasons adjusted for season or time trend.

30 In evidence limited to a small number of studies conducted in Mexico City, O3-associated 

31 pulmonary inflammation and oxidative stress were not found to be confounded by PM2.5

32 or PM10. These studies, which analyzed 8-hour averages for both O3 and PM, found 

33 robust associations for O3 (Barraza-Villarreal et al., 2008; Romieu et al., 2008; Sienra34 Monge et al., 2004). Ozone and PM, both measured at central sites located within 5 km of 
Draft – Do Not Cite or Quote 6-94 June 2012

1 subjects’ schools or homes, were moderately correlated (r = 0.46-0.54). Weak 

2 correlations have been found between personal exposures of O3 and PM2.5 

3 (Section 4.3.4.1). Only Romieu et al. (2008) provided quantitative results. Lag 0 of 

4 8-h max O3 was associated with the same magnitude of increase in MDA without and 

5 with adjustment for lag 0 of 8-h max PM2.5 (ratio of geometric means for a 30-ppb 

6 increase: 1.3 [95% CI: 1.0, 1.7]). In comparison, the O3-adjusted effect estimate for PM2.5

7 was cut in half.

Summary of Epidemiologic Studies of Pulmonary Inflammation and 

Oxidative Stress

8 Many epidemiologic studies provided evidence that short-term increases in ambient O3

9 exposure increase pulmonary inflammation and oxidative stress in children with asthma, 

10 with evidence primarily provided by studies conducted in Mexico City. By also finding 

11 that associations were attenuated with higher antioxidant intake, these studies indicated 

12 that inhaled O3 may be an important source of ROS in airways and/or may increase 

13 pulmonary inflammation via oxidative stress-mediated mechanisms. Studies found 

14 O3-associated increases in pulmonary inflammation in children with allergy (Berhane et 

15 al., 2011; Barraza-Villarreal et al., 2008). The limited available evidence in children and 

16 adults with increased outdoor exposures and older adults was inconclusive. Temperature 

17 and humidity were not found to confound O3 associations. Copollutant models were 

18 analyzed in a few studies conducted in Mexico City; O3 effect estimates were robust to 

19 adjustment for moderately correlated (r = 0.46-0.54) PM2.5 or PM10 (Barraza-Villarreal et 

20 al., 2008; Romieu et al., 2008; Sienra-Monge et al., 2004).

21 Ozone-associated increases in pulmonary inflammation and oxidative stress were found 

22 in studies that used varied exposure assessment methods: measurement on site of 

23 subjects’ outdoor activity (Nickmilder et al., 2007), average of concentrations measured 

24 at the closest site each hour Khatri et al. (2009), measurement at a site within 5 km of 

25 subjects’ schools or homes (Barraza-Villarreal et al., 2008; Romieu et al., 2008; Sienra26 Monge et al., 2004), and measurement at single site per town (Berhane et al., 2011). 

27 While these methods may differ in the degree of exposure measurement error, in the 

28 limited body of evidence, there was not a clear indication that the method of exposure 

29 assessment influenced the strength or magnitude of associations.

30 Most studies examined and found associations with 8-h max or daytime 8-h avg O3

31 concentrations, although associations were found for 1-h max (Nickmilder et al., 2007)

32 and 24-h avg O3 (Delfino et al., 2010a). Collectively, studies examined single-day O3 

33 concentrations lagged from 0 to 5 days and concentrations averaged over 2 to 9 days. Lag 

34 0 of 8-h max O3 was most frequently examined and consistently associated with 
Draft – Do Not Cite or Quote 6-95 June 2012

1 pulmonary inflammation and oxidative stress. However, in the few studies that examined 

2 multiple O3 lags, multiday average 8-h max or 8-h avg concentrations were associated 

3 with larger increases in pulmonary inflammation and oxidative stress (Berhane et al., 

4 2011; Delfino et al., 2010a; Sienra-Monge et al., 2004). These findings for multiday 

5 average O3 concentrations are supported by controlled human exposure (Section 6.2.3.1) 

6 and animal studies (Section 6.2.3.3) that similarly have found that some markers of 

7 pulmonary inflammation remain elevated with O3 exposures repeated over multiple days.

8 Several epidemiologic studies concurrently examined associations of ambient O3

9 concentrations with biological markers of pulmonary inflammation and lung function or 

10 respiratory symptoms. Whether evaluated at the same or different lags of O3, associations 

11 generally were stronger for biological markers of airway inflammation than for lung 

12 function (Khatri et al., 2009; Barraza-Villarreal et al., 2008; Nickmilder et al., 2007). 

13 Controlled human exposure studies also have demonstrated a lack of correlation between 

14 inflammatory and spirometric responses induced by O3 exposure (Section 6.2.3.1). 

15 Evidence has suggested that O3-related respiratory morbidity may occur via multiple 

16 mechanisms with varying time courses of action, and the examination of a limited 

17 number of O3 lags in these aforementioned studies may explain some of the 

18 inconsistencies in associations of O3 with measures of pulmonary inflammation and lung 

19 function. In contrast, based on examination in a few studies, increases in ambient O3 

20 concentration were associated concurrently (at the same lag) with increases in pulmonary 

21 inflammation and increases in respiratory symptoms or activity limitations in the same 

22 population of individuals with asthma (Khatri et al., 2009; Barraza-Villarreal et al., 

23 2008). 

6.2.3.3 Toxicology: Inflammation and Injury

24 The 2006 O3 AQCD states that the “extensive human clinical and animal toxicological 

25 evidence, together with the limited available epidemiologic evidence, is clearly indicative 

26 of a causal role for O3 in inflammatory responses in the airways” (U.S. EPA, 2006b). 

27 Airway ciliated epithelial cells and Type 1 cells are the most O3-sensitive cells and are 

28 initial targets of O3. These cells are damaged by O3 and produce a number of 

29 pro-inflammatory mediators (e.g., interleukins [IL-6, IL-8], PGE2) capable of initiating a 

30 cascade of events leading to PMN influx into the lung, activation of alveolar 

31 macrophages, inflammation, and increased permeability across the epithelial barrier. One 

32 critical aspect of inflammation is the potential for metaplasia and alterations in 

33 pulmonary morphology. Studies have observed increased thickness of the alveolar septa, 

34 presumably due to increased cellularity after acute exposure to O3. Epithelial hyperplasia 

35 starts early in exposure and increases in magnitude for several weeks, after which it 
Draft – Do Not Cite or Quote 6-96 June 2012

1 plateaus until exposure ceases. When exposure persists for a month and longer, excess 

2 collagen and interstitial fibrosis are observed. This response, discussed in Chapter 7, 

3 continues to increase in magnitude throughout exposure and can even continue to 

4 increase after exposure ends (Last et al., 1984). Previously reviewed toxicological studies 

5 of the ability of O3 to cause inflammation, injury, and morphological changes are 

6 described in Table 6-5 on page 6-25 (U.S. EPA, 1996f) and Table 6-10 (U.S. EPA, 

7 1996k) and Table 6-11 (U.S. EPA, 1996l) beginning on page 6-61 of the 1996 O3 AQCD, 

8 and Tables AX5-8 (U.S. EPA, 2006d) and AX5-9 (U.S. EPA, 2006e), beginning on page 

9 AX5-17 of the 2006 O3 AQCD. Numerous recent in vitro and in vivo studies add to this 

10 very large body of evidence for O3-induced inflammation and injury, and provide new 

11 information regarding the underlying mechanisms (see Section 5.3). 

12 A number of species, including dogs, rabbits, guinea pigs, rats, and mice have been used 

13 as models to study the pulmonary effects of O3, but the similarity of non-human primates 

14 to humans makes them an attractive model in which to study the pulmonary response to 

15 O3. As reviewed in the 1996 and 2006 O3 AQCDs, several pulmonary effects, including 

16 inflammation, changes in morphometry, and airway hyperresponsiveness, have been 

17 observed in macaque and rhesus monkeys after acute exposure to O3 (Table 6-18 presents 

18 a highlight of these studies). Increases in inflammatory cells were observed after a single 

19 8-h exposure of adult rhesus monkeys to 1 ppm O3 (Hyde et al., 1992). Inflammation was 

20 linked to morphometric changes, such as increases in necrotic cells, smooth muscle, 

21 fibroblasts, and nonciliated bronchiolar cells, which were observed in the trachea, 

22 bronchi, or respiratory bronchioles. Effects have also been observed after short-term 

23 repeated exposure to O3 at concentrations that are more relevant to ambient O3 

24 concentrations. Morphometry changes in the lung, nose, and vocal cords were observed 

25 after exposure to 0.15 ppm O3 for 8-h/day for 6 days (Harkema et al., 1993; Dimitriadis, 

26 1992; Harkema et al., 1987a). Since 2006, however, only one study has been published 

27 regarding acute exposure of non-human primates to O3 (a number of recent chronic 

28 studies in non-human primates are described in Chapter 7). In this study, a single 6-hour 

29 exposure of adult male cynomolgus monkeys to 1 ppm O3 induced significant increases 

30 in inflammatory and injury markers, including BAL neutrophils, total protein, alkaline 

31 phosphatase, IL-6, IL-8, and G-CSF (Hicks et al., 2010a). Gene expression analysis 

32 confirmed the increases in the pro-inflammatory cytokine IL-8, which had been 

33 previously described in O3 exposed rhesus monkeys (Chang et al., 1998). The 

34 anti-inflammatory cytokine IL-10 was also elevated, but the fold changes in IL-10 and 

35 G-CSF were relatively low and highly variable. The single exposure also caused necrosis 

36 and sloughing of the epithelial lining of the most distal portions of the terminal 

37 bronchioles and the respiratory bronchioles. Bronchiolitis, alveolitis, parenchymal and 

38 centriacinar inflammation were also observed. A second exposure protocol (two 

39 exposures with a 2-week inter-exposure period) resulted in similar inflammatory 
Draft – Do Not Cite or Quote 6-97 June 2012

1 responses, with the exception of total protein and alkaline phosphatase levels which were 

2 attenuated, indicating that attenuation of some but not all lavage parameters occurred 

3 upon repeated exposure of non-human primates to O3 (Hicks et al., 2010a). This 

4 variability in attenuation is similar to the findings of earlier reports in rodents (Wiester et 

5 al., 1996c) and non-human primates (Tyler et al., 1988). 

6 Table 6-18 describes key morphometric studies conducted in non-human primates 

7 exposed to O3. Morphologic observations made by Dungworth (1976); (1975) indicate 

8 that the rat and Bonnet monkey (Macaca radiata) are approximately equal in 

9 susceptibility to short-term effects of O3. Mild but discernible lesions were caused in both 

10 species by exposure to 0.2 ppm O3 for 8 h/day for 7 days. The authors stated that 

11 detectable morphological effects in the rat occurred at levels as low as 0.1 ppm O3. In 

12 both species, the lesion occurred at the junction of the small airways and the gaseous 

13 exchange region. In rats, the prominent features were accumulation of macrophages, 

14 replacement of necrotic Type 1 epithelial cells with Type 2 cells, and damage to ciliated 

15 and nonciliated Clara cells. The principal site of damage was the alveolar duct. In 

16 monkeys, the prominent O3-induced injury was limited to the small airways. At 0.2 ppm 

17 O3, the lesion was observed at the proximal portion of the respiratory bronchioles. As 

18 concentrations of O3 were increased up to 0.8 ppm, the severity of the lesion increased, 

19 and the damage extended distally to involve the proximal portions of the alveolar duct. 

20 Mellick et al. (1977) found similar but more pronounced effects when rhesus monkeys (3 

21 to 5 years of age) were exposed to 0.5 and 0.8 ppm O3, 8 hours/day for 7 days. In these 

22 experiments, the respiratory bronchioles were the most severely damaged, and more 

23 distal parenchymal regions were unaffected. Major effects were hyperplasia and 

24 hypertrophy of the nonciliated bronchiolar epithelial cells and the accumulation of 

25 macrophages intraluminally. In mice, continuous exposure to 0.5 ppm O3 caused nodular 

26 hyperplasia of Clara cells after 7 days of exposure. Similar findings were reported by 

27 Schwartz (1976) and Schwartz et al. (1976), who exposed rats to 0.2, 0.5 or 0.8 ppm O3

28 for 8 or 24 hours/day for 1 week. Changes observed within the proximal alveoli included 

29 infiltration of inflammatory cells and swelling and necrosis of Type 1 cells. In the 

30 terminal bronchiole, the changes reported were shortened cilia, clustering of basal bodies 

31 in ciliated cells suggesting ciliogenesis, and reduction in height or loss of cytoplasmic 

32 luminal projection of the Clara cells. Effects were seen at O3 concentrations as low as 

33 0.2 ppm. A dose-dependent pulmonary response to the three levels of O3 was evident. No 

34 differences were observed in morphologic characteristics of the lesions between rats 

35 exposed continuously and those exposed intermittently for 8 hours/day.
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Table 6-18 Morphometric observations in non-human primates after acute 

ozone exposure.

Reference O3 concentration 

(ppm)

Exposure 

duration

Species, Sex, Age Observation

Harkema et al. 

(1993)

0.15 8 h/day for 

6 days

Macaca radiata

(bonnet macaques)

2-6 years old

Several fold increase in thickness of surface 

epithelium in respiratory bronchioles; increase in 

interstitial mass with increase in proportion of 

cuboidal cells.

Harkema et al. 

(1987a); (1987b)

0.15 8 h/day for 

6 days

Macaca radiata, 

M, F

2-6 years old

Ciliated cell necrosis, shortened cilia, and increased 

mucous cells in the respiratory epithelium of nose 

after 0.15 ppm; changes in nonciliated cells, 

intraepithelial leukocytes, and mucous cells in the 

transitional epithelium

Dungworth (1976) 0.2

0.5

0.8

8 h/day for 

7 days for 

monkey 

and rat; 

continuous 

at 0.5 ppm 

for 7 days 

for mouse

Adult Rhesus and 

bonnet monkeys; 

S-D rats; 

Mice

In both rats and monkeys mild but discernible

lesions were observed at 0.2 ppm; similar severity 

between species but different site of lesions –

respiratory bronchioles for monkey and damage to 

ciliated, Clara, and alveolar epithelial cells for rat; 

Clara cell hyperplasia in mice

Leonard et al. 

(1991)

0.25 8 h/day for 

7 days

Macaca radiata

age not specified

The O3 exposure level is not clear – the abstract 

states 0.64 ppm, but the text mentions only 

0.25 ppm. Morphometric changes in vocal cord 

mucosa: disruption and hyperplasia of stratified 

squamous epithelium; epithelial and connective 

tissue thickness increased

Chang et al. 

(1998)

0.96 8 h Rhesus, 

M

age not specified

Increase in IL-8 in airway epithelium correlated with 

PMN influx

Hyde et al. (1992) 0.96 8 h Rhesus, 

M

2 - 8.5 years old

Increased PMNs; morphometric changes in trachea, 

conducting airways, respiratory bronchioles

including increased smooth muscle in bronchi and 

RB.

Hicks et al. 

(2010b)

1.0 6 h Cynomolgus, 

M

5-7 kg

(Adult)

Increase in PMNs and IL-8 in lavage fluid

1 Exposure of adult BALB/c mice to 0.1 ppm O3 for 4 hours increased BAL levels of 

2 keratinocyte chemoattractant (KC; IL-8 homologue) (~ fold), IL-6 (~12-fold), and TNF-α 

3 (~ 2-fold) (Damera et al., 2010). Additionally, O3 increased BAL neutrophils by 21% 

4 without changes in other cell types. A trend of increased neutrophils with increased O3

5 concentration (0.12-2 ppm) was observed in BALB/c mice exposed for 3 hours (Jang et 

6 al., 2005). Although alterations in the epithelium of the airways were not evident in 129J 

7 mice after 4 hours of exposure to 0.2 ppm O3 (Plopper et al., 2006), detachment of the 

8 bronchiolar epithelium was observed in SD rats after 5 days or 60 days of exposure to 

9 0.25 ppm O3 (Oyarzún et al., 2005). Subacute (65 hours) exposure to 0.3 ppm O3 induced 

10 pulmonary inflammation, cytokine induction, and enhanced vascular permeability in wild 

11 type mice of a mixed background (129/Ola and C57BL/6) and these effects were 

12 exacerbated in metallothionein I/II knockout mice (Inoue et al., 2008). Three hours or 

13 72 hours of exposure to 0.3 ppm O3 resulted in similar levels of IL-6 expression in the 

14 lungs of C57BL/6 mice (Johnston et al., 2005b), along with increases in BAL protein, 
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1 sTNFR1, and sTNFR2. Increased neutrophils were observed only after the 72-hour 

2 exposure, and neither exposure resulted in detectable levels of IL-6 or KC protein. Levels 

3 of BAL protein, sTNFR1, and sTNFR2 were higher in the 72-hour exposure group than 

4 in the 3-hour exposure group. In another study, the same subacute (72 hours) exposure 

5 protocol elicited increases in BALF protein, IP-10, sTNFR1, macrophages, neutrophils, 

6 and IL-6, IL-1α, and IL-1β expression (Johnston et al., 2007). Yoon et al. (2007) exposed 

7 C57BL/6J mice continuously to 0.3 ppm O3 for 6, 24, 48, or 72 hours, and observed 

8 elevated levels of KC, MIP-2, metalloproteinases, and inflammatory cells in the lungs at 

9 various time points. A similar exposure protocol using C3H/HeJ and C3H/OuJ mice 

10 demonstrated elevations in protein, PMNs, and KC, which were predominantly TLR 4 

11 pathway dependent based on their prominence in the TLR 4 sufficient C3H/OuJ strain 

12 Bauer et al. (2011). C3H/OuJ mice also had elevated levels of the heat-shock protein 

13 HSP70, and further experiments in HSP70 deficient mice indicated a role for this 

14 particular pathway in O3-related injury, discussed in more detail in Chapter 5.

15 As reviewed in the 2006 O3 AQCD, the time course for changes in BAL depends on the 

16 parameters being studied. Similarly, after exposing adult C57BL mice to 0.5 ppm O3 for 

17 3 hours, Han et al. (2008) observed early (5 hours postexposure) increases in BAL TNF-α 

18 and IL-1β, which diminished by 24 hours postexposure. Total BAL protein was elevated 

19 at 24 hours, but there were only minimal or negligible changes in LDH, total cells, or 

20 PMNs. Ozone increased BAL mucin levels (with statistical significance by 24 hours 

21 postexposure), and significantly elevated surfactant protein D at both time points. Prior 

22 intratracheal (IT) exposure to multiwalled carbon nanotubes enhanced most of these 

23 effects, but the majority of responses to the combined exposure were not greater than 

24 those to nanotubes alone. Ozone exposure did not induce markers of oxidative stress in 

25 lung tissue, BAL, or serum. Consistent with this study, Aibo et al. (2010) did not detect 

26 changes in BAL inflammatory cell numbers in the same mouse strain after a 6-hour 

27 exposure to 0.25 or 0.5 ppm. The majority of inflammatory cytokines (pulmonary or 

28 circulating) were not significantly changed (as assessed 9 hours post-O3 exposure). 

29 Exposure of C57BL/6 mice to 1 ppm for 3 hours increased BAL total cells, neutrophils, 

30 and KC; these responses were greatest at 24 hours postexposure. F2-isoprostane 

31 (8-isoprostane), a marker of oxidative stress, was also elevated by O3, peaking at 

32 48 hours postexposure (Voynow et al., 2009).

33 Atopic asthma appears to be a risk factor for more severe O3 induced airway 

34 inflammation in humans (Balmes et al., 1997; Scannell et al., 1996), and allergic animal 

35 models are often used to investigate the effects of O3 on this potentially at-risk 

36 population. Farraj et al. (2010) exposed allergen-sensitized adult male BALB/c mice to 

37 0.5 ppm O3 for 5 hours once per week for 4 weeks. Ovalbumin-sensitized mice exposed 

38 to O3 had significantly increased BAL eosinophils by 85% and neutrophils by 103%
Draft – Do Not Cite or Quote 6-100 June 2012

1 relative to OVA sensitized mice exposed to air, but these changes were not evident upon 

2 histopathological evaluation of the lung, and no O3 induced lesions were evident in the 

3 nasal passages. Ozone increased BAL levels of N-acetyl-glucosaminidase (NAG; a 

marker of injury) and protein. DEP co-exposure (2.0 mg/m3 4 , nose only) inhibited these 

5 responses. These pro-inflammatory effects in an allergic mouse model have also been 

6 observed in rats. Wagner et al. (2007) exposed the relatively O3-resistant Brown Norway 

7 rat strain to 1 ppm O3 after sensitizing and challenging with OVA. Rats were exposed for 

8 2 days, and airway inflammation was assessed one day later. Filtered air for controls 

9 contained less than 0.02 ppm O3. Histopathology indicated O3 induced site-specific lung 

10 lesions in the centriacinar regions, characterized by wall thickening partly due to 

11 inflammatory cells influx. BAL neutrophils were elevated by O3 in allergic rats, and 

12 modestly increased in non-allergic animals (not significant). A slight (but not significant) 

13 increase in macrophages was observed, but eosinophil numbers were not affected by O3. 

14 Soluble mediators of inflammation (Cys-LT, MCP-1, and IL-6) were elevated by O3 in 

15 allergic animals but not non-allergic rats. Treatment with γT, which neutralizes oxidized 

16 lipid radicals and protects lipids and proteins from nitrosative damage, did not alter the 

17 morphologic character or severity of the centriacinar lesions caused by O3, nor did it 

18 reduce neutrophil influx. It did, however, significantly reduce O3-induced soluble 

19 inflammatory mediators in allergic rats. The effects of O3 in animal models of allergic 

20 asthma are discussed in Section 6.2.6. 

21 In summary, a large number of toxicology studies have demonstrated that acute exposure 

22 to O3 produces injury and inflammation in the mammalian lung, supporting the 

23 observations in controlled human exposure studies (Section 6.2.3.1). These acute 

24 changes, both in inflammation and morphology, provide a limited amount of evidence for 

25 long term sequelae of exposure to O3. Related alterations resulting from long term 

26 exposure, such as fibrotic changes, are discussed in Chapter 7.

6.2.4 Respiratory Symptoms and Medication Use

27 Controlled human exposure and toxicological studies have described modes of action 

28 through which short-term O3 exposure may increase respiratory symptoms by 

29 demonstrating O3-induced airway hyperresponsiveness (Section 6.2.2) and pulmonary 

30 inflammation (Section 6.2.3.1 and Section 6.2.3.3). Epidemiologic studies have not 

31 widely examined associations between ambient O3 concentrations and airway 

32 hyperresponsiveness but have found O3-associated increases in pulmonary inflammation 

33 and oxidative stress (Section 6.3.2.2). In addition to lung function decrements, controlled 

34 human exposure studies clearly indicate O3-induced increases in respiratory symptoms 

35 including pain on deep inspiration, shortness of breath, and cough. This evidence is 
Draft – Do Not Cite or Quote 6-101 June 2012

1 detailed in Section 6.2.1.1; however, salient observations include an increase in 

2 respiratory symptoms with increasing concentration and duration of O3 exposure and 

3 activity level of exposed subjects (McDonnell et al., 1999b). Further, increases in total 

4 subjective respiratory symptoms have been reported following 5.6 and 6.6 hours of 

5 exposure to 60 ppb O3 relative to baseline (Adams, 2006a). At 70 ppb, Schelegle et al. 

6 (2009) observed a statistically significant O3-induced FEV1 decrement of 6.1% at 6.6 

7 hours and a significant increase in total subjective symptoms at 5.6 and 6.6 hours. The 

8 findings for O3-induced respiratory symptoms in controlled human exposure studies and 

9 the evidence integrated across disciplines describing underlying modes of action provide 

10 biological plausibility for epidemiologic associations observed between short-term 

11 increases in ambient O3 concentration and increases in respiratory symptoms.

12 In epidemiologic studies, respiratory symptom data typically are collected by having 

13 subjects (or their parents) record symptoms and medication use in a diary without direct 

14 supervision by study staff. Several limitations of symptom reports are well recognized: 

15 recall error if not recorded daily, differences among subjects in the interpretation of 

16 symptoms, differential reporting by subjects with and without asthma, and occurrence in 

17 a smaller percentage of the population compared with changes in lung function and 

18 biological markers of pulmonary inflammation. Nonetheless, symptom diaries remain a 

19 convenient tool to collect individual-level data from a large number of subjects and allow 

20 modeling of associations between daily changes in O3 concentration and daily changes in 

21 respiratory morbidity. Importantly, most of the limitations described above are sources of 

22 random measurement error that can bias effect estimates to the null or increase the 

23 uncertainty around effect estimates. Furthermore, because respiratory symptoms are 

24 associated with limitations in activity and function and are the primary reason for using 

25 medication and seeking medical care, the evidence is directly coherent with the consistent 

26 associations observed between increases in ambient O3 concentration and increases in 

27 asthma ED visits (Section 6.2.7.3). 

28 Most studies were conducted in individuals with asthma, and as was concluded in the 

29 2006 O3 AQCD (U.S. EPA, 2006b, 1996a), the collective body of epidemiologic 

30 evidence indicates that short-term increases in ambient O3 concentrations are associated 

31 with increases in respiratory symptoms in children with asthma. Studies also found 

32 O3-associated increases in the use of asthma medication in children. In a smaller body of 

33 studies, increases in ambient O3 concentration were associated with increases in 

34 respiratory symptoms in adults with asthma. Ozone-associated increases in respiratory 

35 symptoms in healthy populations were not as clearly indicated.
Draft – Do Not Cite or Quote 6-102 June 2012

6.2.4.1 Children with Asthma

Respiratory Symptoms

1 Table 6-19 presents the locations, time periods, and ambient O3 concentrations for studies 

2 examining respiratory symptoms and medication use in children with asthma. The 

3 evidence supporting associations between short-term increases in ambient O3

4 concentration and increases in respiratory symptoms in children with asthma is derived 

5 mostly from examination of 1-h max, 8-h max, or 8-h avg O3 concentrations and strong 

6 findings from a large body of single-region or single-city studies (Figure 6-11 and 

7 Table 6-20). The few available U.S. multicity studies produced less consistent 

8 associations.

9 Similar to lung function, associations with respiratory symptoms in children with asthma 

10 were found with ambient O3 concentrations assigned to subjects using various methods 

11 with potentially different degrees of exposure measurement error. As was discussed for 

12 lung function, methods included measurement of O3 on site of and at the time of outdoor 

13 activity (Thurston et al., 1997), which is associated with higher ambient-personal O3

14 correlations and ratios (Section 4.3.3); O3 concentrations measured at sites within 5 km of 

15 subjects’ home or school (Escamilla-Nuñez et al., 2008; Romieu et al., 2006; 1997; 

16 1996); O3 measured at a single city site (Gielen et al., 1997); and O3 concentrations 

17 averaged across multiple sites (Gent et al., 2003; Mortimer et al., 2002). In analyses with 

18 O3 averaged across multiple sites, which were restricted to warm seasons, O3

19 concentrations within the region were temporally correlated as indicated by high 

20 statewide correlations [median r = 0.83 in Gent et al. (2003)] or similar odds ratios for O3

21 averaged across all within-city monitors and that averaged from the three closest sites 

22 (Mortimer et al., 2002). In these panel studies, the averaged ambient concentrations may 

23 have well represented the temporal variability in subjects’ ambient O3 exposures.
Draft – Do Not Cite or Quote 6-103 June 2012

Table 6-19 Mean and upper percentile ozone concentrations in epidemiologic 

studies of respiratory symptoms, medication use, and activity

levels in children with asthma.

Study* Location Study Period O3

Averaging 

Time

Mean/Median

Concentration 

(ppb)

Upper Percentile 

Concentrations (ppb)

Thurston et 

al. (1997)

CT River Valley, CT June 1991-

1993

1-h max 83.6a Max: 160a

EscamillaNuñez et al. 

(2008)

Mexico City, Mexico July-March 

2003-2005

1-h max 86.5 NR

2006) Mexico City, Mexico October 1998-

April 2000

8-h max

1-h max

69

102

Max: 184

Max: 309

1997) Southern Mexico City, 

Mexico

April-July 1991; 

November 

1991-February 

1992

1-h max 196 Max: 390

Romieu et al.

(1996)

Northern Mexico City, Mexico April-July 1991; 

November 

1991-February 

1992

1-h max 190 Max: 370

Gent et al. 

(2003)

CT, southern MA AprilSeptember 

2001

8-h rolling 

avg

1-h max

51.3, 50.0 (median)

58.6, 55.5 (median)

Max: 99.6

Max: 125.5

Mortimer et 

al. (2002); 

(2000)

Bronx, East Harlem, NY; 

Baltimore, MD; Washington, 

DC; Detroit, MI, Cleveland, 

OH; Chicago, IL; St. Louis, 

MO ; (NCICAS)

June-August 

1993

8-h avg

(10 a.m.-

6 p.m.)

48 NR

Gielen et al. 

(1997)

Amsterdam, Netherlands April-July 1995 8-h max 34.2b Max: 56.5b

Delfino et al. 

(2003)

Los Angeles, CA November 

1999-January 

2000

8-h max

1-h max

17.1

25.4

90th: 26.1, Max: 37

90th: 38.0, Max: 52

Rabinovitch 

et al. (2004)

Denver, CO NovemberMarch 1999-

2002

1-h max 28.2 75th: 60, Max: 70.0

Schildcrout et 

al. (2006)

Albuquerque, NM; Baltimore, 

MD; Boston, MA; Denver, 

CO; San Diego, CA; Seattle, 

WA; St. Louis, MO; Toronto, 

ON, Canada (CAMP)

MaySeptember 

1994-1995

1-h max Range in medians 

across cities: 43.0-

65.8

Range in 90th across cities: 

61.5-94.7

Jalaludin et 

al. (2004)

Sydney, Australia FebruaryDecember 

1994

15-h avg 

(6 a.m.-9 

p.m.)

12 Max: 43
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Study* Location Study Period O3

Averaging 

Time

Mean/Median

Concentration 

(ppb)

Upper Percentile 

Concentrations (ppb)

O'Connor et 

al. (2008)

Boston, MA; Bronx, 

Manhattan NY; Chicago, IL; 

Dallas, TX, Seattle, WA; 

Tucson, AZ (ICAS)

August 1998-

July 2001

24-h avg NR NR

Ostro et al. 

(2001)

Los Angeles, CA AugustOctober 19931-h max Los Angeles: 59.5

Pasadena: 95.8

Max: 130

Max: 220

Mann et al. 

(2010)

Fresno/Clovis, California WinterSummer 2000-

2005

8-h max 49.4 (median) 75th: 69.5, Max: 120.0

Just et al. 

(2002)

Paris, France April-June 

1996

24-h avg 30.0b Max: 61.7b

* Note: Studies presented in order of first appearance in the text of this section.

NCICAS = National Cooperative Inner-City Asthma Study, NR = Not Reported, ICAS = Inner City Asthma Study, CAMP = Childhood 

Asthma Management Program.

a

Measured on site of subjects’ outdoor activity. 

b

Concentrations converted from μg/m3 to ppb using the conversion factor of 0.51 assuming standard temperature (25°C) and 

pressure (1 atm).
Draft – Do Not Cite or Quote 6-105 June 2012

Note: Results are presented first for aggregate indices of symptoms then for individual symptoms. Within each category, results 

generally are organized in order of increasing mean ambient O3 concentration. LRS = lower respiratory symptoms, URS = upper 

respiratory symptoms. Odds ratios are from single-pollutant models and are standardized to a 40-, 30-, and 20-ppb increase for 

1-h max, 8-h max (or 8-h avg or 15-h avg), and 24-h avg O3 concentrations, respectively.

Figure 6-11 Associations between ambient ozone concentrations and 

respiratory symptoms in children with asthma.

Study

Aggregate of symptoms

Rabinovitch et al. (2004)

Delfino et al. (2003)

Schildcrout et al. (2006)

Gielen et al. (1997)

Mortimer et al. (2002)

Mortimer et al. (2000)

Romieu et al. (1996)

Romieu et al. (1997)

Individual symptoms

Jalaludin et al. (2004)

O'Connor et al. (2008)

Ostro et al. (2001)

Escamilla-Nunez et al. 

(2008)

Mann et al. (2010)

Thurston et al. (1997)

Romieu et al. (2006)

Symptom

Daytime symptoms

Bothersome symptoms

Asthma symptoms

LRS

URS

Morning symptoms

LRS

LRS

Wheeze

Wheeze/cough

Noctural cough

Wheeze

Cough

Wheeze

Chest symptoms

Difficulty breathing

O3 Lag

0-2 avg

0, 8-h max

0, 1-h max

0

0-2 avg

0

1

2

3

4

1-4 avg

0

0

0

2

1-19 avg

0

3

1

0

0

0-5 avg

Subgroup

All subjects

All subjects

All subjects

All subjects

All subjects

No medication

Cromolyn use

Beta-agonist/xanthine use

Steroid use

Without allergy

With allergy

All

Fungi allergic

GSTM1 positive

GSTM1 null

GSTP1 Ile/Ile or Ile/Val

GSTP1 Val/Val

►

►

0 0.5 1 1.5 2 2.5

Odds ratio (95% CI)
Draft – Do Not Cite or Quote 6-106 June 2012

Table 6-20 Additional characteristics and quantitative data for studies 

presented in Figure 6-11.

Study* Location/Population O3

Averaging 

Time

O3

Lag

Symptom Subgroup Standardized 

OR (95% CI)a

Studies examining aggregates of symptoms

Delfino et al. 

(2003)

Los Angeles, CA

22 children with asthma, ages 10-

16 yr

8-h max

1-h max

0 Bothersome 

symptoms

0.75 (0.24, 2.30)

1.09 (0.39, 3.03)

Rabinovitch 

et al. (2004)

Denver, CO

86 children with asthma, ages 6-

12 yr

1-h max 0-2 

avg

Daytime 

symptoms

1.32 (1.01, 1.74)

Schildcrout et 

al. (2006)

Albuquerque, NM; Baltimore, MD; 

Boston, MA; Denver, CO; San 

Diego, CA; Seattle, WA; St. Louis, 

MO; Toronto, ON, Canada 

990 children with asthma, ages 5-

12 yr

1-h max 0

0-2 

avg

Asthma 

symptoms

1.08 (0.89, 1.31)

1.01 (0.92, 1.12)

Gielen et al. 

(1997)

Amsterdam, Netherlands

61 children with asthma, ages 7-

13 yr

8-h max 0 LRS

URS

1.04 (0.75, 1.45)

1.16 (1.02, 1.32)

(2002); 

Mortimer et 

al. (2000)

Bronx, East Harlem, NY; Baltimore, 

MD; Washington, DC; Detroit, MI, 

Cleveland, OH; Chicago, IL; St. 

Louis, MO 

846 children with asthma, ages 4-

9 yr

8-h avg

(10 a.m.-

6 p.m.)

1

2

3

4

1-4 

avg

Morning 

symptoms

All subjects

All subjects

All subjects

All subjects

All subjects

No medication 

use

Cromolyn use

βagonist/xanthine 

use

Steroid use

Without allergy

With allergy

1.06 (0.88, 1.27)

1.21 (1.04, 1.41)

1.02 (0.88, 1.18)

1.19 (1.02, 1.38)

1.35 (1.04, 1.74)

1.08 (0.62, 1.87

2.13 (1.12, 4.04)

1.39 (0.98, 1.98)

1.17 (0.79, 1.72)

1.59 (1.00, 2.52)

1.35 (0.92, 1.96)

Romieu et al. 

(1996)

northern Mexico City, Mexico

71 children with asthma, ages 5-

7 yr

1-h max 0 LRS 1.07 (1.02, 1.12)

Romieu et al. 

(1997)

southern Mexico City, Mexico

65 children with asthma, ages 5-

13 yr

1-h max 0 LRS 1.09 (1.04, 1.14)

Studies examining individual symptoms

Jalaludin et 

al. (2004)

Sydney, Australia

125 children with asthma, mean 

age 9.6 yr

15-h avg 

(6 a.m.-

9 p.m.)

0

2

Wheeze 0.93 (0.63, 1.37)

1.15 (0.94, 1.41)

O'Connor et 

al. (2008)

Boston, MA; Bronx, Manhattan NY; 

Chicago, IL; Dallas, TX, Seattle, 

WA; Tucson, AZ 

861 children with asthma, mean 

(SD) age 7.7 (2.0) yr

24-h avg 1-19 

avg

Wheeze/cough 1.02 (0.86, 1.21)
Draft – Do Not Cite or Quote 6-107 June 2012

Study* Location/Population O3

Averaging 

Time

O3

Lag

Symptom Subgroup Standardized 

OR (95% CI)a

Just et al. 

(2002)

Paris, France

82 children with asthma, mean (SD) 

age 10.9 (2.5) yr 

24-h avg 0 Nocturnal 

cough incidence

1.17 (0.72, 1.91)

Ostro et al. 

(2001)

Los Angeles, CA

138 children with asthma, ages 6-

13 yr

1-h max 3 Wheeze 0.95 (0.86, 1.04)

EscamillaNuñez et al. 

(2008)

Mexico City, Mexico

147 children with asthma, mean 

age 9.6 yr

1-h max 1 Wheeze 1.08 (1.03, 1.14)

Mann et al. 

(2010)

Fresno/Clovia, California

280 children with asthma, ages 6-

11 yr

8-h max 0 Wheeze All

Fungi allergic

1.00 (0.84, 1.19)

1.06 (0.84, 1.34)

Thurston et 

al. (1997)

CT River Valley, CT

166 children with asthma, ages 7-

13 yr

1-h max 0 Chest 

symptoms

1.28 (1.09, 1.51)

Romieu et al. 

(2006)

Mexico City, Mexico

151 children with asthma, mean 

age 9 yr

1-h max 0-5 

avg

Difficulty 

breathing

GSTM1 positive

GSTM1 null

GSTP1 Ile/Ile or 

Ile/Val

GSTP1 Val/Val

1.10 (0.98, 1.24)

1.17 (1.02, 1.33)

1.06 (0.94, 1.20)

1.30 (1.10, 1.53)

Gent et al. 

(2003)

b

CT, southern MA

130 children with asthma on 

maintenance medication

1-h max 0 Wheeze O3 <43.2 ppb

O3 43.2-51.5 ppb

O3 51.6-58.8 ppb

O3 58.9-72.6 ppb

O3 ≥ 72.7 ppb

1.00 (reference)

1.04 (0.89, 1.21)

1.16 (1.00, 1.35)

1.16 (1.00, 1.35)

1.22 (0.97, 1.53)

Chest tightness O3 <43.2 ppb

O3 43.2-51.5 ppb

O3 51.6-58.8 ppb

O3 58.9-72.6 ppb

O3 ≥ 72.7 ppb

1.00 (reference)

1.11 (0.91, 1.36)

1.01 (0.83, 1.23)

1.16 (0.97, 1.39)

1.31 (0.97, 1.77)

*Includes studies for Figure 6-11, plus others.

LRS = Lower respiratory symptoms, URS = Upper respiratory symptoms.

a

Effect estimates are standardized to a 40, 30, and 20 ppb increase for 1-h max, 8-h max (or 8-h avg or 15-h avg), and 24-h avg O3, 

respectively.

b

Results not included in Figure 6-11 because results presented per quintile of ambient O3 concentration.

1 Among U.S. multicity studies of children with asthma, each of which examined a 

2 different O3 averaging time, O3 was not consistently associated with increases in 

3 respiratory symptoms (O'Connor et al., 2008; Schildcrout et al., 2006; Mortimer et al., 

4 2002). In the NCICAS cohort (described in Section 6.2.1.2), increases in most evaluated 

5 lags of O3 (1 to 4 and 1-4 avg) were associated with increases in asthma symptoms. A 

6 30-ppb increase in lag 1-4 avg, of 8-h avg (10 a.m.-6 p.m.), O3 was associated with an 

7 increase in morning asthma symptoms with an OR of 1.35 (95% CI: 1.04, 1.69) 

8 (Mortimer et al., 2002). The OR was similar in an analysis restricted to O3 concentrations 

9 <80 ppb. Associations were similarly strong for lags 2 and 4 of O3 but weaker for lags 1 
Draft – Do Not Cite or Quote 6-108 June 2012

1 and 3 (Figure 6-11 and Table 6-20). In the ICAS cohort (described in Section 6.2.1.2), 

2 associations of 19-day avg of 24-h avg O3 with wheeze and nighttime asthma were 

3 positive and negative, respectively (O'Connor et al., 2008). NCICAS collected symptom 

4 data daily (Mortimer et al., 2002; 2000), whereas in ICAS, every 2 months, parents 

5 reported the number of days with symptoms over the previous 2 weeks (O'Connor et al., 

6 2008). Thus, ICAS was precluded from examining associations with single-day O3

7 concentrations and shorter lag periods.

8 Like NCICAS, the U.S. multicity Childhood Asthma Management Program (CAMP, 

9 with cities in common with NCICAS and ICAS, Table 6-19) collected daily symptom 

10 data, analyzed data collected between May and September, and evaluated multiple lags of 

11 O3 (Schildcrout et al., 2006). However, associations in CAMP were weaker for all 

12 evaluated lags of O3. In meta-analyses that combined city-specific estimates, a 40-ppb 

13 increase in lag 0 of 1-h max O3 was associated with asthma symptoms with an OR of 

14 1.08 (95% CI: 0.89, 1.31). Odds ratios for lags 1 and 2 and the 3-day sum of O3 were 

15 between 1.0 and 1.03. In this study, data available from an average of 12 subjects per day 

16 per city were used to produce city-specific ORs. These city-specific ORs then were 

17 combined in meta-analyses to produce study-wide ORs. Because O3 analyses were 

18 restricted to warm seasons, there likely was less power to detect associations with O3 than 

19 with other pollutants, which were analyzed using year-round data. 

20 Several longitudinal studies conducted in different cohorts of children with asthma in 

21 Mexico City, Mexico examined and found increases in respiratory symptoms in 

22 association with 1-h max O3 concentrations (Escamilla-Nuñez et al., 2008; Romieu et al., 

23 2006; 1997; 1996).1997); (1996) Romieu et al. (1997); (1996) found larger increases in 

24 symptoms in association with increases in 1-h max O3 at lag 0, than at lag 1 or 2. Recent 

25 studies expanded on earlier evidence by indicating associations with multiday averages of 

26 O3 concentrations. Romieu et al. (2006) and Escamilla-Nuñez et al. (2008) found that 

27 ORs for associations of ambient 1-h max O3 concentrations with respiratory symptoms 

28 and medication use increased as the number of averaging days increased (up to lag 0-5 

29 avg). 

30 Studies of children with asthma examined factors that may modify symptom responses to 

31 ambient O3 exposure but did not produce conclusive evidence. Larger O3-associated 

32 (8-h avg [10 a.m.-6 p.m.] or 8-h max) increases in symptoms were found in children 

33 taking asthma medication, although the specific medications examined differed between 

34 studies. As with results for PEF, in the NCICAS multicity cohort, O3-associated increases 

35 in morning symptoms were larger in children taking cromolyn (used to treat asthma with 

36 allergy) or beta-agonists/xanthines than in children taking no medication. Odds ratios 

37 were similar in children taking steroids and children taking no medication (Figure 6-11
Draft – Do Not Cite or Quote 6-109 June 2012

1 and Table 6-20) (Mortimer et al., 2000). Among children with asthma in Southern New 

2 England, O3-associated increases in symptoms were limited mostly to children taking 

3 steroids, cromolyn, or leukotriene inhibitors for maintenance (Gent et al., 2003). 

4 In most studies of children with asthma, a majority of subjects (52 to 100%) had atopy as 

5 determined by sensitization to any examined allergen. While studies found O3-associated 

6 increases in pulmonary inflammation in children with atopy (Section 6.2.3.2) and in 

7 animal models of allergy (Section 6.2.3.3), studies did not indicate that the risk of 

8 O3-associated respiratory symptoms differed in children with asthma with and without 

9 atopy. In NCICAS, Mortimer et al. (2000) found that an increase in 8-h avg (10 a.m.-6 

10 p.m.) O3 was associated with a similar increased incidence of asthma symptoms among 

11 the 79% of subjects with atopy and the 21% of subjects without atopy (Figure 6-11 and 

12 Table 6-20). Odds ratios for O3 did not differ by residential allergen levels. Among 

13 children with asthma in Fresno, CA, most associations of single- and multiday lags of 

14 8-h max O3 concentrations (0-14 days) with wheeze were near or below 1.0 among all 

15 subjects. Among the various O3 lags examined, increases in O3 were not consistently 

16 associated with increases in wheeze in subjects with cat or fungi allergy either (Mann et 

17 al., 2010). 

18 Romieu et al. (2006) found differences in O3-associated respiratory symptoms by genetic 

19 variants in GST enzymes, particularly, GSTP1 and less so for GSTM1. Compared with 

20 GSTP1 Ile/Ile or Ile/Val subjects, larger effects were estimated for GSTP1 Val/Val 

21 subjects (Figure 6-11 and Table 6-20). The largest OR was found for difficulty breathing 

22 in children with asthma who had both GSTM1 null and GSTP1 Val/Val genotypes (OR: 

23 1.49 [95% CI: 1.14, 1.93] per 30-ppb increase in lag 0-5 avg of 8-h max O3). While these 

24 results are consistent with those described for antioxidant capacity modifying 

25 O3-associated changes in lung function (Section 6.2.1.2) and pulmonary inflammation 

26 [Section 6.2.3.2 for results in the same cohort (Sienra-Monge et al., 2004)], it is important 

27 to note that effect modification by GSTP1 variants has not been consistent. (Romieu et 

28 al., 2006) found an O3-associated decrease in FEV1 only in children with GSTP1 Ile/Ile 

29 or Ile/Val genotype. Among children in southern California, GSTP1 Ile/Ile was 

30 associated with greater risk of asthma onset (Section 7.2.1). Asthma prevalence has not 

31 been consistently associated with a particular GSTP1 genotype either (Tamer et al., 2004; 

32 Mapp et al., 2002; Hemmingsen et al., 2001). 

Asthma Medication Use

33 Although recent studies contributed mixed evidence, the collective body of evidence 

34 supports associations between increases in ambient O3 concentration and increased 

35 asthma medication use in children (Figure 6-12 and Table 6-21). Most studies examined 
Draft – Do Not Cite or Quote 6-110 June 2012

1 and found associations with lags 0 or 1 of 1-h max O3 concentrations; however, 

2 associations also were found for multiday average O3 concentrations (lag 0-5 avg in 

3 Romieu et al. (2006) and lags 0-2 avg and 0-4 avg in Just et al. (2002). Within several 

4 studies, associations were consistent between respiratory symptoms and asthma 

5 medication use (Escamilla-Nuñez et al., 2008; Romieu et al., 2006; Schildcrout et al., 

6 2006; Jalaludin et al., 2004; Romieu et al., 1997; Thurston et al., 1997). As an exception, 

7 Romieu et al. (1996) found that O3 was associated with an increase in respiratory 

8 symptoms but not bronchodilator use, and Rabinovitch et al. (2004) indicated statistically 

9 significant associations with symptoms but not bronchodilator use (OR not reported). A

10 few studies found higher odds of O3-associated increases in asthma medication use than 

11 in respiratory symptoms (Just et al., 2002; Ostro et al., 2001).

Note: CS = corticosteroid. Results generally are presented in order of increasing mean ambient O3 concentration. Odds ratios are 

from single-pollutant models and are standardized to a 40- ppb for 1-h max O3 and a 30-ppb increase for 8-h max or 15-h avg O3.

Figure 6-12 Associations between ambient ozone concentrations and asthma 

medication use.

Study

Schildcrout et al. (2006)

Thurston et al. (1997)

Ostro et al. (2001)

Romieu et al. (1996)

Romieu et al. (1997)

Romieu et al. (2006)

Gielen et al. (1997)

Jalaludin et al. (2004)

Medication

Rescue inhaler

Beta-agonist

Extra medication

Bronchodilator

Bronchodilator

Bronchodilator

Bronchodilator

Beta-agonist, no steroid

Corticosteroid

O3 Lag

0

0

1

0

0

0-5 avg

0-5 avg

0

1

Subgroup

Pasadena

Los Angeles

GSTM1 positive

GSTM1 null

GSTP1 Ile/Ile Ile/Val

GSTP1 Val/Val

0.5 0.7 0.9 1.1 1.3 1.5

Odds ratio (95% CI)
Draft – Do Not Cite or Quote 6-111 June 2012

Table 6-21 Additional characteristics and quantitative data for studies 

presented in Figure 6-12.

Study* Location/Population O3

Averaging 

Time

O3 Lag Medication Subgroup Standardized 

OR (95% CI)a

Jalaludin et 

al. (2004)

Sydney, Australia

125 children with asthma, 

mean age 9.6 yr

15-h avg 

(6 a.m.-9 p.m.)

1 Beta-agonist, no 

corticosteroid

1.06 (0.91, 1.23)

Inhaled 

corticosteroid

1.06 (0.97, 1.16)

Gielen et al. 

(1997)

Amsterdam, Netherlands

61 children with asthma, 

ages 7-13 yr

8-h max 0 Bronchodilator 1.10 (0.78, 1.55)

Schildcrout 

et al. (2006)

Albuquerque, NM; 

Baltimore, MD; Boston, MA; 

Denver, CO; San Diego, 

CA; Seattle, WA; St. Louis, 

MO; Toronto, ON, Canada 

990 children with asthma, 

ages 5-12 yr

1-h max 0 Rescue inhaler 1.01 (0.89, 1.15)

Ostro et al. 

(2001)

Los Angeles, CA

138 children with 

moderate/severe asthma, 

ages 6-13 yr

1-h max 1 Any extra 

medication

Pasadena

Los Angeles

1.15 (1.12, 1.19)

1.10 (1.03, 1.19)

Thurston et 

al. (1997)

CT River Valley, CT

166 children with asthma, 

ages 7-13 yr

1-h max 0 Beta-agonist 1.17 (0.96, 1.44)

Romieu et 

al. (2006)

Mexico City, Mexico

151 children with asthma, 

mean age 9 yr

1-h max 0-5 avg Bronchodilator GSTM1 

positive

1.04 (0.96, 1.13)

GSTM1 null 1.00 (0.92, 1.09)

GSTP1 Ile/Ile 

or Ile/Val

0.96 (0.90, 1.02)

GSTP1 

Val/Val

1.10 (1.02, 1.19)

Romieu et 

al. (1996)

northern Mexico City, 

Mexico

71 children with asthma, 

ages 5-7 yr

1-h max 0 Bronchodilator 0.97 (0.93, 1.01)

Romieu et 

al. (1997)

southern Mexico City, 

Mexico

65 children with asthma, 

ages 5-13 yr

1-h max 0 Bronchodilator 1.02 (1.00, 1.05)
Draft – Do Not Cite or Quote 6-112 June 2012

Study* Location/Population O3

Averaging 

Time

O3 Lag Medication Subgroup Standardized 

OR (95% CI)a

Just et al. 

(2002)

b

Paris, France

82 Children with asthma, 

mean (SD) age 10.9 (2.5) yr

24-h avg 0 Beta-agonist, no 

steroid

3.95 (1.22, 12.9)

Gent et al. 

(2003)

b

CT, southern MA

130 children with asthma on 

maintenance medication

1-h max 0 Bronchodilator O3 <43.2 ppb 1.00 (reference)

O3 43.2-

51.5 ppb

1.00 (0.96, 1.05)

O3 51.6-

58.8 ppb

1.04 (1.00, 1.09)

O3 58.9-

72.6 ppb

1.02 (0.98, 1.07)

O3 ≥ 72.7 ppb 1.05 (0.97, 1.13)

*Includes studies in Figure 6-12, plus others.

a

Effect estimates are standardized to a 40-ppb increase for 1-h max O3, a 30-ppb increase for 8-h max or 15-h avg O3, and a 20-ppb 

increase for 24-h avg O3.

b

Results not included in Figure 6-12. Results from Just et al. (2002) were out of range of other estimates, and results from Gent et 

al. (2003) were presented per quintile of ambient O3 concentration.

Changes in Activity

1 While investigation has been limited, evidence does not consistently demonstrate O3-

2 associated diminished activity in children with asthma (O'Connor et al., 2008; Delfino et 

3 al., 2003). These studies examined different O3 averaging times and lags. In the multicity 

4 ICAS cohort, O'Connor et al. (2008) found that a 20-ppb increase in lag 1-19 avg of 

5 24-hour O3 was associated with a 10% lower odds (95% CI: -26, 10) of slow play. In a 

6 small (n = 22) panel study conducted in children with asthma in Los Angeles CA, 

7 Delfino et al. (2003) found that a 40-ppb increase in lag 0 of 1-h max O3 was associated 

8 with an increase in symptoms that interfered with daily activity with an OR of 7.41 

9 (95% CI: 1.18, 43.2). Several studies reported increases in school absenteeism in children 

10 with asthma in association with increases in ambient O3 concentration with long lag 

11 periods (14-day and 30-day distributed lags, 19-day avg) (O'Connor et al., 2008; Gilliland 

12 et al., 2001; Chen et al., 2000). Whereas Chen et al. (2000) and O'Connor et al. (2008)

13 examined absences for any reason, Gilliland et al. (2001) found associations with 

14 absences for respiratory illnesses. Despite this evidence, several limitations are notable, 

15 including the lack of a well-characterized mode of action for long lag periods of O3

16 exposure and the potential for residual seasonal confounding with examination of long 

17 lag periods. In analyses of single-day lags, Gilliland et al. (2001) found associations with 

18 O3 lagged 1 to 5 days, indicating respiratory absences may be affected by O3 exposures 

19 with shorter lag periods.
Draft – Do Not Cite or Quote 6-113 June 2012

6.2.4.2 Adults with Respiratory Disease

1 Within a small body of studies, several found that increases in ambient O3 concentration 

2 (8-hour or 1-h max) were associated with increases in respiratory symptoms in adults 

3 with asthma (Khatri et al., 2009; Feo Brito et al., 2007; Ross et al., 2002). Details from 

4 studies of respiratory symptoms in adults with respiratory disease regarding location, 

5 time period, and ambient O3 concentrations are presented in Table 6-22. These studies 

6 used different exposure assessment methods: concentrations averaged from sites closest 

7 to subjects’ location each hour (Khatri et al., 2009) or concentrations measured at one 

8 (Ross et al., 2002) or multiple (Feo Brito et al., 2007) city sites. Park et al. (2005a) found 

9 inconsistent associations for 24-h avg O3 measured at 10 city sites among the various 

10 symptoms and medication use examined in adults with asthma in Korea during a period 

11 of dust storms. In a study of adults with COPD in London, England, increases in lag 1 of 

12 8-h max O3 (at a single city site) were associated with higher odds of dyspnea and sputum 

13 changes but lower odds of nasal discharge, wheeze, or upper respiratory symptoms 

14 (Peacock et al., 2011).
Draft – Do Not Cite or Quote 6-114 June 2012

Table 6-22 Mean and upper percentile ozone concentrations in epidemiologic 

studies of respiratory symptoms and medication use in adults with 

respiratory disease .

Study* Location Study Period O3

Averaging 

Time

Mean/Median 

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

Khatri et al. (2009) Atlanta, GA May-September 

2003, 2005, 2006

8-h max 61a 75th: 74a

Feo Brito et al. 

(2007)

Ciudad Real and 

Puertollano, 

Spain

May-June 2000-

2001

1-h max 65.9 (Ciudad Real)b

56.8 (Puertollano)b

Max: 101.5b (Ciudad 

Real); 138.2b

(Puertollano)

Eiswerth et al. 

(2005)

Glendora, CA October-November 

1983

1-h max NR NR

Ross et al. (2002) East Moline, IL April-October 1994 8-h avg 41.5 Max: 78.3

Peacock et al. 

(2011)

London, England All-year 1995-1997 8-h max 15.5 Autumn/Winter Max: 32

Spring/Summer Max: 74

Park et al. (2005a) Incheon, Korea March-June 2002 24-h avg Dust event days: 23.6

Control days: 25.1

NR

Wiwatanadate and 

Liwsrisakun (2011)

Chiang Mai, 

Thailand

August 2005-June 

2006

24-h avg 17.5 90th: 26.82, Max: 34.65

* Note: Studies presented in order of first appearance in the text of this section.

NR = Not Reported

a

Individual-level estimates were derived based on time spent in the vicinity of various O3 monitors.

b

Concentrations converted from μg/m3 to ppb using the conversion factor of 0.51 assuming standard temperature (25°C) and 

pressure (1 atm).

1 Some studies that included adults with asthma examined populations with a high 

2 prevalence of atopy. In a study of children and adults with asthma (at least 53% with 

3 atopy), Ross et al. (2002) found that an increase in lag 1-3 avg of 8-h max O3 was 

4 associated with an increase in symptom score and asthma medication use. Feo Brito et al. 

5 (2007) followed 137 adults with asthma in two central Spain cities. All subjects had 

6 pollen allergy and were examined during pollen season. In Puertollano, O3 concentrations 

7 were obtained from four city monitors, and a 40-ppb increase in lag 3 of 1-h max O3 was 

8 associated with a 14.3% increase (95% CI: 3.6, 26.0) in the number of subjects reporting 

9 respiratory symptoms, adjusting only for time trend. The association was much weaker in 

10 Ciudad Real (2.3% increase [95% CI: -14, 21%] per 40-ppb increase in lag 4 of 1-h max 

11 O3), a city characterized by lower ambient air pollution levels and a narrower range of 

12 ambient O3 concentrations as measured at a single site established by investigators. 

13 Cross-sectional studies reported ambient O3-associated decreases in activity in adults 

14 with asthma; however, due to various limitations in the collective body of evidence, firm 

15 conclusions are not warranted. Although conducted over single seasons, studies did not 

16 consider confounding by meteorological factors. In a warm season study in Atlanta, GA 

17 (described in Section 6.2.1.2), Khatri et al. (2009) found that a 30-ppb increase in lag 2 of 
Draft – Do Not Cite or Quote 6-115 June 2012

1 8-h max O3 was associated with a 0.69-point decrease (95% CI: -1.28, -0.11) in the 

2 Juniper quality of life score, which incorporates indices for symptoms, mood, and activity 

3 limitations (7-point scale). In a fall study conducted in the Los Angeles, CA area in 

4 individuals with asthma (age 16 years and older), Eiswerth et al. (2005) found that a 

5 40-ppb increase in 1-h max O3 was associated with a 0.24% (95% CI: 0.08, 0.40%) lower 

6 probability of indoor activity but higher probability of outdoor activity. The authors 

7 acknowledged that their findings were unexpected and may have been influenced by lack 

8 of control for potential confounders but interpreted the decrease in indoor activities as 

9 rest replacing chores. In contrast with the aforementioned studies, a panel study of 

10 individuals with asthma (ages 13-78 years) in Thailand found that a 20-ppb increase in 

11 lag 4 of 24-h avg O3 was associated with a 26% (95% CI: 4, 43) lower odds of symptoms 

12 that interfered with activities (Wiwatanadate and Liwsrisakun, 2011).

6.2.4.3 Populations not Restricted to Individuals with Asthma

13 Locations, time periods, and ambient O3 concentrations for studies of symptoms in 

14 populations not restricted to individuals with asthma are presented in Table 6-23. Most 

15 studies examined children, and in contrast with lung function results (Section 6.2.1.2), 

16 short-term increases in ambient O3 concentration were not consistently associated with 

17 increases in respiratory symptoms in children in the general population (Figure 6-13 and 

18 Table 6-24). Because examination of adults was limited, conclusions cannot be drawn.
Draft – Do Not Cite or Quote 6-116 June 2012

Table 6-23 Mean and upper percentile ozone concentrations in epidemiologic 

studies of respiratory symptoms in populations not restricted to 

individuals with asthma.

Study* Location Study Period O3 Averaging 

Time

Mean/Median 

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

Neas et al. 

(1995)

Uniontown, PA June-August 

1990

12-h avg (8 a.m.-8 

p.m.)

37.2 Max: 87.5

Linn et al. 

(1996)

Rubidoux, Upland, 

Torrence, CA

September-June 

1992-1994

24-h avg personal

24-h avg ambient

5

23

Max: 16

Max: 53

Hoek and 

Brunekreef 

(1995)

Deurne and 

Enkhuizen, 

Netherlands

March-July 1989 1-h max Deurne: 57

Enkhuizen: 59

Max: 107

Max: 114

Rodriguez et al. 

(2007)

Perth, Australia All-year, 1996-

2003

24-h avg

1-h max

28

33

Max: 74

Max: 95

Moon et al. 

(2009)

4 cities, South 

Korea

April-May 2003 8-h avg (10 a.m.-6 

p.m.)

NR NR

Ward et al. 

(2002)

Birmingham and 

Sandwell, England

January-March, 

May-July 1997

24-h avg Winter median: 13.0

Summer median: 

22.0

Winter Max: 33

Summer Max: 41

Triche et al. 

(2006)

Southwestern VA June-August 

1995-1996

24-h avg

8-h max

1-h max

35.2

54.5

60.8

75th: 40.6, Max: 56.6

75th: 64.1, Max: 87.6

75th: 70.0, Max: 95.0

Gold et al. 

(1999)

Mexico City, Mexico JanuaryNovember 199124-h avg 52.0a Max: 103a

Apte et al. 

(2008)

Multiple U.S. cities 

(NR)

Winter or 

summer 1994-

1998

Workday avg 

(8 a.m. - 5 p.m.)

34.2b Max: 86.2b

24-h avg 25.5b Max: 67.3b

* Note: Studies presented in order of first appearance in the text of this section.

NR = Not Reported.

a

Measured at subject’s schools.

b

Concentrations converted from μg/m3 to ppb using the conversion factor of 0.51 assuming standard temperature (25°C) and 

pressure (1 atm).

Children

1 Although evidence of O3-associated increases in respiratory symptoms in children was 

2 inconsistent, it did not appear to be attributable to the differences in exposure assessment 

3 method among studies [e.g., O3 measured at a single site (Linn et al., 1996; Hoek and 

4 Brunekreef, 1995), O3 averaged across multiple city sites (Rodriguez et al., 2007), O3

5 measured at sites near schools (Moon et al., 2009; Ward et al., 2002)]. Some studies that 

6 found weak or inconsistent associations between ambient O3 concentrations and 

7 respiratory symptoms found O3-associated decrements in lung function (Ward et al., 

8 2002; Linn et al., 1996). In their study of healthy children in Uniontown, PA, Neas et al. 

9 (1995) found differences in association with respiratory symptoms between two estimates 

10 of O3 exposure. Ambient O3 concentrations were measured at one central site in town. 
Draft – Do Not Cite or Quote 6-117 June 2012

1 Subjects spent a mean 5.4 hours outdoors during the 12-hour period (8 a.m.-8 p.m.) over 

2 which O3 concentrations were averaged and symptoms were reported. Evening cough 

3 was more strongly associated with O3 concentrations weighted by time spent outdoors 

4 (OR: 2.20 [95% CI: 1.02, 4.75] per 30-ppb increase in lag 0 of 12-h avg O3) than with 

5 unweighted O3 concentrations (OR: 1.36 [95% CI: 0.86, 2.13]). Time spent outdoors has 

6 been shown to influence O3 personal-ambient ratios and correlations (Section 4.3.3), thus 

7 the weighted O3 concentrations may have represented personal O3 exposures better.

Note: Results generally are presented in increasing order of mean ambient O3 concentration. URS = Upper respiratory symptoms. 

Odds ratios are from single-pollutant models and are standardized to a 40-, 30-, and 20-ppb increase for 1-h max, 8-h max (or 

12-h avg), and 24-h avg O3 concentrations, respectively.

Figure 6-13 Associations between ambient ozone concentrations and 

respiratory symptoms in children in the general population.

Study

Ward et al. (2002)

Hoek and Brunekreef 

(1995)

Moon et al. (2009)

Neas et al. (1995)

Triche et al. (2006)

Gold et al. (1999)

Symptom

Wheeze, summer

Cough, summer

Cough

Any symptom

URS

Evening cough

Wheeze

Phlegm

Lag

0

0

0

0

0, 24-h avg

0, 8-h max

0, 1-h max

0

Subgroup

All subjects

Jeju Island

►

►

►

►

0 1 2 3

Odds ratio (95% CI)
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Table 6-24 Additional characteristics and quantitative data for studies 

represented inFigure 6-13.

Study* Location/ Population O3 Lag O3 Averaging 

Time

Symptom Subgroup Standardized 

OR (95% CI)a

Ward et al. 

(2002)

Birmingham and Sandwell, 

England

162 children, age 9 yr

0-6 avg 24-h avg Wheeze, summer

Cough, summer

0.69 (0.51, 

0.94)

0.98 (0.80, 

1.21)

Hoek and 

Brunekreef 

(1995)

Enkhuizen, Netherlands

300 children, ages 7 - 11 yr

0 1-h max Cough

Any symptom

0.86 (0.61, 

1.22)

0.94 (0.76, 

1.16)

Moon et al. 

(2009)

4 cities, South Korea

696 children, ages <13 yr

0 8-h avg

(10 a.m.-6 

p.m.)

URS All subjects

Jeju Island

0.96 (0.90, 

1.03)

1.11 (0.95, 

1.30)

Neas et al. 

(1995)

Uniontown, PA

83 healthy children, 4th and 5th 

grades

0 12-h avg

(8 a.m.-8 

p.m.)

Evening cough 2.20 (1.02, 

4.75)b

Triche et al. 

(2006)

Southwestern VA

691 infants of mothers with 

asthma, age <1 yr

0 24-h avg

8-h max

1-h max

Wheeze 2.34 (1.02, 

5.37)

1.48 (0.49, 

4.41)

1.73 (0.48, 

6.22)

Gold et al. 

(1999)

Mexico City, Mexico

40 children, ages 8-11 yr

1 24-h avg Phlegm 1.02 (1.00, 

1.04)

Linn et al. 

(1996)

c

Rubidoux, Upland, Torrence, CA 

269 children, 4th and 5th grades

0 24-h avg Evening symptom 

score

-0.96 (-2.2, 

0.26)

*Includes studies inFigure 6-13, plus others.

URS = Upper respiratory symptoms

a

Effect estimates are standardized to a 40-, 30-, and 20-ppb increase for 1-h max, 8-h max (or 8-h avg or 12-h avg), and 24-h avg 

O3, respectively.

b

O3 concentrations were weighted by the proportion of time spent outdoors.

c

Results not presented in Figure 6-13 because outcome is a continuous variable indicating intensity of symptoms (negative indicates 

improvement in symptoms).

1 Several other panel studies of children, in which asthma prevalence ranged from 0 to 

2 50%, reported null or negative associations between various averaging times and lags of 

3 ambient O3 concentration and respiratory symptoms (Moon et al., 2009; Rodriguez et al., 

4 2007; Ward et al., 2002; Linn et al., 1996; Hoek and Brunekreef, 1995) (Figure 6-13 and 

5 Table 6-24). Among children in Mexico City, Gold et al. (1999) reported an increase in 

6 phlegm in association with an increase in lag 1 of 24-h avg O3 concentration measured at 

7 schools; however, investigators acknowledged being unable to distinguish between the 

8 effects of O3 and PM10 due to their high correlation (r = 0.75).

9 Unlike other studies that examined ambient O3 concentrations from a single monitoring 

10 site, Triche et al. (2006) found respiratory symptoms to be associated with O3 measured 
Draft – Do Not Cite or Quote 6-119 June 2012

1 at a site that for some subjects was located >100 miles away from home (Figure 6-13 and 

2 Table 6-24). Subjects included infants in Southwestern VA. Odds ratios were 46-73% 

3 larger in the group who had mothers with asthma than among all infants (Triche et al., 

4 2006). Larger ORs were found for 24-h avg than 1-hour or 8-h max O3 concentrations, 

5 particularly for wheeze but less so for difficulty breathing. While these results suggested 

6 that children with mothers with asthma may be at increased risk of O3-related respiratory 

7 morbidity, the authors acknowledged that mothers with asthma may be more likely to 

8 report symptoms in their children. Additionally, transient wheeze, which is common in 

9 infants, may not predict respiratory morbidity later in life. In another cohort of children 

10 with parental history of asthma that was followed to an older age (5 years), increases in 

11 ambient O3 concentration (increment of effect estimate not reported) were not associated 

12 with increases in respiratory symptoms (Rodriguez et al., 2007).

Adults

13 A cross-sectional study of 4,200 adult workers from 100 office buildings across the U.S. 

14 found that multiple ambient O3 metrics, including the 24-h, workday (8 a.m.-5 p.m.), and 

15 late workday (3-6 p.m.) average, were associated with similar magnitudes of increase in 

16 building-related symptoms (Apte et al., 2008). It should be noted that office workers 

17 likely have a low personal-ambient O3 correlation and ratio, thus the implications of these 

18 findings compared to those of the other respiratory symptom studies are limited.

6.2.4.4 Confounding in Epidemiologic Studies of Respiratory 

Symptoms and Medication Use

19 Epidemiologic evidence does not indicate that confounding by meteorological factors or 

20 copollutant exposures fully accounts for associations observed between short-term 

21 increases in ambient O3 concentration and respiratory symptoms and medication use. 

22 Except where specified in the text, studies found O3-associated increases in respiratory 

23 symptoms or medication in statistical models that adjusted for temperature. Thurston et 

24 al. (1997) found no independent association between temperature and respiratory 

25 symptoms among children with asthma at summer camps. A few studies additionally 

26 included humidity in models (Triche et al., 2006; Ross et al., 2002). 

27 Several studies that examined populations with a high prevalence of atopy found 

28 O3-associated increases in respiratory symptoms and asthma medication use with 

29 adjustment for daily pollen counts (Just et al., 2002; Ross et al., 2002; Gielen et al., 

30 1997). Gielen et al. (1997) and Ross et al. (2002) examined populations with a high 

31 prevalence of grass pollen allergy (52% and 38%, respectively). In a study conducted 
Draft – Do Not Cite or Quote 6-120 June 2012

1 over multiple seasons, Ross et al. (2002) found a similar magnitude of association 

2 between O3 and morning symptoms and medication use with adjustment for pollen 

3 counts. Feo Brito et al. (2007) followed adults in central Spain specifically with asthma 

4 and pollen allergy. In one city, O3 was associated with an increase in the number of 

5 subjects reporting symptoms. A smaller increase was estimated for pollen. Conversely, in 

6 another city, pollen was associated with an increased reporting of respiratory symptoms, 

7 whereas O3 was not. The results suggested that O3 and pollen may have independent 

8 effects that vary by location, depending on the mix of ambient pollutants.

9 Results from copollutant models did not indicate strong confounding by copollutants 

10 such as PM2.5, PM10, sulfate, SO2, or NO2 (Table 6-25). Notably, studies examined 

11 different averaging times for O3 (1-h max or 8-h avg) and copollutants (3-hour to 

12 24-h avg) and reported a range of correlations between O3 and copollutants, which may 

13 complicate interpretation of copollutant model results. Information on potential 

14 copollutant confounding of asthma medication use results was limited. The association 

15 between O3 and bronchodilator use did not change with adjustment for PM2.5 in Gent et 

16 al. (2003) but decreased in magnitude with adjustment for 12-h avg sulfate in Thurston et 

17 al. (1997). In Thurston et al. (1997) and Gent et al. (2003), 1-h max O3 was highly 

18 correlated with 12-h avg sulfate (r = 0.74) and 24-h avg PM2.5 (r = 0.77), respectively, 

19 making it difficult to distinguish the independent effects of O3. Studies conducted 

20 concurrently in two areas of Mexico City examined 1-h max O3 and 24-h avg PM10 or 

21 PM2.5 and found robust ORs for respiratory symptoms for both O3 and PM (Romieu et al., 

22 1997; Romieu et al., 1996). Romieu et al. (1997) reported a moderate correlation between 

23 1-h max O3 and 24-h avg PM10 (r = 0.47). Associations between O3 and respiratory 

24 symptoms were observed in NCICAS in copollutant models with SO2, NO2, or PM10, 

25 which were examined with different averaging times and lags than was O3 (Mortimer et 

26 al., 2002) (Table 6-25). Also difficult are interpretations of the O3-associated increases in 

27 respiratory symptoms found with adjustment for two copollutants in the same model 

28 (i.e., PM2.5 plus NO2 or PM10-2.5) (Escamilla-Nuñez et al., 2008; Triche et al., 2006).
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Table 6-25 Associations between ambient ozone concentrations and 

respiratory symptoms in single- and co-pollutant models.

Study Location/Population O3

Metrics

Symptom OR for O3 in 

Single-Pollutant 

Model (95% CI)a

OR for O3 in Copollutant 

Model (95% CI)a

Mortimer et 

al. (2002)

Bronx, East Harlem, NY; Baltimore, 

MD; Washington, DC; Detroit, MI, 

Cleveland, OH; Chicago, IL; St. 

Louis, MO

846 children with asthma, ages 4-

9 yr

8-h avg 

(10 a.m.-

6 p.m.)

Lag 1-4 

avg

Morning 

symptoms

8 cities with SO2

data

1.35 (1.04, 1.74)

With lag 1-2 avg, 3-h avg SO2

1.23 (0.94, 1.61)

7 cites with NO2

data

1.25 (0.94, 1.67)

With lag 1-6 avg, 24-h avg NO2

1.14 (0.85, 1.55)

3 cities with PM10

data

1.21 (0.61, 2.41)

With lag 1-2 avg, 24-h avg 

PM10

1.08 (0.49, 2.39)

Thurston et 

al. (1997)

CT River Valley

166 children with asthma, ages 

7-13 yr

1-h max Chest 

symptoms

1.21 (1.12, 1.31)b

With lag 0, 12-h avg sulfate

1.19 (1.06, 1.35)b

Lag 0 Beta-agonist use 1.20 (1.09, 1.32)b With lag 0, 12-h avg sulfate

1.07 (0.92, 1.24)b

Romieu et al. 

(1996)

Mexico City, Mexico

71 children with asthma, ages 5-7 yr

1-h max

Lag 0

Lower respiratory 

symptoms

1.07 (1.02, 1.12) With lag 0, 24-h avg PM2.5

1.06 (1.02, 1.10)

Romieu et al. 

(1997)

Mexico City, Mexico

65 children with asthma, ages 5-

13 yr

1-h max

Lag 0

Lower respiratory 

symptoms

1.09 (1.04, 1.14) With lag 0, 24-h avg PM10

1.09 (1.01, 1.19)

Results generally are presented in order of increasing mean ambient O3 concentration.

a

ORs are standardized to a 40- and 30-ppb increase for 1-h max and 8-h avg O3, respectively.

b

Temperature not included in models.

6.2.4.5 Summary of Epidemiologic Studies of Respiratory 

Symptoms and Asthma Medication Use

1 Comprising a majority of available evidence, single-city and -region epidemiologic 

2 studies provide consistent evidence for the effects of short-term increases in ambient O3

3 exposure on increasing respiratory symptoms and asthma medication use in children with 

4 asthma (Figure 6-11 and Figure 6-12 and Table 6-20 and Table 6-21). Evidence from the 

5 few available U.S. multicity studies is less consistent (O'Connor et al., 2008; Schildcrout 

6 et al., 2006; Mortimer et al., 2002). Findings from a small body of studies indicate 

7 O3-associated increases in respiratory symptoms in adults with asthma. Associations 

8 between short-term increases in ambient O3 concentration and reduced activity in 

9 children or adults with asthma are not clearly demonstrated. While O3-associated 

10 increases in school absenteeism were found in children with asthma, evidence for 

11 respiratory-related absences and for O3 exposure lag periods shorter than 14 days is 

12 sparse. Short-term increases in ambient O3 concentration were not consistently associated 
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1 with increases in respiratory symptoms in groups comprising children with and without 

2 asthma.

3 Increases in respiratory symptoms and medication use were associated with increases in 

4 ambient O3 concentration assigned to subjects using various methods. Associations were 

5 found with methods likely to represent better ambient exposures, including O3 measured 

6 on site and at the time of children’s outdoor activity (Thurston et al., 1997) and 

7 concentrations weighted by time spent outdoors (Neas et al., 1995). However, 

8 associations also were found with methods that varied in their representation of ambient 

9 exposures and spatial variability in ambient concentrations, i.e., concentrations averaged 

10 among subjects’ locations each hour (Khatri et al., 2009), measured within 5 km of 

11 schools or homes (Escamilla-Nuñez et al., 2008; Romieu et al., 2006; 1997; 1996), 

12 averaged across multiple sites (Feo Brito et al., 2007; Gent et al., 2003; Mortimer et al., 

13 2002), and measured at a single site (Ross et al., 2002; Gielen et al., 1997).

14 Associations with respiratory symptoms were demonstrated most frequently for 1-h max 

15 and 8-h max or avg O3, and within-study comparisons indicated similar ORs for 1-h max 

16 and 8-h max O3 (Delfino et al., 2003; Gent et al., 2003). Respiratory symptoms also were 

17 associated with 12-hour and 24-h avg O3 (Jalaludin et al., 2004; Gold et al., 1999; Neas et 

18 al., 1995). Epidemiologic studies examined respiratory symptoms associated with O3 

19 concentrations lagged 0 to 5 days and those averaged over 2 to 19 days. While O3 at lags 

20 0 or 1 were consistently associated with respiratory symptoms, several studies found 

21 larger ORs for multiday averages (3- to 6-day) of O3 (Escamilla-Nuñez et al., 2008; 

22 Romieu et al., 2006; Just et al., 2002; Mortimer et al., 2002; Ross et al., 2002). 

23 Epidemiologic findings for lagged or multiday average O3 are supported by evidence that 

24 O3 sensitizes bronchial smooth muscle to hyperreactivity and thus acts as a primer for 

25 subsequent exposure to antigens such as allergens (Section 5.3.5). Many studies 

26 examined populations with asthma with a high prevalence of atopy (52-100%). In these 

27 populations, sensitization of airways provides a biologically plausible mode of action by 

28 which increases in respiratory symptoms result from increases in O3 exposure after a lag 

29 or accumulated over several days. Further support is provided by findings that airway 

30 hyperresponsiveness (Section 6.2.2.1) and some indicators of inflammation 

31 (Section 6.2.3.1) remained elevated following repeated O3 exposures in controlled human 

32 exposure studies and by observations from epidemiologic studies that increases in 

33 pulmonary inflammation were associated with multiday average O3 concentrations 

34 (Section 6.2.3.2).

35 There is not strong evidence that O3-associated increases in respiratory symptoms are 

36 confounded by temperature, pollen, or copollutants. In limited analysis, ambient O3 was 

37 associated with respiratory symptoms with adjustment for copollutants, primarily PM. 
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1 However, identifying the independent effects of O3 in some studies was complicated due 

2 to the high correlations observed between O3 and PM or different lags and averaging 

3 times examined for copollutants. Nonetheless, the consistency of associations among 

4 individuals with asthma with and without adjustment for ambient copollutant 

5 concentrations combined with findings from controlled human exposure studies for the 

6 direct effect of O3 exposure provide substantial evidence for the independent effects of 

7 short-term ambient O3 exposure on increasing respiratory symptoms.

6.2.5 Lung Host Defenses

8 The mammalian respiratory tract has a number of closely integrated defense mechanisms 

9 that, when functioning normally, provide protection from the potential health effects 

10 attributed to exposure to a wide variety of inhaled particles and microbes. For simplicity, 

11 these interrelated defenses can be divided into two major parts: (1) nonspecific (transport, 

12 phagocytosis, and bactericidal activity) and (2) specific (immunologic) defense 

13 mechanisms. A variety of sensitive and reliable methods have been used to assess the 

14 effects of O3 on these components of the lung’s defense system to provide a better 

15 understanding of the health effects associated with the inhalation of this pollutant. The 

16 previous O3 AQCD stated that animal toxicological studies provide extensive evidence 

17 that acute O3 exposures as low as 0.08 to 0.5 ppm can cause increases in susceptibility to 

18 infectious diseases due to modulation of lung host defenses. Table 6-6 through Table 6-9 

19 (U.S. EPA, 1996g, h, i, j) beginning on page 6-41 of the 1996 O3 AQCD (U.S. EPA, 

20 1996a), and Table AX5-7 (U.S. EPA, 2006c), beginning on page AX5-8 of the 2006 O3

21 AQCD (U.S. EPA, 2006b), present studies on the effects of O3 on host defense 

22 mechanisms. This section discusses the various components of host defenses, such as the 

23 mucociliary escalator, the phagocytic, bactericidal, and regulatory role of the alveolar 

24 macrophages (AMs), the adaptive immune system, and integrated mechanisms that are 

25 studied by investigating the host’s response to experimental pulmonary infections.

6.2.5.1 Mucociliary Clearance 

26 The mucociliary system is one of the lung’s primary defense mechanisms. It protects the 

27 conducting airways by trapping and quickly removing material that has been deposited or 

28 is being cleared from the alveolar region by migrating alveolar macrophages. Ciliary 

29 movement directs particles trapped on the overlying mucous layer toward the pharynx, 

30 where the mucus is swallowed or expectorated. 
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1 The effectiveness of mucociliary clearance can be determined by measuring such 

2 biological activities as the rate of transport of deposited particles; the frequency of ciliary 

3 beating; structural integrity of the ciliated cells; and the size, number, and distribution of 

4 mucus-secreting cells. Once this defense mechanism has been altered, a buildup of both 

5 viable and nonviable inhaled substances can occur on the epithelium and may jeopardize 

6 the health of the host, depending on the nature of the uncleared substance. Impaired 

7 mucociliary clearance can result in an unwanted accumulation of cellular secretions, 

8 increased infections, chronic bronchitis, and complications associated with COPD. A 

9 number of previous studies with various animal species have examined the effect of O3

10 exposure on mucociliary clearance and reported morphological damage to the cells of the 

11 tracheobronchial tree from acute and sub-chronic exposure to O3 0.2 ppm and higher. The 

12 cilia were either completely absent or had become noticeably shorter or blunt. After 

13 placing these animals in a clean-air environment, the structurally damaged cilia 

14 regenerated and appeared normal (U.S. EPA, 1986). Based on such morphological 

15 observations, related effects such as ciliostasis, increased mucus secretions, and a slowing 

16 of mucociliary transport rates might be expected. However, no measurable changes in 

17 ciliary beating activity have been reported due to O3 exposure alone. Essentially no data 

18 are available on the effects of prolonged exposure to O3 on ciliary functional activity or 

19 on mucociliary transport rates measured in the intact animal. In general, functional 

20 studies of mucociliary transport have observed a delay in particle clearance soon after 

21 acute exposure. Decreased clearance is more evident at higher doses (1 ppm), and there is 

22 some evidence of attenuation of these effects (U.S. EPA, 1986). However, no recent 

23 studies have evaluated the effects of O3 on mucociliary clearance.

6.2.5.2 Alveolobronchiolar Transport Mechanism 

24 In addition to the transport of particles deposited on the mucous surface layer of the 

25 conducting airways, particles deposited in the deep lung may be removed either up the 

26 respiratory tract or through interstitial pathways to the lymphatic system. The pivotal 

27 mechanism of alveolobronchiolar transport involves the movement of AMs with 

28 phagocytized particles to the bottom of the mucociliary escalator. Failure of the AMs to 

29 phagocytize and sequester the deposited particles from the vulnerable respiratory 

30 membrane can lead to particle entry into the interstitial spaces. Once lodged in the 

31 interstitium, particle removal is more difficult and, depending on the toxic or infectious 

32 nature of the particle, its interstitial location may allow the particle to set up a focus for 

33 pathologic processes. Although some studies show reduced early (tracheobronchial) 

34 clearance after O3 exposure, late (alveolar) clearance of deposited material is accelerated, 
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1 presumably due to macrophage influx (which in itself can be damaging due to proteases 

2 and oxidative reactions in these cells). 

6.2.5.3 Alveolar Macrophages 

3 Within the gaseous exchange region of the lung, the first line of defense against 

4 microorganisms and nonviable particles that reach the alveolar surface is the AM. This 

5 resident phagocyte is responsible for a variety of activities, including the detoxification 

6 and removal of inhaled particles, maintenance of pulmonary sterility via destruction of 

7 microorganisms, and interaction with lymphocytes for immunologic protection. Under 

8 normal conditions, AMs seek out particles deposited on the alveolar surface and ingest 

9 them, thereby sequestering the particles from the vulnerable respiratory membrane. To 

10 adequately fulfill their defense function, the AMs must maintain active mobility, a high 

11 degree of phagocytic activity, and an optimally functioning biochemical and enzyme 

12 system for bactericidal activity and degradation of ingested material. As discussed in 

13 previous AQCDs, short periods of O3 exposure can cause a reduction in the number of 

14 free AMs available for pulmonary defense, and these AMs are more fragile, less 

15 phagocytic, and have decreased lysosomal enzyme activities required for killing 

16 pathogens. For example, in results from earlier work in rabbits, a 2-hour exposure to 

17 0.1 ppm O3 inhibited phagocytosis and a 3-hour exposure to 0.25 ppm decreased 

18 lysosomal enzyme activities (Driscoll et al., 1987; Hurst et al., 1970). Similarly, AMs 

19 from rats exposed to 0.1 ppm O3 for 1 or 3 weeks exhibited reduced hydrogen peroxide 

20 production (Cohen et al., 2002). A controlled human exposure study reported decrements 

21 in the ability of alveolar macrophages to phagocytize yeast following exposure of healthy 

22 volunteers to 80 to 100 ppb O3 for 6.6-hour during moderate exercise (Devlin et al., 

23 1991). Although the percentage of phagocytosis-capable macrophages was unchanged by 

24 O3 exposure, the number of yeast engulfed was reduced when phagocytosis was 

25 complement-dependent. However, there was no difference in the ability of macrophages 

26 to produce superoxide anion after O3 exposure. These results are consistent with those 

27 from another controlled human exposure study in which no changes in the level of 

28 lysosomal enzymes or superoxide anion production were observed in macrophages 

29 lavaged from healthy human subjects exposed to 400 ppb O3 for 2 hours with heavy 

30 intermittent exercise (Koren et al., 1989). More recently, Lay et al. (2007) observed no 

31 difference in phagocytic activity or oxidative burst capacity in macrophages or 

32 monocytes from sputum or blood collected from healthy volunteers after a 2-hour 

33 exposure to 400 ppb O3 with moderate intermittent exercise. However, another study 

34 found that oxidative burst and phagocytic activity in macrophages increased in GSTM1 

35 null subjects compared to GSTM1 positive subjects, who had relatively unchanged 
Draft – Do Not Cite or Quote 6-126 June 2012

1 macrophage function parameters after an O3 exposure identical to that of Lay et al. 

2 described above (Alexis et al., 2009). Collectively, these studies demonstrate that O3 can 

3 affect multiple steps or aspects required for proper macrophage function, but any C-R 

4 relationship appears complex and genotype may be a consideration. A few other recent 

5 studies have evaluated the effects of O3 on macrophage function, but these are of 

6 questionable relevance due to the use of in vitro exposure systems and amphibian animal 

7 models (Mikerov et al., 2008c; Dohm et al., 2005; Klestadt et al., 2005).

6.2.5.4 Infection and Adaptive Immunity 

General Effects on the Immune System

8 The effects of O3 on the immune system are complex and dependent on the exposure 

9 regimen and the observation period. According to toxicological studies it appears that the 

10 T-cell-dependent functions of the immune system are more affected than B-cell11 dependent functions (U.S. EPA, 2006b). Generally, there is an early immunosuppressive 

12 effect that subsides with continued O3 exposure, resulting in either a return to normal 

13 responses or an enhancement of immune responses. However, this is not always the case 

14 as Aranyi et al. Aranyi et al. (1983) showed decreased T-cell mitogen reactions in mice 

15 after subchronic (90-day) exposure to 0.1 ppm O3. Earlier studies report changes in cell 

16 populations in lymphatic tissues (U.S. EPA, 2006b). A more recent study in mice 

17 demonstrated that numbers of certain T-cell subsets in the spleen were reduced after 

18 exposure to 0.6 ppm O3 (10h/day x 15d) (Feng et al., 2006).

19 The inflammatory effects of O3 involve the innate immune system, and as such, O3 can 

20 affect adaptive (or acquired) immunity via alterations in antigen presentation and 

21 costimulation by innate immune cells such as macrophages and dendritic cells. Several 

22 recent controlled human exposure studies demonstrate increased expression of molecules 

23 involved in antigen presentation or costimulation. Lay et al. (2007) collected sputum 

24 monocytes from healthy volunteers exposed to 400 ppb O3 for 2 hours with moderate 

25 intermittent exercise and detected increases in HLA-DR, used to present antigen to 

26 T-cells, and CD86, a costimulatory marker necessary for T-cell activation. Upregulation 

27 of HLA-DR was also observed by Alexis et al. (2009) in sputum dendritic cells and 

28 macrophages from GSTM1 null subjects exposed to 400 ppb O3 for 2 hours with 

29 moderate intermittent exercise. On airway monocytes from healthy volunteers 24 hours 

30 after exposure to 80 ppb O3 for 6.6 hours with moderate intermittent exercise, HLA-DR, 

31 CD86, and CD14 (a molecule involved in bacterial endotoxin reactivity) were increased, 

32 whereas CD80, a costimulatory molecule of more heterogeneous function, was decreased 

33 (Alexis et al., 2010). Patterns of expression on macrophages were similar, except that 
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1 HLA-DR was found to be significantly decreased after O3 exposure and CD86 was not 

2 significantly altered. An increase in IL-12p70, a macrophage and dendritic cell product 

3 that activates T-cells, was correlated with increased numbers of dendritic cells. It should 

4 be noted that these results are reported as comparisons to baseline as there was no clean 

5 air control (Alexis et al., 2010; Alexis et al., 2009). Another controlled human exposure 

6 study reported no increase in IL-12p70 in sputum from healthy, atopic, or atopic 

7 asthmatic subjects following a 2-hour exposure to 400 ppb O3 with intermittent moderate 

8 exercise (Hernandez et al., 2010). Levels of HLA-DR, CD14 and CD86 were not 

9 increased on macrophages collected from any of these subjects. It is difficult to compare 

10 these results to those of Lay et al. (2007) and Alexis et al. (2010) due to differences in O3

11 concentration, cell type examined, and timing of postexposure analysis. 

12 Although no controlled human exposure studies have examined the effects of O3 on the 

13 ability to mount antigen-specific responses, upregulation of markers associated with 

14 innate immune activation and antigen presentation could potentially enhance adaptive 

15 immunity and increase immunologic responses to antigen. While this may bolster 

16 defenses against infection, it also may enhance allergic responses (Section 6.2.6).

17 In animal models, O3 has been found to alter responses to antigenic stimulation. For 

18 example, antibody responses to a T-cell-dependent antigen were suppressed after a 

19 56-day exposure of mice to 0.8 ppm O3, and a 14-day exposure to 0.5 ppm O3 decreased 

20 the antiviral antibody response following influenza virus infection (Jakab and Hmieleski, 

21 1988); the latter impairment may pave the way for lowered resistance to re-infection. The 

22 immune response is highly influenced by the temporal relationship between O3 exposure 

23 and antigenic stimulation. When O3 exposure preceded Listeria infection, there were no 

24 effects on delayed-type hypersensitivity or splenic lymphoproliferative responses; 

25 however, when O3 exposure occurred during or after Listeria infection was initiated, 

26 these immune responses were suppressed (Van Loveren et al., 1988). In another study, a 

27 reduction in mitogen activated T-cell proliferation was observed after exposure to 

28 0.6 ppm O3 for 15 days that could be ameliorated by antioxidant supplementation. 

29 Antigen-specific proliferation decreased by 60%, indicating attenuation of the acquired 

30 immunity needed for subsequent memory responses (Feng et al., 2006). O3 exposure also 

31 skewed the ex-vivo cytokine responses elicited by non-specific stimulation toward 

32 inflammation, decreasing IL-2 and increasing IFN-γ. Modest decreases in immune 

33 function assessed in the offspring of O3-exposed dams (mice) were observed by Sharkhuu 

34 et al. (2011). The ability to mount delayed-type hypersensitivity responses was 

35 significantly suppressed in 42 day-old offspring when dams were exposed to 0.8 or 

36 1.2 ppm O3, but not 0.4 ppm, from gestational day 9-18. Humoral responses to 

37 immunization with sheep red blood cells were unaffected, as were other immune 

38 parameters such as splenic populations of CD45+ T-cells, iNKT-cells, and levels of IFN-
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1 γ, IL-4, and IL-17 in the BALF. Generally, continuous exposure to O3 impairs immune 

2 responses for the first several days of exposure, followed by an adaptation to O3 that 

3 allows a return of normal immune responses. Most species show little effect of O3

4 exposures prior to immunization, but show a suppression of responses to antigen in O3

5 exposures post-immunization. 

Microbial Infection

Bacterial infection

6 A relatively large body of evidence shows that O3 increases susceptibility to bacterial 

7 infections. The majority of studies in this area were conducted before the 1996 O3 AQCD 

8 was published and many are included in Table 6-9 (U.S. EPA, 1996j) on page 6-53 of 

9 that document. Known contributing factors are impaired mucociliary streaming, altered 

10 chemotaxis/motility, defective phagocytosis of bacteria, decreased production of 

11 lysosomal enzymes or superoxide radicals by alveolar macrophages, and decreased IFN-γ 

12 levels. In animal models of bacterial infection, exposure to 0.08 ppm O3 increases 

13 streptococcus-induced mortality, regardless of whether O3 exposure precedes or follows 

14 infection (Miller et al., 1978; Coffin and Gardner, 1972; Coffin et al., 1967). Increases in 

15 mortality are due to the infectious agent, thereby reflecting functional impairment of host 

16 defenses. Exercise and copollutants can enhance the effects of O3 in infectivity models. 

17 Although both mice and rats exhibit impaired bactericidal macrophage activity after O3

18 exposure, mortality due to infection is only observed in mice. Additionally, although 

19 mice and humans share many host defense mechanisms, there is little compelling 

20 evidence from epidemiologic studies to suggest an association between O3 exposure and 

21 decreased resistance to bacterial infection, and the etiology of respiratory infections is not 

22 easily identified via ICD codes (Section 6.2.7.3). 

Viral infection

23 Only a few studies, described in previous AQCDs, have examined the effects of O3

24 exposure on the outcome of viral respiratory infection [see Table 6-9 on page 6-53 of the 

25 1996 O3 AQCD (U.S. EPA, 1996j)]. Some studies show increased mortality, while others 

26 show diminished severity and increased survival time. There is little to no evidence from 

27 studies of animals or humans to suggest that O3 increases the incidence of respiratory 

28 viral infection in humans. In human volunteers infected with rhinovirus prior to O3

29 exposure (0.3 ppm for 5 consecutive days), no effect on viral titers, IFN-γ production, or 

30 blood lymphocyte proliferative responses to viral antigen was observed (Henderson et al., 

31 1988). In vitro cell culture studies of human bronchial epithelial cells indicate O3-induced 

32 exacerbation of human rhinovirus infection (Spannhake et al., 2002), but this is of limited 

33 relevance. More recent studies on the interactions of O3 and viral infections have not been 
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1 published. Natural killer (NK) cells, which destroy virally infected cells and tumors in the 

2 lung, appear to be inhibited by higher concentrations of O3 and either unaffected or 

3 stimulated at lower concentrations. Several studies show decreases in NK cell activity 

4 following acute exposures ranging from 0.8 to 1 ppm (Gilmour and Jakab, 1991; Van 

5 Loveren et al., 1990; Burleson et al., 1989). However, Van Loveren et al. (1990) showed 

6 that a 1-week exposure to 0.2 or 0.4 ppm O3 increased NK cell activity, and an urban 

7 pattern of exposure (base of 0.06 ppm with peaks of 0.25 ppm) had no effect on NK cell 

8 activity after 1, 3, 13, 52, or 78 weeks of exposure (Selgrade et al., 1990). A more recent 

9 study demonstrated a 35% reduction in NK cell activity after exposure of mice to 

10 0.6 ppm O3 (10h/day x 15d) (Feng et al., 2006). The defective IL-2 production 

11 demonstrated in this study may impair NK cell activation. Alternatively, NK cell surface 

12 charge may be altered by ROS, decreasing their adherence to target cells (Nakamura and 

13 Matsunaga, 1998). 

6.2.5.5 Summary of Lung Host Defenses

14 Taken as a whole, the data clearly indicate that an acute O3 exposure impairs the host 

15 defense capability of animals, primarily by depressing AM function and perhaps also by 

16 decreasing mucociliary clearance of inhaled particles and microorganisms. Coupled with 

17 limited evidence from controlled human exposure studies, this suggests that humans 

18 exposed to O3 could be predisposed to bacterial infections in the lower respiratory tract. 

19 The seriousness of such infections may depend on how quickly bacteria develop 

20 virulence factors and how rapidly PMNs are mobilized to compensate for the deficit in 

21 AM function. It remains unclear how O3 might affect antigen presentation and the 

22 costimulation required for T-cell activation, given the mixed results from controlled 

23 human exposure studies, but there is toxicological evidence for suppression of T-cell24 dependent functions by O3, including reductions in antigen-specific proliferation and 

25 antibody production, indicating the potential for impaired acquired immunity and 

26 memory responses. To date, a limited number of epidemiologic studies have examined 

27 associations between O3 exposure and hospital admissions or ED visits for respiratory 

28 infection, pneumonia, or influenza. Results have been mixed, and in some cases 

29 conflicting (see Section 6.2.7.2 and Section 6.2.7.3). With the exception of influenza, it is 

30 difficult to ascertain whether cases of respiratory infection or pneumonia are of viral or 

31 bacterial etiology. A study that examined the association between O3 exposure and 

32 respiratory hospital admissions in response to an increase in influenza intensity did 

33 observe an increase in respiratory hospital admissions (Wong et al., 2009), but 

34 information from toxicological studies of O3 and viral infections is ambiguous.
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6.2.6 Allergic and Asthma-Related Responses

1 Effects resulting from combined exposures to O3 and allergens have been studied in a 

2 variety of animal species, generally as models of experimental asthma. Pulmonary 

3 function and airways hyperresponsiveness in animal models of asthma are discussed in 

4 Section 6.2.1.3 and Section 6.2.2.2. Previous evidence indicates that O3 exposure skews 

5 immune responses toward an allergic phenotype. For example, Gershwin et al. (1981)

6 reported that O3 (0.8 and 0.5 ppm for 4 days) exposure caused a 34-fold increase in the 

7 number of IgE (allergic antibody)-containing cells in the lungs of mice. In general, the 

8 number of IgE-containing cells correlated positively with levels of anaphylactic 

9 sensitivity. In humans, allergic rhinoconjunctivitis symptoms are associated with 

10 increases in ambient O3 concentrations (Riediker et al., 2001). Recent controlled human 

11 exposure studies have observed O3-induced changes indicating allergic skewing. Airway 

12 eosinophils, which participate in allergic disease and inflammation, were observed to 

13 increase in atopic, mildly asthmatic volunteers 18 hours following a 7.6-hour exposure to 

14 160 ppb O3 with light intermittent exercise (Peden et al., 1997). No increase in airway 

15 eosinophils was observed 4 hours after exposure of healthy, atopic, or atopic asthmatic 

16 subjects to 400 ppb O3 for 2 hours with moderate intermittent exercise (Hernandez et al., 

17 2010). However, atopic subjects did exhibit increased IL-5, a cytokine involved in 

18 eosinophil recruitment and activation, suggesting that perhaps these two studies observed 

19 the same effect at different time points. Epidemiologic studies discussed in Section 7.2.5

20 describe an association between eosinophils and long-term O3 exposure, consistent with 

21 chronic exposure studies in non-human primates. Hernandez et al. (2010) also observed 

22 increased expression of high and low affinity IgE receptors on sputum macrophages from 

23 atopic asthmatics, which may enhance IgE-dependent inflammation. Sputum levels of 

24 IL-4 and IL-13, both pro-allergic cytokines that aid in the production of IgE, were 

25 unaltered in all groups. The lack of increase in IL-4 levels in sputum reported by 

26 Hernandez et al. (2010), along with increased IL-5, is consistent with results from Bosson 

27 et al. (2003), in which IL-5 (but not IL-4 levels) increased in bronchial epithelial biopsy 

28 specimens following exposure of mild atopic asthmatics to 200 ppb O3 for 2 hours with 

29 moderate intermittent exercise. IL-5 was not elevated in specimens obtained from healthy 

30 (non-asthmatic) O3-exposed subjects. Collectively, findings from these studies suggest 

31 that O3 can induce or enhance certain components of allergic inflammation in atopic and 

32 atopic asthmatic individuals.

33 Ozone enhances inflammatory and allergic responses to allergen challenge in sensitized 

34 animals. Short-term exposure (2 days) to 1 ppm O3 exacerbated allergic rhinitis and lower 

35 airway allergic inflammation in Brown Norway rats, a rat strain that is comparatively less 

36 sensitive to O3 than other rats or humans (Wagner et al., 2009; 2007). OVA-sensitized 

37 rats were intranasally challenged with OVA on days 1 and 2, and exposed to 0 or 1 ppm 
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1 O3 (8 h/day) on days 4 and 5. Analysis at day 6 indicated that O3 exposure enhanced 

2 intraepithelial mucosubstances in the nose and airways, induced cys-LTs, MCP-1, and 

3 IL-6 production in BALF, and upregulated expression of the proallergic cytokines IL-5 

4 and IL-13. These changes were not evident in non-allergic controls. All of these 

5 responses were blunted by gamma-tocopherol (γT; vitamin E) therapy. γT neutralizes 

6 oxidized lipid radicals, and protects lipids and proteins from nitrosative damage from 

7 NO-derived metabolites. Farraj et al. (2010) exposed allergen-sensitized adult male 

8 BALB/c mice to 0.5 ppm O3 for 5 hours once per week for 4 weeks. Ozone exposure and 

O3/DEP (2.0 mg/m3 9 ) co-exposure of OVA-sensitized mice elicited significantly greater 

10 serum IgE levels than in DEP-exposed OVA-sensitized mice (98% and 89% increases, 

11 respectively). Ozone slightly enhanced levels of BAL IL-5, but despite increases in IgE, 

12 caused a significant decrease in BAL IL-4 levels. IL-10, IL-13, and IFN-γ levels were 

13 unaffected. Lung resistance and elastance were unaffected in allergen sensitized mice 

14 exposed solely to 0.5 ppm O3 once a week for 4 weeks (Farraj et al., 2010). However, 

15 co-exposure to O3 and diesel exhaust particles increased lung resistance. 

16 In addition to exacerbating existing allergic responses, O3 can also act as an adjuvant to 

17 produce sensitization in the respiratory tract. In a model of murine asthma, using OVA 

18 free of detectable endotoxin, inclusion of 1 ppm O3 during the initial exposures to OVA 

19 (2 h, days 1 and 6) enhanced the inflammatory and allergic responses to subsequent 

20 allergen challenge (Hollingsworth et al., 2010). Compared to air exposed animals, 

21 O3-exposed mice exhibited significantly higher levels of total cells, macrophages, 

22 eosinophils, and PMNs in BALF, and increased total serum IgE. Pro-allergic cytokines 

23 IL-4, and IL-5 were also significantly elevated, along with pleiotropic Th2 cytokine IL-9 

24 (associated with bronchial hyperresponsiveness) and pro-inflammatory IL-17, produced 

25 by activated T-cells. Based on lower inflammatory, IgE, and cytokine responses in 

26 Toll-like receptor 4 deficient mice, the effects of O3 seem to be dependent on TLR 4 

27 signaling, as are a number of other biological responses to O3 according to studies by 

28 Hollingsworth et al. (2004), Kleeberger et al. (2000) and Garantziotis et al. (2010). The 

29 involvement of TLR 4, along with its endogenous ligand, hyaluronan, in O3-induced 

30 responses described in these studies has been corroborated by a controlled human 

31 exposure study by Hernandez et al. (2010), who found increased TLR 4 expression and 

32 elevated levels of hyaluronic acid in atopic and atopic asthmatic volunteers exposed to 

33 400 ppb O3. This pathway is discussed in more detail in Chapter 5. Examination of 

34 dendritic cells (DCs) from the draining thoracic lymph nodes indicated that O3 did not 

35 enhance the migration of DCs from the lungs to the lymph nodes, nor did it alter the 

36 expression of functional DC markers such as CD40, MHC class II, or CD83. However, 

37 O3 did increase expression of CD86, which is generally associated with Th2 responses 

38 and is detected at higher levels on DCs from allergic asthmatics compared to those from 

39 healthy donors Chen et al. (2006b). Increased CD86 has also been observed on airway 
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1 cells collected from human subjects following exposure to O3 in studies by Lay et al. 

2 (2007) and Alexis et al. (2009), but not Hernandez et al. (2010) (study details described 

3 in Section 6.2.5.4).

4 Ozone exposure during gestation has modest effects on allergy and asthma related 

5 endpoints in adult offspring. When dams were exposed to 1.2 ppm O3 (but not 0.8 ppm) 

6 from gestational day 9-18, some allergic and inflammatory responses to OVA 

7 sensitization and challenge were reduced compared to air exposed controls. This included 

8 IgE levels and eosinophils, and was only true of mice that were immunized early in life 

9 (PND 3) as opposed to later (PND 42), perhaps due to the proximity of O3 and antigen 

10 exposure. The effects of gestational O3 exposure on immune function have not been 

11 widely studied, and although reductions in allergic endpoints are not generally observed 

12 in association with O3, other parameters of immune function were found to be reduced, so 

13 a more global immunosuppression may underlie these effects. 

14 In addition to pro-allergic effects, O3 could also make airborne allergens more allergenic. 

15 When combined with NO2, O3 has been shown to enhance nitration of common protein 

16 allergens, which may increase their allergenicity Franze et al. (2005). 

6.2.7 Hospital Admissions, Emergency Department Visits, and Physicians 

Visits

6.2.7.1 Summary of Findings from 2006 Ozone AQCD

17 The 2006 O3 AQCD evaluated numerous respiratory ED visits and hospital admissions 

18 studies, which consisted primarily of time-series studies conducted in the U.S., Canada, 

19 Europe, South America, Australia and Asia. Upon collectively evaluating the scientific 

20 evidence, the 2006 O3 AQCD concluded that “the overall evidence supports a causal 

21 relationship between acute ambient O3 exposures and increased respiratory morbidity 

22 resulting in increased ED visits and [hospital admissions] during the warm season” U.S. 

23 EPA (2006b). This conclusion was “strongly supported by the human clinical, animal 

24 toxicologic[al], and epidemiologic evidence for [O3-induced] lung function decrements, 

25 increased respiratory symptoms, airway inflammation, and airway hyperreactivity” U.S. 

26 EPA (2006b). 

27 Since the completion of the 2006 O3 AQCD, relatively fewer studies conducted in the 

28 U.S., Canada, and Europe have examined the association between short-term exposure to 

29 ambient O3 and respiratory hospital admissions and ED visits with a growing number of 

30 studies having been conducted in Asia. This section focuses primarily on multicity 
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1 studies because they examine the effect of O3 on respiratory-related hospital admissions 

2 and ED visits over a large geographic area using a consistent statistical methodology. 

3 Single-city studies that encompass a large number of hospital admissions or ED visits, or 

4 included a long study-duration were also evaluated because these studies have more 

5 power to detect whether an association exists between short-term O3 exposure and 

6 respiratory hospital admissions and ED visits compared to smaller single-city studies. 

7 Additional single-city studies were also evaluated within this section, if they were 

8 conducted in locations not represented by the larger single-city and multicity studies, or 

9 examined population-specific characteristics not included in the larger studies that may 

10 modify the association between short-term O3 exposure and respiratory-related hospital 

11 admissions or ED visits. The remaining single-city studies identified were not evaluated 

12 in this section due to factors such as inadequate study design or insufficient sample size.

13 It should be mentioned that when examining the association between short-term O3

14 exposure and respiratory health effects that require medical attention, it is important to 

15 distinguish between hospital admissions and ED visits. This is because it is likely that a 

16 small percentage of respiratory ED visits will be admitted to the hospital; therefore, 

17 respiratory ED visits may represent potentially less serious, but more common outcomes. 

18 As a result, in the following sections respiratory hospital admission and ED visit studies 

19 are evaluated individually. Additionally, within each section, results are presented as 

20 either a collection of respiratory diagnoses or as individual diseases (e.g., asthma, COPD, 

21 pneumonia and other respiratory infections) in order to evaluate the potential effect of 

22 short-term O3 exposure on each respiratory-related outcome. The ICD codes (i.e., ICD-9 

23 or ICD-10) that encompass each of these endpoints are presented in Table 6-26 along 

24 with the air quality characteristics of the city, or across all cities, included in each study 

25 evaluated in this section.
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Table 6-26 Mean and upper percentile concentrations of respiratory-related 

hospital admission and emergency department (ED) visit studies 

evaluated

Study Location Type of Visit (ICD9/10) Averaging 

Time

Mean 

Concentration (ppb)a Upper Percentile 

Concentrations (ppb)a

Katsouyanni et 

al. (2009)

b,c

90 U.S. cities 

(NMMAPS)d

32 European 

cities (APHEA)d

12 Canadian 

cities

Hospital Admissions:

NMMAPS: 

All respiratory (460-519)

APHEA: 

All respiratory (460-519)

12 Canadian cities:

All respiratory (460-519)e

1-h max NMMAPS:

50th: 34.9-60.0

APHEA:

50th: 11.0-38.1

12 Canadian cities:

50th: 6.7-8.3

NMMAPS:

75th: 46.8-68.8

APHEA:

75th: 15.3-49.4

12 Canadian cities:

75th: 8.4-12.4

Cakmak et al. 

(2006b)

10 Canadian 

cities

Hospital Admissions:

All respiratory (466, 480-486, 

490, 491, 492, 493, 494, 496)

24-h avg 17.4 Max: 38.0-79.0

Biggeri et al. 

(2005)

c

4 Italian citiesf Hospital Admissions:

All respiratory (460-519)

8-h max Warm season

(May-September):

5.7-60.0

95th: 86.1-90.0

Max: 107.5-115.1

Dales et al. 

(2006)

11 Canadian 

cities

Hospital Admissions:

Respiratory disorders (486, 

768.9, 769, 770.8, 786, 799.0, 

799.1)

24-h avg 17.0 95th: 24.9-46.0

Lin et al. 

(2008a)

11 New York 

regions

Hospital Admissions:

Respiratory diseases (466, 490-

493, 496)

8-h maxg 44.1 75th: 54.0

Max: 217.0

Wong et al. 

(2009)

c

Hong Kong Hospital Admissions:

All respiratory (460-519)

COPD (490-496)

8-h maxg 18.8 75th: 25.9

Max: 100.3

Medina-Ramon 

et al. (2006)

h

36 U.S. cities Hospital Admissions:

COPD (490-496, 

excluding 493)

Pneumonia (480-487)

8-h max Warm

(May-September): 45.8

Cool

(October-April): 27.6

NR

Yang et al. 

(2005b)

Vancouver, 

Canada

Hospital Admissions:

COPD (490-492, 494, 496)

24-h avg All year: 14.1

Winter

(January-March): 13.2

Spring

(April-June): 19.4

Summer

(July-September): 13.8

Fall

(October-December): 

10.0

Max: 38.6

Zanobetti and 

Schwartz 

(2006)

b

Boston, MA Hospital Admissions:

Pneumonia (480-487)

24-h avg 22.4 75th: 31.0

95th: 47.6

Silverman and 

Ito (2010)

b

New York, NY Hospital Admissions:

Asthma (493)

8-h max Warm

(April-August): 41.0

75th: 53

90th: 68
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Study Location Type of Visit (ICD9/10) Averaging 

Time

Mean 

Concentration (ppb)a Upper Percentile 

Concentrations (ppb)a

Stieb et al. 

(2009)

7 Canadian 

cities

ED Visits:

Asthma (493)

COPD (490-492, 494-496)

Respiratory infection (464, 466, 

480-487)

24-h avg 18.4 75th: 19.3-28.6

Tolbert et al. 

(2007)

Atlanta, GA ED Visits:

All respiratory (460-465, 460.0, 

466.1, 466.11, 466.19, 477, 480-

486, 491, 492, 493, 496, 786.07, 

786.09)

8-h max Warm: 53.0 75th: 67.0

90th: 82.1

Max: 147.5

Darrow et al. 

(2011a)

Atlanta, GA ED Visits:

All respiratory (460-466, 477, 

480-486, 491, 492, 493, 496, 

786.09)

8-h max Warm

(March-October):

8-h max: 53

8-h max :75th: 67

8-h max :Max: 148

1-h max Warm

(March-October):

1-h max: 62

1-h max :75th: 76

1-h max :Max: 180

24-h avg Warm

(March-October):

24-h avg: 30

24-h avg :75th: 37

24-h avg :Max: 81

Commute Warm

(March-October):

Commute: 35i

Commute :75th: 45

Commute :Max: 106

Day-time Warm

(March-October):

Day-time: 45i

Day-time :75th: 58

Day-time :Max: 123

Night-time Warm

(March-October):

Night-time: 14i

Night-time :75th: 22

Night-time :Max: 64

Villeneuve et al. 

(2007)

b

Alberta, CAN ED Visits:

Asthma (493)

8-h max Summer

(April-September): 38.0

Winter

(October-March): 24.3

Summer:

75th: 46.0

Winter:

75th: 31.5

Ito et al. (2007b) New York, NY ED Visits:

Asthma (493)

8-h max All year: 30.4

Warm

(April-September): 42.7

Cold

(October-March): 18.0

All year:

95th: 68.0

Warm months:

95th: 77.0

Cold months:

95th: 33.0

Strickland et al. 

(2010)

Atlanta, GA ED Visits:

Asthma (493)

Wheeze (786.07 after 10/1/98, 

786.09 before 10/1/98)

8-h max All year: 45.4j

Warm

(May-October): 55.2j

Cold

(November-April): 34.5j

NR

Mar and Koenig 

(2009)

Seattle, WA ED Visits:

Asthma (493-493.9)

1-h max

8-h max

Warm (May-October):

1-h max: 38.6

8-h max: 32.2

75th:

1-h max: 45.5

8-h max: 39.2

Arbex et al. 

(2009)

Sao Paulo, 

Brazil

ED Visits:

COPD (J40-44)

1-h max 48.8 75th: 61.0

Max: 143.8
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Study Location Type of Visit (ICD9/10) Averaging 

Time

Mean 

Concentration (ppb)a Upper Percentile 

Concentrations (ppb)a

Orazzo et al. 

(2009)

c

6 Italian cities ED Visits:

Wheezing 

8-h maxk Summer

(April-September):

21.1-44.3

Winter

(October-March): 

11.5-27.9

NR

Burra et al. 

(2009)

Toronto, 

Canada

Physician Visits:

ED Asthma (493)

1-h max 33.3 95th: 66

Max: 121

Villeneuve et al. 

(2006b)

Toronto, 

Canada

Physician Visits:

Allergic rhinitis (177)

8-h max 30.0 Max: 98.7

Sinclair et al.

(2010)

l

Atlanta, GA Physician Visits:

Asthma

Upper respiratory infection

Lower respiratory infection

8-h max Total Study Period:

All-year: 44.0

25 mo Period:

All-year: 47.9

Warm: 61.2

Cold: 27.8

28 mo Period:

All-year: 40.7

Warm: 51.8

Cold: 26.0

NR

a

Some studies did not present an overall value for the mean, middle and/or upper percentiles of the O3 distribution; as a result, the 

range of the mean, middle, and/or upper percentiles across all of the cities included in the study are presented. 

b

Study only presented median concentrations.

c

Study presented concentrations as μg/m3 Concentration was converted to ppb using the conversion factor of 0.51 assuming 

standard temperature (25°C) and pressure (1 atm).

d

A subset of the European and U.S. cities included in the mortality analyses were used in the hospital admissions analyses: 8 of the 

32 European cities and 14 of 90 U.S. cities.

e

Hospital admission data was coded using three classifications (ICD-10-CA, ICD-9, and ICD-9-CM). Attempts were made by the 

original investigators to convert diagnosis from ICD-10-CA back to ICD-9. 

f

Only 4 of the 8 cities included in the study collected O3 data.

g

O3 measured from 10:00 a.m. to 6:00 p.m.

h

Only 35 of the 36 cities included in the analysis had O3 data.

i

Commute (7:00 a.m. to 10:00 a.m., 4:00 p.m. to 7:00 p.m.); day-time (8:00 a.m. to 7:00 p.m.); Night-time (12:00 a.m. to 6:00 a.m.).

j

Means represent population-weighted O3 concentrations.

k

O3 measured from 8:00 a.m. to 4:00 p.m.

l

This study did not report the ICD codes used for the conditions examined. The 25-month period represents August 1998-August 

2000, and the 28-month period represents September 2000-December 2002. This study defined the warm months as April –

October and the cold months as November-March.

6.2.7.2 Hospital Admission Studies

Respiratory Diseases

1 The association between exposure to an air pollutant, such as O3, and daily respiratory2 related hospital admissions has primarily been examined using all respiratory-related 

3 hospital admissions within the range of ICD-9 codes 460-519. Recent studies published 

4 since the 2006 AQCD (U.S. EPA, 2006b) attempt to further examine the effect of O3

5 exposure on respiratory-related hospital admissions through a multicity design that 

6 examines O3 effects across countries using a standardized methodology; multicity studies 
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1 that examine effects within one country; and multi- and single-city studies that attempt to 

2 examine potential modifiers of the O3-respiratory-related hospital admission relationship. 

3 The Air Pollution and Health: A European and North American Approach (APHENA) 

4 study combined data from existing multicity study databases from Canada, Europe 

5 (APHEA2) (Katsouyanni et al., 2001), and the U.S. (NMMAPS) (Samet et al., 2000) in 

6 order to “develop more reliable estimates of the potential acute effects of air pollution on 

7 human health [and] provide a common basis for [the] comparison of risks across 

8 geographic areas” (Katsouyanni et al., 2009). In an attempt to address both of these 

9 issues, the investigators conducted extensive sensitivity analyses to evaluate the 

10 robustness of the results to different model specifications (e.g., penalized splines [PS] 

11 versus natural splines [NS]) and the extent of smoothing to control for seasonal and 

12 temporal trends. The trend analyses consisted of subjecting the models to varying extent 

13 of smoothing selected either a priori (i.e., 3 df/year, 8 df/year, and 12 df/year), which was 

14 selected through exploratory analyses using between 2 and 20 df, or by using the absolute 

15 sum of the residuals of the partial autocorrelation function (PACF). Although the 

16 investigators did not identify the model they deemed to be the most appropriate for 

17 comparing the results across study locations, they did specify that “overall effect 

18 estimates (i.e., estimates pooled over several cities) tended to stabilize at high degrees of 

19 freedom” (Katsouyanni et al., 2009). Therefore, in discussion of the results across the 

20 three study locations below, the 8 df/year results are presented for both the PS and NS 

21 models because: (1) 8 df/year is most consistent with the extent of temporal adjustment 

22 used in previous and recent large multicity studies in the U.S. (e.g., NMMAPS); (2) the 

23 risk estimates for 8 df/year and 12 df/year are comparable for all three locations; (3) the 

24 models that used the PACF method did not report the actual degrees of freedom chosen; 

25 and (4) the 3 df/year and the PACF method resulted in negative O3 risk estimates, which 

26 is inconsistent with the results obtained using more aggressive seasonal adjustments and 

27 suggests inadequate control for seasonality. Additionally, in comparisons of results across 

28 studies in figures, only the results from one of the spline models (i.e., NS) are presented 

29 because it has been previously demonstrated that alternative spline models result in 

30 relatively similar effect estimates (HEI, 2003). This observation is consistent with the 

31 results of the APHENA analysis that was conducted with a higher number of degrees of 

32 freedom (e.g., ≥ 8 df/year) to account for temporal trends.

33 Katsouyanni et al. (2009) examined respiratory hospital admissions for people aged 

34 65 years and older using 1-h max O3 data. The extent of hospital admission and O3 data 

35 varied across the 3 datasets: Canadian dataset included 12 cities with data for 3 years 

36 (1993-1996) per city; European dataset included 8 cities with each city having data for 

37 between 2 and 8 years from 1988-1997; and the U.S. dataset included 14 cities with each 

38 city having data for 4 to 10 years from 1985-1994 and 7 cities having only summer O3
Draft – Do Not Cite or Quote 6-138 June 2012

1 data. The investigators used a three-stage hierarchical model to account for within-city, 

2 within region, and between region variability. Results were presented individually for 

3 each region (Figure 6-14; Table 6-27). Ozone and PM10 concentrations were weakly 

4 correlated in all locations in the summer (r = 0.27-0.40), but not in the winter. 

5 In the Canadian cities, using all-year data, a 40 ppb increase in 1-h max O3

6 concentrations at lag 0-1 was associated with an increase in respiratory hospital 

7 admissions of 8.9% (95% CI: 0.79, 16.8%) in a PS model and 8.1% (95% CI: 0.24, 

8 16.8%) in a NS model (Katsouyanni et al., 2009). The results were somewhat sensitive to 

9 the lag day selected, reduced when using a single-day lag (e.g., lag 1) (PS: 6.0%; NS: 

10 5.5%) and increased when using a distributed lag model (PS: 18.6%; NS: 20.4%). When 

11 adjusting for PM10, the magnitude of the effect estimate was attenuated, but remained 

12 positive with it being slightly larger in the NS model (5.1% [95% CI: -6.6, 18.6%]) 

13 compared to the PS model (3.1% [95% CI: -8.3, 15.9%]). However, in the Canadian 

14 dataset the copollutant analysis was only conducted using a 1-day lag. The large 

15 confidence intervals for both models could be attributed to the reduction in days included 

16 in the copollutant analyses as a result of the every-6th-day PM sampling schedule. When 

17 the analysis was restricted to the summer months, stronger associations were observed 

18 between O3 and respiratory hospital admissions across the lags examined, ranging from 

19 ~22 to 37% (the study does not specify whether these effect estimates are from a NS or 

20 PS model). Because O3 concentrations across the cities included in the Canadian dataset 

21 are low (median concentrations ranging from 6.7-8.3 ppb [Table 6-26]), the standardized 

22 increment of 40 ppb for a 1-h max increase in O3 concentrations represents an unrealistic 

23 increase in O3 concentrations in Canada and increases the magnitude, not direction, of the 

24 observed risk estimate. As a result, calculating the O3 risk estimate using the standardized

25 increment does not accurately reflect the observed risk of O3-related respiratory hospital 

26 admissions. Although this increment adequately characterizes the distribution of 1-h max 

27 O3 concentrations across the U.S. and European datasets, it misrepresents the observed O3

28 concentrations in the Canadian dataset. As a result in summary figures, for comparability, 

29 effect estimates from the Canadian dataset are presented for both a 5.1 ppb increase in 

30 1-h max O3 concentrations (i.e., an approximate interquartile range [IQR] increase in O3

31 concentrations across the Canadian cities) as well as the standardized increment used 

32 throughout the ISA.

33 In Europe, weaker but positive associations were also observed in year round analyses; 

34 2.9% (95% CI: 0.63, 5.0%) in the PS model and 1.6% (95% CI: -1.7, 4.2%) in the NS 

35 model at lag 0-1 for a 40 ppb increase in 1-h max O3 concentrations (Katsouyanni et al., 

36 2009). Additionally, at lag 1, associations between O3 and respiratory hospital admissions 

37 were also reduced, but in contrast to the lag 0-1 analysis, greater effects were observed in 

38 the NS model (2.9% [95% CI: 1.0, 4.9%]) compared to the PS model (1.5% [95% CI: 
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1 -2.2, 5.4]). Unlike the Canadian analysis, a distributed lag model provided limited 

2 evidence of an association between O3 and respiratory hospital admissions. To compare 

3 with the Canadian results, with adjustment for PM10 at lag 1, O3 effect estimates were 

4 increased in the PS model (2.5% [95% CI: 0.39-4.8%]) and remained robust in the NS 

5 model (2.4% [95% CI: 0.08, 4.6%]). However, the European analysis also examined the 

6 effect of adjusting for PM10 at lag 0-1 and found results were attenuated, but remained 

7 positive in both models (PS: 0.8% [95% CI: -2.3, 4.0%]; NS: 0.8% [95% CI: -1.8, 

8 3.6%]). Unlike the Canadian and U.S. datasets, the European dataset consisted of daily 

9 PM data. The investigators did not observe stronger associations in the summer-only 

10 analyses for the European cities at lag 0-1 (PS: 0.4% [95% CI: -3.2, 4.0%]; NS: 0.2% 

11 [95% CI: -3.3, 3.9%]), but did observe some evidence for larger effects during the 

12 summer, an ~2.5% increase, at lag 1 in both models (the study does not present the extent 

13 of temporal smoothing used for these models). 
Draft – Do Not Cite or Quote 6-140 June 2012

Note: Black circles = all-year results; open circles = all-year results in copollutant model with PM10; and red circles = summer only 

results. For Canada, lag days with an “a” next to them represent the risk estimates standardized to an approximate IQR of 5.1 ppb 

for a 1-h max increase in O3 concentrations.

Figure 6-14 Percent increase in respiratory hospital admissions from natural 

spline models with 8 df/yr for a 40 ppb increase in 1-h max ozone 

concentrations for each location of the APHENA study.

Location

U.S.

Canada

Europe

All-Year

Summer

All-Year

Summer

All-Year

Summer

►

►

►

Lag

1

1

0-1

0-1

DL (0-2)

0-1

1

1

1a

1

1a

0-1

0-1a

DL (0-2)

DL (0-2)a

1

1a

0-1

0-1a

DL (0-2)

DL (0-2)a

1

1

0-1

0-1

DL (0-2)

1

0-1

-10 -5 0 5 10 15 20 25 30 35 40

% Increase
Draft – Do Not Cite or Quote 6-141 June 2012

Table 6-27 Corresponding effect estimates for Figure 6-14.

Location* Season Laga Copollutant % Increase (95% CI)b

U.S. All-year 1 2.62 (0.63, 4.64)

1 PM10 2.14 (-0.08, 4.40)

0-1 2.38 (0.00, 4.89)

0-1 PM10 1.42 (-1.33, 4.23)

DL(0-2) 3.34 (0.02-6.78)

Summer 0-1 2.14 (-0.63, 4.97)

1 2.78 (-0.02, 5.71)

Canada All-year 1 5.54 (-0.94, 12.4)

1a 0.69 (-0.12, 1.50)a

1 PM10 5.13 (-6.62, 18.6)

1a PM10 0.64 (-0.87, 2.20)a

0-1 8.12 (0.24, 16.8)

0-1a 1.00 (0.03, 2.00)a

DL(0-2) 20.4 (4.07, 40.2)

DL(0-2)a 2.4 (0.51, 4.40)a

Summer 1 21.4 (15.0, 29.0)

1a 2.50 (1.80, 3.30)a

0-1 32.0 (18.6, 47.7)

0-1a 3.60 (2.20, 5.10)a

DL(0-2) 37.1 (11.5, 67.5)

DL(0-2)a 4.1 (1.40, 6.80)a

Europe All-year 1 2.94 (1.02, 4.89)

1 PM10 2.38 (0.08, 4.64)

0-1 1.58 (-1.71, 4.15)

0-1 PM10 0.87 (-1.79, 3.58)

DL(0-2) 0.79 (-4.46, 6.37)

Summer 1 2.46 (-0.63, 5.54)

0-1 0.24 (-3.32, 3.91)

*For effect estimates in Figure 6-14.

a

For Canada, lag days with an “a” next to them represent the risk estimates standardized to an approximate IQR of 5.1 ppb for a 

1-h max increase in O3 concentrations.

b

Unless noted, risk estimates standardized to 40 ppb for a 1-h max increase in O3 concentrations.

1 For the U.S. in year round analyses, the investigators reported a 1.4% (95% CI: -0.9, 

2 3.9%) increase in the PS model and 2.4% (95% CI: 0.0, 4.9%) increase in the NS model 

3 in respiratory hospital admissions at lag 0-1 for a 40 ppb increase in 1-h max O3

4 concentrations with similar results for both models at lag 1 (Katsouyanni et al., 2009). 

5 The distributed lag model provided results similar to those observed in the European 
Draft – Do Not Cite or Quote 6-142 June 2012

1 dataset with the PS model (1.1% [95% CI: -3.0, 5.3%]), but larger effects in the NS 

2 model (3.3% [95% CI: 0.02, 6.8%]), which is consistent with the Canadian results. With 

3 adjustment for PM10 using the U.S. data (i.e., every-6th-day PM data), results were 

4 attenuated, but remained positive at lag 0-1 (PS: 0.6% [95% CI: -2.0, 3.3%]; NS: 1.4% 

5 [95% CI: -1.3, 4.2%]) which is consistent with the results presented for the European 

6 dataset. However, at lag 1, U.S. risk estimates remained robust to the inclusion of PM10 in 

7 copollutant models as was observed in the Canadian and European datasets. Compared to 

8 the all-year analyses, the investigators did not observe stronger associations in the 

9 summer-only analysis at either lag 0-1 (~2.2%) or lag 1 (~2.8%) in both the PS and NS 

10 models (the study does not present the extent of temporal smoothing used for these 

11 models).

12 Several additional multicity studies examined respiratory disease hospital admissions in 

13 Canada and Europe. Cakmak et al. (2006b) evaluated the association between ambient O3

14 concentrations and respiratory hospital admissions for all ages in 10 Canadian cities from 

15 April 1993 to March 2000. The primary objective of this study was to examine the 

16 potential modification of the effect of ambient air pollution on daily respiratory hospital 

17 admissions by education and income using a time-series analysis conducted at the city18 level. The authors calculated a pooled estimate across cities for each pollutant using a 

19 random effects model by first selecting the lag day with the strongest association from the 

20 city-specific models. For O3, the mean lag day across cities that provided the strongest 

21 association and for which the pooled effect estimate was calculated was 1.2 days. In this 

22 study, all-year O3 concentrations were used in the analysis, and additional seasonal 

23 analyses were not conducted. Cakmak et al. (2006b) reported a 4.4% increase (95% CI: 

24 2.2, 6.5%) in respiratory hospital admissions for a 20 ppb increase in 24-hour average O3

25 concentrations. The investigators only examined the potential effect of confounding by 

26 other pollutants through the use of a multipollutant model (i.e., two or more additional 

27 pollutants included in the model), which is difficult to interpret due to the potential 

28 multicollinearity between pollutants. Cakmak et al. (2006b) also conducted an extensive 

29 analysis of potential modifiers, specifically sex, educational attainment, and family 

30 income, on the association between air pollution and respiratory hospital admissions. 

31 When stratifying by sex, the increase in respiratory hospital admissions due to short-term 

32 O3 exposure were similar in males (5.2% [95% CI: 3.0, 7.3%]) and females (4.2% 

33 [95% CI: 1.8, 6.6%]). In addition, the examination of effect modification by income 

34 found no consistent trend across the quartiles of family income. However, there was 

35 evidence that individuals with an education level less than the 9th grade were 

36 disproportionately affected by O3 exposure (4.6% [95% CI: 1.8, 7.5%]) compared to 

37 individuals that completed grades 9-13 (1.7% [95% CI: -1.9, 5.3%]), some university or 

38 trade school (1.4% [95% CI: -2.0, 5.1%]), or have a university diploma (0.66% [95% CI: 

39 -3.3, 4.7%]). The association between O3 and respiratory hospital admissions in 
Draft – Do Not Cite or Quote 6-143 June 2012

1 individuals with an education level less than the 9th grade was the strongest association 

2 across all of the pollutants examined. 

3 A multicity study conducted in Europe by Biggeri et al. (2005) examined the association 

4 between short-term O3 exposure and respiratory hospital admissions for all ages in four 

5 Italian cities from 1990 to 1999. In this study, O3 was only measured during the warm 

6 season (May-September). The authors examined associations between daily respiratory 

7 hospital admissions and short-term O3 exposure at the city-level using a time-series 

8 analysis. Pooled estimates were calculated by combining city-specific estimates using 

9 fixed and random effects models. The investigators found no evidence of an association 

10 between O3 exposure and respiratory hospital admissions in the warm season in both the 

11 random (0.1% [95% CI: -5.2, 5.7%]; distributed lag 0-3) and fixed effects (0.1% 

12 [95% CI: -5.2, 5.7%]; distributed lag 0-3) models for a 30 ppb increase in 8-h max O3

13 concentrations. 

14 Additional studies examined associations between short-term O3 exposure and respiratory 

15 hospital admissions specifically in children. In a multicity study conducted in Canada, 

16 Dales et al. (2006) examined the association between all-year ambient O3 concentrations 

17 and neonatal (ages 0-27 days) respiratory hospital admissions in 11 Canadian cities from 

18 1986 to 2000. The investigators used a statistical analysis approach similar to Cakmak et 

19 al. (2006b) (i.e., time-series analysis to examine city-specific associations, and then a 

20 random effects model to pool estimates across cities). The authors reported that for O3,

21 the mean lag day across cities that provided the strongest association was 2 days. The 

22 authors reported a 5.4% (95% CI: 2.9, 8.0%) increase in neonatal respiratory hospital 

23 admissions for a 20 ppb increase in 24-h avg O3 concentrations at lag-2 days. The results 

24 from Dales et al. (2006) provide support for the associations observed in a smaller scale 

25 study that examined O3 exposure and pediatric respiratory hospital admissions in 

26 New York state (Lin et al., 2008a). Lin et al. (2008a), when examining single-day lags of 

27 0 to 3 days, observed a positive association between O3 and pediatric (i.e., <18 years) 

28 respiratory admissions at lag 2 (results not presented quantitatively) in a two-stage 

29 Bayesian hierarchical model analysis of 11 geographic regions of New York state from 

30 1991 to 2001. Additionally, in copollutant models with PM10, collected every-6th day, the 

31 authors found region-specific O3 associations with respiratory hospital admissions 

32 remained relatively robust.

33 Overall, the evidence from epidemiologic studies continues to support an association 

34 between short-term O3 exposure and respiratory-related hospital admissions, but it 

35 remains unclear whether certain factors (individual- or population-level) modify this 

36 association. Wong et al. (2009) examined the potential modification of the relationship 

37 between ambient O3 (along with NO2, SO2, and PM10) and respiratory hospital 
Draft – Do Not Cite or Quote 6-144 June 2012

1 admissions by influenza intensity in Hong Kong for the period 1996 – 2002. In this study 

2 air pollution concentrations were estimated by centering non-missing daily air pollution 

3 data on the annual mean for each monitor and then an overall daily concentration was 

4 calculated by taking the average of the daily centered mean across all monitors. Influenza 

5 intensity was defined as a continuous variable using the proportion of weekly specimens 

6 positive for influenza A or B instead of defining influenza epidemics. This approach was 

7 used to avoid any potential bias associated with the unpredictable seasonality of influenza 

8 in Hong Kong where there are traditionally two seasonal peaks, which is in contrast to the 

9 single peaking influenza season in the U.S. (Wong et al., 2009). In models that examined 

10 the baseline effect (i.e., without taking into consideration influenza intensity) of short11 term O3 exposure, the authors found a 3.6% (95% CI: 1.9, 5.3%) and 3.2% (95% CI: 1.0, 

12 5.4%) increase in respiratory hospital admissions at lag 0-1 for a 30 ppb increase in 

13 8-h max O3 concentrations for the all age and ≥ 65 age groups, respectively. When 

14 examining influenza intensity, Wong et al. (2009) reported that the association between 

15 short-term exposure to O3 and respiratory hospital admissions was stronger with higher 

16 levels of influenza intensity: additional increase in respiratory hospital admissions above 

17 baseline of 1.4% (95% CI: 0.24, 2.6%) for all age groups and 2.4% (95% CI: 0.94, 3.8%) 

18 for those 65 and older when influenza activity increased from 0% to 10%. No difference 

19 in effects was observed when stratifying by sex. 

Cause-Specific Respiratory Outcomes

20 In the 2006 O3 AQCD a limited number of studies were identified that examined the 

21 effect of short-term O3 exposure on cause-specific respiratory hospital admissions. The 

22 limited evidence “reported positive O3 associations with... asthma and COPD, 

23 especially... during the summer or warm season” (U.S. EPA, 2006b). Of the studies 

24 evaluated since the completion of the 2006 O3 AQCD, more have focused on identifying 

25 whether O3 exposure is associated with specific respiratory-related hospital admissions, 

26 including COPD, pneumonia, and asthma, but the overall body of evidence remains 

27 small. 

Chronic Obstructive Pulmonary Disease

28 Medina-Ramon et al. (2006) examined the association between short-term exposure to 

29 ambient O3 and PM10 concentrations and Medicare hospital admissions among 

30 individuals ≥ 65 years of age for COPD in 35 cities in the U.S. for the years 1986-1999. 

31 The cities included in this analysis were selected because they monitored PM10 on a daily 

32 basis. In this study, city-specific results were obtained using a monthly time-stratified 

33 case-crossover analysis. A meta-analysis was then conducted using random effects 

34 models to combine the city-specific results. All cities measured O3 from May through 
Draft – Do Not Cite or Quote 6-145 June 2012

1 September, while only 16 of the cities had year-round measurements. The authors 

2 reported a 1.6% increase (95% CI: 0.48, 2.9%) in COPD admissions for lag 0-1 in the 

3 warm season for a 30 ppb increase in 8-h max O3 concentrations. When examining 

4 single-day lags, stronger associations were observed for lag 1 (2.9% [95% CI: 1.8, 4.0%]) 

5 compared to lag 0 (-1.5% [95% CI: -2.7, -0.24%]). The authors found no evidence of 

6 associations in cool season (-1.9% [95% CI: -3.6, -0.06%]; lag 0-1) or year round (0.24% 

7 [95% CI: -0.78, 1.2%]; lag 0-1) analyses. In a copollutant model restricted to days in 

8 which PM10 was available, the association between O3 and COPD hospital admissions 

9 remained robust. Of note, the frequency of PM10 measurements varied across cities with 

10 measurements collected either every 2, 3, or 6 days. The authors conducted additional 

11 analyses to examine potential modification of the warm season estimates for O3 and 

12 COPD admissions by several city-level characteristics: percentage living in poverty, 

13 emphysema mortality rate (as an indication of smoking), daily summer apparent 

14 temperature, and percentage of households using central air conditioning. Of the city15 level characteristics examined, stronger associations were only reported for cities with a 

16 smaller variability in daily apparent summer temperature.

17 In a single-city study conducted in Vancouver from 1994-1998, a location with low 

18 ambient O3 concentrations (Table 6-26), Yang et al. (2005b) examined the association 

19 between O3 and COPD. Ozone was moderately inversely correlated with CO (r = -0.56), 

20 NO2 (r = -0.32), and SO2 (r = -0.34), and weakly inversely correlated with PM10

21 (r = -0.09), suggesting that the observed O3 effect is likely not only due to a positive 

22 correlation with other pollutants. Yang et al. (2005b) examined 1- to 7-day (e.g., (0-

23 6 days) lagged moving averages and observed an 8.8% (95% CI: -12.5, 32.6%) increase 

24 in COPD admissions for lag 0-3 per 20 ppb increase in 24-h avg O3 concentrations. In 

25 two-pollutant models with every-day data for NO2, SO2, and PM10 at lag 0-3, O3 risk 

26 estimates remained robust, but were increased slightly when CO was added to the model 

27 (Figure 6-19; Table 6-29). 

28 In the study discussed above, Wong et al. (2009) also examined the potential 

29 modification of the relationship between ambient O3 and COPD hospital admissions by 

30 influenza intensity. The authors also found evidence of an additional increase in COPD 

31 admissions above baseline when influenza activity increased from 0% to 10% of 1.0% 

32 (95% CI: -0.82, 2.9%) for all age groups and 2.4% (95% CI: 0.41, 4.4%) for those 65 and 

33 older. The baseline increase in COPD hospital admissions at lag 0-1 for a 30 ppb increase 

34 in 8-h max O3 concentrations was 8.5% (95% CI: 5.6, 11.4%) for the all age and 4.2% 

35 (95% CI: 1.1, 7.3%) ≥ 65 age groups.
Draft – Do Not Cite or Quote 6-146 June 2012

Pneumonia

1 In addition to COPD, Medina-Ramon et al. (2006) examined the association between 

2 short-term exposure to ambient O3 and PM10 concentrations and Medicare hospital 

3 admissions among individuals ≥ 65 years of age for pneumonia (ICD-9: 480-487). The 

4 authors reported an increase in pneumonia-hospital admissions in the warm season (2.5% 

5 [95% CI: 1.6, 3.5%] for a 30 ppb increase in 8-h max O3 concentrations; lag 0-1). Similar 

6 to the results observed for COPD hospital admissions, pneumonia-hospital admissions 

7 associations were stronger at lag 1 (2.6% [95% CI: 1.8, 3.4%]) compared to lag 0 (0.06% 

8 [95% CI: -0.72, 0.78%]), and no evidence of an association was observed in the cool 

9 season or year round. In two-pollutant models restricted to days for which PM10 data was 

10 available, as discussed above, the association between O3 exposure and pneumonia11 hospital admissions remained robust (results not presented quantitatively). The authors 

12 also examined potential effect modification of the warm season estimates for O3-related 

13 pneumonia-hospital admissions, as was done for COPD, by several city-level 

14 characteristics. Stronger associations were reported in cities with a lower percentage of 

15 central air conditioning use. Across the cities examined, the percentage of households 

16 having central air conditioning ranged from 6 to 93%. The authors found no evidence of 

17 effect modification of the O3-pneumonia-hospital admission relationship when examining 

18 the other city-level characteristics.

19 Results from a single-city study conducted in Boston did not support the results presented 

20 by Medina-Ramon et al. (2006). Zanobetti and Schwartz (2006) examined the association 

21 of O3 and pneumonia Medicare hospital admissions for the period 1995-1999. Ozone was 

22 weakly positively correlated with PM2.5 (r = 0.20) and weakly inversely correlated with 

23 black carbon, NO2, and CO (-0.25, -0.14, and -0.30, respectively). In an all-year analysis, 

24 the investigators reported a 3.8% (95% CI: -7.9, -0.1%) decrease in pneumonia 

25 admissions for a 20 ppb increase in 24-hour average O3 concentrations at lag 0 and a 

26 6.0% (95% CI: -11.1, -1.4%) decrease for the average of lags 0 and 1. It should be noted 

27 that the mean daily counts of pneumonia admissions was low for this study, ~14 

28 admissions per day compared to ~271 admissions per day for Medina-Ramon et al. 

29 (2006). However, in analyses with other pollutants Zanobetti and Schwartz (2006) did 

30 observe positive associations with pneumonia-hospital admissions, indicating that the low 

31 number of daily hospital admission counts probably did not influence the O3 pneumonia32 hospital admissions association in this study. 

Asthma

33 There are relatively fewer studies that examined the association between short-term 

34 exposure to O3 and asthma hospital admissions, presumably due to the limited power 

35 given the relative rarity of asthma hospital admissions compared to ED or physician 
Draft – Do Not Cite or Quote 6-147 June 2012

1 visits. A study from New York City examined the association of 8-h max O3

2 concentrations with severe acute asthma admissions (i.e., those admitted to the Intensive 

3 Care Unit [ICU]) during the warm season in the years 1999 through 2006 (Silverman and 

4 Ito, 2010). In this study, O3 was moderately correlated with PM10 (r = 0.59). When 

5 stratifying by age, the investigators reported positive associations with ICU asthma 

6 admissions for the 6- to 18-year age group (26.8% [95% CI: 1.4, 58.2%] for a 30 ppb 

7 increase in maximum 8-h avg O3 concentrations at lag 0-1), but little evidence of 

8 associations for the other age groups examined (<6 years, 19-49, 50+, and all ages). 

9 However, positive associations were observed for each age-stratified group and all ages 

10 for non-ICU asthma admissions, but again the strongest association was reported for the 

11 6- to 18-years age group (28.2% [95% CI: 15.3, 41.5%]; lag 0-1). In two-pollutant 

12 models, O3 effect estimates for both non-ICU and ICU hospital admissions remained 

13 robust to adjustment for PM2.5. In an additional analysis, using a smooth function, the 

14 authors examined whether the shape of the C-R curve for O3 and asthma hospital 

15 admissions (i.e., both general and ICU for all ages) is linear. To account for the potential 

16 confounding effects of PM2.5, Silverman and Ito (2010) also included a smooth function 

17 of PM2.5 lag 0-1. When comparing the curve to a linear fit line the authors found that the 

18 linear fit is a reasonable approximation of the C-R relationship between O3 and asthma 

19 hospital admissions around and below the level of the 1997 O3 NAAQS (Figure 6-15). 
Draft – Do Not Cite or Quote 6-148 June 2012

Note: The average of 0-day and 1-day lagged 8-hour O3 was used in a two-pollutant model with PM2.5 lag 0-1, adjusting for temporal 

trends, day of the week, and immediate and delayed weather effects. The solid lines are smoothed fit data, with long broken lines 

indicating 95% confidence bands. The density of lines at the bottom of the figure indicates sample size.

Source: Reprinted with permission of the American Academy of Allergy, Asthma & Immunology (Silverman and Ito, 2010).

Figure 6-15 Estimated relative risks (RRs) of asthma hospital admissions for 

8-h max ozone concentrations at lag 0-1 allowing for possible 

nonlinear relationships using natural splines.

Averting Behavior

1 The studies discussed above have found consistent positive associations between short2 term O3 exposure and respiratory-related hospital admissions, however, the strength of 

3 these associations may be underestimated due to the studies not accounting for averting 

4 behavior. As discussed in Section 4.6.5, a recent study (Neidell and Kinney, 2010; 

5 Neidell, 2009) conducted in Southern California demonstrate that controlling for 

6 avoidance behavior increases O3 effect estimates for respiratory hospital admissions, 

7 specifically for children and older adults. These studies show that on days where no 

8 public alert was issued warning of high O3 concentrations there was an increase in asthma 

9 hospital admissions. Although only one study has examined averting behavior and this 
Draft – Do Not Cite or Quote 6-149 June 2012

1 study is limited to the outcome of asthma hospital admissions in one location (i.e., Los 

2 Angeles, CA) for the years 1989-1997, it does provide preliminary evidence indicating 

3 that epidemiologic studies may underestimate associations between O3 exposure and 

4 health effects by not accounting for behavioral modification when public health alerts are 

5 issued. 

6.2.7.3 Emergency Department Visit Studies

6 Overall, relatively fewer studies have examined the association between short-term O3 

7 exposure and respiratory-related ED visits, compared to hospital admissions. In the 2006 

8 O3 AQCD, positive, but inconsistent, associations were observed between O3 and 

9 respiratory-related ED visits with effects generally occurring during the warm season. 

10 Since the completion of the previous AQCD, larger studies have been conducted, in 

11 terms of sample size, study duration, and in some cases multiple cities, to examine the 

12 association between O3 and ED visits for all respiratory diseases, COPD, and asthma. 

Respiratory Disease

13 A large single-city study conducted in Atlanta, by Tolbert et al. (2007), and subsequently 

14 re analyzed by Darrow et al. (2011a) using different air quality data, provides evidence 

15 for an association between short-term exposures to ambient O3 concentrations and 

16 respiratory ED visits. Tolbert et al. (2007) examined the association between air 

17 pollution, both gaseous pollutants and PM and its components, and respiratory disease 

18 ED visits in all ages from 1993 to 2004. The correlations between O3 and the other 

19 pollutants examined ranged from 0.2 for CO and SO2 to 0.5-0.6 for the PM measures. 

20 Using an a priori average of lags 0-2 for each air pollutant examined, the authors reported 

21 a 3.9% (95% CI: 2.7, 5.2%) increase in respiratory ED visits for a 30 ppb increase in 

22 8-h max O3 concentrations during the warm season [defined as March-October in Darrow 

23 et al. (2011a)]. In copollutant models, limited to days in which data for all pollutants were

24 available, O3 respiratory ED visits associations with CO, NO2, and PM10, were attenuated, 

25 but remained positive (results not presented quantitatively). 

26 Darrow et al. (2011a) examined the same health data as Tolbert et al. (2007), but used air 

27 quality data from one centrally located monitor instead of the average of multiple 

28 monitors. This study primarily focused on exploring whether differences exist in the 

29 association between O3 exposure and respiratory-related ED visits depending on the 

30 exposure metric used (i.e., 8-h max, 1-h max, 24-hour average, commuting period [7:00 

31 a.m. to 10:00 a.m.; 4:00 p.m. to 7:00 p.m.], day-time [8:00 a.m. to 7:00 p.m.] and night32 time [12:00 a.m. to 6:00 a.m.]). An ancillary analysis of the spatial variability of each 

33 exposure metric conducted by Darrow et al. (2011a) found a rather homogenous spatial 
Draft – Do Not Cite or Quote 6-150 June 2012

1 distribution of O3 concentrations (r~>0.8) as the distance from the central monitor 

2 increased from 10 km to 60 km for all exposure durations, except the night-time metric. 

3 The relatively high spatial correlation gives confidence in the use of a single monitor and 

4 the resulting risk estimates. To examine the association between the various O3 exposure 

5 metrics and respiratory ED visits, the authors conceptually used a time-stratified case6 crossover framework where control days were selected as those days within the same 

7 calendar month and maximum temperature as the case day. However, instead of 

8 conducting a traditional case-crossover analysis, the authors used a Poisson model with 

9 indicator variables for each of the strata (i.e., parameters of the control days). Darrow et 

10 al. (2011a) found using an a prior lag of 1 day, the results were somewhat variable across 

11 exposure metrics. The strongest associations with respiratory ED visits were found when 

12 using the 8-h max, 1-h max, and day-time exposure metrics with weaker associations 

13 using the 24-h avg and commuting period exposure metrics; a negative association was 

14 observed when using the night-time exposure metric (Figure 6-16). These results indicate 

15 that using the 24-h avg exposure metric may lead to smaller O3-respiratory ED visits risk 

16 estimates due to: (1) the dilution of relevant O3 concentrations by averaging over hours 

17 (i.e., nighttime hours) during which O3 concentrations are known to be low and (2) 

18 potential negative confounding by other pollutants (e.g., CO, NO2) during the nighttime 

19 hours (Darrow et al., 2011a).
Draft – Do Not Cite or Quote 6-151 June 2012

Source: Reprinted with permission of Nature Publishing Group (Darrow et al., 2011a).

Figure 6-16 Risk ratio for respiratory ED visits and different ozone exposure 

metrics in Atlanta from 1993-2004.

1 In an additional study conducted in 6 Italian cities, Orazzo et al. (2009) examined 

2 respiratory ED visits for ages 0-2 years in 6 Italian cities from 1996 to 2000. However, 

3 instead of identifying respiratory ED visits using the traditional approach of selecting 

4 ICD codes as was done by Tolbert et al. (2007) and Darrow et al. (2011a), Orazzo et al. 

5 (2009) used data on wheeze extracted from medical records as an indicator of lower 

6 respiratory disease. This study examined daily counts of wheeze in relation to air 

7 pollution using a time-stratified case-crossover approach in which control days were 

8 matched on day of week in the same month and year as the case day. The authors found 

9 no evidence of an association between 8-h max O3 concentrations and respiratory ED 

10 visits in children aged 0-2 years in models that examined both single-day lags and 

11 moving averages of lags from 0-6 days in year-round and seasonal analyses (i.e., warm 

12 and cool seasons). In all-year analyses, the percent increase in total wheeze ranged from -

13 1.4% to -3.3% for a 0-1 to 0-6 day lag, respectively. 
Draft – Do Not Cite or Quote 6-152 June 2012

COPD

1 Stieb et al. (2009) also examined the association between short-term O3 exposure and 

2 COPD ED visits in 7 Canadian cities. Across cities, in an all-year analysis, O3 was found 

3 to be positively associated with COPD ED visits (2.4% [95% CI: -1.9, 6.9%] at lag 1 and 

4 4.0% [95% CI: -0.54, 8.6%] at lag 2 for a 20 ppb increase in 24-h avg O3 concentrations). 

5 In seasonal analyses, larger effects were observed between O3 and COPD ED visits 

6 during the warm season (i.e., April-September) 6.8% [95% CI: 0.11, 13.9%] (lag day not 

7 specified); with no associations observed in the winter season. Stieb et al. (2009) also 

8 examined associations between respiratory-related ED visits, including COPD, and air 

9 pollution at sub-daily time scales (i.e., 3-h avg of ED visits versus 3-h avg pollutant 

10 concentrations) and found no evidence of consistent associations between any pollutant 

11 and any respiratory outcome. 

12 In a single-city study, Arbex et al. (2009) examined the association between COPD and 

13 several ambient air pollutants, including O3, in Sao Paulo, Brazil for the years 2001-2003 

14 for individuals over the age of 40. Associations between O3 exposure and COPD ED 

15 visits were examined in both single-day lag (0-6 days) and polynomial distributed lag 

16 models (0-6 days). In all-year analyses, O3 was not found to be associated with an 

17 increase in COPD ED visits (results not presented quantitatively). The authors also 

18 conducted stratified analyses to examine the potential modification of the air pollutant19 COPD ED visits relationship by age (e.g., 40-64, >64) and sex. In these analyses O3 was 

20 found to have an increase in COPD ED visits for women, but not for men or either of the 

21 age groups examined.

Asthma 

22 In a study of 7 Canadian cities, Stieb et al. (2009) also examined the association between 

23 exposure to air pollution (i.e., CO, NO2, O3, SO2, PM10, PM2.5, and O3) and asthma ED 

24 visits. Associations between short-term O3 exposure and asthma ED visits were examined 

25 at the city level and then pooled using either fixed or random effects models depending 

26 on whether heterogeneity among effect estimates was found to be statistically significant. 

27 Across cities, in an all-year analysis, the authors found that short-term O3 exposure was 

28 associated with an increase (4.7% [95% CI: -1.4, 11.1%] at lag 1 and 3.5% [95% CI: 

29 0.33, 6.8%] at lag 2 for a 20 ppb increase in 24-h avg O3 concentrations) in asthma ED 

30 visits. The authors did not present the results from seasonal analyses for asthma, but 

31 stated that no associations were observed between any pollutant and respiratory ED visits 

32 in the winter season. As stated previously, in analyses of 3-h avg O3 concentrations, the 

33 authors observed no evidence of consistent associations between any pollutant and any 

34 respiratory outcome, including asthma. A single-city study conducted in Alberta, Canada 

35 Villeneuve et al. (2007) from 1992-2002 among individuals two years of age and older 
Draft – Do Not Cite or Quote 6-153 June 2012

1 provides additional support for the findings from Stieb et al. (2009), but also attempts to 

2 identify those lifestages (i.e., 2-4, 5-14, 15-44, 45-64, 65-74, or 75+) at greatest risk to 

3 O3-induced asthma ED visits. In a time-referent case-crossover analysis, Villeneuve et al. 

4 found an increase in asthma ED visits in an all-year analysis across all ages (12.0% 

5 [95% CI: 6.8, 17.2] for a 30 ppb increase in max 8-h avg O3 concentrations at lag 0-2) 

6 with associations being stronger during the warmer months (19.0% [95% CI: 11.9, 28.1]). 

7 When stratified by age, the strongest associations were observed in the warm season for 

8 individuals 5-14 (28.1% [95% CI: 11.9, 45.1]; lag 0-2) and 15-44 (19.0% [95% CI: 8.5, 

9 31.8]; lag 0-2). These associations were not found to be confounded by the inclusion of 

10 aeroallergens in age-specific models.

11 Several additional single-city studies have also provided evidence of an association 

12 between asthma ED visits and ambient O3 concentrations. Ito et al. (2007b) examined the 

13 association between short-term exposure to air pollution and asthma ED visits for all ages 

14 in New York City from 1999 to 2002. Similar to Darrow et al. (2011a), when examining 

15 the spatial distribution of O3 concentrations, Ito et al. (2007b) found a rather homogenous 

16 distribution (r~≥ 0.80) when examining monitor-to-monitor correlations at distances up to 

17 20 miles. Ito et al. (2007b) used three different weather models with varying extent of 

18 smoothing to account for temporal relationships and multicollinearity among pollutants 

19 and meteorological variables (i.e., temperature and dew point) to examine the effect of 

20 model selection on the air pollutant-asthma ED visit relationship. When examining O3, 

21 the authors reported a positive association with asthma ED visits, during the warm season 

22 across the models (ranging from 8.6 to 16.9%) and an inverse association in the cool 

23 season (ranging from -23.4 to -25.1%), at lag 0-1 for a 30 ppb increase in 8-h max O3

24 concentrations. Ito et al. (2007b) conducted copollutant models using a simplified version 

25 of the weather model used in NMMAPS analyses (i.e., terms for same-day temperature 

26 and 1-3 day average temperature). The authors found that O3 risk estimates were not 

27 substantially changed in copollutant models that used every-day data for PM2.5, NO2, 

28 SO2, and CO during the warm season (Figure 6-19; Table 6-29).
Draft – Do Not Cite or Quote 6-154 June 2012

Note: The reference for the rate ratio is the estimated rate at the 5th percentile of the pollutant concentration. Estimates are 

presented for the 5th percentile through the 95th percentile of pollutant concentrations due to instability in the C-R estimates at the 

distribution tails.

Source: Reprinted with permission of American Thoracic Society (Strickland et al., 2010).

Figure 6-17 Loess C-R estimates and twice-standard error estimates from 

generalized additive models for associations between 8-h max 

3-day average ozone concentrations and ED visits for pediatric 

asthma.

1 Strickland et al. (2010) examined the association between O3 exposure and pediatric 

2 asthma ED visits (ages 5-17 years) in Atlanta between 1993 and 2004 using air quality 

3 data over the same years as Darrow et al. (2011a) and Tolbert et al. (2007). However, 

4 unlike Darrow et al. (2011a) and Tolbert et al. (2007), which used single centrally located 

5 monitors or an average of monitors, respectively, Strickland et al. (2010) used 

6 population-weighting to combine daily pollutant concentrations across monitors. In this 

7 study, the authors developed a statistical model using hospital-specific time-series data 

8 that is essentially equivalent to a time-stratified case-crossover analysis (i.e., using 

9 interaction terms between year, month, and day-of-week to mimic the approach of 

10 selecting referent days within the same month and year as the case day). The authors 

11 observed a 6.4% (95% CI: 3.2, 9.6%) increase in ED visits for a 30 ppb increase in 

12 8-h max O3 concentrations at lag 0-2 in an all-year analysis. In seasonal analyses, 

13 stronger associations were observed during the warm season (i.e., May-October) (8.4% 

14 [95% CI: 4.4, 12.7%]; lag 0-2) than the cold season (4.5% [95% CI: -0.82, 10.0%]; lag 0-

15 2). Strickland et al. (2011) confirmed these findings in an additional analysis using the 

16 same dataset, and found that the exposure assignment approach used (i.e., centrally 
Draft – Do Not Cite or Quote 6-155 June 2012

1 located monitor, unweighted average across monitors, and population-weighted average 

2 across monitors) did not influence pediatric asthma ED visit risk estimates for spatially 

3 homogeneous pollutants such as O3.

4 In copollutant analyses conducted over the entire dataset for the gaseous pollutants 

5 (i.e., (CO, NO2), and limited to a subset of years (i.e., 1998-2004) for which daily PM 

6 data (i.e., PM2.5 elemental carbon, PM2.5 sulfate) were available, Strickland et al. (2010)

7 found that O3 risk estimates were not substantially changed when controlling for other 

8 pollutants (results not presented quantitatively). The authors also examined the C-R 

9 relationship between O3 exposure and pediatric asthma ED visits and found that both 

10 quintile and loess C-R analyses (Figure 6-17) suggest that there are elevated associations 

11 with O3 at 8-h max concentrations as low as 30 ppb. These C-R analyses do not provide 

12 evidence of a threshold level.

13 In a single-city study conducted on the West coast, Mar and Koenig (2009) examined the 

14 association between O3 exposure and asthma ED visits (ICD-9 codes: 493-493.9) for 

15 children (<18) and adults (≥ 18) in Seattle, WA from 1998 to 2002. Of the total number 

16 of visits over the study duration, 64% of visits in the age group <18 comprised boys, and 

17 70% of visits in the ≥ 18 age group comprised females. Mar and Koenig (2009)

18 conducted a time-series analysis using both 1-h max and max 8-h avg O3 concentrations. 

19 A similar magnitude and pattern of associations was observed at each lag examined using 

20 both metrics. Mar and Koenig (2009) presented results for single day lags of 0 to 5 days, 

21 but found consistent positive associations across individual lag days which supports the 

22 findings from the studies discussed above that examined multi-day exposures. For 

23 children, consistent positive associations were observed across all lags, ranging from a 

24 19.1-36.8% increase in asthma ED visits for a 30 ppb increase in 8-h max O3

25 concentrations with the strongest associations observed at lag 0 (33.1% [95% CI: 3.0, 

26 68.5]) and lag 3 (36.8% [95% CI: 6.1, 77.2]). O3 was also found to be positively 

27 associated with asthma ED visits for adults at all lags, ranging from 9.3-26.0%, except at 

28 lag 0. The slightly different lag times for children and adults suggest that children may be 

29 more immediately responsive to O3 exposures than adults Mar and Koenig (2009). 

Respiratory Infection

30 Although an increasing number of studies have examined the association between O3

31 exposure and cause-specific respiratory ED visits this trend has not included an extensive 

32 examination of the association between O3 exposure and respiratory infection ED visits. 

33 Stieb et al. (2009) also examined the association between short-term O3 exposure and 

34 respiratory infection ED visits in 7 Canadian cities. In an all-year analysis, there was no 

35 evidence of an association between O3 exposure and respiratory infection ED visits at any 

36 lag examined (i.e., 0, 1, and 2). Across cities, respiratory infections comprised the single 
Draft – Do Not Cite or Quote 6-156 June 2012

1 largest diagnostic category, approximately 32%, of all the ED visits examined, which 

2 also included myocardial infarction, heart failure, dysrhythmia, asthma, and COPD.

6.2.7.4 Outpatient and Physician Visit Studies

3 Several studies have examined the association between ambient O3 concentrations and 

4 physician or outpatient (non-hospital, non-eD) visits for acute conditions in various 

5 geographic locations. Burra et al. (2009) examined asthma physician visits among 

6 patients aged 1-17 and 18-64 years in Toronto, Canada from 1992 to 2001. The authors 

7 found little or no evidence of an association between asthma physician visits and O3; 

8 however, seasonal analyses were not conducted. It should be noted that in this study, 

9 most of the relative risks for O3 were less than one and statistically significant, perhaps 

10 indicating an inverse correlation with another pollutant or an artifact of the strong 

11 seasonality of asthma visits. Villeneuve et al. (2006b) also focused on physician visits to 

12 examine the effect of short-term O3 exposure on allergic rhinitis among individuals aged 

13 65 or older in Toronto from 1995 to 2000. The authors did not observe any evidence of 

14 an association between allergic rhinitis physician visits and ambient O3 concentrations in 

15 single-day lag models in an all-year analysis (results not presented quantitatively). 

16 In a study conducted in Atlanta, Sinclair et al. (2010) examined the association of acute 

17 asthma and respiratory infection (e.g., upper respiratory infections and lower respiratory 

18 infections) outpatient visits from a managed care organization with ambient O3

19 concentrations as well as multiple PM size fractions and species from August 1998 

20 through December 2002. The authors separated the analysis into two time periods (the 

21 first 25 months of the study period and the second 28 months of the study period), in 

22 order to compare the air pollutant concentrations and relationships between air pollutants 

23 and acute respiratory visits for the 25-month time-period examined in Sinclair and 

24 Tolsma (2004) to an additional 28-month time-period of available data from the Atlanta 

25 Aerosol Research Inhalation Epidemiology Study (ARIES). The authors found little 

26 evidence of an association between O3 and asthma visits, for either children or adults, or 

27 respiratory infection visits in all-year analyses and seasonal analyses. For example, a 

28 slightly elevated relative risk (RR) for childhood asthma visits was observed during the 

29 25-month period in the cold season (RR: 1.12 [95% CI: 0.86, 1.41]; lag 0-2 for a 30 ppb 

30 increase in 8-h max O3), but not in the warm season (RR: 0.97 [95% CI: 0.86, 1.10]; lag 

31 0-2). During the 28-month period at lag 0-2, a slightly larger positive effect was observed 

32 during the warm season (RR: 1.06 [95% CI: 0.97, 1.17]), compared to the cold season 

33 (RR: 1.03 [95% CI: 0.87, 1.21]). Overall, these results contradict those from Strickland et 

34 al. (2010) discussed above. Although the mean number of asthma visits and O3

35 concentrations in Sinclair et al. (2010) and Strickland et al. (2010) are similar the 
Draft – Do Not Cite or Quote 6-157 June 2012

1 difference in results between the two studies could potentially be attributed to the severity 

2 of O3-induced asthma exacerbations (i.e., more severe symptoms requiring a visit to a 

3 hospital) and behavior, such as delaying a visit to the doctor for less severe symptoms. 

6.2.7.5 Summary

4 The results of the recent studies evaluated largely support the conclusion of the 2006 O3

5 AQCD. While fewer studies were published overall since the previous review, several 

6 multicity studies (e.g., Cakmak et al., 2006b; Dales et al., 2006) and a multi-continent 

7 study (Katsouyanni et al., 2009) provide supporting evidence for an association between 

8 short-term O3 exposure and an increase in respiratory-related hospital admissions and ED 

9 visits. Across studies, different ICD-9 codes were used to define total respiratory causes, 

10 which may contribute to some heterogeneity in the magnitude of association.These 

11 findings are supported by single-city studies that used different exposure assignment 

12 approaches (i.e., average of multiple monitors, single monitor, population-weighted 

13 average) and averaging times (i.e., 1-h max and 8-h max). 

14 Collectively, in both single-city and multicity studies there is continued evidence for 

15 increases in both hospital admissions and ED visits when examining all respiratory 

16 outcomes combined. Additionally, recent studies published since the 2006 O3 AQCD 

17 support an association between short-term O3 exposure and asthma (Strickland et al., 

18 2010; Stieb et al., 2009) and COPD (Stieb et al., 2009; Medina-Ramon et al., 2006)

19 hospital admissions and ED visits, with more limited evidence for pneumonia-hospital 

20 admissions and ED visits (Medina-Ramon et al., 2006; Zanobetti and Schwartz, 2006). 

21 As with total respiratory causes, studies used slightly different ICD-9 codes to define 

22 specific conditions. In seasonal analyses, stronger associations were observed in the 

23 warm season or summer months compared to the cold season, particularly for asthma 

24 (Strickland et al., 2010; Ito et al., 2007b) and COPD (Medina-Ramon et al., 2006)

25 (Figure 6-18; Table 6-28), which is consistent with the conclusions of the 2006 O3

26 AQCD. There is also continued evidence that children are particularly at greatest risk to 

27 O3-induced respiratory effects (Silverman and Ito, 2010; Strickland et al., 2010; Mar and 

28 Koenig, 2009; Villeneuve et al., 2007; Dales et al., 2006). Of note, the consistent 

29 associations observed across studies for short-term O3 exposure and respiratory-related 

30 hospital admissions and ED visits was not supported by studies that focused on 

31 respiratory-related outpatient or physician visits. These differences could potentially be 

32 attributed to the severity of O3-induced respiratory effects requiring more immediate 

33 treatment or behavioral factors that result in delayed visits to a physician. Although the 

34 collective evidence across studies indicates a consistent positive association between O3

35 exposure and respiratory-related hospital admissions and ED visits, the magnitude of 
Draft – Do Not Cite or Quote 6-158 June 2012

1 these associations may be underestimated due to behavioral modification in response to 

2 forecasted air quality (Neidell and Kinney, 2010; Neidell, 2009) (Section 4.6.5).

3 The studies that examined the potential confounding effects of copollutants found that O3

4 effect estimates remained relatively robust upon the inclusion of PM (measured using 

5 different sampling strategies ranging from every-day to every-6th day) and gaseous 

6 pollutants in two-pollutant models (Figure 6-19; Table 6-29). Additional studies that 

7 conducted copollutant analyses, but did not present quantitative results, also support these 

8 conclusions (Strickland et al., 2010; Tolbert et al., 2007; Medina-Ramon et al., 2006). 

9 Overall, recent studies provide copollutant results that are consistent with the studies 

10 evaluated in the 2006 O3 AQCD [(U.S. EPA, 2006b), Figure 7-12, page 7-80 of the 2006 

11 O3 AQCD], which found that O3 respiratory hospital admissions risk estimates remained 

12 robust to the inclusion of PM in copollutant models. 

Note: Effect estimates are for a 20 ppb increase in 24-h; 30 ppb increase in 8-h max; and 40 ppb increase in 1-h max O3

concentrations. HA=hospital admission; ED=emergency department. Black=All-year analysis; Red=Summer only analysis; 

Blue=Winter only analysis. 

a Wheeze used as indicator of lower respiratory disease.

b APHENA-Canada results standardized to approximate IQR of 5.1 ppb for 1-h max O3 concentrations.

c Study included 8 cities; but of those 8, only 4 had O3 data.

d non-ICU effect estimates.

e The study did not specify the lag day of the summer season estimate.

Figure 6-18 Percent increase in respiratory-related hospital admission and ED 

visits in studies that presented all-year and/or seasonal results.

Study

Wong et al. (2009)

Cakmak et al. (2006)

Dales et al. (2006)

Orazzo et al. (2009)a

Katsouyanni et al. (2009)

Darrow et al. (2009)

Tolbert et al. (2007)

Biggeri et al. (2005)c

Katsouyanni et al. (2009)

Stieb et al. (2009)

Villeneuve et al. (2007)

Strickland et al. (2010)

Silverman and Ito (2010)d

Ito et al. (2007)

Villeneuve et al. (2007)

Mar and Koenig (2009)

Strickland et al. (2010)

Silverman and Ito (2010)d

Mar and Koenig (2009)

Ito et al. (2007)

Villeneuve et al. (2007)

Strickland et al. (2010)

Wong et al. (2009)

Stieb et al. (2009)

Yang et al. (2006)

Medina-Ramon et al. (2006) Stieb et al. (2009)e

Medina-Ramon et al. (2006)

Zanobetti and Schwartz (2006)

Medina-Ramon et al. (2006)

Location

Hong Kong 10 Canadian cities

11 Canadian cities 6 Italian cities

APHENA-Europe APHENA-U.S. APHENA-Canada APHENA-Canada Atlanta

Atlanta 8 Italian cities

APHENA-Europe APHENA-U.S. APHENA-Canada APHENA-Canada

7 Canadian Cities Alberta, CAN Atlanta

New York

New York

Alberta, CAN

Seattle, WA Atlanta

New York

Seattle, WA

New York

Alberta, CAN Atlanta

Hong Kong 7 Canadian Cities Vancouver

36 U.S. cities 7 Canadian Cities 36 U.S. cities

36 U.S. cities

Boston 36 U.S. cities

36 U.S. cities

36 U.S. cities

Age

All

All 0-27 days 

0-2 65+

65+

65+

65+

All 

All

All

65+

65+

65+

65+

All

> 2 Children All

All

> 2

18+ Children

6-18

<18

All

> 2 Children

All

All

65+

65+

All

65+

65+

65+

65+

65+

65+

Respiratory

Asthma

COPD

Pneumonia

◄

►

►

►

►

►

Lag

0-1 1.2

2

0-6 0-1 0-1 DL (0-2) DL (0-2)b 1

0-2 0-3 0-1 0-1 DL (0-2) DL (0-2)b

2

0-2 0-2 0-1 0-1 0-2

2

0-2 0-1

0

0-1 0-2 0-2

0-1

2

0-3 DL (0-1) NR DL (0-1) DL (0-1)

0-1 DL (0-1) DL (0-1) DL (0-1)

Visit Type

HA

HA

HA

ED

HA

HA

HA

HA

ED

ED

HA

HA

HA

HA

HA

ED

ED

ED

HA

ED

ED

ED

ED

HA

ED

ED

ED

ED

HA

ED

HA

HA

ED

HA

HA

HA

HA

HA

HA

-25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40

% Increase
Draft – Do Not Cite or Quote 6-159 June 2012

Table 6-28 Corresponding Effect Estimates for Figure 6-18.

Study* ED Visit or 

Hospital 

Admission 

Location Age Lag Avg Time % Increase

(95% CI)

Respiratory

All-year

Wong et al. (2009) Hospital 

Admission

Hong Kong All 0-1 8-h max 3.58 (1.90, 5.29)

Cakmak et al. (2006b) Hospital 

Admission

10 Canadian cities All 1.2 24-h avg 4.38 (2.19, 6.46)

Dales et al. (2006) Hospital 

Admission

11 Canadian cities 0-27 days 2 24-h avg 5.41 (2.88, 7.96)

Orazzo et al. (2009)

a ED Visit 6 Italian cities 0-2 0-6 8-h max -3.34 (-11.2, 5.28)

Katsouyanni et al. (2009) Hospital 

Admission

APHENA-europe 65+ 0-1 1-h max 1.58 (-1.71, 4.15)

APHENA-U.S. 65+ 0-1 1-h max 2.38 (0.00, 4.89)

APHENA-Canada 65+ DL(0-2) 1-h max 20.4 (4.07, 40.2)

APHENA-Canada 65+ DL(0-2)b 1-h max 2.4 (0.51, 4.40)

Warm

Darrow et al. (2011a) ED Visit Atlanta All 1 8-h max 2.08 (1.25, 2.91)

Tolbert et al. (2007) ED Visit Atlanta All 0-2 8-h max 3.90 (2.70, 5.20)

Biggeri et al. (2005)

c Hospital 

Admission

8 Italian cities All 0-3 8-h max 0.06 (-5.24, 5.66)

Katsouyanni et al. (2009) Hospital 

Admission

APHENA-europe 65+ 0-1 1-h max 0.24 (-3.32, 3.91)

APHENA-U.S. 65+ 0-1 1-h max 2.14 (-0.63, 4.97)

APHENA-Canada 65+ DL(0-2) 1-h max 37.1 (11.5, 67.5)

APHENA-Canada 65+ DL(0-2)b 1-h max 4.1 (1.40, 6.80)

Asthma

All-year

Stieb et al. (2009) ED Visit 7 Canadian cities All 2 24-h avg 3.48 (0.33, 6.76)

Villeneuve et al. (2007) ED Visit Alberta, CAN >2 0-2 8-h max 11.9 (6.8, 17.2)

Strickland et al. (2010) ED Visit Atlanta Children 0-2 8-h max 6.38 (3.19, 9.57)

Warm

Silverman and Ito (2010)

d Hospital 

Admission

New York All 0-1 8-h max 12.5 (8.27, 16.7)

Ito et al. (2007b) ED Visit New York All 0-1 8-h max 16.9 (10.9, 23.4)

Villeneuve et al. (2007) ED Visit Alberta, CAN >2 0-2 8-h max 19.0 (11.9, 28.1)

Mar and Koenig (2009) ED Visit Seattle, WA 18+ 2 8-h max 19.1 (3.00, 40.5)

Strickland et al. (2010) ED Visit Atlanta Children 0-2 8-h max 8.43 (4.42, 12.7)

Silverman and Ito (2010)

d Hospital 

Admission

New York 6-18 0-1 8-h max 28.2 (15.3, 41.5)

Mar and Koenig (2009) ED Visit Seattle, WA <18 0 8-h max 33.1 (3.00, 68.5)
Draft – Do Not Cite or Quote 6-160 June 2012

Study* ED Visit or 

Hospital 

Admission 

Location Age Lag Avg Time % Increase

(95% CI)

Cold

Ito et al. (2007b) ED Visit New York All 0-1 8-h max -23.4 (-27.3, -19.3)

Villeneuve et al. (2007) ED Visit Alberta, CAN >2 0-2 8-h max 8.50 (0.00, 17.2)

Strickland et al. (2010) ED Visit Atlanta Children 0-2 8-h max 4.52 (-0.82, 10.1)

COPD

All-year

Stieb et al. (2009) ED Visit 7 Canadian cities All 2 24-h avg 4.03 (-0.54, 8.62)

Medina-Ramon et al. (2006) Hospital 

Admission

36 U.S. cities 65+ 0-1 8-h max 0.24 (-0.78, 1.21)

Yang et al. (2005b) Hospital 

Admission

Vancouver 65+ 0-3 24-h avg 8.80 (-12.5, 32.6)

Warm

Stieb et al. (2009)

e ED Visit 7 Canadian cities All NR 24-h avg 6.76 (0.11, 13.9)

Medina-Ramon et al. (2006) Hospital 

Admission

36 U.S. cities 65+ 0-1 8-h max 1.63 (0.48, 2.85)

Cold

Medina-Ramon et al. (2006) Hospital 

Admission

36 U.S. cities 65+ 0-1 8-h max -1.85 (-3.60, -0.06)

Pneumonia

All-year

Zanobetti and Schwartz 

(2006)

Hospital 

Admission

Boston 65+ 0-1 24-h avg -5.96 (-11.1, -1.36)

Medina-Ramon et al. (2006) Hospital 

Admission

36 U.S. cities 65+ 0-1 8-h max 1.81 (-0.72, 4.52)

Warm

Medina-Ramon et al. (2006) Hospital 

Admission

36 U.S. cities 65+ 0-1 8-h max 2.49 (1.57, 3.47)

Cold

Medina-Ramon et al. (2006) Hospital 

Admission

36 U.S. cities 65+ 0-1 8-h max -4.88 (-6.59, -3.14)

*Includes studies in Figure 6-18.

a

Wheeze used as indicator of lower respiratory disease.

b

APHENA-Canada results standardized to approximate IQR of 5.1 ppb for 1-h max O3 concentrations.

c

Study included 8 cities, but of those 8 only 4 had O3 data.

d

Non-ICU effect estimates.

e

The study did not specify the lag day of the summer season estimate.
Draft – Do Not Cite or Quote 6-161 June 2012

Notes: Effect estimates are for a 20 ppb increase in 24 hours; 30 ppb increase in 8-h max; and 40 ppb increase in 1-h max O3

concentrations. 

a

Studies that examined hospital admissions, 

b

A study that examined ED visits, 

c

Risk estimates from APHENA -Canada standardized to an approximate IQR of 5.1 ppb for a 1-h max increase in O3 concentrations. 

Black = results from single-pollutant models; Red = results from copollutant models with PM10 or PM2.5; Yellow = results from 

copollutant models with CO; Blue = results from copollutant models with NO2; Green = results from copollutant models with SO2.

Figure 6-19 Percent increase in respiratory-related hospital admissions and ED 

visits for studies that presented single and copollutant model 

results.

►

►

►

►

►

◄

◄

Copollutant

PM10

PM10

PM10

PM10

CO

NO2

SO2

PM10

CO

NO2

SO2

PM2.5

Lag

1

c

c

0-3

0-1

All-Year

Summer

Respiratory

COPD

Asthma

Location

APHENA-U.S.

APHENA-Europe

APHENA-Canada

Vancouver

New York

Age

65+

65+

All

Study

Katsouyanni et al. (2009)a

Yang et al. (2006)a

Ito et al. (2007)b

-10 -5 0 5 10 15 20 25 30

% Increase
Draft – Do Not Cite or Quote 6-162 June 2012

Table 6-29 Corresponding effect estimates for Figure 6-19.

Study*

,a Location Visit Type Age Lag Copollutant % Increase (95% CI)

All-year: Respiratory

Katsouyanni 

et al. (2009)

APHENA-U.S. Hospital 

Admission

65+ 1 2.62 (0.63, 4.64)

PM10 2.14 (-0.08, 4.40)

APHENA-europe 2.94 (1.02, 4.89)

PM10 2.38 (0.08, 4.64)

APHENACanada5.54 (-0.94, 12.4)

0.69 (-0.12, 1.50)b

PM10 5.13 (-6.62, 18.6)

PM10 0.64 (-0.87, 2.20)b

COPD

Yang et al. 

(2005b)

Vancouver Hospital 

Admission

65+ 0-3 8.80 (-12.5, 32.6)

CO 22.8 (-2.14, 50.7)

NO2 11.1 (-10.4, 37.6)

SO2 13.4 (-8.40, 40.2)

PM10 11.1 (-8.40, 37.6)

Summer: Asthma

Ito et al. 

(2007b)

New York ED All 0-1 16.9 (10.9, 23.4)

CO 18.1 (12.1, 24.5)

NO2 10.2 (4.29, 16.4)

SO2 13.1 (7.16, 19.5)

PM2.5 12.7 (6.37, 19.3)

*Studies include in Figure 6-19.

a

Averaging times: Katsouyanni et al. (2009) = 1-h max; Yang et al. (2005b) = 24-h avg; and Ito et al. (2007b) = 8-h max.

b

Risk estimates standardized to an approximate IQR of 5.1 ppb for a 1-h max increase in O3 concentrations.

1 To date only a few studies have examined the C-R relationship between short-term O3

2 exposure and respiratory-related hospital admissions and ED visits. A preliminary 

3 examination of the C-R relationship found no evidence of a deviation from linearity when 

4 examining the association between short-term O3 exposure and asthma hospital 

5 admissions (Silverman and Ito, 2010). Additionally, an examination of the C-R 

6 relationship for O3 exposure and pediatric asthma ED visits found no evidence of a 

7 threshold with elevated associations with O3 at concentrations as low as 30 ppb 

8 (Silverman and Ito, 2010; Strickland et al., 2010). However, in both studies there is 

9 uncertainty in the shape of the C-R curve at the lower end of the distribution of O3

10 concentrations due to the low density of data in this range.
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1 In totality, building upon the conclusions of the 2006 AQCD, the evidence from recent 

2 studies continues to support an association between short-term O3 exposure and 

3 respiratory-related hospital admissions and ED visits. Additional evidence also supports 

4 stronger associations during the warm season for specific respiratory outcomes such as 

5 asthma and COPD. 

6.2.8 Respiratory Mortality

6 The epidemiologic, controlled human exposure, and toxicological studies discussed 

7 within this section (Section 6.2) provides evidence for multiple respiratory effects in 

8 response to short-term O3 exposure. Additionally, the evidence from experimental studies 

9 indicates multiple potential pathways of O3-induced respiratory effects, which support the 

10 continuum of respiratory effects that could potentially result in respiratory-related 

11 mortality. The 2006 O3 AQCD found inconsistent evidence for an association between 

12 short-term O3 exposure and respiratory mortality (U.S. EPA, 2006b). Although some 

13 studies reported a strong positive association between O3 exposure and respiratory 

14 mortality, additional studies reported a small association or no association. The majority 

15 of recent multicity studies found consistent positive associations between short-term O3

16 exposure and respiratory mortality, specifically during the summer months. 

17 The APHENA study, described earlier in Section 6.2.7.2, (Katsouyanni et al., 2009) also

18 examined associations between short-term O3 exposure and mortality and found 

19 consistent positive associations for respiratory mortality in all-year analyses, except in the 

20 Canadian data set for ages ≥ 75, with an increase in the magnitude of associations in 

21 analyses restricted to the summer season across data sets and age ranges. Additional 

22 multicity studies from the U.S. (Zanobetti and Schwartz, 2008b), Europe (Samoli et al., 

23 2009), Italy (Stafoggia et al., 2010), and Asia (Wong et al., 2010) that conducted summer 

24 season and/or all-year analyses provide additional support for an association between 

25 short-term O3 exposure and respiratory mortality (Figure 6-36). 

26 Of the studies evaluated, only the APHENA study (Katsouyanni et al., 2009) and the 

27 Italian multicity study (Stafoggia et al., 2010) conducted an analysis of the potential for 

28 copollutant confounding of the O3-respiratory mortality relationship. In the APHENA 

29 study, specifically the European dataset, focused on the natural spline model with 

30 8 df/year (as discussed in Section 6.2.7.2) and lag 1 results (as discussed in 

31 Section 6.6.2.1), respiratory mortality risk estimates were robust to the inclusion of PM10

32 in copollutant models in all-year analyses with O3 respiratory mortality risk estimates 

33 increasing in the Canadian and U.S. datasets compared to single-pollutant model results. 

34 In summer season analyses, respiratory O3 mortality risk estimates were robust in the 
Draft – Do Not Cite or Quote 6-164 June 2012

1 U.S. dataset and attenuated in the European dataset. Similarly, in the Italian multicity 

2 study (Stafoggia et al., 2010), which was limited to the summer season, respiratory 

3 mortality risk estimates were attenuated in copollutant models with PM10. Based on the 

4 APHENA and Italian multicity results, O3 respiratory mortality risk estimates appear to 

5 be moderately to substantially sensitive (e.g., increased or attenuated) to inclusion of 

6 PM10. However, in the APHENA study, the mostly every-6th-day sampling schedule for 

7 PM10 in the Canadian and U.S. datasets greatly reduced their sample size and limits the 

8 interpretation of these results. 

6.2.9 Summary and Causal Determination

9 The 2006 O3 AQCD concluded that there was clear, consistent evidence of a causal 

10 relationship between short-term O3 exposure and respiratory effects (U.S. EPA, 2006b). 

11 This conclusion was substantiated by evidence from controlled human exposure and 

12 toxicological studies indicating a range of respiratory effects in response to short-term O3

13 exposure, including pulmonary function decrements and increases in respiratory 

14 symptoms, lung inflammation, lung permeability, and airway hyperresponsiveness. 

15 Toxicological studies provided additional evidence for O3-induced impairment of host 

16 defenses. Combined, these findings from experimental studies provided support for

17 epidemiologic evidence, in which short-term increases in O3 concentration were 

18 consistently associated with decreases in lung function in populations with increased 

19 outdoor exposures, children with asthma, and healthy children; increases in respiratory 

20 symptoms and asthma medication use in children with asthma; and increases in 

21 respiratory-related hospital admissions and asthma-related ED visits. Short-term 

22 increases in ambient O3 concentration also were consistently associated with increases in 

23 all-cause and cardiopulmonary mortality; however, the contribution of respiratory causes 

24 to these findings was uncertain.

25 Building on the large body of evidence presented in the 2006 O3 AQCD, recent studies 

26 support associations between short-term O3 exposure and respiratory effects. Controlled 

27 human exposure studies continue to provide the strongest evidence for lung function 

28 decrements in young healthy adults over a range of O3 concentrations. Studies previously 

29 reported mean O3-induced FEV1 decrements of 6-8% at 80 ppb O3 (Adams, 2006a, 

30 2003a; McDonnell et al., 1991; Horstman et al., 1990), and recent evidence additionally 

31 indicates mean FEV1 decrements of 6% at 70 ppb O3 (Schelegle et al., 2009) and 2-3% at 

32 60 ppb O3 (Kim et al., 2011; Brown et al., 2008; Adams, 2006a) (Section 6.2.1.1). In 

33 healthy young adults, O3-induced decrements in FEV1 do not appear to depend on sex 

34 (Hazucha et al., 2003), body surface area or height (McDonnell et al., 1997), lung size or 

35 baseline FVC (Messineo and Adams, 1990). There is limited evidence that blacks may 
Draft – Do Not Cite or Quote 6-165 June 2012

1 experience greater O3-induced decrements in FEV1 than do age-matched whites (Que et 

2 al., 2011; Seal et al., 1993). Healthy children experience similar spirometric responses 

3 but lesser symptoms from O3 exposure relative to young adults (McDonnell et al., 

4 1985a). On average, spirometric and symptom responses to O3 exposure appear to decline 

5 with increasing age beyond about 18 years of age (McDonnell et al., 1999b; Seal et al., 

6 1996). There is also a tendency for slightly increased spirometric responses in mild 

7 asthmatics and allergic rhinitics relative to healthy young adults (Jorres et al., 1996).

8 Spirometric responses in asthmatics appear to be affected by baseline lung function, 

9 i.e., responses increase with disease severity (Horstman et al., 1995).

10 Available information from controlled human exposure studies on recovery from O3

11 exposure indicates that an initial phase of recovery in healthy individuals proceeds 

12 relatively rapidly, with acute spirometric and symptom responses resolving within about 

13 2 to 4 hours (Folinsbee and Hazucha, 1989). Small residual lung function effects are 

14 almost completely resolved within 24 h. Effects of O3 on the small airways persisting 

15 a day following exposure, assessed by persistent decrement in FEF25-75% and altered 

16 ventilation distribution, may be due in part to inflammation (Frank et al., 2001; Foster et 

17 al., 1997). In more responsive individuals, this recovery in lung function takes longer (as 

18 much as 48 hours) to return to baseline. Some cellular responses may not return to 

19 baseline levels in humans for more than 10-20 days following O3 exposure (Devlin et al., 

20 1997). Airway hyperresponsiveness and increased epithelial permeability are also 

21 observed as late as 24 hours postexposure (Que et al., 2011). 

22 With repeated O3 exposures over several days, spirometric and symptom responses 

23 become attenuated in both healthy individuals and asthmatics, but this attenuation is lost 

24 after about a week without exposure (Gong et al., 1997a; Folinsbee et al., 1994; Kulle et 

25 al., 1982). Airway responsiveness also appears to be somewhat attenuated with repeated 

26 O3 exposures in healthy individuals, but becomes increased in individuals with 

27 preexisting allergic airway disease (Gong et al., 1997a; Folinsbee et al., 1994). Some 

28 indicators of pulmonary inflammation are attenuated with repeated O3 exposures. 

29 However, other markers such as epithelial integrity and damage do not show attenuation, 

30 suggesting continued tissue damage during repeated O3 exposure (Devlin et al., 1997).

31 Consistent with controlled human exposure study findings, epidemiologic evidence 

32 indicates that lung function decrements are related to short-term increases in ambient O3

33 concentration (Section 6.2.1.2). As described in the 1996 and 2006 O3 AQCDs, the most 

34 consistent observations were those in populations engaged in outdoor recreation, 

35 exercise, or work. Epidemiologic evidence also demonstrates that increases in ambient O3

36 concentration are associated with decreases in lung function in children with asthma 

37 (Figure 6-6 and Figure 6-7 and Table 6-8 and Table 6-9) and children without asthma 
Draft – Do Not Cite or Quote 6-166 June 2012

1 (Figure 6-8 and Table 6-12). Evidence in adults with respiratory disease and healthy 

2 adults is inconsistent. In children with asthma, lung function mostly was found to 

decrease by <1-2% per unit increase in O3 concentration1 3 . However, in children with 

4 asthma, O3-associated lung function decrements were found in conjunction with O3-

5 assocated increases in respiratory symptoms (Just et al., 2002; Mortimer et al., 2002; 

6 Ross et al., 2002; Gielen et al., 1997; Romieu et al., 1997; Thurston et al., 1997; Romieu 

7 et al., 1996). Biological plausibility for O3-associated decrements in lung function in 

8 controlled human exposure, epidemiologic, and animal studies is provided by the well9 documented effects of O3 on activation of bronchial C-fibers (Section 5.3.2).

10 Across disciplines, studies have examined factors that may potentially increase the risk of 

11 O3-induced decrements in lung function. In the controlled human exposure studies, there 

12 is a large degree of intersubject variability in lung function decrements, symptomatic 

13 responses, pulmonary inflammation, airway hyperresponsiveness, and altered epithelial 

14 permeability in healthy adults exposed to O3 (Que et al., 2011; Holz et al., 2005; 

15 McDonnell, 1996). The magnitude of pulmonary inflammation, airway 

16 hyperresponsiveness, and increases in epithelial permeability do not appear to be 

17 correlated, nor are these responses to O3 correlated with changes in lung function, 

18 suggesting that different mechanisms may be responsible for these processes (Que et al., 

19 2011; Balmes et al., 1997; Balmes et al., 1996; Aris et al., 1995). However, these 

20 responses tend to be reproducible within a given individual over a period of several 

21 months indicating differences in the intrinsic responsiveness of individuals (Holz et al., 

22 2005; Hazucha et al., 2003; Holz et al., 1999; McDonnell et al., 1985b). Numerous 

23 reasons for differences in the risk of individuals to O3 exposure have been reported in the 

24 literature. These include dosimetric and mechanistic differences (Section 5.4). Further, 

25 evidence in all three disciplines suggests a role for antioxidant defenses (i.e., vitamin 

26 supplementation, genetic variants in oxidative metabolizing enzymes) in modulating 

27 respiratory responses to O3. The biological plausibility of these findings is provided by

28 the well-characterized evidence for O3 exposure leading to the formation of secondary 

29 oxidation products that subsequently activate neural reflexes that mediate lung function 

30 decrements (Section 5.3.2) and that initiate pulmonary inflammation (Section 5.3.3). 

31 Recent controlled human exposure studies (Section 6.2.3.1) and toxicological studies 

32 (Section 6.2.3.3) also continue to demonstrate lung injury and inflammatory responses 

33 upon O3 exposure. Evidence from more than a hundred toxicological studies clearly 

34 indicates that O3 induces damage and inflammation in the lung, and studies continue to 

35 elucidate the mechanistic pathways involved (Section 5.3). Though inflammation may 

36 resolve, continued cellular damage may alter the structure and function of pulmonary 

 1 Effect estimates were standardized to a 40-ppb increase for 1-h max O3, a 30-ppb increase for 8-h max O3, and a 20-ppb 

increase for 24-h avg O3.
Draft – Do Not Cite or Quote 6-167 June 2012

1 tissues. Recent controlled human studies support previous findings for pulmonary 

2 inflammation but demonstrate effects at 60 ppb O3, the lowest concentration evaluated. 

3 Building on the extensive experimental evidence, recent epidemiologic studies, most of 

4 which were conducted in Mexico City, indicate ambient O3-associated increases in 

5 pulmonary inflammation in children with asthma. Multiple studies examined and found 

6 increases in eNO (Berhane et al., 2011; Khatri et al., 2009; Barraza-Villarreal et al., 

7 2008). In subjects with asthma, these O3-associated increases in pulmonary inflammation 

8 were found concomitantly with O3-associated increases in respiratory symptoms (Khatri 

9 et al., 2009; Barraza-Villarreal et al., 2008). Although more limited in number, 

10 epidemiologic studies also found associations with cytokines such as IL-6 or IL-8 

11 (Barraza-Villarreal et al., 2008; Sienra-Monge et al., 2004), eosinophils (Khatri et al., 

12 2009), antioxidants (Sienra-Monge et al., 2004), and indicators of oxidative stress 

13 (Romieu et al., 2008) (Section 6.2.3.2). This epidemiologic evidence is coherent with 

14 results from controlled human exposure and toxicological studies that demonstrated an 

15 induction or reduction of these same endpoints after O3 exposure.

16 The evidence for O3-induced pulmonary inflammation and airway hyperresponsiveness, 

17 largely demonstrated in controlled human exposure and toxicological studies, provides 

18 mechanistic support for O3-associated increases in respiratory symptoms observed in both 

19 controlled human exposure and epidemiologic studies. Controlled human exposure 

20 studies of healthy, young adults demonstrate increases in respiratory symptoms induced 

21 by O3 exposures <80 ppb (Schelegle et al., 2009; Adams, 2006a) (Section 6.2.1.1). 

22 Adding to this evidence, epidemiologic studies find effects in children with asthma. 

23 Although the epidemiologic evidence was less consistent in the few available U.S. 

24 multicity studies (O'Connor et al., 2008; Schildcrout et al., 2006; Mortimer et al., 2002), 

25 the weight of evidence, provided by a larger body of single-city and -region studies, 

26 indicates that short-term increases in ambient O3 concentration are associated with 

27 increases in respiratory symptoms and asthma medication use in children with asthma 

28 (Section 6.2.4.1). Several epidemiologic studies found associations between ambient O3 

29 concentrations and respiratory symptoms in populations with asthma that also had a high 

30 prevalence of allergy (52-100%) (Escamilla-Nuñez et al., 2008; Feo Brito et al., 2007; 

31 Romieu et al., 2006; Just et al., 2002; Mortimer et al., 2002; Ross et al., 2002; Gielen et 

32 al., 1997). The strong evidence in populations with asthma and allergy is supported by 

33 observations of O3-induced inflammation in animal models of allergy (Section 6.2.3.3), 

34 and may be explained mechanistically by the action of O3 to sensitize bronchial smooth 

35 muscle to hyperreactivity and thus, potentially act as a primer for subsequent exposure to 

36 antigens such as allergens (Section 5.3.5).

37 Modification of innate and adaptive immunity is emerging as a mechanistic pathway 

38 contributing to the effects of O3 on asthma and allergic airways disease (Section 5.3.6). 
Draft – Do Not Cite or Quote 6-168 June 2012

1 While the majority of evidence comes from animal studies, controlled human exposure 

2 studies have found differences between asthmatics and healthy controls in O3-mediated 

3 innate and adaptive immune responses (Section 5.4.2.2), suggesting that these pathways 

4 may be relevant to humans and may lead to the induction and exacerbation of asthma 

5 (Alexis et al., 2010; Hernandez et al., 2010; Alexis et al., 2009; Bosson et al., 2003).

6 The subclinical and overt respiratory effects observed across disciplines, as described 

7 above, collectively provide support for epidemiologic studies that demonstrate 

8 consistently positive associations between short-term O3 exposure and respiratory-related 

9 hospital admissions and ED visits (Section 6.2.7). Consistent with evidence presented in 

10 the 2006 O3 AQCD, recent multicity studies and a multicontinent study (i.e., APHENA) 

11 (Katsouyanni et al., 2009) found risk estimates ranging from an approximate 1.6 to 5.4% 

12 increase in all respiratory-related hospital admissions and ED visits in all-year analyses 

13 for a unit increase in ambient O3 concentration (as described in Section 2.1). Positive 

14 associations persisted in analyses restricted to the summer season, but the magnitude 

15 varied depending on the study location (Figure 6-18). Compared with studies reviewed in 

16 the 2006 O3 AQCD, a larger number of recent studies examined hospital admissions and 

17 ED visits for specific respiratory outcomes. Although limited in number, both single- and 

18 multi-city studies found consistent, positive associations between short-term O3

19 exposures and asthma and COPD hospital admissions and ED visits, with more limited 

20 evidence for pneumonia. Consistent with the conclusions of the 2006 O3 AQCD, in 

21 studies that conducted seasonal analyses, risk estimates were elevated in the warm season 

22 compared to cold season or all-season analyses, specifically for asthma and COPD. 

23 Although recent studies did not include detailed age-stratified results, the increased risk 

24 of asthma hospital admissions (Silverman and Ito, 2010; Strickland et al., 2010; Dales et 

25 al., 2006) observed for children strengthens the conclusion from the 2006 O3 AQCD that 

26 children are potentially at increased risk of O3-induced respiratory effects (U.S. EPA, 

27 2006b). Although the C-R relationship has not been extensively examined, preliminary 

28 examinations found no evidence of a threshold between short-term O3 exposure and 

29 asthma hospital admissions and pediatric asthma ED visits, with uncertainty in the shape 

30 of the C-R curve at the lower limit of ambient concentrations in the U.S. (Silverman and 

31 Ito, 2010; Strickland et al., 2010). 

32 Recent evidence extends the potential range of well-established O3-associated respiratory 

33 effects by demonstrating associations between short-term ambient O3 exposure and 

34 respiratory-related mortality. In all-year analyses, a multicontinent (APHENA) and 

35 multicity (PAPA) study found consistent, positive associations with respiratory mortality 

36 with evidence of an increase in the magnitude of associations in analyses restricted to the 

37 summer months. Further, additional multicity studies conducted in the U.S. and Europe 
Draft – Do Not Cite or Quote 6-169 June 2012

1 provide evidence supporting stronger O3-respiratory mortality associations during the 

2 summer season (Section 6.2.8). 

3 Several studies of respiratory morbidity and mortality evaluated the potential 

4 confounding effects of copollutants, in particular, PM10, PM2.5, or NO2. In most cases, 

5 effect estimates remained robust to the inclusion of copollutants. In some studies of lung 

6 function and respiratory symptoms, larger effects were estimated for O3 when 

7 copollutants were added to models. Ozone effect estimates for respiratory-related hospital 

8 admissions and ED visits remained relatively robust upon the inclusion of PM and 

9 gaseous pollutants in two-pollutant models (Strickland et al., 2010; Tolbert et al., 2007; 

10 Medina-Ramon et al., 2006). Although copollutant confounding was not extensively 

11 examined in studies of cause-specific mortality, O3-respiratory mortality risk estimates 

12 remained positive but were moderately to substantially sensitive (e.g., increased or 

13 attenuated) to the inclusion of PM10 in copollutant models (Stafoggia et al., 2010; 

14 Katsouyanni et al., 2009). However, interpretation of these results requires caution due to 

15 the limited PM datasets used in these studies as a result of the every 3rd- or 6th-day PM 

16 sampling schedule employed in most cities. Together, these copollutant-adjusted findings 

17 across respiratory endpoints provide support for the independent effects of short-term 

18 exposures to ambient O3.

19 Across the respiratory endpoints examined in epidemiologic studies, associations were 

20 found using several different exposure assessment methods that likely vary in how well 

21 ambient O3 concentrations represent ambient exposures and between-subject variability 

22 in exposures. Evidence clearly demonstrated O3-associated lung function decrements in 

23 populations with increased outdoor exposures for whom ambient O3 concentrations 

24 measured on site of outdoor activity and/or at the time of outdoor activity have been more 

25 highly correlated and similar in magnitude to personal O3 exposures (Section 4.3.3). 

26 However, associations with respiratory effects also were found with ambient O3

27 concentrations expected to have weaker personal-ambient relationships, including those 

28 measured at home or school, measured at the closest site, averaged from multiple 

29 community sites, and measured at a single site. Overall, there was no clear indication that 

30 a particular method of exposure assessment produced stronger findings.

31 An additional consideration in the evaluation of the epidemiologic evidence is the impact 

32 of behavioral modifications on observed associations. A study demonstrated that the 

33 magnitude of O3-associated asthma hospitalizations in Los Angeles, CA was 

34 underestimated due to behavioral modification in response to forecasted air quality 

35 (Section 4.6.5). It is important to note that the study was limited to one metropolitan area 

36 and used air quality data for the years 1989-1997, when the O3 concentration that 

37 determines the designation of an O3 action day, was much higher than it is currently. 
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1 Both panel and time-series epidemiologic studies found increases in respiratory effects in 

2 association with increases in O3 concentrations using various exposure metrics 

3 (i.e., 24-h avg, 1-h max, and 8-h max O3 concentrations). However, for respiratory 

4 symptoms and pulmonary inflammation, a majority of studies examined and found 

5 associations with 1-h max or 8-h max and 8-h max or daytime avg O3, respectively. 

6 Within study comparisons of associations among various exposure metrics with lung 

7 function and respiratory symptoms yielded mixed evidence. Within some studies, larger 

8 effects were estimated for shorter O3 averaging times whereas in other studies, larger 

9 effects were estimated for longer averaging times or no difference was found among 

10 averaging times. Comparisons in a limited number of time-series studies indicate rather 

11 comparable risk estimates across exposure metrics with some evidence indicating that 

12 24-h avg O3 was associated with a smaller increase in risk of respiratory ED visits 

13 (Section 6.2.7.3). Overall, there was no indication that the consistency or magnitude of 

14 the observed association was stronger for a particular O3 exposure metric. In examination 

15 of the lag structure of associations, the weight of epidemiologic evidence for the range of 

16 respiratory endpoints supports associations with ambient O3 concentrations lagged 0 to 

17 1 day, which is consistent with the O3-induced respiratory effects observed in controlled 

18 human exposure studies. Several studies also found increased respiratory morbidity in 

19 association with O3 concentrations averaged over multiple days (2 to 5 days). Across 

20 respiratory endpoints examined in epidemiologic studies, there was not strong evidence 

21 that the magnitude of association was larger for any particular lag.

22 In summary, recent studies evaluated since the completion of the 2006 O3 AQCD support 

23 and expand upon the strong body of evidence that indicated a causal relationship between 

24 short-term O3 exposure and respiratory health effects. Controlled human exposure studies 

25 continue to demonstrate O3-induced decreases in FEV1 and pulmonary inflammation at 

26 concentrations as low as 60 ppb. Epidemiologic studies provide evidence that increases in 

27 ambient O3 exposure can result in lung function decrements, increases in respiratory 

28 symptoms, and pulmonary inflammation in children with asthma; increases in 

29 respiratory-related hospital admissions and ED visits; and increases in respiratory 

30 mortality. Recent toxicological studies demonstrating O3-induced inflammation, airway 

31 hyperresponsiveness, and impaired lung host defense have continued to support the 

32 biological plausibility for the O3-induced respiratory effects observed in the controlled 

33 human exposure and epidemiologic studies. Additionally, recent epidemiologic studies 

34 further confirm that respiratory morbidity and mortality associations are stronger during 

35 the warm/summer months and remain relatively robust after adjustment for copollutants. 

36 The recent evidence integrated across toxicological, controlled human exposure, and 

37 epidemiologic studies, along with the total body of evidence evaluated in previous 

38 AQCDs, is sufficient to conclude that there is a causal relationship between short39 term O3 exposure and respiratory health effects.
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6.3 Cardiovascular Effects

1 Overall, there have been a relatively small number of studies that have examined the 

2 potential effect of short-term O3 exposure on the cardiovascular system. This was 

3 reflected in the 1996 O3 AQCD by the limited discussion on possible O3-related 

4 cardiovascular effects. The 2006 O3 AQCD (U.S. EPA, 2006b) built upon the limited 

5 evidence described in the 1996 O3 AQCD and further explored the potential relationship 

6 between short-term O3 exposure and cardiovascular outcomes. The 2006 O3 AQCD 

7 concluded that “O3 directly and/or indirectly contributes to cardiovascular-related 

8 morbidity” but added that the body of evidence was limited. This conclusion was based 

9 on a controlled human exposure study that included hypertensive adult males, a few 

10 epidemiologic studies of physiologic effects, heart rate variability, arrhythmias, 

11 myocardial infarctions, and hospital admissions, and toxicological studies of heart rate, 

12 heart rhythm, and blood pressure.

6.3.1 Controlled Human Exposure

13 O3 reacts rapidly on contact with respiratory system tissue and is not absorbed or 

14 transported to extrapulmonary sites to any significant degree as such. Controlled human 

15 exposure studies discussed in the previous AQCDs failed to demonstrate any consistent 

16 extrapulmonary effects. Some controlled human exposure studies have attempted to 

17 identify specific markers of exposure to O3 in blood. Buckley et al. (1975) reported a 

18 28% increase in serum α-tocopherol and a 26% increase in erythrocyte fragility in healthy 

19 males immediately following exposure to 500 ppb O3 for 2.75 hours with exercise 

20 (unspecified activity level). However, in healthy adult males exposed during exercise 

(V̇ 21 E=44 L/min) to 323 ppb O3 (on average) for 130 min on 3 consecutive days, Foster et 

22 al. (1996) found a 12% reduction in serum α-tocopherol 20 hours after the third day of O3

23 exposure. Liu et al. (1999); (1997) used a salicylate metabolite, 2,3, dehydroxybenzoic 

24 acid (DHBA), to indicate increased levels of hydroxyl radical which hydroxylates 

25 salicylate to DHBA. Increased DHBA levels after exposure to 120 and 400 ppb suggest 

26 that O3 increases production of hydroxyl radical. The levels of DHBA were correlated 

27 with changes in spirometry. Interestingly, simultaneous exposure of healthy adults to O3

28 (120 ppb for 2 hours at rest) and concentrated ambient particles (CAPs) resulted in a 

29 diminished systemic IL-6 response compared with exposure to CAPs alone (Urch et al., 

30 2010).

31 Gong et al. (1998) exposed hypertensive (n = 10) and healthy (n = 6) adult males, 41 to 

32 78 years of age, to FA and on the subsequent day to 300 ppb O3 for 3 hours with 

intermittent exercise (V̇ 33 E = 30 L/min). The overall results did not indicate any major acute 
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1 cardiovascular effects of O3 in either the hypertensive individuals or healthy controls. 

2 Statistically significant O3 effects for both groups combined were increases in heart rate, 

3 rate-pressure product, and the alveolar-to-arterial PO2 gradient, suggesting that impaired 

4 gas exchange was being compensated for by increased myocardial work. The mechanism 

5 for the decrease in arterial oxygen tension in the Gong et al. (1998) study could be due to 

6 an O3-induced ventilation-perfusion mismatch. Gong et al. (1998) suggested that by 

7 impairing alveolar-arterial oxygen transfer, the O3 exposure could potentially lead to 

8 adverse cardiac events by decreasing oxygen supply to the myocardium. The subjects in 

9 the Gong et al. (1998) study had sufficient functional reserve so as to not experience 

10 significant ECG changes or myocardial ischemia and/or injury. In studies evaluating the 

11 exercise performance of healthy adults, no significant effect of O3 on arterial O2

12 saturation has been observed (Schelegle and Adams, 1986).

13 Fakhri et al. (2009) evaluated changes in HRV among adult volunteers (n = 50; 

27 ± 7 years) during 2-hour exposures to PM2.5 CAPs (127 ± 62 μg/m3 14 ) and O3

15 (114 ± 7 ppb), alone and in combination. High frequency HRV was increased following 

16 CAPs-only (p = 0.046) and O3-only (p = 0.051) exposures, but not in combination. The 

17 standard deviation of NN intervals and the square root of the mean squared differences of 

18 successive NN intervals also showed marginally significant (0.05< p <0.10) increase due 

19 to O3 but not CAPS. Ten of the subjects in this study were characterized as “mildly” 

20 asthmatic, however, asthmatic status was not found to modify these effects. Power et al. 

21 (2008) also investigated HRV in a small group of mild-to-moderate allergic asthmatics 

22 (n = 5; mean age = 37 years) exposed for 4 hours during moderate intermittent exercise to 

FA, carbon and ammonium nitrate particles (313 ± 20 μg/m3 23 ), and carbon and ammonium 

nitrate particles (255 ± 37 μg/m3 24 ) + O3 (200 ppb). Changes in frequency-domain variables 

25 for the particle and particle + O3 exposures were not statistically significant compared 

26 with FA. Seemingly in contrast to Fakhri et al. (2009), the standard deviation of NN 

27 intervals and the square root of the mean squared differences of successive NN intervals 

28 also showed a significant (p = 0.01) decrease for both the particle and particle + O3

29 exposures relative to FA responses. Using a similar protocol, Sivagangabalan et al. 

30 (2011) concluded that spatial dispersion of cardiac repolarization was most affected by 

31 the combined pollutant exposure of CAP + O3 compared to FA in healthy adults. 

32 Diastolic blood pressure increased by 2 mmHg following the combined O3 + CAPs 

33 exposure, but was not altered by either O3 or CAPs alone in the Fakhri et al. (2009) study. 

34 For a subset of the subjects without asthma in the Fakhri et al. (2009) study, Urch et al. 

35 (2005) previously reported a 6 mmHg increase in diastolic blood pressure following a 

2-hour resting exposure to O3 (120 ppb) + PM2.5 CAPs (150 μg/m3 36 ) in healthy adults 

37 (n = 23; 32 ± 10 years), which was statistically different from the 1 mmHg increase seen 

38 following FA exposure. Brook et al. (2002) found O3 (120 ppb) + PM2.5 CAPs (150 
Draft – Do Not Cite or Quote 6-173 June 2012

μg/m3 1 ) in healthy adults (n = 25; 35 ± 10 years) caused brachial artery vasoconstriction. 

2 However, minimal change in diastolic blood pressure (0.9 mmHg increase) relative to FA 

3 (0.4 mmHg decrease) was observed. More recently, Sivagangabalan et al. (2011)

4 observed reported a 4.2 mmHg increase in diastolic blood pressure following a 2-hour 

resting exposure to O3 (110 ppb) + PM2.5 CAPs (150 μg/m3 5 ) in healthy adults (n = 25; 

6 27 ± 8 years), which was statistically different from the 1.7 mmHg increase seen 

7 following the FA exposure. The CAP exposure alone also caused a 3 mmHg increase in 

8 diastolic blood pressure which was significantly more than following FA. However, 

9 similar to FA, the O3 exposure alone caused a 1.8 mmHg increase in diastolic blood 

10 pressure. Overall, these studies indicate an effect of CAPs and CAP + O3, but not O3

11 alone, on diastolic blood pressure. 

6.3.2 Epidemiology

12 The 2006 O3 AQCD concluded that the “generally limited body of evidence is highly 

13 suggestive that O3 directly and/or indirectly contributes to cardiovascular-related 

14 morbidity,” including physiologic effects (e.g., release of platelet activating factor 

15 [PAF]), HRV, arrhythmias, and myocardial infarctions, although the available body of 

16 evidence reviewed during the 2006 O3 AQCD does not “fully substantiate links between 

17 ambient O3 exposure and adverse cardiovascular outcomes” (U.S. EPA, 2006b). Since 

18 the completion of the 2006 O3 AQCD an increasing number of studies have examined the 

19 relationship between short-term O3 exposure and cardiovascular morbidity and mortality. 

20 These recent studies, as well as evidence from the previous AQCDs, are presented within 

21 this section.

6.3.2.1 Arrhythmia 

22 In the 2006 O3 AQCD, conflicting results were observed when examining the effect of O3

23 on arrhythmias (Dockery et al., 2005; Rich et al., 2005). A study by Dockery et al. (2005)

24 reported no association between O3 concentration and ventricular arrhythmias among 

25 patients with implantable cardioverter defibrillators (ICD) living in Boston, MA, 

26 although when O3 concentration was categorized into quintiles, there was weak evidence 

27 of an association with increasing O3 concentration (median O3 concentration: 22.9 ppb). 

28 Rich et al. (2005) performed a re-analysis of this cohort using a case-crossover design 

29 and detected a positive association between O3 concentration and ventricular arrhythmias. 

30 Recent studies were conducted in various locations and each used a different cardiac 

31 episode to define an arrhythmic event and a different time period of exposure, which may 
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1 help explain observed differences across studies. Study-specific characteristics and air 

2 quality data for recent studies are reported in Table 6-30.

Table 6-30 Characterization of ozone concentrations (in ppb) from studies of 

arrhythmias.

Study* Location Averaging Time Mean Concentration 

(Standard Deviation)

Upper Range 

of Concentration

Metzger et al. (2007) Atlanta, GA 8-h max

Summer only

53.9 (23) Max: 148

Rich et al. (2006b) Boston, MA 1-h 22.2* 75th: 33

Max: 119.5

24-h 22.6* 75th: 30.9

Max: 77.5

Rich et al. (2006a) St. Louis, MO 24-h 21* 75th: 31

Anderson et al. (2010) London, England 8-h max 8.08 75th: 11.5

(Sarnat et al., 2006b) Steubenville, OH 24-h

Summer and Fall only

21.8 (12.6) 75th: 28.5

Max: 74.8

5 days 22.2 (9.1) 75th: 29.1

Max: 44

Note: Median presented (information on mean not given); studies presented in order of first appearance in the text of this section.

3 Multiple studies examined O3-related effects on individuals with ICDs. A study of 518 

4 ICD patients who had at least 1 tachyarrythmia within a 10-year period (totaling 6,287 

5 tachyarrhythmic event-days; 1993-2002) was conducted in Atlanta, Georgia (Metzger et 

6 al., 2007). Tachyarrhythmic events were defined as any ventricular tachyarrhythmic 

7 event, any ventricular tachyarrhythmic event that resulted in electrical therapy, and any 

8 ventricular tachyarrhythmic event that resulted in defibrillation. In the primary analysis, 

9 no evidence of an association was observed for a 30 ppb increase in 8-h max O3

10 concentrations and tachyarrhythmic events (OR: 1.00 [95% CI: 0.92, 1.08]; lag 0). 

11 Season-specific as well as several sensitivity analyses (including the use of an 

12 unconstrained distributed lag model [lags 0-6]) were conducted resulting in similar null 

13 associations.

14 In a case-crossover analysis, a population of ICD patients in Boston, previously examined 

15 by (Rich et al., 2005) was used to assess the association between air pollution and 

16 paroxysmal atrial fibrillation (PAF) episodes (Rich et al., 2006b). In addition to 

17 ventricular arrhythmias, ICD devices may also detect supraventricular arrhythmias, of 

18 which atrial fibrillation is the most common. Although atrial fibrillation is generally not 

19 considered lethal, it has been associated with increased premature mortality as well as 

20 hospitalization and stroke. Ninety-one electrophysiologist-confirmed episodes of PAF 
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1 were ascertained among 29 patients. An association (OR: 3.86 [95% CI: 1.44, 10.28] per 

2 40 ppb increase in 1-h max O3 concentrations) was observed between increases in O3

3 concentration during the concurrent hour (lag 0-h) and PAF episodes. The estimated OR 

4 for the 24-hour moving average concentration was elevated (OR: 1.81 [95% CI: 0.86, 

5 3.83] per 20 ppb), but weaker than the estimate for the shorter exposure window. The 

6 association between PAF and O3 concentration in the concurrent hour during the cold 

7 months was comparable to that during the warm months. In addition, no evidence of a 

8 deviation from linearity between O3 concentration and the log odds of PAF was observed. 

9 Authors report that the difference between O3 concentration and observed effect between 

10 this study (PAF and 1-hour O3) and their previous study (ventricular arrhythmias and 

11 24-hour moving average O3) (Rich et al., 2005) suggest a more rapid response to air 

12 pollution for PAF (Rich et al., 2006b).

13 In an additional study, Rich et al. (2006a) employed a case-crossover design to examine 

14 the association between air pollution and 139 confirmed ventricular arrhythmias among 

15 56 ICD patients in St Louis, Missouri. The authors observed a positive association with 

16 O3 concentration (OR: 1.17 [95% CI: 0.58, 2.38] per 20 ppb increase in 24-hour moving 

17 avg O3 concentrations [lags 0-23 hours]). Although the authors concluded these results 

18 were similar to their results from Boston (Rich et al., 2005), they postulated that the 

19 pollutants responsible for the increased risk in ventricular arrhythmias are different (O3

20 and PM2.5 in Boston and sulfur dioxide in St Louis). 

21 Anderson et al. (2010) used a case-crossover framework to assess air pollution and 

22 activation of ICDs among patients from all 9 ICD clinics in the London National Health 

23 Service hospitals. “Activation” was defined as tachycardias for which the defibrillator 

24 delivered treatment. Investigators modeled associations using unconstrained distributed 

25 lags from 0 to 5 days. The sample consisted of 705 patients with 5,462 activation days 

26 (O3 concentration information was for 543 patients and 4,092 activation days). Estimates 

27 for the association with O3 concentration were consistently positive, although weak (OR: 

28 1.09 [95% CI: 0.76, 1.55] per 30 ppb increase in 8-h max O3 concentrations at 0-1 day 

29 lag; OR: 1.04 [95% CI: 0.60, 1.81] per 30 ppb increase in 8-h max O3 concentrations at 

30 0-5 day lag) (Anderson et al., 2010). 

31 In contrast to arrhythmia studies conducted among ICD patients, Sarnat et al. (2006b)

32 recruited non-smoking adults (age range: 54-90 years) to participate in a study of air 

33 pollution and arrhythmias conducted over two 12-week periods during summer and fall 

34 of 2000 in a region characterized by industrial pollution (Steubenville, Ohio). Continuous 

35 ECG data acquired on a weekly basis over a 30-minute sampling period were used to 

36 assess ectopy, defined as extra cardiac depolarizations within the atria (supraventricular 

37 ectopy, SVE) or the ventricles (ventricular ectopy, VE). Increases in the 5-day moving 
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1 average (days 1-5) of O3 concentration were associated with an increased odds of SVE 

2 (OR: 2.17 [95% CI: 0.93, 5.07] per 20 ppb increase in 24-h avg O3 concentrations). A 

3 weaker association was observed for VE (OR: 1.62 [95% CI: 0.54, 4.90] per 20 ppb 

4 increase in 24-h avg O3 concentrations). The results of the effect of 5-day O3

concentration on SVE were robust to the inclusion of SO4

2- 5 in the model [OR: 1.62 

6 (95% CI: 0.54, 4.90)]. The authors indicate that the strong associations observed at the 

7 5-day moving averages, as compared to shorter time periods, suggests a relatively long8 acting mechanistic pathways, such as inflammation, may have promoted the ectopic beats 

9 in this population (Sarnat et al., 2006b).

10 Although many studies report positive associations, collectively, studies of arrhythmias 

11 report inconsistent results. This may be due to variation in study populations, length and 

12 season of averaging time, and outcome under study.

6.3.2.2 Heart Rate/Heart Rate Variability

13 In the 2006 O3 AQCD, two large population-based studies of air pollution and HRV were 

14 summarized (Park et al., 2005b; Liao et al., 2004a). In addition, the biological 

15 mechanisms and potential importance of HRV were discussed. Briefly, the study of acute 

16 effects of air pollution on cardiac autonomic control is based on the hypothesis that 

17 increased air pollution levels may stimulate the autonomic nervous system and lead to an 

18 imbalance of cardiac autonomic control characterized by sympathetic activation 

19 unopposed by parasympathetic control (U.S. EPA, 2006b). Examples of HRV indices 

20 include the standard deviation of normal-to-normal intervals (SDNN), the square root of 

21 the mean of the sum of the squares of differences between adjacent NN intervals (r22 MSSD), high-frequency power (HF), low-frequency power (LF), and the LF/HF ratio. 

23 Liao et al. (2004a) examined the association between air pollution and cardiac autonomic 

24 control in the fourth cohort examination (1996-1998) of the U.S.-based Atherosclerosis 

25 Risk in Communities Study. A decrease in log-transformed HF was associated with an 

26 increase in O3 concentration among white study participants. Park et al. (2005b)

27 examined the effects of air pollution on indices of HRV in a population-based study 

28 among men from the Normative Aging Study in Boston, Massachusetts. Several 

29 associations were observed with O3 concentration and HRV outcomes. A reduction in LF 

30 was associated with increased O3 concentration, which was robust to inclusion of PM2.5. 

31 The associations with all HRV indices and O3 concentration were stronger among those 

32 with ischemic heart disease and hypertension. In addition to the population-based studies 

33 included in the 2006 O3 AQCD was a study by Schwartz et al. (2005), who conducted a 

34 panel study to assess the relationship between exposure to summertime air pollution and 

35 HRV. A weak association of O3 concentration during the hour immediately preceding the 
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1 health measures was observed with r-MSSD among a study population that consisted of 

2 mostly older female participants. In summary, these studies suggest that short-term 

3 exposures to ambient O3 concentrations are predictors of decreased HRV and that the 

4 relationship may be stronger among certain subgroups. More recent studies that examined 

5 the association between O3 concentration and HRV are described below. Study-specific 

6 characteristics and O3 concentrations for these studies are presented in Table 6-31.

Table 6-31 Characterization of ozone concentrations (in ppb) from studies of 

heart rate variability.

Study* Location Averaging Time Mean Concentration 

(Standard Deviation)

Upper Range of 

Concentration

Park et al. (2007) Boston, MA 24-h Range of 17.0-29.1

Park et al. (2008) Boston, MA 24-h 23.4 (13)

Baja et al. (2010) Boston, MA 0 lag

10-h lag

23 (16)

21 (15)

Wheeler et al. (2006) Atlanta, GA 4-h

24-h

18.5

29.4

75th: 22.5

Zanobetti et al. (2010) Boston, MA 0.5-h

2-h

3-D

5-D

20.7*

20.5*

21.9*

22.8*

75th: 30.33

75th: 30.08

75th: 28.33

75th: 29.28

Chan et al. (2005a) Taipei, Taiwan 1-h 21.9 (15.4) Max: 114.9

Wu et al. (2010) Taipei, Taiwan Working period 24.9 (14.0) Max: 59.2

Ruidavets et al. (2005a) Toulouse, France 8-h max 38.3 (14.8) 75th: 46.9

Max: 80.3

Chuang et al. (2007a) Taipei, Taiwan 24-h

48-h

72-h

28.4 (12.1)

33.3 (8.9)

33.8 (7.1)

Max: 49.3

Max: 47.8

Max: 48.3

Chuang et al. (2007b) Taipei, Taiwan 1-h 35.1 Max: 192.0

*Note: Median presented (information on mean not given); studies presented in order of first appearance in the text of this section.

7 Several follow-up examinations of HRV were conducted among the participants of the 

8 Normative Aging Study in Boston. A trajectory cluster analysis was used to assess 

9 whether pollution originating from different locations had varying relationships with 

10 HRV (Park et al., 2007). Subjects who were examined on days when air parcels 

11 originated in the west had the strongest associations with O3; however, the O3

12 concentration in this cluster was low (24-h avg, 17.0 ppb) compared to the other clusters 

13 (24-h avg of 21.3-29.1 ppb). LF and SDNN decreased with increases in the 4-hour 

14 moving average of O3 concentration from the west (LF decreased by 51.2% [95% CI: 1.6, 

15 75.9%] and SDNN decreased by 28.2% [95% CI: -0.5, 48.7%] per 30 ppb increase in 

16 4-h avg O3 concentrations) (Park et al., 2007). The Boston air mass originating in the 
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1 west traveled over Illinois, Indiana, and Ohio; states typically characterized by coal2 burning power plants. Due to the low O3 concentrations observed in the west cluster, the 

3 authors hypothesize that O3 concentration on those days could be capturing the effects of 

4 other, secondary and/or transported pollutants from the coal belt or that the relationship 

5 between ambient O3 concentration and personal exposure to O3 is stronger during that 

6 period (supported by a comparatively low apparent temperature which could indicate a 

7 likelihood to keep windows open and reduced air conditioning use) (Park et al., 2007). 

8 An additional follow-up evaluation using the Normative Aging Study examined the 

9 potential for effect modification by chronic lead (Pb) exposure on the relationship 

10 between air pollution and HRV (Park et al., 2008). Authors observed graded reductions in 

11 HF and LF of HRV in relation to O3 (and sulfate) concentrations across increasing 

12 quartiles of tibia and patella lead (HF: percent change 32.3% [95% CI: -32.5, 159.3] for 

13 the first quartile of tibia Pb and -59.1 [95% CI: -77.3, -26.1] for the fourth quartile of 

14 tibia Pb per 30 ppb increase in 4-h avg O3 concentrations; LF: percent change 8.0% 

15 [95% CI: -36.9, 84.9] for the first quartile of tibia Pb and -59.3 [95% CI: -74.6, -34.8] for 

16 the fourth quartile of tibia Pb per 30 ppb increase in 4-h avg O3 concentrations). In 

17 addition, associations were similar when education and cumulative traffic-adjusted bone 

18 Pb levels were used in analyses. Authors indicate the possibility that O3 (which has low 

19 indoor concentrations) was acting as a proxy for sulfate (correlation coefficient for O3

20 and sulfate = 0.57). Investigators of a more recent follow-up to the Normative Aging 

21 Study hypothesized that the relationships between short-term air pollution exposures and 

22 ventricular repolarization, as measured by changes in the heart-rate corrected QT interval 

23 (QTc), would be modified by participant characteristics (e.g., obesity, diabetes, smoking 

24 history) and genetic susceptibility to oxidative stress (Baja et al., 2010). No evidence of 

25 an association between O3 concentration (using a quadratic constrained distributed lag 

26 model and hourly exposure lag models over a 10-hour time window preceding the visit) 

27 and QTc was reported (change in mean QTc -0.74 [95% CI: -3.73, 2.25]); therefore, 

28 potential effect modification of personal and genetic characteristics with O3 concentration 

29 was not assessed (Baja et al., 2010). Collectively, the results from studies that examined 

30 the Normative Aging Study cohort found an association between increases in short-term 

31 O3 concentration and decreases in HRV (Park et al., 2008; Park et al., 2007; Park et al., 

32 2005b) although not consistently in all of the studies (Baja et al., 2010). Further, observed 

33 relationships appear to be stronger among those with ischemic heart disease, 

34 hypertension, and elevated bone lead levels, as well as when air masses arrive from the 

35 west (the coal belt). However, it is not clear if O3 concentration is acting as a proxy for 

36 other, secondary particle pollutants (such as sulfate) (Park et al., 2008). In addition, since 

37 the Normative Aging Study participants were older, predominately white men, results 

38 may not be generalizable to the a large proportion of the U.S. population.
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1 Additional studies of populations not limited to the Normative Aging Study have also 

2 examined associations between O3 exposure and HRV. A panel study among 18 

3 individuals with COPD and 12 individuals with recent myocardial infarction (MI) was 

4 conducted in Atlanta, Georgia (Wheeler et al., 2006). HRV was assessed for each 

5 participant on 7 days in fall 1999 and/or spring 2000. Ozone concentrations were not 

6 associated with HRV (SDNN) among all subjects (percent change of 2.36% [95% CI: 

7 -10.8%, 17.5%] per 30 ppb 4-hour O3 increase) or when stratified by disease type 

8 (COPD, recent MI, and baseline FEV1) (Wheeler et al., 2006).

9 HRV and air pollution was assessed in a panel study among 46 predominately white male 

10 patients (study population: 80.4% male, 93.5% white) aged 43-75 years in Boston, 

11 Massachusetts, with coronary artery disease (Zanobetti et al., 2010). Up to four home 

12 visits were made to assess HRV over the year following the index event. Pollution lags 

13 used in analyses ranged between 30 minutes to a few hours and up to 5 days prior to the 

14 HRV assessments, calculated from hourly O3 measurements averaged over three 

15 monitoring sites in Boston. Decreases in r-MSSD were reported for all averaging times of 

16 O3 concentration (percent change of -5.18% [95% CI: -7.89, -2.30] per 20 ppb of 5-day 

17 moving average of O3 concentration), but no evidence of an association between O3

18 concentration and HF was observed (quantitative results not provided). In two-pollutant 

19 models with O3 and either PM2.5 or BC, O3 associations remained robust. 

20 A few recent studies were conducted outside of the U.S. that examined the relationship 

21 between air pollution concentrations and heart rate and HRV (Wu et al., 2010; Chuang et 

22 al., 2007b; Chuang et al., 2007a; Chan et al., 2005a; Ruidavets et al., 2005a). No 

23 associations were reported between O3 concentration and HRV among CHD patients and 

24 patients with one or more major CHD risk factors residing in Taipei, Taiwan (Chan et al., 

25 2005a). Another study in Taipei, Taiwan examined mail carriers and reported O3

26 concentration measured using personal monitors. No association was observed between 

27 O3 concentration and the measures of HRV (percent change for SDNN: 0.57 [95% CI: 

28 -21.27, 28.46], r-MSSD: -7.10 [95% CI: -24.24, 13.92], HF: -1.92 [95% CI: -23.68, 

29 26.02], LF: -4.82 [95% CI: -25.34, 21.35] per 40 ppb O3) (Wu et al., 2010). In addition, 

30 no consistent relationships were identified between O3 concentration and resting heart 

31 rate among middle-aged (35-64 years) participants residing in Toulouse, France 

32 (Ruidavets et al., 2005a). A negative trend was reported for the 3-day cumulative 

33 (lag days 1-3) concentration of 8-h max O3 with heart rate (p for trend = 0.02); however, 

34 the individual odds ratios comparing quintiles of exposure showed no association (OR for 

35 O3 concentraction of 0.93 [95% CI: 0.86, 1.01] for the highest quintile of resting heart rate 

36 compared to the lowest). When stratified by current smoking status, non-smokers had a 

37 decreased trend with increased 3-day cumulative O3 concentrations but none of the 

38 quintiles for heart rate were statistically significant. A panel study was conducted in 
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1 Taiwan to assess the relationship between air pollutants and inflammation, oxidative 

2 stress, blood coagulation, and autonomic dysfunction (Chuang et al., 2007b; Chuang et 

3 al., 2007a). Participants were apparently healthy college students (aged 18-25 year) who 

4 were living in a university dormitory in metropolitan Taipei. Health endpoints were 

5 measured three times from April to June in 2004 or 2005. Ozone concentration was 

6 assessed in statistical models using the average of the 24, 48, and 72 hours before the 

7 hour of each blood sampling. Decreases in HRV (measured as SDNN, r-MSSD, LF, and 

8 HF) were associated with increases in O3 concentrations in single-pollutant models 

9 (percent change for SDNN: -13.45 [95% CI: -16.26, -10.60], r-MSSD -13.76 [95% CI: 

10 -21.62, -5.44], LF -9.16 [95% CI: -13.29, -4.95], HF -10.76 [95% CI: -18.88, -2.32] per 

11 20 ppb cumulative 3-day avg O3 concentrations) and remained associated with 3-day O3

12 concentrations in two-pollutant models with sulfate. Another study in Taiwan recruited 

13 individuals with CHD or at risk for cardiovascular disease from outpatient clinics during 

14 the study period (two weeks in February) (Chuang et al., 2007b). No association was 

15 observed between O3 concentration and HRV measures (SDNN, r-MSSD, LF, HF) 

16 (numerical results not provided in publication).

17 Overall, studies of O3 concentration and HRV report inconsistent results. Multiple studies 

18 conducted in Boston observed positive associations but the authors of many of these 

19 studies postulated that O3 concentration was possibly acting as a proxy for other 

20 pollutants. The majority of other studies, both in the U.S. and internationally, report null 

21 findings. The inconsistencies observed are further complicated by the different HRV 

22 measures and averaging times used by the studies.

6.3.2.3 Stroke

23 The 2006 O3 AQCD did not identify any studies that examined the association between 

24 short-term O3 exposure and stroke. However, recent studies have attempted to examine 

25 this relationship. Lisabeth et al. (2008) used a time-series approach to assess the 

26 relationship between daily counts of ischemic stroke and transient ischemic attack (TIA) 

27 with O3 concentrations in a southeast Texas community among residents 45 years and 

28 older (2001-2005; median age of cases, 72 years). The median O3 concentration (hourly 

29 average per 24-hour time-period) was 25.6 ppb (IQR 18.1-33.8). The associations 

30 between same-day O3 concentrations and stroke/TIA risk were positive (RR: 1.03 

31 [95% CI: 0.96, 1.10] per 20 ppb increase in 24-h avg O3 concentrations) and previous-day 

32 (RR: 1.05 [95% CI: 0.99, 1.12] per 20 ppb increase in 24-h avg O3 concentrations). 

33 Associations were robust to adjustment for PM2.5. 
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1 A case-crossover design was used in a study conducted in Dijon, France between March 

2 1994 and December 2004, among those 40 years of age and older who presented with 

3 first-ever stroke (Henrotin et al., 2007). The mean O3 concentration, calculated over 

4 8-hour daytime periods, was 14.95 ppb (IQR: 6-22 ppb). No association was observed 

5 between O3 concentration at any of the single-day lags examined (i.e., 0-3 days) and 

6 hemorrhagic stroke. However, an association between ischemic stroke occurrence and O3

7 concentrations with a 1-day lag was observed (OR: 1.54 [95% CI: 1.14, 2.09] per 30 ppb 

8 increase in 8-h max O3 concentrations). The observed association between short-term O3

9 exposure and ischemic stroke persisted in two-pollutant models with PM10, SO2, NO2, or 

10 CO. This association was stronger among men (OR: 2.12 [95% CI: 1.36, 3.30] per 30 ppb 

11 increase in 8-h max O3 concentrations) than among women (OR: 1.17 [95% CI: 0.77, 

12 1.78] per 30 ppb increase in 8-h max O3 concentrations) in single pollutant models. When 

13 stroke was examined by subtype among men, an association was observed for ischemic 

14 strokes of large arteries and for transient ischemic attacks, but not for cardioembolic or 

15 lacunar ischemic strokes. The subtype analysis was not performed for women. 

16 Additionally, for men a linear exposure-response was observed when O3 concentration 

17 was assessed based on quintiles (p for trend = 0.01) (Figure 6-20). A potential limitation 

18 of this study is that 67.4% of the participating men were smokers compared to 9.3% of 

19 the women. 

20 Another case-crossover study performed in Dijon, France examined the association 

21 between O3 concentration and incidence of fatal and non-fatal ischemic cerebrovascular 

22 events (ICVE) (Henrotin et al., 2010). Mean 8-hour O3 concentration was 19.1 ppb (SD 

23 12.2 ppb). A positive association was observed between recurrent ICVE and 8-h O3

24 concentration with a 3-day lag (OR: 1.92 [95% CI 1.17, 3.12]), but not for other lags (0, 

25 1, 2, 4) or cumulative days (0-1, 0-2, 1-2, 1-3). Although some ORs for incident ICVEs 

26 were elevated, none were statistically significant. Results for associations using the 

27 maximum daily 1-hour O3 concentrations were similar to the 8-hour results but slightly 

28 attenuated. ORs were similar in two pollutant models with SO2, NO2, CO, and PM10 (data 

29 not given). In stratified analyses, the association between 1-day lagged O3 concentration 

30 and incident and recurrent ICVE was greater among individuals with diabetes or 

31 individuals with multiple preexisting vascular conditions. 
Draft – Do Not Cite or Quote 6-182 June 2012

Source: Henrotin et al. (2007).

Figure 6-20 Odds ratio (95% confidence interval) for ischemic stroke by 

quintiles of ozone exposure.

6.3.2.4 Biomarkers

1 An increasing number of studies have examined the relationship between air pollution 

2 and biomarkers in an attempt to elucidate the biological mechanisms linking air pollution 

3 and cardiovascular disease. A wide range of markers assessed as well as different types 

4 of study designs and locations chosen make comparisons across studies difficult. 

5 Table 6-32 provides an overview of the O3 concentrations reported in each of the studies 

6 evaluated.

0-8 9-20 21-32 33-48 48-115

0

0.5

1

1.5

2

2.5

3

3.5

O3 concentration (ppb)

Odds ratio (95% CI)
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Table 6-32 Characterization of ozone concentrations (in ppb) from studies of 

biomarkers.

Study* Location Averaging 

Time

Mean 

Concentration

(Standard 

Deviation)

Upper Range of 

Concentration

Liao et al. (2005) 3 U.S. counties 8-h 40 (20)

Thompson et al. 

(2010)

Toronto, Ontario 1-h / 1 yr 21.94 (15.78)

Rudez et al. (2009) Rotterdam, the Netherlands 24-h 22* 75th: 31.5

Max: 90

Chuang et al. 

(2007a)

Taipei, Taiwan 24-h 28.4 (12.1) Max: 49.3

48-h 33.3 (8.9) Max: 47.8

72-h 33.8 (7.1) Max: 48.3

Steinvil et al. (2008) Tel-Aviv, Israel 0.5-h 29.2 (9.7) 75th: 36

Chen et al. (2007a) Los Angeles and 

San Francisco, CA

8-h / 2 weeks 30.8* Max: 47.9

8-h / 1 mo 28.3* Max: 43.1

Wellenius et al. 

(2007)

Boston, MA 1-h / 24-h 25.1 (12.9)

Goldberg et al. 

(2008)

Montreal, Quebec 24-h NS

Baccarelli et al. 

(2007)

Lombardia, Italy 1-h 18.3* 75th: 35.1

Max: 202.3

Chuang et al. 

(2010)

Taiwan 26.83 (9.7) Max: 62.1

*Note: Median presented (information on mean not given); studies presented in order of first appearance in the text of this section.

Hemostasis and coagulation markers

1 Multiple studies used various markers to examine if associations were present between 

2 short-term O3 exposure and hemostasis and coagulation. Some of the markers included in 

3 these studies were as follows: fibrinogen, von Willebrand factor (vWF), plasminogen 

4 activator fibrinogen inhibitor-1 (PAI-1), tissue-type plasminogen activator (tPA), platelet 

5 aggregation, and thrombin generation.

6 A population-based study in the United States was conducted to assess the relationship 

7 between short-term exposure to air pollution and markers of blood coagulation using the 

8 Atherosclerosis Risk in Communities (ARIC) study cohort (Liao et al., 2005). Significant 

9 curvilinear associations were observed for O3 (1 day prior to blood draw) and fibrinogen 

10 and vWF (quantitative results not provided for regression models although adjusted 

11 means [SE] of vWF were given as 118% [0.79%] for O3 concentrations <40 ppb, 117% 

12 [0.86%] for O3 concentrations 40-70 ppb, and 124% [1.97%] for O3 concentrations of 

13 70 ppb). The association between short-term O3 exposure and fibrinogen was more 
Draft – Do Not Cite or Quote 6-184 June 2012

1 pronounced among those with a history of cardiovascular disease (CVD) and was 

2 statistically significant among only this subgroup of the population. The curvilinear 

3 relationship between concentration and outcome suggested stronger relationships at 

4 higher concentrations of O3. The authors note that the most pronounced associations 

5 occurred when the pollutant concentrations were 2-3 standard deviations above the mean. 

6 The results from this relatively large-scale cross-sectional study suggest weak 

7 associations with between short-term O3 exposure and increases in fibrinogen (among 

8 those with a history of CVD) and vWF. A retrospective repeated measures analysis was 

9 performed in Toronto, Canada among adults aged 18-40 years (n = 45) between the years 

10 of 1999 and 2006 (Thompson et al., 2010). Single pollutant models were used with 

11 moving averages up to 7 days. No evidence of an association was observed between 

12 short-term O3 exposure and increases in fibrinogen. 

13 A repeated measures study was conducted among 40 healthy individuals living or 

14 working in the city center of Rotterdam, the Netherlands to assess the relationship 

15 between air pollution and markers of hemostatis and coagulation (platelet aggregation, 

16 thrombin generation, and fibrinogen) (Rudez et al., 2009). Each participant provided 

17 between 11 and 13 blood samples throughout a 1-year period (498 samples on 197 days). 

18 Examined lags ranged from 6 hours to 3 days prior to blood sampling. No consistent 

19 evidence of an association was observed between O3 concentration and any of the 

20 biomarkers (percent change of max platelet aggregation: -6.87 [95% CI: -21.46, 7.70] per 

21 20 ppb increase in 24-h avg O3 concentration at 4-day average; percent change of 

22 endogenous thrombin potential: 0.95 [95% CI: -3.05, 4.95] per 20 ppb increase in 

23 24-h avg O3 concentration at 4-day avg; percent change of fibrinogen: -0.57 [95% CI: 

24 -3.05, 2.00] per 20 ppb increase in 24-h avg O3 concentration at lag 1-day). Some 

25 associations with O3 were in the opposite direction to that hypothesized which may be 

26 explained by the negative correlation between O3 and other pollutants (correlation 

27 coefficients ranged from -0.4 to -0.6). The statistically significant inverse effects 

28 observed in single-pollutant models with O3 were no longer apparent when PM10 was 

29 included in the model (Rudez et al., 2009).

30 A panel study in Taiwan measured health endpoints using blood samples from healthy 

31 individuals (n = 76) at three times from April to June in 2004 or 2005 (Chuang et al., 

32 2007a). Increases in fibrinogen and PAI-1 were associated with increases in O3

33 concentrations in single-pollutant models (percent change in fibrinogen: 11.76 [95% CI: 

34 4.03, 19.71] per 20 ppb 3-day cumulative avg O3 concentration; percent change in PAI-1: 

35 6.08 [95% CI: 38.91, 84.27] per 20 ppb 3-day cumulative avg O3 concentration). These 

36 associations were also observed at 1 and 2 day averaging times. Associations between 

37 PAI-1 and 3-day O3 concentrations remained robust in two-pollutant models with sulfate. 
Draft – Do Not Cite or Quote 6-185 June 2012

1 No association was observed between O3 concentration and tPA, a fibrinolytic factor 

2 (percent change 16.15 [95% CI: -4.62, 38.34] per 20 ppb 3-day avg O3 concentration). 

3 A study in Israel examined the association between pollutant concentrations and

4 fibrinogen among 3659 apparently healthy individuals (Steinvil et al., 2008). In single 

5 pollutant models, O3 was associated with an increase in fibrinogen at a 4-day lag among 

6 men and a same-day O3 concentration among women but results for other lags (0 through 

7 7 days) were mixed (i.e., some positive and some negative; none statistically significant). 

Inflammatory markers

8 Potential associations between short-term exposures to air pollution and inflammatory 

9 markers (C-reactive protein [CRP], white blood cell [WBC] count, albumin, and 

10 Interleukin-6 [IL-6]) were also examined in several studies.

11 The ARIC study cohort, which included men and women aged 45-64 years old at the start 

12 of the study, was utilized to assess the association between O3 concentrations and 

13 markers of inflammation, albumin and WBC count (Liao et al., 2005). No association 

14 was observed between O3 concentrations and albumin or WBC count. 

15 Thompson et al. (2010) assessed ambient air pollution exposures and IL-6. This 

16 retrospective repeated measures analysis was conducted among 45 adults (18-40 years of 

17 age) in Toronto, Canada between the years of 1999 and 2006. Single pollutant models 

18 were used to analyze the repeated-measures data using moving averages up to 7 days. A 

19 positive association was observed between IL-6 and short-term 1-h O3 exposure with the 

20 strongest effects observed for the average of lags 0-3 days(quantitative results not 

21 provided). No association was observed for shorter averaging times (average lags of 

22 <1 day). When examined by season using 2-day moving averages, the association 

23 between short-term O3 exposure and IL-6 was positive during only the spring and 

24 summer. 

25 In Rotterdam, the Netherlands, a repeated measures study of healthy individuals living or 

26 working in the city center reported no association between short-term O3 exposure and 

27 CRP (Rudez et al., 2009). Each of the 40 participants provided between 11 and 13 blood 

28 samples throughout a 1-year period (498 samples on 197 days). No consistent evidence of 

29 an association was observed between O3 concentration and CRP (percent change: -0.48 

30 [95% CI: -14.05, 13.10] per 20 ppb increase in 24-h avg O3 concentration at lag 1-day). 

31 Additionally, no association was observed with 2 or 3 day lags. 

32 The relationship between pollutant concentrations and one-time measures of 

33 inflammatory biomarkers was assessed in sex-stratified analyses among 3,659 apparently 
Draft – Do Not Cite or Quote 6-186 June 2012

1 healthy individuals in Tel Aviv, Israel (Steinvil et al., 2008). No evidence of an 

2 association was observed between O3 concentration and CRP or WBC for men and 

3 women. 

4 A panel study of healthy individuals (n = 76) was conducted in Taiwan to assess the 

5 relationship between air pollutants and inflammation (Chuang et al., 2007a). Health 

6 endpoints were measured three times from April to June in 2004 or 2005. Ozone effects 

7 were assessed in statistical models using the average of the 24 hours (1 day), 48 hours 

8 (2 days), and 72 hours (3 days) before the hour of each blood sampling. Increases in CRP 

9 were associated with increases in O3 concentrations in single-pollutant models (percent 

10 change in CRP: 244.38 [95% CI: 4.54, 585.15] per 20 ppb 3-day avg O3 concentration). 

11 The association was also observed using a 2-day cumulative averaging time, but no 

12 association was present with a 1-day averaging time.

Oxidative stress markers

13 A few studies have reported on the relationships between short-term O3 exposure and 

14 increases in markers of oxidative stress. The association between O3 concentration and 

15 markers of lipid peroxidation and antioxidant capacity was examined among 120 

16 nonsmoking healthy college students, aged 18-22 years, from the University of 

17 California, Berkeley (February-June 2002) (Chen et al., 2007a). By design, students were 

18 chosen that had experienced different geographic concentrations of O3 over their lifetimes 

19 and during recent summer vacation in either greater Los Angeles (LA) or the 

20 San Francisco Bay Area (SF). Long-term (based on lifetime residential history) and 

21 shorter-term (based on the moving averages of 8-h max concentrations 1-30 days prior to 

22 the day of blood collection) O3 concentration were estimated (lifetime exposure results 

23 are presented in Chapter 7). A marker of lipid peroxidation, 8-isoprostane (8-iso-PGF), 

24 was assessed. This marker is formed continuously under normal physiological conditions 

25 but has been found at elevated concentrations in response to environmental exposures. A 

26 marker of overall antioxidant capacity, ferric reducing ability of plasma (FRAP), was also 

27 measured. Levels of 8-iso-PGF were associated with 2-week (β = 0.035 

28 [pg/mL]/8-hour ppb O3, p = 0.007) and 1-month (β = 0.031 [pg/mL]/8-hour ppb O3, 

29 p = 0.006) estimated O3 concentrations. No evidence of association was observed 

30 between short-term O3 exposure and increases in FRAP. A chamber study performed 

31 among a subset of study participants supported the primary study results. The

32 concentrations of 8-iso-PGF increased immediately after the 4-hour controlled O3

33 exposure ended (p = 0.10). However, levels returned to near baseline by 18 hours without 

34 further exposure. The authors note that O3 was highly correlated with PM10-2.5 and NO2 in 

35 this study population; however, O3 associations remained robust in copollutant models. 
Draft – Do Not Cite or Quote 6-187 June 2012

1 Using blood samples collected between April and June of 2004 or 2005 in Taiwan, the 

2 association between short-term O3 exposure and a marker of oxidative stress (i.e., 8-

3 hydroxy-2’-deoxyguanosine (8-OHdG)) was studied among healthy individuals (n = 76) 

4 (Chuang et al., 2007a). Increases in 8-OHdG were associated with increases in O3

5 concentrations in single-pollutant models (percent change in 8-OHdG: 2.46 [95% CI: 

6 1.01, 3.92] per 20 ppb increase in 24-h avg O3). The association did not persist with 2- or 

7 3-day cumulative averaging times.

Markers of overall cardiovascular health

8 Multiple studies used markers that assess overall cardiovascular well-being. Wellenius et 

9 al. (2007) examined Β-type natriuretic peptide (BNP), a marker of heart failure, in a 

10 repeated-measures study conducted in Boston among 28 patients with congestive heart 

11 failure and impaired systolic function. The authors found no evidence of an association 

12 between BNP and short-term O3 exposures at lags 0-3 days (quantitative results not 

13 provided). BNP was chosen because it is directly associated with cardiac hemodynamics 

14 and symptom severity among those with heart failure and is considered a marker of 

15 functional status. However, the authors conclude that the use of BNP may not be useful 

16 in studies of the health effects of ambient air pollutants due to the large amount of within17 person variability in BNP levels observed in this population.

18 The relationship between air pollution and oxygen saturation and pulse rate, markers of 

19 physiological well-being, was examined in a 2-month panel study among 31 congestive 

20 heart failure patients (aged 50-85 years) in Montreal, Canada from July 2002 to October 

21 2003 (Goldberg et al., 2008). All participants had limited physical functioning 

22 (New York Heart Association Classification ≥ II) and an ejection fraction (the fraction of 

23 blood pumped out of the heart per beat) less than or equal to 35% (normal is above 55%). 

24 Daily mean O3 concentrations were calculated based on hourly measures at 10 monitoring 

25 stations. There was an inverse association between O3 concentration (lag-0) and oxygen 

26 saturation when adjustment was made for temporal trends. In the models incorporating 

27 personal covariates and weather factors, the association remained but was not statistically 

28 significant. The associations of O3 concentration with a lag of 1 day or a 3-day mean 

29 were not statistically significant. No evidence of association was observed between O3

30 concentration and pulse rate. 

31 Total homocysteine (tHcy) is an independent risk factor for vascular disease and 

32 measurement of this marker after oral methionine load is used to identify individuals with 

33 mild impairment of homocysteine metabolism. The effects of air pollution on fasting and 

34 postmethionine-load tHcy levels were assessed among 1,213 apparently healthy 

35 individuals from Lombardia, Italy from January 1995 to September 2005 (Baccarelli et 
Draft – Do Not Cite or Quote 6-188 June 2012

1 al., 2007). A 20-ppb increase in the 24-h avg O3 concentrations was associated with an 

2 increase in fasting tHcy (percent change 6.25 [95% CI: 0.84, 11.91]) but no association 

3 was observed with postmethionine-load tHcy (percent change 3.36 [95% CI: -1.30, 

4 8.39]). In addition, no evidence of an association was observed between 7-day 

5 cumulative averaged O3 concentrations and tHcy (percent change for fasting tHcy 4.16 

6 [95% CI: -1.76, 10.42] and percent change for postmethionine-load tHcy -0.65 [95% CI: 

7 -5.66, 4.71] per 20 ppb increase in 24-h avg O3 concentrations). No evidence of effect 

8 modification by smoking was observed. 

Blood lipids and glucose metabolism markers

9 Chuang et al. (2010) conducted a population-based cross-sectional analysis of data 

10 collected on 7,778 participants during the Taiwanese Survey on Prevalence of 

11 Hyperglycemia, Hyperlipidemia, and Hypertension in 2001. Apolipoprotein B (ApoB), 

12 the primary apolipoprotein among low-density lipoproteins, was associated with 3-day 

13 avg O3 concentration at the p <0.10 level. The 5-day mean O3 concentration was 

14 associated with an increase in triglycerides at p <0.10. In addition, the 1-, 3-, and 5-day 

15 mean O3 concentrations were associated with increased HbA1c levels (a marker used to 

16 monitor the degree of control of glucose metabolism) at the p <0.05 level. The 5-day 

17 mean O3 concentration was associated with increased fasting glucose levels (p <0.10). No 

18 association was observed between O3 concentration and ApoA1. 

6.3.2.5 Myocardial Infarction (MI)

19 The 2006 O3 AQCD did not report consistent results indicating an association between 

20 short-term O3 exposure and MI. One study reported a positive association between 

21 current day O3 concentration and acute MI, especially among the oldest age group (55 to 

22 64 year-olds) (Ruidavets et al., 2005b). No association was observed in a case-crossover 

23 study of O3 concentration during the surrounding hours and MI (Peters et al., 2001). Since 

24 the 2006 O3 AQCD, a few recent epidemiologic studies have examined the association 

25 between O3 concentration and MI (Henrotin et al., 2010; Rich et al., 2010), arterial 

26 stiffness (Wu et al., 2010) and ST-segment depression (Delfino et al., 2011). 

27 One of the studies conducted in the U.S. examined hospital admissions for first MI and 

28 reported no association with O3 concentration (Rich et al., 2010). More details on this 

29 study are reported in the section on hospital admissions (Section 6.3.2.7). A study 

30 performed in Dijon, France examined the association between O3 concentration and 

31 incident and recurrent MI (Henrotin et al., 2010). The mean 8-hour O3 concentration was 

32 19.1 ppb (SD 12.2 ppb). Odds ratios for the association between cumulative O3
Draft – Do Not Cite or Quote 6-189 June 2012

1 concentrations and recurrent MIs were elevated but none of the results were statistically 

2 significant (OR: 1.71 [95% CI: 0.91, 3.20] per 20 ppb increase in 24-h avg O3

3 concentration for a cumulative lag of 1-3 days). No association was observed for incident 

4 MIs. In analyses stratified by vascular risk factors, positive associations were observed 

5 between 1-day lagged O3 concentration and MIs (incident and recurrent combined) 

6 among those who reported having hypercholesterolaemia (OR: 1.52 [95% CI: 1.08, 2.15] 

7 per 20 ppb increase in 24-h avg O3 concentration) and a slight inverse association was 

8 observed among those who reported not having hypercholesterolaemia (OR: 0.69 

9 [95% CI: 0.50, 0.94] per 20 ppb increase in 24-h avg O3 concentration). In other stratified 

10 analyses combining different vascular factors, only those containing individuals with 

11 hypercholesterolaemia demonstrated a positive association; none were inverse 

12 associations. 

13 Wu et al. (2010) examined mail carriers aged 25-46 years and measured exposure to O3 

14 concentrationsthrough personal monitors [mean O3 24.9 (SD 14.0) ppb]. Ozone

15 concentration was positively associated with arterial stiffness (percent change 11.24% 

16 [95% CI: 3.67, 19.62] per 40 ppb O3) and was robust to adjustment for ultrafine PM. 

17 A study performed in the Los Angeles basin reported on the association between O3 

18 concentration and ST-segment depression, a measure representing cardiac ischemia 

19 (Delfino et al., 2011). Study participants were nonsmokers, at least 65 years old, had a 

20 history of coronary artery disease, and were living in a retirement community. Study 

21 periods included five consecutive days in both July to mid-October and mid-October to 

22 February. Mean 24-hour O3 concentrations were 27.1 ppb (SD 11.5 ppb). No association 

23 was observed between O3 concentration and ST-segment depression of at least 1.0 mm 

24 during any of the exposure periods (i.e., 1-h, 8-h, 1-day, 2-day avg, 3-day avg, 

25 4-day avg). 

6.3.2.6 Blood Pressure

26 In the 2006 O3 AQCD, no epidemiologic studies examined O3-related effects on blood 

27 pressure (BP). Recent studies have been conducted to evaluate this relationship and 

28 overall the findings are inconsistent. The O3 concentrations for these studies are listed in 

29 Table 6-33.
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Table 6-33 Characterization of ozone concentrations (in ppb) from studies of 

blood pressure.

Study* Location Averaging Time Mean Concentration 

(Standard Deviation)

Upper Range of 

Concentration

Zanobetti et al. (2004) Boston, 

Massachusetts

1-h 20

5-days 24

Delfino et al. (2010b) Los Angeles, 

California

24-h 27.1 (11.5) Max: 60.7

Choi et al. (2007) Incheon, 

South Korea

8-h

(warm season)

26.6 (11.8) 75th: 34.8

Max: 62.4

8-h

(cold season)

17.5 (7.3) 75th: 22.9

Max: 33.9

Chuang et al. (2010) Taiwan 26.83 (9.7) Max: 62.1

*Note: Studies presented in order of first appearance in the text of this section.

1 Zanobetti et al. (2004) examined the relationship between air pollutants and BP from 

2 May 1999 to January 2001 for 631 repeat visits among 62 Boston residents with CVD. In 

3 single-pollutant models, higher resting diastolic blood pressure (DBP) was associated 

4 with the 5-day (0-4 days) averages of O3 concentration (RR: 1.03 [95% CI: 1.00, 1.05] 

5 per 20 ppb increase in 24-hour O3 concentrations). However, this effect was no longer 

6 apparent when PM2.5 was included in the model (data were not presented) (Zanobetti et 

7 al., 2004). Delfino et al. (2010b) examined 64 subjects 65 years and older with coronary 

8 artery disease, no tobacco smoke exposure, and living in retirement communities in the 

9 Los Angeles air basin with hourly (up to 14-h/day) ambulatory BP monitoring for 5 days 

10 during a warm period (July-mid-October) and 5 days during a cool period (mid-October11 February). Investigators assessed lags of 1, 4, and 8 hours, 1 day, and up to 9 days before 

12 each BP measure; no evidence of an association was observed for O3 (change in BP 

13 associated with a 20 ppb increase in 24-h avg O3 concentration was 0.67 [95% CI: -1.16, 

14 2.51 for systolic BP [SBP] and -0.25 [95% CI: -1.25, 0.75] for DBP) (Delfino et al., 

15 2010b). Choi et al. (2007) conducted a cross-sectional study to investigate the 

16 relationship between air pollutants and BP among 10,459 participants of the Inha 

17 University Hospital health examination from 2001 to 2003. These individuals had no 

18 medical history of cardiovascular disease or hypertension. O3 concentration was 

19 associated with an increase in SBP for 1-day lag in the warm season and similar effect 

20 estimates were observed during the cold season but were not statistically significant 

21 (quantitative results not provided). Associations between O3 concentration and DBP were 

22 present in the cold season but not the warm season (quantitative results not provided). 

23 Chuang et al. (2010) conducted a similar type of study among 7,578 participants of the 

24 Taiwanese Survey on Prevalence of Hyperglycemia, Hyperlipidemia, and Hypertension 

25 in 2001. Investigators examined 1-, 3-, and 5-day avg O3 concentrations. An increase in 
Draft – Do Not Cite or Quote 6-191 June 2012

1 DBP was associated with the 3-day mean O3 concentration (change in BP for a 20 ppb 

2 increase in 24-h avg O3 concentration was 0.61 [95% CI: 0.07, 1.14]) (Chuang et al., 

3 2010). Associations were not observed for other days or with SBP.

6.3.2.7 Hospital Admissions and Emergency Department Visits

4 Upon evaluating the collective evidence for O3-related cardiovascular hospital admissions 

5 and emergency department (ED) visits, the 2006 O3 AQCD concluded that “a few studies 

6 observed positive O3 associations, largely in the warm season. Overall, however, the 

7 currently available evidence is inconclusive regarding any association between ambient 

8 O3 exposure on cardiovascular hospitalizations” (U.S. EPA, 2006b). Table 6-34 below 

9 provides information on the O3 concentrations reported in each of the recent hospital 

10 admission and ED visit studies evaluated.
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Table 6-34 Characterization of ozone concentrations (in ppb) from studies of 

hospital admissions and ED visits.

Study* Location Averaging 

Time

Mean Concentration 

(Standard Deviation)

Upper Range of 

Concentration

Peel et al. (2007) Atlanta, GA 8-h max

warm season

55.6 (23.8)

Tolbert et al. (2007) Atlanta, GA 8-h max

warm season

53.0 75th: 67.0

Max: 147.5

Katsouyanni et al. (2009) 12 Canadian cities 1-h 6.7-8.3* 75th: 8.4-12.4

8 European cities 1-h 11.0-38.1* 75th: 15.3-49.4

14 United 

Statescities

1-h 34.9-60.0* 75th: 46.8-68.8

Rich et al. (2010) New Jersey 24-h NR

Cakmak et al. (2006a) 10 Canadian cities 1-h max 17.4

Stieb et al. (2009) 7 Canadian cities 24-h 18.4

Szyszkowicz (2008) Edmonton, Canada 24-h 18.6 (9.3)

Villeneuve et al. (2006a) Edmonton, Canada 24-h 17 (9.1) 75th: 23.5

24-h

warm season

21.8 (8) 75th: 27.0

24-h

cold season

12.2 (7.4) 75th: 17.0

Symons et al. (2006) Baltimore, MD 8-h

warm season

31.0 (20.0) Max: 120.0

Wellenius et al. (2005) Allegheny County, 

PA

24-h 24.3 (12.2) 75th: 32.0

Zanobetti and Schwartz (2006) Boston, MA 24-h 22.4* 75th: 31.0

Yang (2008) Taipei, Taiwan 24-h 21.0 75th: 26.3

Max: 62.8

Lee et al. (2007) Kaohsiung, Taiwan 24-h 26.5 75th: 35.5

Max: 83.0

Chan et al. (2006) Taipei, Taiwan 1-h max 50.9 (26.4) Max: 150.3

Chiu and Yang (2009) Taipei, Taiwan 24-h 23.0 75th: 28.7

Max: 62.8

Lee et al. (2008a) Taipei, Taiwan 24-h 21.0 75th: 26.4

Max: 62.8

Wong et al. (2009) Hong Kong 8-h 18.5 (11.5) 75th: 25.4

Max: 48.3

Bell et al. (2008) Taipei, Taiwan 24-h 21.4 Max: 53.4

Buadong et al. (2009) Bangkok, Thailand 1-h 14.4 (3.2) Max: 41.9

Lee et al. (2003b) Seoul, Korea 1-h max 36.0 (18.6) 75th: 44.9

Azevedo et al. (2011) Portugal 1-h NR

Linares and Diaz (2010) Madrid,Spain 24-h 17.4 (8.9)

Middleton et al. (2008) Nicosia, Cyprus 8-h max 28.7 - 54.9
Draft – Do Not Cite or Quote 6-193 June 2012

Study* Location Averaging 

Time

Mean Concentration 

(Standard Deviation)

Upper Range of 

Concentration

Turner et al. (2007) Sydney, Australia 24-h 28 75th: 33

Ballester et al. (2006) 14 Spanish cities 8-h

warm season

24.2 - 44.3

DePablo et al. (2006) Castilla-Leon, Spain 24-h 23.2-33.6

VonKlot et al. (2005) 5 European cities 8 h max

warm season

16.4 - 28.0

Oudin et al. (2010) Scania, Sweden 24-h 30.5

Halonen et al. (2009) Helsinki, Finland 8-h max

warm season

35.7* 75th: 42.1

Max: 79.6

Larrieu et al. (2007) 8 French cities 8-h max

warm season

34.2 - 53.1

Barnett et al. (2006) 4 Australian cities 8-h 19.0-28.5 Max: 58.4-86.8

Hinwood et al. (2006) Perth, Australia 8-h max 25.9 (6.5)

Lanki et al. (2006) 5 European cities 8-h max

warm season

31.7 - 57.2*

Hosseinpoor et al. (2005) Tehran, Iran 8-h max 4.9 (4.8) 75th: 7.2

Max: 99.0

Simpson et al. (2005) 4 Australian cities 1-h max 24.4-33.8 Max: 96.0-111.5

Dennekamp et al. (2010) Melbourne, Australia 24-h 13.34 75th: 16.93

Silverman et al. (2010) New York City, NY 8-h max 28* 75th: 40

*Notes: Median presented (information on mean not given); NR: Not reported; studies presented in order of first appearance in the 

text of this section.

1 Multiple recent studies of O3 concentration and cardiovascular hospital admissions and 

2 ED visits have been conducted in the U.S. and Canada. Peel et al. (2007) used a case3 crossover framework (using a time-stratified approach matching on day of the week in 

4 the calendar month of the event) to assess the relationship between air pollutants and 

5 cardiovascular disease ED visits among those with and without secondary comorbid 

6 conditions (hypertension, diabetes, chronic obstructive pulmonary disease [COPD], 

7 congestive heart failure [CHF], and dysrhythmia). Data on over 4 million ED visits from 

8 31 hospitals were collected from January 1993 to August 2000. Ozone was monitored 

9 from March to October. This study was a re-analysis of a time series study conducted to 

10 assess the main effects of air pollutants on cardiovascular ED visits in Atlanta (Tolbert et 

11 al., 2007; Metzger et al., 2004). In the initial study, no evidence of associations was 

12 observed between O3 concentration and all CVD visits or visits for CVD subgroups, such 

13 as dysrhythmia, CHF, ischemic heart disease (IHD), and peripheral vascular and 

14 cerebrovascular disease. The relative risk for all CVD visits was 1.01 (95% CI: 0.98, 

15 1.04) for a 30 ppb increase in the 3-day moving avg (lags 0-2 days) of 8-hour O3

16 concentration (Metzger et al., 2004). Similar to the initial investigation using a time17 series analysis, no evidence of an association was observed between short-term O3
Draft – Do Not Cite or Quote 6-194 June 2012

1 exposure and CVD visits at lag 0-2 among the entire population using the case-crossover 

2 design (Peel et al., 2007). However, the relationship between O3 concentration and 

3 peripheral and cerebrovascular disease visits was stronger among patients with comorbid 

4 COPD (OR: 1.29 [95% CI: 1.05-1.59] per 30 ppb, lag 0-2 days) as compared to patients 

5 without COPD (OR: 1.01 [95% CI: 0.96-1.06] per 30 ppb, lag 0-2 days). The same 

6 research group expanded upon the number of Atlanta hospitals providing ED visit data 

7 (41 hospitals) as well as the length of the study period (1993-2004) (Tolbert et al., 2007). 

8 Again, models assessing the health effects of O3 concentration utilized data collected 

9 from March through October. Similar to the results presented by Metzger et al. (2004)

10 and Peel et al. (2007) among the entire study population, no evidence of associations was 

11 observed for O3 concentration and CVD visits (Tolbert et al., 2007). 

12 Existing multicity studies in North America and Europe were evaluated under a common 

13 framework in the Air Pollution and Health: A European and North American Approach 

14 (APHENA) study (Katsouyanni et al., 2009). One component of the study examined the 

15 relationship between short-term O3 exposure and CVD hospital admissions among 

16 individuals 65 years of age and older. The study presented multiple models but this 

17 section focuses on the results for the models that used 8 df to account for temporal trends 

18 and natural splines (see Section 6.2.7.2 for additional explanation). Across the study 

19 locations, no associations were observed between O3 concentration and CVD hospital 

20 admissions at lags 0-1, lag 1, or a distributed lag of 0-2. Additionally, there was no 

21 evidence of an association when restricting the analysis to the summer months. 

22 A study of hospital admissions for MI was performed using a statewide registry from 

23 New Jersey between January 2004 and December 2006 (Rich et al., 2010). Using a case24 crossover design, the association between the previous 24-h O3 concentration and 

25 transmural infarction (n = 1,003) was examined. No association was observed (OR: 0.94 

26 [95% CI: 0.79, 1.13] per 20 ppb increase in 24-h avg O3 concentration) and this did not 

27 change with the inclusion of PM2.5 in the model. 

28 Cakmak et al. (2006a) investigated the relationship between gaseous air pollutants and 

29 cardiac hospitalizations in 10 large Canadian cities using a time-series approach. A total 

30 of 316,234 hospital discharge records for primary diagnosis of congestive heart failure, 

31 ischemic heart disease, or dysrhythmia were obtained from April 1993 through March 

32 2000. Correlations between pollutants varied substantially across cities, which could 

33 partially explain discrepancies in effect estimates observed across the cities. In addition, 

34 pollutant lags differed across cities; the average lag for O3 was 2.9 days. The pooled 

35 effect estimate for a 20 ppb increase in the daily 1-h max O3 concentration and the 

36 percent change in hospitalizations among all 10 cities was 2.3 (95% CI: 0.11, 4.50) in an 

37 all-year analysis. The authors reported no evidence of effect modification by sex, 
Draft – Do Not Cite or Quote 6-195 June 2012

1 neighborhood-level education, or neighborhood-level income. A similar multicity time2 series study was conducted using nearly 400,000 ED visits to 14 hospitals in seven 

3 Canadian cities from 1992 to 2003 (Stieb et al., 2009). Primary analyses considered daily 

4 O3 single day lags of 0-2 days; in addition, sub-daily lags of 3-h avg concentrations up to 

5 12 hours before presentation to the ED were considered. Seasonal variation was assessed 

6 by stratifying analyses by warm and cold seasons. No evidence of associations between 

7 short-term O3 exposure and CVD ED visits was observed. One negative, statistically 

8 significant association was reported between a 1-day lag of O3 concentration and visits 

9 for angina/myocardial infarction. Ozone concentration was negatively correlated with 

10 many of the other pollutants, particularly during the cold season.

11 The effect of air pollution on daily ED visits for ischemic stroke (n = 10,881 visits) in 

12 Edmonton, Canada was assessed from April 1992 through March 2002 (Szyszkowicz, 

13 2008). A 26.4% (95% CI: 3.16-54.5) increase in stroke ED visits was associated with a 

14 20 ppb increase in 24-hour average O3 concentration at lag 1 among men aged 20-

15 64 years in the warm season. No associations were present among women or among men 

16 age 65 and older. In addition, no associations were observed for the cold season or for 

17 other lags (lag 0 or lag 2). A similar investigation over the same time period in 

18 Edmonton, Canada, assessed the relationship between air pollutants and ED visits for 

19 stroke (ischemic stroke, hemorrhagic stroke, and transient ischemic attack) among those 

20 65 years of age and older using a case-crossover framework (Villeneuve et al., 2006a). 

21 No evidence of association was reported for O3 concentration and stroke hospitalization 

22 in single or co-pollutant models (Villeneuve et al., 2006a).

23 Additional studies in the U.S. reported no evidence of an association between O3

24 concentrations and ED visits, hospitalizations, or symptoms leading to hospitalization 

25 (Symons et al., 2006; Zanobetti and Schwartz, 2006; Wellenius et al., 2005). Symons et 

26 al. (2006) used a case-crossover framework to assess the relationship between air 

27 pollutants and the onset of symptoms (dyspnea) severe enough to lead to hospitalization 

28 (through the ED) for congestive heart failure. The study was conducted from April to 

29 December of 2002 in Baltimore, Maryland. Exposures were assigned using 3 index times: 

30 8-hour and 24-hour periods prior to symptom onset and date of hospital admission. No 

31 evidence of association was reported for O3 concentrations. Although seasonal variation 

32 was not assessed, the time frame for the study did not involve an entire year (April to 

33 December). Wellenius et al. (2005) investigated the association between air pollutants 

34 and congestive heart failure hospitalization among Medicare beneficiaries in Pittsburgh, 

35 Pennsylvania from 1987 to 1999 utilizing a case-crossover framework. A total of 55,019 

36 admissions from the emergency room with a primary discharge diagnosis of CHF were 

37 collected. No evidence of an association was reported for O3 concentration and CHF 

38 hospitalization (Wellenius et al., 2005). Finally, Zanobetti and Schwartz (2006) assessed 
Draft – Do Not Cite or Quote 6-196 June 2012

1 the relationship between air pollutants and hospital admissions through the ED for MI 

2 and pneumonia among patients aged 65 and older residing in the greater Boston area 

3 (1995-1999) using a case-crossover framework with control days in the same month 

4 matched on temperature. Pollution exposures were assigned for the same day and for the 

5 mean of the exposure the day of and the day before the admission. Ozone concentration 

6 was not associated with MI admissions in all-year and seasonal analyses. 

7 Several recent studies have examined the relationship between air pollution and CVD 

8 hospital admissions and/or emergency department visits in Asia. Of note, some areas of 

9 Asia have a more tropical climate than the U.S. and do not experience similar seasonal 

10 changes. In Taiwan, fairly consistent positive associations have been reported for O3

11 concentration and congestive heart failure hospital admissions (for single- and 

12 copollutant models) in Taipei on warm days (Yang, 2008) and in Kaohsiung (Lee et al., 

13 2007); cerebrovascular disease ED visits (for lag 0 single- and two-pollutant models but 

14 not other lags) in Taipei (Chan et al., 2006); and arrhythmia ED visits in Taipei among 

15 those without comorbid conditions (Chiu et al., 2009; Lee et al., 2008a) and in Taipei on 

16 warm days among those with and without comorbid conditions (Lee et al., 2008a). 

17 However, one study in Taiwan did not show an association. Bell et al. (2008) reported no 

18 evidence of an association between O3 concentration and hospital admissions for 

19 ischemic heart disease or cerebrovascular disease. Studies based in Asia but outside 

20 Taiwan were also performed. A Hong Kong-based investigation (Wong et al., 2009)

21 reported no consistent evidence of a modifying effect of influenza on the relationship 

22 between O3 concentration and CVD admissions. Among elderly populations in Thailand, 

23 O3 concentration was associated with CVD visits, but this association was not detected 

24 among younger age groups (15-64) (Buadong et al., 2009). Also, a study performed in 

25 Seoul, Korea reported a positive association between O3 concentration and hospital 

26 admissions for ischemic heart disease; the association was slightly greater among those 

27 over 64 years of age (Lee et al., 2003b). 

28 Positive associations between short-term O3 exposure and CVD hospital admissions 

29 and/or ED visits have been reported in other areas of the world as well (Azevedo et al., 

30 2011; Linares and Diaz, 2010; Middleton et al., 2008; Turner et al., 2007; Ballester et al., 

31 2006; DePablo et al., 2006; VonKlot et al., 2005), although not consistently as some 

32 studies reported no association (Oudin et al., 2010; Halonen et al., 2009; Larrieu et al., 

33 2007; Barnett et al., 2006; Hinwood et al., 2006; Lanki et al., 2006; Hosseinpoor et al., 

34 2005; Simpson et al., 2005). 

35 A couple of studies (U.S. and Australia) have examined cardiac arrests where emergency 

36 services attempted treatment/resuscitation. No evidence of an association between O3
Draft – Do Not Cite or Quote 6-197 June 2012

1 concentration and out-of-hospital cardiac arrest was observed (Dennekamp et al., 2010; 

2 Silverman et al., 2010).

3 An increasing number of air pollution studies have investigated the relationship between 

4 O3 concentrations and CVD hospital admissions and/or ED visits. As summarized in the 

5 2006 O3 AQCD, some, especially those reporting results stratified by season (or 

6 temperature) or comorbid conditions have reported positive associations. However, even 

7 studies performing these stratified analyses are not consistent and the overall evidence 

8 remains inconclusive regarding the association between short-term O3 exposure and CVD 

9 hospital admissions and ED visits. The Hospital Admission (HA) and ED visit studies 

10 evaluated in this section are summarized in Figure 6-21 through Figure 6-25, which 

11 depict the associations for studies in which quantitative data were presented. Table 6-35

12 through Table 6-39 provide the numerical results displayed in the figures. 
Draft – Do Not Cite or Quote 6-198 June 2012

Note: Change in O3 standardized to 20 ppb for 24-h avg period, 30 ppb for 8-h avg period, and 40 ppb for 1-h avg period (see 

Section 2.2). Ozone concentrations in ppb. Seasons depicted by colors – black: all year; red: warm season; light blue: cold season. 

Age groups of study populations were not specified or were adults with the exception of Katsouyanni et al. (2009), Fung et al. 

(2005), Wong et al. (1999b), and Prescott et al. (1998), which included only individuals aged 65+. Studies organized by outcome 

and season and then listed in descending order of publication date.

Figure 6-21 Effect estimate (95% CI) per increment ppb increase in ozone for 

over all cardiovascular ED visits or hospital admissions.

Reference

Buadong et al. (2009)

Katsouyanni et al. (2009)

Katsouyanni et al. (2009)

Katsouyanni et al. (2009)

Middleton et al. (2008)

Fung et al. (2005)

Ballester et al. (2001)

Petroeschevsky et al. (2001)

Linn et al. (2000)

Atkinson et al. (1999)

Wong et al. (1999a)

Wong et al. (1999b)

Prescott et al. (1998)

Poloniecki et al. (1997)

Halonen et al. (2009)

Katsouyanni et al. (2009)

Katsouyanni et al. (2009)

Katsouyanni et al. (2009)

Larrieu et al. (2007)

Peel et al. (2007)

Ballester et al. (2006)

Chang et al. (2005)

Yang et al. (2004)

Wong et al. (1999b)

Chang et al. (2005)

Yang et al. (2004)

Wong et al. (1999a)

Wong et al. (1999b)

Cakmak et al. (2006)

Ballester et al. (2001)

Morgan et al. (1998)

Larrieu et al. (2007)

Ballester et al. (2006)

von Klot et al. (2005)

Bell et al. (2008)

Chan et al. (2006)

Ballester et al. (2001)

Wong et al. (1999a)

Wong et al. (1999b)

Poloniecki et al. (1997)

Peel et al. (2007)

Wong et al. (1999b)

Wong et al. (1999b)

Location 

Bangkok, Thailand

14 U.S. cities

12 Canadian cities

8 European cities

Nicosia, Cyprus

Windsor, Canada

Valencia, Spain

Brisbane, Australia

Los Angeles, CA

London, England

Hong Kong

Hong Kong

Edinburgh, Scotland

London, England

Helsinki, Finland

14 U.S. cities

12 Canadian cities

8 European cities

8 French cities

Atlanta, GA

14 Spanish cities

Taipei, Taiwan

Kaohsiung, Taiwan

Hong Kong

Taipei, Taiwan

Kaohsiung, Taiwan

Hong Kong

Hong Kong

10 Canadian cities 

Valencia, Spain

Sydney, Australia

8 French cities

14 Spanish cities

5 European cities 

Taipei, Taiwan

Taipei, Taiwan

Valencia, Spain

Hong Kong

Hong Kong

London, England

Atlanta, GA

Hong Kong

Hong Kong

Cerebrovascular disease

Cardiac disease

Cardiovascular disease

0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50

Effect Estimate
Draft – Do Not Cite or Quote 6-199 June 2012

Table 6-35 Effect estimate (95% CI) per increment ppb increase in ozone for 

overall cardiovascular ED visits or hospital admissions in studies 

presented inFigure 6-21.

Study* Location Outcome Averaging Time Effect Estimate (95% CI)

Atkinson et al. (1999) London, England Cardiovascular 

disease

8-h 1.03 (1.00, 1.05)

Ballester et al. (2006) 14 Spanish cities Cardiovascular 

disease

8-h warm season 1.04 (1.02 , 1.06)

Cardiac disease 8-h warm season 1.04 (1.01, 1.07)

Ballester et al. (2006) Valencia, Spain Cardiovascular 

disease

8-h 0.94 (0.84, 1.06)

Cardiac disease 8-h 0.88 (0.75, 1.03)

Cerebrovascular 

disease 

8-h 0.86 (0.72, 1.04)

Bell et al. (2008) Taipei, Taiwan Cerebrovascular 

disease

24-h 0.94 (0.87, 1.02)

Buadong et al. (2009) Bangkok, 

Thailand

Cardiovascular 

disease

1-h 1.01 (1.00, 1.02)

Cakmak et al. (2006a) 10 Canadian 

cities

Cardiac disease 1-h max 1.02 (1.00, 1.04)

Chan et al. (2006) Taipei, Taiwan Cerebrovascular 

disease

1-h max 1.02 (1.01, 1.03)

Chang et al. (2005) Taipei, Taiwan Cardiovascular 

disease

24-h warm season 1.42 (1.33 , 1.50)

24-h cold season 1.15 (1.04, 1.27)

Fung et al. (2005) Windsor, Canada Cardiovascular 

disease

1-h 1.02 (0.92, 1.13)

Halonen et al. (2009) Helsinki, Finland Cardiovascular 

disease

8-h max warm 

season

1.05 (0.96, 1.14)

Katsouyanni et al. 

(2009)

14 U.S. cities Cardiovascular 

disease

1-h max 1.01 (0.99, 1.03)

1-h max warm 

season

1.00 (0.97, 1.03)

12 Canadian 

cities

Cardiovascular 

disease

1-h max 1.00 (0.95, 1.04)

1-h max warm 

season

0.98 (0.94, 1.02)

8 European cities Cardiovascular 

disease

1-h max 0.99 (0.96, 1.02)

1-h max warm 

season

0.98 (0.94, 1.03)

Larrieu et al. (2007) 8 French cities Cardiac disease 8-h max warm 

season

1.01 (0.98, 1.04)

Linn et al. (2000) Los Angeles, 

California

Cardiovascular 

disease

24-h 0.99 (0.98, 1.00)

Middleton et al. (2008) Nicosia, Cyprus Cardiovascular 

disease

8-h max 1.09 (1.00, 1.18)
Draft – Do Not Cite or Quote 6-200 June 2012

Study* Location Outcome Averaging Time Effect Estimate (95% CI)

Morgan et al. (1998) Sydney, 

Australia

Cardiac disease 1-h max 1.02 (0.99, 1.05)

Peel et al. (2007) Atlanta, GA Cardiovascular 

disease

8-h warm season 1.00 (0.98, 1.02)

Cerebrovascular 

disease

8-h warm season 1.03 (0.97, 1.08)

Petroeschevsky et al. 

(2001)

Brisbane, 

Australia

Cardiovascular 

disease

8-h 0.96 (0.92, 1.01)

Poloniecki et al. 

(1997)

London, England Cardiovascular 

disease

8-h 0.97 (0.93, 1.01)

Cerebrovascular 

disease

8-h 0.98 (0.95, 1.02)

Prescott et al. (1998) Edinburgh, 

Scotland

Cardiovascular 

disease

24-h 0.89 (0.78, 1.00)

VonKlot et al. (2005) 5 European cities Cardiac disease 8-h max warm 

season

1.11 (1.00, 1.22)

Wong et al. (1999b) Hong Kong Cardiovascular 

disease

24-h 1.08 (1.03 , 1.13)

24-h cold season 1.15 (1.04, 1.26)

Cerebrovascular 

disease

24-h 0.95 (0.90, 1.01)

Wong et al. (1999a) Hong Kong Cardiovascular 

disease

24-h 1.02 (1.03 , 1.06)

24-h warm season 1.01 (0.96, 1.06)

24-h cold season 1.06 (1.02, 1.11)

Cerebrovascular 

disease

24-h 0.99 (0.95, 1.04)

24-h warm season 0.98 (0.90, 1.08)

24-h cold season 1.02 (0.96, 1.10)

Yang et al. (2004) Kaohsiung, 

Taiwan

Cardiovascular 

disease

24-h warm season 1.33 (1.26 , 1.40)

24-h cold season 1.05 (0.96, 1.15)

*Studies included in Figure 6-21..

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, and 

40 ppb for 1-hour averaging period (see Section 2.2). Ozone concentrations in ppb. Age groups of study populations 

were not specified or were adults with the exception of Katsouyanni et al. (2009), Fung et al. (2005), Wong et al. 

(1999a), and Prescott et al. (1998), which included only individuals aged 65+. Studies listed in alphabetical order.

Warm season defined as: March-October (Peel et al., 2007), May-October (Ballester et al., 2005; Wong et al., 

1999a), May-September (Halonen et al., 2009), April-September (Larrieu et al., 2007; VonKlot et al., 2005)

Katsouyanni et al. (2009), ≥ 20°C (Chang et al., 2005) and ≥ 25°C (Yang et al., 2004). Cold season defined as: 

November-April (Wong et al., 1999a), <20°C (Chang et al., 2005) and <25°C (Yang et al., 2004), December-March 

(Wong et al., 1999b)
Draft – Do Not Cite or Quote 6-201 June 2012

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, and 40 ppb for 1-hour 

averaging period (see Section 2.2). Ozone concentrations in ppb. Seasons depicted by colors: black: all year; red: warm season; 

light blue: cold season. Outcomes were all congestive heart failure, with the exception of Symons et al. (2006), which examined 

onset of congestive heart failure symptoms leading to a heart attack. Age groups of study populations were not specified or were 

adults with the exception of Wellenius et al. (2005) and Wong et al. (1999a), which included only individuals aged 65+. Studies 

organized by outcome and season and then listed in descending order of publication date.

Figure 6-22 Effect estimate (95% CI) per increment ppb increase in ozone for 

congestive heart failure ED visits or hospital admissions.

Reference

Stieb et al. (2009)

Wellenius et al. (2005)

Wong et al. (1999a)

Wong et al. (1999b)

Poloniecki et al. (1997)

Yang (2008)

Peel et al. (2007)

Lee et al. (2007)

Symons et al. (2006)

Wong et al. (1999b)

Yang (2008)

Lee et al. (2007)

Wong et al. (1999b)

Location

7 Canadian cities 

Allegheny county, PA

Hong Kong

Hong Kong

London, England

Taipei, Taiwan

Atlanta, GA

Kaohsiung, Taiwan

Baltimore, MD

Hong Kong

Taipei, Taiwan

Kaohsiung, Taiwan

Hong Kong

0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

Effect Estimate
Draft – Do Not Cite or Quote 6-202 June 2012

Table 6-36 Effect estimate (95% CI) per increment ppb increase in ozone for 

congestive heart failure ED visits or hospital admissions for 

studies in Figure 6-22.

Study* Location Outcome Averaging Time Effect Estimate 

(95% CI)

Lee et al. (2007) Kaohsiung, Taiwan Congestive heart failure 24-h warm season 1.25 (1.15, 1.36)

Congestive heart failure 24-h cold season 1.24 (1.09, 1.41)

Peel et al. (2007) Atlanta, GA Congestive heart failure 8-h warm season 0.94 (0.89, 1.00)

Poloniecki et al. 

(1997)

London, England Congestive heart failure 8-h 0.99 (0.95, 1.03)

Stieb et al. (2009) 7 Canadian cities Congestive heart failure 24-h 1.03 (0.98, 1.07)

Symons et al. 

(2006)

Baltimore, MD Onset of congestive heart 

failure symptoms leading to 

heart attack

8-h warm season 0.83 (0.49, 1.41)

Wellenius et al. 

(2005)

Allegheny county, PA Congestive heart failure 24-h 0.98 (0.96, 1.01)

Wong et al. 

(1999a)

Hong Kong Congestive heart failure 24-h 1.11 (1.04, 1.80)

24-h warm season 1.09 (0.96, 1.23)

24-hcold season 1.16 (1.06, 1.27)

Yang (2008) Taipei, Taiwan Congestive heart failure 24-h warm season 1.39 (1.27, 1.51)

Congestive heart failure 24-h cold season 0.61 (0.52, 0.73)

Wong et al. 

(1999b)

Hong Kong Congestive heart failure 24-h 1.25 (1.11, 1.41)

*Studies include those from Figure 6-22.

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, 

and 40 ppb for 1-hour averaging period (see Section 2.2). Ozone concentrations in ppb. Outcomes were all 

congestive heart failure, with the exception of Symons et al. (2006), which examined onset of congestive heart 

failure symptoms leading to a heart attack. Age groups of study populations were not specified or were adults 

with the exception of Wellenius et al. (2005) and Wong et al. (1999a), which included only individuals aged 65+. 

Studies listed in alphabetical order.

Warm season defined as: March-October (Peel et al., 2007), April-November (Symons et al., 2006), MayOctober (Wong et al., 1999a) ≥ 20°C (Yang, 2008), and >25°C (Lee et al., 2007). Cold season defined as: 

November-April (Wong et al., 1999a), <20°C (Yang, 2008), and <25°C (Lee et al., 2007). 
Draft – Do Not Cite or Quote 6-203 June 2012

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, and 40 ppb for 1-hour 

averaging period (see Section 2.2). Ozone concentrations in ppb. Seasons depicted by colors: black: all year; red: warm season; 

light blue: cold season. Age groups of study populations were not specified or were adults with the exception of Wong et al. (1999a)

and Atkinson et al. (1999), which included only individuals aged 65+. Studies organized by outcome and season and then listed in 

descending order of publication date.

Figure 6-23 Effect estimate (95% CI) per increment ppb increase in ozone for 

ischemic heart disease, coronary heart disease, myocardial 

infarction, and angina pectoris ED visits or hospital admissions.

Reference

Buadong et al. (2009)

Bell et al. (2008)

Lee et al. (2003)

Atkinson et al. (1999)

Wong et al. (1999a)

Wong et al. (1999b)

Larrieu et al. (2007)

Peel et al. (2007)

Lee et al. (2003)

Wong et al. (1999b)

Wong et al. (1999b)

Halonen et al. (2009)

Rich et al. (2010)

Buadong et al. (2009)

Stieb et al. (2009)

Zanobetti et al. (2006)

Poloniecki et al. (1997)

Lanki et al. (2006)

von Klot et al. (2005)

Hosseinpoor et al. (2005)

Poloniecki et al. (1997)

von Klot et al. (2005)

Angina pectoris

Myocardial infarction

Ischemic heart disease

Coronary heart disease

Location

Bangkok, Thailand

Taipei, Taiwan

Seoul, Korea

London, England

Hong Kong

Hong Kong

8 French cities

Atlanta, GA 

Seoul, Korea

Hong Kong

Hong Kong

Helsinki, Finland

New Jersey

Bangkok, Thailand

7 Canadian cities

Boston, MA

London, England

5 European cities

5 European cities

Tehran, Iran

London, England

5 European cities

0.5 0.7 0.9 1.1 1.3 1.5

Effect Estimate
Draft – Do Not Cite or Quote 6-204 June 2012

Table 6-37 Effect estimate (95% CI) per increment ppb increase in ozone for 

ischemic heart disease, coronary heart disease, myocardial 

infarction, and angina pectoris Evisits or hospital admissions for 

studies presented in Figure 6-23.

Study* Location Outcome Averaging Time Effect Estimate 

(95% CI)

Atkinson et al. (1999) London, England Ischemic heart disease 8-h 0.97 (0.94, 1.01)

Bell et al. (2008) Taipei, Taiwan Ischemic heart disease 24-h 1.01 (0.91, 1.12)

Buadong et al. (2009) Bangkok, 

Thailand

Ischemic heart disease 1-h 1.00 (0.98, 1.02)

Myocardial infarction 1-h 0.97 (0.94, 1.01)

Halonen et al. (2009) Helsinki, Finland Coronary heart 

disease

8-h max warm 

season

0.99 (0.79, 1.25)

Hosseinpoor et al. (2005) Tehran, Iran Angina 8-h max 0.80 (0.70, 0.92)

Lanki et al. (2006) 5 European cities Myocardial infarction 8-h max warm 

season

0.96 (0.92, 1.01)

Larrieu et al. (2007) 8 French cities Ischemic heart disease 8-h max warm 

season

1.02 (0.98, 1.07)

Lee et al. (2003b) Seoul, Korea Ischemic heart disease 1-h max 1.07 (1.02, 1.13)

Ischemic heart disease 1-h max warm 

season

1.07 (1.00, 1.17)

Peel et al. (2007) Atlanta, GA Ischemic heart disease 8-h warm season 1.00 (0.96, 1.05)

Poloniecki et al. (1997) London, England Myocardial infarction 8-h 0.98 (0.94, 1.02)

Angina 8-h 0.98 (0.94, 1.03)

Rich et al. (2010) New Jersey Myocardial infarction 24-h 0.94 (0.79, 1.13)

Stieb et al. (2009) 7 Canadian cities Myocardial infarction 2-h 1.00 (0.96, 1.04)

VonKlot et al. (2005) 5 European cities Myocardial infarction 8-h max warm 

season

1.00 (0.83, 1.21)

Angina 8-h max warm 

season

1.19 (1.05, 1.35)

Wong et al. (1999a) Hong Kong Ischemic heart disease 24-h 1.01 (0.94, 1.06)

24-h warm season 1.02 (0.94, 1.11)

24-h cold season 1.02 (0.95, 1.09)

Wong et al. (1999b) Hong Kong Ischemic heart disease 24-h 1.03 (0.98, 1.08)

Zanobetti and Schwartz 

(2006)

Boston, MA Myocardial infarction 24-h 0.98 (0.92, 1.03)

*Sudies included from Figure 6-23.

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, and 

40 ppb for 1-hour averaging period (see Section 2.2). Ozone concentrations in ppb. Age groups of study populations 

were not specified or were adults with the exception of Wong et al. (1999a) and Atkinson et al. (1999), which included 

only individuals aged 65+. Studies listed in alphabetical order.

Warm season defined as: March-October (Peel et al., 2007), June-August (Lee et al., 2003b), May-September 

(Halonen et al., 2009), May-October (Buadong et al., 2009), and April-September (Larrieu et al., 2007; Lanki et al., 

2006; VonKlot et al., 2005). Cold season defined as: November-April (Buadong et al., 2009).
Draft – Do Not Cite or Quote 6-205 June 2012

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, and 40 ppb for 1-hour 

averaging period (see Section 2.2). Ozone concentrations in ppb. Seasons depicted by colors: black: all year; red: warm season; 

light blue: cold season. Age groups of study populations were not specified or were adults with the exception of Villeneuve et al. 

(2006a), which included only individuals aged 65+, and.Chan et al. (2006), which included only individuals aged 50+. Studies 

organized by outcome and season and then listed in descending order of publication date.

Figure 6-24 Effect estimate (95% CI) per increment ppb increase in ozone for 

stroke ED visits or hospital admissions.

Chan et al. (2006)

Halonen et al. (2009)

Larrieu et al. (2007)

Chan et al. (2006)

Villeneuve et al. (2006)

Villeneuve et al. (2006)

Villeneuve et al. (2006)

Chan et al. (2006)

Villeneuve et al. (2006)

Villeneuve et al. (2006)

Villeneuve et al. (2006)

Villeneuve et al. (2006)

Villeneuve et al. (2006)

Villeneuve et al. (2006)

Reference

All

Ischemic 

Hemorrhagic 

Transient ischemic 

Taipei, Taiwan

Helsinki, Finland

8 French cities

Taipei, Taiwan

Edmonton, Canada

Edmonton, Canada

Edmonton, Canada

Taipei, Taiwan

Edmonton, Canada

Edmonton, Canada

Edmonton, Canada

Edmonton, Canada

Edmonton, Canada

Edmonton, Canada

Location

0.5 0.7 0.9 1.1 1.3 1.5

Effect Estimate
Draft – Do Not Cite or Quote 6-206 June 2012

Table 6-38 Effect estimate (95% CI) per increment ppb increase in ozone for 

stroke ED visits or hospital admissions for studies presented in

Figure 6-24. 

Study* Location Outcome Averaging Time Effect Estimate 

(95% CI)

Chan et al. (2006) Taipei, Taiwan All/non-specified stoke 1-h max 1.01 (0.99 ,1.03)

Ischemic stroke 1-h max 1.03 (0.99, 1.07)

Hemorrhagic stroke 1-h max 0.99 (0.92, 1.06)

Halonen et al. (2009) Helsinki, Finland All/non-specified stoke 8-h max warm 

season

1.08 (0.83, 1.41)

Larrieu et al. (2007) 8 French cities All/non-specified stoke 8-h max warm 

season

0.98 (0.93 , 1.02)

Villeneuve et al. (2006a) Edmonton, 

Canada

Ischemic stroke 24-h 1.00 (0.88, 1.13)

Ischemic stroke 24-h warm season 1.09 (0.91, 1.32)

Ischemic stroke 24-h cold season 0.98 (0.80, 1.18)

Hemorrhagic stroke 24-h 1.02 (0.87, 1.20)

Hemorrhagic stroke 24-h warm season 1.12 (0.88, 1.43)

Hemorrhagic stroke 24-h cold season 0.97 (0.76, 1.22)

Transient ischemic stroke 24-h 0.98 (0.87, 1.10)

Transient ischemic stroke 24-h warm season 0.85 (0.70, 1.01)

Transient ischemic stroke 24-h cold season 1.11 (0.93, 1.32)

*Studies included from Figure 6-24..

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, and 40 ppb for 1-hour 

averaging period (see Section 2.2). Ozone concentrations in ppb. Age groups of study populations were not specified or were adults 

with the exception of Villeneuve et al. (2006a), which included only individuals aged 65+, and Chan et al. (2006), which included 

only individuals aged 50+. Studies listed in alphabetical order.

Warm season defined as: May-September (Halonen et al., 2009), and April-September (Larrieu et al., 2007; Villeneuve et al., 

2006a). Cold season defined as: October-March (Villeneuve et al., 2006a). 
Draft – Do Not Cite or Quote 6-207 June 2012

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, and 40 ppb for 1-hour 

averaging period (see Section 2.2). Ozone concentrations in ppb. Seasons depicted by colors: black: all year; red: warm season; 

light blue: cold season. Age groups of study populations were not specified or were adults with the exception of Wong et al. (1999a), 

which included only individuals aged 65+. Studies organized by outcome and season and then listed in descending order of 

publication date.

Figure 6-25 Effect estimate (95% CI) per increment ppb increase in ozone for 

arrhythmia and dysrhythmia ED visits or hospital admissions.

Reference

Stieb et al. (2009)

Peel et al. (2007)

Buadong et al. (2009)

Wong et al. (1999b)

Poloniecki et al. (1997)

Halonen et al. (2009)

Wong et al. (1999b)

Wong et al. (1999b)

Arrhythmia

Dysrhythmia

Location

7 Canadian cities 

Atlanta, GA

Bangkok, Thailand

Hong Kong

London, England

Helsinki, Finland

Hong Kong

Hong Kong

0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40

Effect Estimate
Draft – Do Not Cite or Quote 6-208 June 2012

Table 6-39 Effect estimate (95% CI) per increment ppb increase in ozone for 

arrhythmia and dysrhythmia ED visits or hospital admissions for 

studies presented in Figure 6-25. 

Study Location Outcome Averaging Time Effect Estimate 

(95% CI)

Buadong et al. (2009) Bangkok, Thailand Arrhythmia 1-h 0.99 (0.95, 1.04)

Halonen et al. (2009) Helsinki, Finland Arrhythmia 8-h max warm season 1.04 (0.80, 1.35)

Peel et al. (2007) Atlanta, GA Dysrhythmia 8-h warm season 1.01 (0.97, 1.06)

Poloniecki et al. (1997) London, England Arrhythmia 8-h 1.02 (0.96, 1.07)

Stieb et al. (2009) 7 Canadian cities Dysrhythmia 24-h 1.02 (0.95, 1.09)

Wong et al. (1999a) Hong Kong Arrhythmia 24-h 1.06 (0.99, 1.12)

24-h warm season 1.10 (0.96, 1.26)

24-h cold season 1.11 (1.01, 1.23)

*Studies included from Figure 6-25..

Note: Change in O3 standardized to 20 ppb for 24-hour averaging period, 30 ppb for 8-hour averaging period, and 40 ppb for 1-hour 

averaging period (see Section 2.2). Ozone concentrations in ppb. Age groups of study populations were not specified or were adults 

with the exception of (Wong et al., 1999a), which included only individuals aged 65+. Studies listed in alphabetical order. Warm 

season defined as: March-October (Peel et al., 2007), May-October (Wong et al., 1999a) and May-September (Halonen et al., 

2009). Cold season defined as: November-April (Wong et al., 1999a). 

6.3.2.8 Cardiovascular Mortality

1 As discussed within this section (Section 6.3), epidemiologic studies provide inconsistent 

2 evidence of an association between short-term O3 exposure and cardiovascular effects. 

3 However, toxicological studies have demonstrated O3-induced cardiovascular effects, 

4 specifically enhanced atherosclerosis and ischemia, which could lead to death. The 2006 

5 O3 AQCD provided evidence, primarily from single-city studies, of consistent positive 

6 associations between short-term O3 exposure and cardiovascular mortality. Recent 

7 multicity studies conducted in the U.S., Canada, and Europe further support the 

8 association between short-term O3 exposure and cardiovascular mortality. 

9 As discussed in Section 6.2.7.2, the APHENA study (Katsouyanni et al., 2009) also 

10 examined associations between short-term O3 exposure and mortality and found 

11 consistent positive associations for cardiovascular mortality in all-year analyses. 

12 However, in analyses restricted to the summer season, results were more variable with no 

13 evidence of an association in the Canadian dataset in the population <75 years of age, and 

14 evidence of associations persisting or increasing in magnitude in the Canadian 

15 (population ≥ 75 years of age), U.S., and European datasets. Additional multicity studies 

16 from the U.S. (Zanobetti and Schwartz, 2008b), Europe (Samoli et al., 2009), Italy 

17 (Stafoggia et al., 2010), and Asia (Wong et al., 2010) that conducted summer season 
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1 and/or all-year analyses provide additional support for an association between short-term 

2 O3 exposure and cardiovascular mortality (Figure 6-36). 

3 Of the studies evaluated, only the APHENA study (Katsouyanni et al., 2009) and the 

4 Italian multicity study (Stafoggia et al., 2010) conducted an analysis of the potential for 

5 copollutant confounding of the O3-cardiovascular mortality relationship. In the European 

6 dataset, when focusing on the natural spline model with 8 df/year (Section 6.2.7.2) and 

7 lag 1 results in order to compare results across study locations (Section 6.6.2.1), 

8 cardiovascular mortality risk estimates were robust to the inclusion of PM10 in 

9 copollutant models in all-year analyses with more variability in the Canadian and U.S. 

10 datasets (i.e., cardiovascular O3 mortality risk estimates were reduced or increased in 

11 copollutant models). In summer season analyses, cardiovascular O3 mortality risk 

12 estimates were robust in the European dataset and attenuated but remained positive in the

13 U.S. dataset. Similarly, in the Italian multicity study (Stafoggia et al., 2010), which was 

14 limited to the summer season, cardiovascular mortality risk estimates were robust to the 

15 inclusion of PM10 in copollutant models. Based on the APHENA and Italian multicity 

16 results, O3 cardiovascular mortality risk estimates appear to be robust to inclusion of 

17 PM10 in copollutant models. However, in the U.S. and Canadian datasets there was 

18 evidence that O3 cardiovascular mortality risk estimates are moderately to substantially 

19 sensitive (e.g., increased or attenuated) to PM10. The mostly every-6th-day sampling 

20 schedule for PM10 in the Canadian and U.S. datasets greatly reduced their sample size 

21 and limits the interpretation of these results. 

6.3.2.9 Summary of Epidemiologic Studies

22 Overall, the available body of evidence examining the relationship between short-term 

23 exposures to O3 concentrations and cardiovascular morbidity is inconsistent. Across 

24 studies, different definitions, i.e., ICD-9 diagostic codes were used for both all-cause and 

25 cause-specific cardiovascular morbidity (Table 6-35, Table 6-36, Table 6-37, Table 6-38, 

26 and Table 6-39), which may contribute to inconsistency in results. However, within 

27 diagnostic categories, no consistent pattern of association was found with O3. Generally, 

28 the studies summarized in this section used nearest air monitors to assess O3 

29 concentrations, with a few exceptions that used modeling or personal exposure monitors 

30 (these exceptions were noted throughout the previous sections). The inconsistencies in 

31 the associations observed between short-term O3 and CVD morbidities are unlikely to be 

32 explained by the different exposure assignment methods used (see Section 4.6). The wide 

33 variety of biomarkers considered and the lack of consistency among definitions used for 

34 specific cardiovascular disease endpoints (e.g., arrhythmias, HRV) make comparisons 

35 across studies difficult. Despite the inconsistent evidence for an association between O3
Draft – Do Not Cite or Quote 6-210 June 2012

1 concentration and CVD morbidity, mortality studies indicate a consistent positive 

2 association between short-term O3 exposure and cardiovascular mortality in multicity 

3 studies and a multicontinent study. 

6.3.3 Toxicology: Cardiovascular Effects

4 In the previous O3 AQCDs (U.S. EPA, 2006b, 1996a) experimental animal studies have 

5 reported relatively few cardiovascular system alterations after exposure to O3 and other 

6 photochemical oxidants. The limited amount of research directed at examining 

7 O3-induced cardiovascular effects has primarily found alterations in heart rate (HR), heart 

8 rhythm, and BP after O3 exposure. Although O3 induced changes in HR and core 

9 temperature (TCO) in a number of rat studies, these responses have not been reported or 

10 extensively studied in humans exposed to O3 and may be unique to rodents. 

11 According to recent animal toxicology studies, short-term O3 exposure induces vascular 

12 oxidative stress and proinflammatory mediators, alters HR and HRV, and disrupts the 

13 regulation of the pulmonary endothelin system (study details are provided in Table 6-40). 

14 A number of these effects were variable between strains examined, suggesting a genetic 

15 component to development of O3 induced cardiovascular effects. Further, recent studies 

16 provide evidence that extended O3 exposure enhances the risk of ischemia-reperfusion 

17 (I/R) injury and atherosclerotic lesion development. Still, few studies have investigated 

18 the role of O3 reaction products in these processes, but more evidence is provided for

19 elevated inflammatory and reduction-oxidation (redox) cascades known to initiate these 

20 cardiovascular pathologies. 

Heart Rate, Rhythm, and Heart Rate Variability

21 Studies (Arito et al., 1992; Arito et al., 1990; Uchiyama and Yokoyama, 1989; 

22 Yokoyama et al., 1989; Uchiyama et al., 1986) report O3 exposure (0.2-1.0 ppm, 3 hours 

23 to 3 days) in rats decreased TCO, HR, and mean arterial pressure (MAP). In addition, O3

24 exposure (0.1 – 1.0 ppm, 3 hours to 3 days) in rats induced arrhythmias, including 

25 increased PR interval and QRS complex, premature atrial contraction, and incomplete 

26 A-V block (Arito et al., 1990; Yokoyama et al., 1989; Uchiyama et al., 1986). The effects 

27 were more pronounced in adult and awake rats than in younger or sleeping animals, 

28 whereas no sex-related differences were noted in these O3 induced outcomes (Uchiyama 

29 et al., 1986). However, these cardiovascular responses to O3, including decreased TCO and 

30 HR, could be attenuated by increased ambient temperatures and environmental stress and 

31 exhibited adaptation (Watkinson et al., 2003; Watkinson et al., 1993). These studies 

32 suggest that these responses to O3 were the result of the rodent hypothermic response, 
Draft – Do Not Cite or Quote 6-211 June 2012

1 which serves as a physiological and behavioral defense mechanism to minimize the 

2 irritant effects of O3 inhalation, (Iwasaki et al., 1998; Arito et al., 1997). As humans do 

3 not appear to exhibit decreased HR, MAP, and TCO with routine environmental 

4 (Section 6.3.2) or controlled laboratory (Section 6.3.1) exposures to O3, caution must be 

5 used in extrapolating the results of these animal studies to humans. 

6 Other studies have shown that O3 can increase BP in animal models. Rats exposed to 

7 0.6 ppm O3 for 33 days had increased systolic pressure and HR (Revis et al., 1981). 

8 Increased BP triggers the release of atrial natriuretic factor (ANF), which has been found 

9 in increased levels in the heart, lungs, and circulation of O3 exposed (0.5 ppm) rats 

10 (Vesely et al., 1994a, b, c). Exposures to high concentrations of O3 (1.0 ppm) have also 

11 been found to lead to heart and lung edema (Friedman et al., 1983), which could be the 

12 result of increased ANF levels. Thus, O3 may increase blood pressure and HR, leading to 

13 increased ANF and tissue edema. 

14 Recent studies report strain differences in HR and HRV in response to a 2-hour O3

15 pretreatment followed by exposure to carbon black (CB) in mice (C3H/HeJ [HeJ], 

16 C57BL/6J [B6], and C3H/HeOuJ [OuJ]) (Hamade and Tankersley, 2009; Hamade et al., 

17 2008). These mice strains were chosen from prior studies on lung inflammatory and 

18 hyperpermeability responses to be at increased risk (B6 and OuJ) or resistant (HeJ) to 

19 O3-induced health effects (Kleeberger et al., 2000). HR decreased during O3 pre-exposure 

20 for all strains, but recovered during the CB exposure (Hamade et al., 2008). Percent 

21 change in HRV parameters, SDNN (indicating total HRV) and rMSSD (indicating beat22 to-beat HRV), were increased in both C3H mice strains, but not B6 mice, during O3

23 pre-exposure and recovered during CB exposure when compared to the filtered air group. 

24 The two C3H strains differ by a mutation in the Toll-like receptor 4 (TLR4) gene, but 

25 these effects did not seem to be related to this mutation since similar responses were 

26 observed. Hamade et al. (2008) speculate that the B6 and C3H strains differ in 

27 mechanisms of HR response after O3 exposure between withdrawal of sympathetic tone 

28 and increase of parasympathetic tone; however, no direct evidence for this conclusion 

29 was reported. The strain differences observed in HR and HRV suggest that genetic 

30 variability affects cardiac responses after acute air pollutant exposures. 

31 Hamade and Tankersley (2009) continued this investigation of gene-environment 

32 interactions on cardiopulmonary adaptation of O3 and CB induced changes in HR and 

33 HRV using the previously described (Hamade et al., 2008) daily exposure scheme for 3 

34 consecutive days. By comparing day-1 interim values it is possible to observe that O3

35 exposure increased SDNN and rMSSD, but decreased HR in all strains. Measures of HR 

36 and HRV in B6 and HeJ mice recovered to levels consistent with filtered air treated mice 

37 by day 3; however, these responses in OuJ mice remained suppressed. B6 mice had no 
Draft – Do Not Cite or Quote 6-212 June 2012

1 change in respiratory rate (RR) after O3 treatment, whereas HeJ mice on days 1 and 2 had 

2 increased RR and OuJ mice on days 2 and 3 exhibited increased RR. VT did not change 

3 with treatment among the strains. Overall, B6 mice were mildly responsive with rapid 

4 adaptation, whereas C3 mice were highly responsive with adaptation only in HeJ mice 

5 with regards to changes in cardiac and respiratory responses. HR and HRV parameters 

6 were not equally correlated with VT and RR between the three mice strains, which 

7 suggest that strains vary in the integration of the cardiac and respiratory systems. These 

8 complex interactions could help explain variability in interindividual responses to air 

9 pollution.

10 Hamade et al. (2010) expanded their investigation to explore the variation of these strain 

11 dependent cardiopulmonary responses with age. As was observed previously, all 

12 experimental mouse strains (B6, HeJ, and OuJ) exhibited decreased HR and increased 

13 HRV after O3 exposure. Younger O3-exposed mice had a significantly lower HR 

14 compared to older exposed mice, indicating an attenuation of the bradycardic effect of O3

15 with age. Younger mice also had a greater increase in rMSSD in HeJ and OuJ strains and 

16 SDNN in HeJ mice. Conversely, B6 mice had a slightly greater increase in SDNN in 

17 aged mice compared to the young mice. No change was observed in the magnitude of the 

18 O3 induced increase of SDNN in OuJ mice or rMSSD in B6 mice. The B6 and HeJ mice 

19 genetically vary in respect to the nuclear factor erythroid 2-related factor 2 (Nrf-2). The 

20 authors propose that the genetic differences between the mice strains could be altering the 

21 formation of ROS, which tends to increase with age, thus modulating the changes in 

22 cardiopulmonary physiology after O3 exposure. 

23 Strain and age differences in HR and heart function were further investigated in B6 and 

24 129S1/SvlmJ (129) mice in response to a sequential O3 and filtered air or CB exposure 

25 (Tankersley et al., 2010). Young 129 mice showed a decrease in HR after O3 or O3 and 

26 CB exposure. This bradycardia was not observed in B6 or older animals in this study, 

27 suggesting a possible alteration or adaptation of the autonomic nervous system activity 

28 with age. However, these authors did previously report bradycardia in similarly aged 

29 young B6 mice (Hamade et al., 2010; Hamade and Tankersley, 2009; Hamade et al., 

30 2008). Ozone exposure in 129 mice also resulted in an increase in left ventricular 

31 chamber dimensions at end diastole (LVEDD) in young and old mice and a decrease in 

32 left ventricular posterior wall thickness at end systole (PWTES) in older mice. The 

33 increase in LVEDD caused a decrease in fractional shortening, which can be used as a 

34 rough indicator of left ventricular function. Regression analysis revealed a significant 

35 interaction between age and strain on HR and PWTES, which implies that aging affects 

36 HR and heart function in response to O3 differently between mouse strains.
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Vascular Disease and Injury

1 A recent study in young mice (C57Bl/6) and rhesus monkeys examined the effects of 

2 short-term O3 exposure (0.5 ppm, 1 or 5 days) on a number of cardiovascular endpoints 

3 (Chuang et al., 2009). Mice exposed to O3 for 5 days had increased HR as well as mean 

4 and diastolic blood pressure. This is in contrast to the bradycardia that was reported in 

5 18-20 week-old B6 mice treated with O3, as described above (Hamade and Tankersley, 

6 2009; Hamade et al., 2008). Increased blood pressure could be explained by the inhibition 

7 in endothelial-dependent (acetylcholine) vasorelaxation from decreased bioavailability of 

8 aortic nitric oxide (·NO). Ozone caused a decrease in aortic NOX (nitrite and nitrate 

9 levels) and a decrease in total, but not phosphorylated, endothelial nitric oxide synthase 

10 (eNOS). Ozone also increased vascular oxidative stress in the form of increased aortic 

11 and lung lipid peroxidation (F2-isoprostane), increased aortic protein nitration (3-

12 nitrotyrosine), decreased aortic superoxide dismutase (SOD2) protein and activity, and 

decreased aortic aconitase activity, indicating specific inactivation by O2

- and ONOO- 13 . 

14 Mitochondrial DNA (mtDNA) damage was also used as a measure of oxidative and 

15 nitrative stress in mice and infant rhesus monkeys exposed to O3. Chuang et al. (2009)

16 observed that mtDNA damage accumulated in the lung and aorta of mice after 1 and 

17 5 days of O3 exposure and in the proximal and distal aorta of O3 treated nonhuman 

18 primates. Additionally, genetically hyperlipidemic mice exposed to O3 (0.5 ppm) for 

19 8 weeks had increased aortic atherosclerotic lesion area (Section 7.3.1), which may be 

20 associated with the short-term exposure changes discussed. Overall, this study suggests 

that O3 initiates an oxidative environment by increasing O2

- 21 production, which leads to 

22 mtDNA damage and ·NO consumption, known to perturb endothelial function (Chuang 

23 et al., 2009). Endothelial dysfunction is characteristic of early and advanced 

24 atherosclerosis and coincides with impaired vasodilation and blood pressure regulation.

25 Vascular occlusion resulting from atherosclerosis can block blood flow causing ischemia. 

26 The restoration of blood flow in the vessel or reperfusion can cause injury to the tissue 

27 from subsequent inflammation and oxidative damage. Perepu et al. (2010) observed that 

28 O3 exposure (0.8 ppm, 28 or 56 days) enhanced the sensitivity to myocardial I/R injury in 

29 Sprague-Dawley rats while increasing oxidative stress levels and pro-inflammatory 

30 mediators and decreasing production of anti-inflammatory proteins. Ozone was also 

31 found to decrease the left ventricular developed pressure, rate of change of pressure 

32 development, and rate of change of pressure decay while increasing left ventricular end 

33 diastolic pressure in isolated perfused hearts. In this ex vivo heart model, O3 induced 

34 oxidative stress by decreasing SOD enzyme activity and increasing malondialdehyde 

35 levels. Ozone also elicited a proinflammatory state which was evident by an increase in 

36 TNF-α and a decrease in the anti-inflammatory cytokine IL-10. Perepu et al. (2010)

37 concluded that O3 exposure may result in a greater I/R injury.
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Effects on Cardiovascular-Related Proteins

1 Increased BP, changes in HRV, and increased atherosclerosis may be related to increases 

2 in the vasoconstrictor peptide, endothelin-1 (amino acids 1-21, ET-1[1-21]). Regulation of 

3 the pulmonary endothelin system can be affected in rats by inhalation of PM (0, 5, 

50 mg/m3 4 , EHC-93) and O3 (Thomson et al., 2006; Thomson et al., 2005). Exposure to 

either O3 (0.8 ppm) or PM increased plasma ET-1[1-21], ET-3[1-21] 5 , and the ET-1 precursor 

6 peptide, bigET-1. Increases in circulating ET-1[1-21] could be a result of a transient 

7 increase in the gene expression of lung preproET-1 and endothelin converting enzyme-1 

8 (ECE-1) immediately following inhalation of O3 or PM. These latter gene expression 

9 changes (e.g., preproET-1 and ECE-1) were additive with co-exposure to O3 and PM. 

10 Conversely, preproET-3 decreased immediately after O3 exposure, suggesting the 

11 increase in ET-3[1-21] was not through de novo production. A recent study also found 

12 increased ET-1 gene expression in the aorta of O3-exposed rats (Kodavanti et al., 2011). 

13 These rats also exhibited an increase in ETBR after O3 exposure; however, they did not 

14 demonstrate increased biomarkers for vascular inflammation, thrombosis, or oxidation.

15 O3 can oxidize protein functional groups and disturb the affected protein. For example, 

16 the soluble plasma protein fibrinogen is oxidized by O3 (0.01-0.03 ppm) in vitro, creating 

17 fibrinogen and fibrin aggregates, characteristically similar to defective fibrinogen 

18 (Rosenfeld et al., 2009; Rozenfeld et al., 2008). In these studies, oxidized fibrinogen 

19 retained the ability to form fibrin gels that are involved in coagulation, however the 

20 aggregation time increased and the gels were rougher than normal with thicker fibers. 

21 Oxidized fibrinogen also developed the ability to self assemble creating fibrinogen 

22 aggregates that may play a role in thrombosis. Since O3 does not readily translocate past 

23 the ELF and pulmonary epithelium and fibrinogen is primarily a plasma protein, it is 

24 uncertain if O3 would have the opportunity to react with plasma fibrinogen. However, 

25 fibrinogen can be released from the basolateral face of pulmonary epithelial cells during 

26 inflammation, where the deposition of fibrinogen could lead to lung injury (Lawrence 

27 and Simpson-Haidaris, 2004).

Studies on Ozone Reaction Products

28 Although toxicological studies have demonstrated O3-induced effects on the 

29 cardiovascular system, it remains unclear if the mechanism is through a reflex response 

30 or the result of effects from O3 reaction products (U.S. EPA, 2006b, 1996a). Oxysterols 

31 derived from cholesterol ozonation, such as β-epoxide and 5β,6β-epoxycholesterol (and 

32 its metabolite cholestan-6-oxo-3,5-diol), have been implicated in inflammation associated 

33 with cardiovascular disease (Pulfer et al., 2005; Pulfer and Murphy, 2004). Two other 

34 cholesterol ozonolysis products, atheronal-A and -B (e.g., cholesterol secoaldehyde), 
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1 have been found in human atherosclerotic plaques and shown in vitro to induce foam cell 

2 formation and induce cardiomyocyte apoptosis and necrosis (Sathishkumar et al., 2005; 

3 Wentworth et al., 2003); however, these products have not been found in the lung 

4 compartment or systemically after O3 exposure. The ability to form these cholesterol 

5 ozonation products in the circulation in the absence of O3 exposure complicates their 

6 implication in O3 induced cardiovascular disease.

7 Although it has been proposed that O3 reaction products released after the interaction of 

8 O3 with ELF constituents (see Section 5.2.3) on O3 interaction with ELF) are responsible 

9 for systemic effects, it is not known whether they gain access to the vascular space. 

10 Alternatively, extrapulmonary release of diffusible mediators, such as cytokines or 

11 endothelins, may initiate or propagate inflammatory responses in the vascular or systemic 

12 compartments (Cole and Freeman, 2009) (Section 5.3.8). Ozone reacts within the lung to 

13 amplify ROS production, induce pulmonary inflammation, and activate inflammatory 

14 cells, resulting in a cascading proinflammatory state and extrapulmonary release of 

15 diffusible mediators that could lead to cardiovascular injury. 

16 A recent study that examined O3 reaction byproducts has shown that cholesterol 

17 secoaldehyde (e.g., atheronal A) induces apoptosis in vitro in mouse macrophages (Gao 

18 et al., 2009b) and cardiomyocytes (Sathishkumar et al., 2009). Additionally, atheronal-A 

19 and -B has been found to induce in vitro macrophage and endothelial cell 

20 proinflammatory events involved in the initiation of atherosclerosis (Takeuchi et al., 

21 2006). These O3 reaction products when complexed with low density lipoprotein 

22 upregulate scavenger receptor class A and induce dose-dependent macrophage 

23 chemotaxis. Atheronal-A increases expression of the adhesion molecule, E-selectin, in 

24 endothelial cells, while atheronal-B induces monocyte differentiation. These events 

25 contribute to both monocyte recruitment and foam cell formation in atherosclerotic 

26 vessels. It is unknown whether these O3 reaction products gain access to the vascular 

27 space from the lungs. Alternative explanations include the extrapulmonary release of 

28 diffusible mediators that may initiate or propagate inflammatory responses in the vascular 

29 or systemic compartments.
Draft – Do Not Cite or Quote 6-216 June 2012

Table 6-40 Characterization of study details for Section 6.3.3.

Studya* Model O3 (ppm) Exposure Duration Effects

Chuang et al. (2009) Mice; C57Bl/6; 

M; 6 weeks

0.5 1 or 5 days, 8-h/day Increased HR and blood pressure. 

Initiated an oxidative environment by 

increasing vascular O2

-

production, which 

lead to mtDNA damage and ·NO 

consumption, known to perturb 

endothelial function.

Monkey; rhesus 

Macaca mulatta; 

M; Infant (180 days 

old)

0.5 5 days, 8-h/day Increased aortic mtDNA damage.

Perepu et al. (2010) Rat; Sprague-Dawley; 

50-75 g

0.8 28 days, 8-h/day Enhanced the sensitivity to myocardial I/R 

injury while increasing oxidative stress 

and pro-inflammatory mediators and 

decreasing production of 

anti-inflammatory proteins.

Hamade et al. (2008) Mice; C57Bl/6J, 

C3H/HeJ, and 

C3H/HeOuJ; 

M; 18-20 weeks

0.6

(subsequent 

CB 

exposure, 

536 μg/m3

)

2-h

followed by 3 h of CB

Decreased HR. Strain differences 

observed in HRV suggest that genetic 

variability affects cardiac responses.

Hamade and 

Tankersley (2009)

Mice; C57Bl/6J, 

C3H/HeJ, and 

C3H/HeOuJ; 

M; 18-20 weeks

0.6

(subsequent 

CB 

exposure, 

536 μg/m3

)

3 days, 2-h/day 

followed by 3-h of CB

Strains varied in integration of the cardiac 

and respiratory systems, implications in 

interindividual variability. B6 mice were 

mildly responsive with rapid adaptation, 

whereas C3 mice were highly responsive 

with adaptation only in HeJ mice with 

regards to changes in cardiac and 

respiratory responses.

Hamade et al. (2010) Mice; C57Bl/6J, 

C3H/HeJ, and 

C3H/HeOuJ; M; 

5 or 12 mo old

0.6

(subsequent 

CB 

exposure, 

536 μg/m3

)

2-h

followed by 3-h of CB

Aged mice exhibited attenuated changes 

in cardiopulmonary physiology after O3

exposure. Genetic differences between 

mice strains could be altering formation of 

ROS, which tends to increase with age, 

thus modulating O3 induced effects.

Tankersley et al. 

(2010)

Mice; C57Bl/6J, 

129S1/SvlmJ; 

M/F; 5 or 18 mo old

0.6

(subsequent 

CB 

exposure, 

556 μg/m3

)

2-h

followed by 3-h of CB

Significant interaction between age and 

strain on HR and PWTES, which implies 

that aging affects the HR and function in 

response to O3 differently between mouse 

strains.

Thomson et al. 

(2005)

Rat; Fischer-344; 

M; 200-250 g

0.4 or 0.8 4-h Activation of the vasoconstricting ET 

system. Increased plasma ET-1 through 

higher production and slower clearance.

Thomson et al. 

(2006)

Rat; Fischer-344; 

M; 200-250 g

0.8 4-h Increased plasma ET-3 not due to de 

novo synthesis, unlike ET-1.

Kodavanti et al. 

(2011)

Rat; Wistar; 

M; 10-12 weeks

0.5 or 1.0 2 days, 5-h/day No changes to aortic genes of 

thrombosis, inflammation, or proteolysis, 

except ET-1 and ETBR (1.0 ppm).

a

Results from previous studies are presented in Table AX5-14 of the 2006 O3 AQCD and Table 6-23 of the 1996 O3 AQCD.

*Study details for Section 6.3.3a
Draft – Do Not Cite or Quote 6-217 June 2012

Summary of Toxicological Studies

1 Overall, animal studies suggest that O3 exposure may result in O3 induced cardiovascular 

2 effects. Studies provide evidence for both increased and decreased HR, however it is 

3 uncertain if O3-induced bradycardia would also occur in humans or if it is due solely to a 

4 rodent hypothermic response. Animal studies also provide evidence for increased HRV, 

5 arrhythmias, vascular disease, and injury following short-term O3 exposure. In addition, a 

6 series of studies highlight the role of gene-environment interactions and age in the 

7 induction of effects and attenuation of responses to O3 exposure.

8 Biologically plausible mechanisms are present for the cardiovascular effects observed in 

9 animal exposure studies, however there is a lack of coherence with controlled human 

10 exposure and epidemiologic studies. Further discussion of the modes of action that may 

11 lead to cardiovascular effects can be found in Section 5.3.8. Recent studies suggest that 

12 O3 exposure may disrupt both the NO ̇ and endothelin systems, which can result in an 

13 increase in HR, HRV, and ANF. The observed bradycardia following O3 exposure may 

14 be the result of reflex reactions, including the trigeminocardiac reflex, evoked following 

15 the stimulation of sensory receptors lining the nose and RT. These mechanisms of 

16 parasympathetically-derived cardiac effects are described in more detail in Section 5.3.2. 

17 Additionally, O3 may increase oxidative stress and vascular inflammation promoting the 

18 progression of atherosclerosis and leading to increased susceptibility to I/R injury. As O3

19 reacts quickly with the ELF and does not translocate to the heart and large vessels, 

20 studies suggest that the cardiovascular effects exhibited could be caused by reaction 

21 byproducts of O3 exposure. However, direct evidence of translocation of O3 reaction 

22 products to the cardiovascular system has not been demonstrated in vivo. Alternatively, 

23 extrapulmonary release of diffusible mediators, such as cytokines or endothelins, may 

24 initiate or propagate inflammatory responses in the vascular or systemic compartments 

25 leading to the reported cardiovascular pathologies.

6.3.4 Summary and Causal Determination

26 In previous O3 reviews (U.S. EPA, 2006b, 1996a) very few studies examined the effect of 

27 short-term O3 exposure on the cardiovascular system. More recently, the body of 

28 scientific evidence available that has examined the effect of O3 on the cardiovascular 

29 system has advanced, but overall still remains small.

30 Although limited in number, toxicological studies have provided evidence of O3-induced 

31 cardiovascular effects. Animal toxicological studies have reported enhanced I/R injury, 

32 disrupted NO-induced vascular reactivity, decreased cardiac function, increased vascular 

33 disease, and increased HRV following short-term O3 exposure. The observed increase in 
Draft – Do Not Cite or Quote 6-218 June 2012

1 HRV is supported by a recent controlled human exposure study that also found increased 

2 high frequency HRV, but not altered blood pressure, following O3 exposure (Fakhri et al., 

3 2009). Toxicological studies investigating the role of O3 in heart rate regulation are 

4 mixed with both bradycardic and tachycardic responses observed. However, these 

5 changes in cardiac function provide preliminary evidence for O3-induced modulation of 

6 the autonomic nervous system leading to cardiovascular complications. It is still 

7 uncertain how O3 inhalation may cause systemic toxicity; however the cardiovascular 

8 effects of O3 found in animals correspond to the development and maintenance of an 

9 extrapulmonary oxidative, proinflammatory environment that may result from pulmonary 

10 inflammation.

11 The epidemiologic studies evaluated do not support the evidence of O3-induced 

12 cardiovascular effects observed in the toxicological studies. This is highlighted by the 

13 multiple studies that examined the association between short-term O3 exposure and 

14 cardiovascular-related hospital admissions and ED visits and other various cardiovascular 

15 effects and found no evidence of a consistent relationship with O3 exposure. Although 

16 there is inconsistent evidence for O3-induced cardiovascular morbidity in the 

17 epidemiologic literature, single-city studies reviewed in the 2006 O3 AQCD, and recent 

18 multicity studies, and a multicontinent study demonstrate consistent positive associations 

19 between short-term O3 exposure and cardiovascular mortality. Additionally, O3 mortality 

20 associations were found to remain robust in copollutant models with PM. However, the 

21 lack of coherence between the results from studies that examined associations between 

22 short-term O3 exposure and cardiovascular morbidity and subsequently cardiovascular 

23 mortality complicate the interpretation of the overall evidence for O3-induced 

24 cardiovascular effects.

25 In conclusion, animal toxicological studies provide some evidence for O3-induced 

26 cardiovascular effects, but the effects observed were not consistently supported by 

27 controlled human exposure studies or epidemiologic studies. Although the toxicological 

28 evidence provides initial support to the relatively strong body of evidence indicating 

29 O3-induced cardiovascular mortality, there is a lack of coherence with controlled human 

30 exposure and epidemiologic studies of cardiovascular morbidity which together do not 

31 support O3-induced cardiovascular effects. Thus, the overall body of evidence across 

32 disciplines is suggestive of a causal relationship between relevant short-term 

33 exposures to O3 and cardiovascular effects.
Draft – Do Not Cite or Quote 6-219 June 2012

6.4 Central Nervous System Effects 

1 The 2006 O3 AQCD included toxicological evidence that acute exposures to O3 are 

2 associated with alterations in neurotransmitters, motor activity, short and long term 

3 memory, and sleep patterns. Additionally, histological signs of neurodegeneration have 

4 been observed. Reports of headache, dizziness, and irritation of the nose with O3

5 exposure are common complaints in humans, and some behavioral changes in animals 

6 may be related to these symptoms rather than indicative of neurotoxicity. Peterson and 

7 Andrews (1963) and Tepper et al. (1983) showed that mice would alter their behavior to 

8 avoid O3 exposure. Murphy et al. (1964) and Tepper et al. (1982) showed that running9 wheel behavior was suppressed, and Tepper et al. (1985) subsequently demonstrated the 

10 effects of a 6-hour exposure to O3 on the suppression of running-wheel behavior in rats 

11 and mice, with the lowest effective concentration being about 0.12 ppm O3 in the rat and 

12 about 0.2 ppm in the mouse. The suppression of active behavior by 6 hours of exposure 

13 to 0.12 ppm O3 has recently been confirmed by Martrette et al. (2011) in juvenile female 

14 rats, and the suppression of three different active behavior parameters was found to 

15 become more pronounced after 15 days of exposure. A table of studies examining the 

16 effects of O3 on behavior can be found on p 6-128 of the 1996 O3 AQCD. Generally 

17 speaking, transient changes in behavior in rodent models appear to be dependent on a 

18 complex interaction of factors such as (1) the type of behavior being measured, with 

19 some behaviors increased and others suppressed; (2) the factors motivating that behavior 

20 (differences in reinforcement); and (3) the sensitivity of the particular behavior 

21 (e.g., active behaviors are more affected than more sedentary behaviors). Many 

22 behavioral changes are likely to result from avoidance of irritation, but more recent 

23 studies indicate that O3 also directly affects the CNS.

24 Research in the area of O3-induced neurotoxicity has notably increased over the past few 

25 years, with the majority of the evidence coming from toxicological studies that examined 

26 the association between O3 exposure, neuropathology, and neurobehavioral effects, and 

27 more limited evidence from epidemiologic studies. In an epidemiologic study conducted 

28 by Chen and Schwartz (2009), data from the NHANES III cohort was utilized to study 

29 the relationship between long-term O3 exposure (mean annual O3 concentration of 

30 26.5 ppb) and neurobehavioral effects among adults aged 20-59 years. The authors 

31 observed an association between annual exposure to O3 and tests measuring coding 

32 ability and attention/short-term memory. Each 10-ppb increase in annual O3 levels 

33 corresponded to an aging-related cognitive performance decline of 3.5 years for coding 

34 ability and 5.3 years for attention/short-term memory. These associations persisted in 

35 both crude and adjusted models. There was no association between annual O3

36 concentrations and reaction time tests. The authors conclude that overall there is a 

37 positive association between O3 exposure and reduced performance on neurobehavioral 
Draft – Do Not Cite or Quote 6-220 June 2012

1 tests. Although Chen and Schwartz (2009) is a long-term exposure study, it is included in 

2 this section because it is the first epidemiologic study to demonstrate that exposure to 

3 ambient O3 is associated with decrements in neurocognitive tests related to memory and 

4 attention in humans. This epidemiologic evidence of an effect on the CNS due to 

5 exposure to ambient concentrations of O3 is coherent with animal studies demonstrating 

6 that exposure to O3 can produce a variety of CNS effects including behavioral deficits, 

7 morphological changes, and oxidative stress in the brains of rodents. In these rodent 

8 studies, interestingly, CNS effects were reported at O3 concentrations that were generally 

9 lower than those concentrations commonly observed to produce pulmonary or cardiac 

10 effects in rats. 

11 A number of new studies demonstrate various perturbations in neurologic function or 

12 histology, including changes similar to those observed with Parkinson’s and Alzheimer’s 

13 disease pathologies occurring in similar regions of the brain (Table 6-41). Many of these 

14 include exposure durations ranging from short-term to long-term, and as such are 

15 discussed here and in Chapter 7 with emphasis on the effects resulting from exposure 

16 durations relevant to the respective chapter. Several studies assess short- and long-term 

17 memory acquisition via passive avoidance behavioral testing and find decrements in test 

18 performance after O3 exposure, consistent with the aforementioned observation made in 

19 humans by Chen and Schwartz (2009). Impairment of long-term memory has been 

20 previously described in rats exposed to 0.2 ppm O3 for 4 hours (Rivas-Arancibia et al., 

21 1998) and in other studies of 4-hour exposures at concentrations of 0.7 to 1 ppm (Dorado22 Martinez et al., 2001; Rivas-Arancibia et al., 2000; Avila-Costa et al., 1999). More 

23 recently, statistically significant decreases in both short and long-term memory were 

24 observed in rats after 15 days of exposure to 0.25 ppm O3 (Rivas-Arancibia et al., 2010).

25 The central nervous system is very sensitive to oxidative stress, due in part to its high 

26 content of polyunsaturated fatty acids, high rate of oxygen consumption, and low 

27 antioxidant enzyme capacity. Oxidative stress has been identified as one of the 

28 pathophysiological mechanisms underlying neurodegenerative disorders such as 

29 Parkinson’s and Alzheimer’s disease, among others (Simonian and Coyle, 1996). It is 

30 also believed to play a role in altering hippocampal function, which causes cognitive 

31 deficits with aging (Vanguilder and Freeman, 2011). A particularly common finding in 

32 studies of O3-exposed rats is lipid peroxidation in the brain, especially in the 

33 hippocampus, which is important for higher cognitive function including contextual 

34 memory acquisition. Performance in passive avoidance learning tests is impaired when 

35 the hippocampus is injured, and the observed behavioral effects are well correlated with 

36 histological and biochemical changes in the hippocampus, including reduction in spine 

37 density in the pyramidal neurons (Avila-Costa et al., 1999), lipoperoxidation (Rivas38 Arancibia et al., 2010; Dorado-Martinez et al., 2001), progressive neurodegeneration, and 
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1 activated and phagocytic microglia (Rivas-Arancibia et al., 2010). The hippocampus is 

2 also one of the main regions affected by age-related neurodegenerative diseases, 

3 including Alzheimer’s disease, and it may be more sensitive to oxidative damage in aged 

4 rats. In a study of young (47 days) and aged (900 days) rats exposed to 1 ppm O3 for 4 h, 

5 O3-induced lipid peroxidation occurred to a greater extent in the striatum of young rats, 

6 whereas it was highest in the hippocampus in aged rats (Rivas-Arancibia et al., 2000). 

7 Martínez-Canabal and Angora-Perez (2008) showed exposure of rats to 0.25 ppm, 

8 4h/day, for 7, 15, or 30 days increased lipoperoxides in the hippocampus. This effect was 

9 observed at day 7 and continued to increase with time, indicating cumulative oxidative 

10 damage. O3-induced changes in lipid peroxidation, neuronal death, and COX-2 positive 

11 cells in the hippocampus could be significantly inhibited by daily treatment with growth 

12 hormone (GH), which declines with age in most species. The protective effect of GH on 

13 -induced oxidative stress was greatest at 15 days of exposure and was non-significant at 

14 day 30. Consistent with these findings, lipid peroxidation in the hippocampus of rats was 

15 observed to increase significantly after a 30-day exposure to 0.25 ppm , but not after a 

16 single 4-hour exposure to the same concentration (Mokoena et al., 2010). However, 

17 4 hours of exposure was sufficient to cause significant increases in lipid peroxidation 

18 when the concentration was increased to 0.7 ppm, and another study observed lipid 

19 peroxidation after a 4-hour exposure to 0.4 ppm (Dorado-Martinez et al., 2001). 

20 Other commonly affected areas of the brain include the striatum, substantia nigra, 

21 cerebellum, olfactory bulb, and frontal/prefrontal cortex. The striatum and substantia 

22 nigra are particularly sensitive to oxidative stress because the metabolism of dopamine, 

23 central to their function, is an oxidative process perturbed by redox imbalance. Oxidative 

24 stress has been implicated in the premature death of substantia nigra dopamine neurons in 

25 Parkinson’s disease. Angoa-Pérez et al. (2006) have shown progressive lipoperoxidation 

26 in the substantia nigra and a decrease in nigral dopamine neurons in ovariectomized 

27 female rats exposed to 0.25 ppm O3, 4h/day, for 7, 15, or 30 days. Estradiol, an 

28 antioxidant, attenuated O3-induced oxidative stress and nigral neuronal death, and the 

29 authors note that in humans, estrogen therapy can ameliorate symptoms of Parkinson’s 

30 disease, which is more prevalent in men. Progressive oxidative stress has also been 

31 observed in the striatum and substantia nigra of rats after 15 and 30 days of exposure to 

32 0.25 ppm O3 for 4 h/day, along with a loss of dopaminergic neurons from the substantia 

33 nigra (Pereyra-Muñoz et al., 2006). Decreases in motor activity were also observed at 15 

34 and 30 days of exposure, consistent with other reports (Martrette et al., 2011; Dorado35 Martinez et al., 2001). Using a similar O3 exposure protocol, Santiago-López et al. (2010)

36 also observed a progressive loss of dopaminergic neurons within the substantia nigra, 

37 accompanied by alterations in the morphology of remaining cells and an increase in p53 

38 levels and nuclear translocation. 
Draft – Do Not Cite or Quote 6-222 June 2012

1 The olfactory bulb also undergoes oxidative damage in O3 exposed animals, in some 

2 cases altering olfactory-dependent behavior. Lipid peroxidation was observed in the 

3 olfactory bulbs of ovariectomized female rats exposed to 0.25 ppm O3 (4 h/day) for 30 or 

4 60 days (Guevara-Guzmán et al., 2009). O3 also induced decrements in a selective 

5 olfactory recognition memory test, and the authors note that early deficits in odor 

6 perception and memory are components of human neurodegenerative diseases. The 

7 decrements in olfactory memory were not due to damaged olfactory perception based on 

8 other tests. However, deficits in olfactory perception emerged with longer exposures 

9 (discussed in Chapter 7). As with the study by Angoa-Pérez et al. (2006) described 

10 above, a protective effect for estradiol was demonstrated for both lipid peroxidation and 

11 olfactory memory defects. The role of oxidative stress in memory deficits and associated 

12 morphological changes has also been demonstrated via attenuation by other antioxidants 

13 as well, such as α-tocopherol (Guerrero et al., 1999) and taurine (Rivas-Arancibia et al., 

14 2000).It is unclear how persistent these effects might be. One study of acute exposure, 

15 using 1 ppm O3 for 4 hours, observed morphological changes in the olfactory bulb of rats 

16 at 2 hours, and 1 and 10 days, but not 15 days, after exposure (Colín-Barenque et al., 

17 2005). 

18 Other acute studies also report changes in the CNS. Lipid peroxidation was observed in 

19 multiple regions of the brain after a 1- to 9-hour exposure to 1 ppm O3 (Escalante20 Membrillo et al., 2005). Ozone has also been shown to alter gene expression of 

21 endothelin-1 (pituitary) and inducible nitric oxide synthase (cerebral hemisphere) after a 

22 single 4-hour exposure to 0.8 ppm O3, indicating potential cerebrovascular effects. This 

23 concentration-dependent effect was not observed at 0.4 ppm O3 (Thomson et al., 2007). 

24 Vascular endothelial growth factor was upregulated in astroglial cells in the central 

25 respiratory areas of the brain of rats exposed to 0.5 ppm O3 for 3 hours (Araneda et al., 

26 2008). The persistence of CNS changes after a single exposure was also examined and 

27 the increase in vascular endothelial growth factor was present after a short (3 hours) 

28 recovery period. Thus, there is evidence that O3-induced CNS effects are both 

29 concentration- and time-dependent. 

30 Because O3 can produce a disruption of the sleep-wake cycle (U.S. EPA, 2006b), Alfaro31 Rodríguez and González-Piña (2005) examined whether acetylcholine in a region of the 

32 brain involved in sleep regulation was altered by O3. After a 24-hour exposure to 0.5 ppm 

33 O3, the acetylcholine concentration in the medial preoptic area was decreased by 58% and 

34 strongly correlated with a disruption in paradoxical sleep. Such behavioral-biochemical 

35 effects of O3 are confirmed by a number of studies which have demonstrated 

36 morphological and biochemical changes in rats.
Draft – Do Not Cite or Quote 6-223 June 2012

1 CNS effects have also been demonstrated in newborn and adult rats whose only exposure 

2 to O3 occurred in utero. Several neurotransmitters were assessed in male offspring of 

3 dams exposed to 1 ppm O3 during the entire pregnancy (Gonzalez-Pina et al., 2008). The 

4 data showed that catecholamine neurotransmitters were affected to a greater degree than 

5 indole-amine neurotransmitters in the cerebellum. CNS changes, including behavioral, 

6 cellular, and biochemical effects, have also been observed after in utero exposure to 

7 0.5 ppm O3 for 12 h/day from gestational days 5-20 (Boussouar et al., 2009). Tyrosine 

8 hydroxylase labeling in the nucleus tractus solatarius was increased after in utero 

9 exposure to O3 whereas Fos protein labeling did not change. When these offspring were 

10 challenged by immobilization stress, neuroplasticity pathways, which were activated in 

11 air-exposed offspring, were inhibited in O3-exposed offspring. Although an O3 exposure 

12 C-R was not studied in these two in utero studies, it has been examined in one study. 

13 Santucci et al. (2006) investigated behavioral effects and gene expression after in utero 

14 exposure of mice to as little as 0.3 ppm O3. Increased defensive/submissive behavior and 

15 reduced social investigation were observed in both the 0.3 and 0.6 ppm O3 groups. 

16 Changes in gene expression of brain-derived neurotrophic factor (BDNF, increased in 

17 striatum) and nerve growth factor (NGF, decreased in hippocampus) accompanied these 

18 behavioral changes. Thus, these three studies demonstrate that CNS effects can occur as a 

19 result of in utero exposure to O3, and although the mode of action of these effects is not 

20 known, it has been suggested that circulating lipid peroxidation products may play a role 

21 (Boussouar et al., 2009). Importantly, these CNS effects occurred in rodent models after 

22 in utero only exposure to relevant concentrations of O3. 
Draft – Do Not Cite or Quote 6-224 June 2012

Table 6-41 Central nervous system and behavioral effects of short-term ozone

exposure in rats

Study Model O3

(ppm)

Exposure 

Duration

Effects

Martrette et al. (2011) Rat; Wistar; 

F; Weight: 152g; 

7 weeks old

0.12 1-15 days, 

6 h/day

Significant decrease in rearing, locomotor 

activity, and jumping activity at day 1, with a 

further decrease in these activities by day 

15. 

Angoa-Pérez et al. (2006) Rat; Wistar; 

F; Weight: 300g; 

ovariectomized

0.25 7 to 60 days, 

4-h/day, 

5 days/week

Progressive lipid peroxidation and loss of 

tyrosine hydrolase-immunopositive neurons 

in the substantia nigra starting at 7 days. 

Guevara-Guzmán et al. 

(2009)

Rat; Wistar; 

F; 264g; 

ovariectomized

0.25 30 and 60 days, 

4h/day

Estradiol treatment protected against lipid 

peroxidation and decreases in estrogen 

receptors and dopamine β-hydroxylase in 

olfactory bulbs along with deficits in olfactory 

recognition memory.

Martínez-Canabal and 

Angora-Perez (2008)

Rat; Wistar; 

M; Weight: 300g

0.25 7 to 30 days, 

4-h/day

Growth hormone inhibited O3-induced 

increases in lipoperoxidation and COX-2 

positive cells in the hippocampus.

Pereyra-Muñoz et al. (2006) Rat; Wistar; 

M; 250-300g

0.25 15 and 30 days, 

4-h/day

Decreased motor activity, increased lipid 

peroxidation, altered morphology, and loss 

of dopamine neurons in substantia nigra and 

striatum, increased expression of DARPP32, iNOS, and SOD.

Rivas-Arancibia et al. (2010) Rat; Wistar; 

M; 250-300g

0.25 15 to 90 days, 

4-h/ day

Ozone produced significant increases in lipid 

peroxidation in the hippocampus, and 

altered the number of p53 positive 

immunoreactive cells, activated and 

phagocytic microglia cells, GFAP 

immunoreactive cells, and doublecortine 

cells, and short- and long-term memoryretention latency.

Santiago-López et al. (2010) Rat; Wistar; 

M; 250-300g

0.25 15, 30, and 60 

days, 4-h/day

Progressive loss of dopamine reactivity in 

the substantia nigra, along with 

morphological changes. Increased p53 

levels and nuclear translocation.

Thomson et al. (2007) Rat; Fischer-344; 

M; 200-250g

0.4; 0.8 4-h; 

assays at 0 and 

24 h postexposure

At 0.8 ppm, O3 produced rapid perturbations 

in the ET-NO pathway gene expression in 

the brain. Ozone induced a small but 

significant time- and concentrationdependent increase in prepro-endothelin-1 

mRNA levels in the cerebral hemisphere and 

pituitary, whereas TNFa and iNOS mRNA 

levels were decreased at 0 h and 

unchanged or increased, respectively, at 24 

h.

Alfaro-Rodríguez and 

González-Piña (2005)

Rat; Wistar; 

M; 292g

0.5 24-h During the light phase, O3 caused a 

significant decrease in paradoxical sleep 

accompanied by a significant decrease in 

Ach levels in the hypothalamic medial 

preoptic area. The same effects occurred 

during the dark phase exposure to O3 in 

addition to a significant increase in slowwave sleep and decrease in wakefulness.

Araneda et al. (2008) Rats; SpragueDawley; M; 280-

320g

0.5 3-h 

(measurements 

taken at 0 h and 3 

h after exposure)

Ozone upregulated VEGF in astroglial cells 

located in the respiratory center of the brain. 

VEGF co-located with IL-6 and TNF in cells 

near blood vessel walls, and blood vessel 

area was markedly increased. 
Draft – Do Not Cite or Quote 6-225 June 2012

Study Model O3

(ppm)

Exposure 

Duration

Effects

Boussouar et al. (2009) Rat; SpragueDawley; M; adult 

offspring of 

prenatally exposed 

dams; 403-414g

0.5 From embryonic 

day E5 to E20 for 

1-h/day; 

immobilization 

stress

Prenatal O3 exposure had a long term 

impact on the nucleus tractus solitarius of 

adult rats, as revealed during immobilization 

stress.

Soulage et al. (2004) Rat; SpragueDawley; M; Approx. 

7 weeks old

0.7 5-h Ozone produced differential effects on 

peripheral and central components of the 

sympatho-adrenal system. While 

catecholamine biosynthesis was increased 

in portions of the brain, the catecholamine 

turnover rate was significantly increased in 

the heart and cerebral cortex and inhibited in 

the lung and striatum. 

Calderón Guzmán et al. 

(2006); (2005)

Rat; Wistar; 

M; 21 days old; 

well-nourished and 

malnourished 

groups

0.75 15 successive 

days for 4-h/day

A significant decrease in body weight was 

observed in both well nourished (WN) and 

malnourished (MN) rats after O3 exposure. 

Localized ATPase, TBARS, and GSH levels 

changed in response to O3 in certain brain 

areas and the O3-induced changes were 

dependent on nutritional condition.

Colín-Barenque et al. (2005) Rats; Wistar; M; 

250-300g

1.0 4-h; assays 

at 2-h, 24-h, 10 

days, and 15 days 

after exposure

A significant loss of dendritic spines in 

granule cells of the olfactory bulb occurred 

at 2 hrs to 10 days after exposure. 

Cytological and ultrastructural changes 

returned towards normal morphology by 15 

days.

Escalante-Membrillo et al. 

(2005)

Rats; Wistar; 

M; 280-320g

1.0 1-, 3-, 6-, or 9-h Significant increases in TBARS occurred in 

hypothalamus, cortex, striatum, midbrain, 

thalamus, and pons. Partial but significant 

recovery was observed by 3 h after the 9 h 

exposure.

Gonzalez-Pina et al. (2008) Rat; Wistar; 

M; 

1 12-h/day, 

21 days of 

gestation; assays 

at 0, 5, & 10 days 

postnatal

Prenatal O3 exposure produced significant 

decreases in cerebellar monoamine but not 

indolamine content at 0 and 5 days after 

birth with a partial recovery by 10 days. 5-

hydroxy-indole-acetic acid levels were 

significantly increased at 10 days.

6.4.1 Neuroendocrine Effects

1 According to the 2006 O3 AQCD, early studies suggested an interaction of O3 with the 

2 pituitary-thyroid-adrenal axis, because thyroidectomy, hypophysectomy, and 

3 adrenalectomy protected against the lethal effects of O3. Concentrations of 0.7-1.0 ppm 

4 O3 for a 1-day exposure in male rats caused changes in the parathyroid, thymic atrophy, 

5 decreased serum levels of thyroid hormones and protein binding, and increased prolactin. 

6 Increased toxicity to O3 was reported in hyperthyroid rats and T3 supplementation was 

7 shown to increase metabolic rate and pulmonary injury in the lungs of O3-treated animals. 

8 The mechanisms by which O3 affects neuroendocrine function are not well understood, 

9 but previous work suggests that high ambient levels of O3 can produce marked neural 

10 disturbances in structures involved in the integration of chemosensory inputs, arousal, 
Draft – Do Not Cite or Quote 6-226 June 2012

1 and motor control, effects that may be responsible for some of the behavioral effects seen 

2 with O3 exposure. A more recent study exposing immature female rats to 0.12 ppm O3

3 demonstrated significantly increased serum levels of the thyroid hormone free T3 after 

4 15 days of exposure, whereas free T4 was unchanged (Martrette et al., 2011). These 

5 results are in contrast to those previously presented whereby 1 ppm O3 for 1 day 

6 significantly decreased T3 and T4 (Clemons and Garcia, 1980), although comparisons are 

7 made difficult by highly disparate exposure regimens along with sex differences. 

8 Martrette et al. (2011) also demonstrated significantly increased corticosterone levels 

9 after 15 days of exposure, suggesting a stress related response.

6.4.2 Summary and Causal Determination 

10 In rodents, O3 exposure has been shown to cause physicochemical changes in the brain 

11 indicative of oxidative stress and inflammation. Newer toxicological studies add to earlier 

12 evidence that acute exposures to O3 can produce a range of effects on the central nervous 

13 system and behavior. Previously observed effects, including neurodegeneration, 

14 alterations in neurotransmitters, short and long term memory, and sleep patterns, have 

15 been further supported by recent studies. In instances where pathology and behavior are 

16 both examined, animals exhibit decrements in behaviors tied to the brain regions or 

17 chemicals found to be affected or damaged. For example, damage in the hippocampus, 

18 which is important for memory acquisition, was correlated with impaired performance in 

19 tests designed to assess memory. Thus the brain is functionally affected by O3 exposure. 

20 The single epidemiologic study conducted showed an association between O3 exposure 

21 and memory deficits in humans as well, albeit on a long-term exposure basis. Notably, 

22 exposure to O3 levels as low as 0.25 ppm for 7 days has resulted in progressive 

23 neurodegeneration and deficits in both short and long-term memory in rodents. 

24 Examination of changes in the brain at lower exposure concentrations or at 0.25 ppm for 

25 shorter durations has not been reported, but 0.12 ppm O3 has been shown to alter 

26 behavior. It is possible that some behavioral changes may reflect avoidance of irritation 

27 as opposed to functional changes in brain morphology or chemistry, but in many cases 

28 functional changes are related to oxidative stress and damage. In some instances, changes 

29 were dependent on the nutritional status of the rats (high versus low protein diet). For 

30 example, O3 produced an increase in glutathione in the brains of rats fed the high protein 

31 diet but decreases in glutathione in rats fed low protein chow (Calderón Guzmán et al., 

32 2006). The hippocampus, one of the main regions affected by age-related 

33 neurodegenerative diseases, appears to be more sensitive to oxidative damage in aged rats 

34 (Rivas-Arancibia et al., 2000), and growth hormone, which declines with age in most 

35 species, may be protective (Martínez-Canabal and Angora-Perez, 2008). Developing 
Draft – Do Not Cite or Quote 6-227 June 2012

1 animals may also be sensitive, as changes in the CNS, including biochemical, cellular, 

2 and behavioral effects, have been observed in juvenile and adult animals whose sole 

3 exposure occurred in utero, at levels as a low as 0.3 ppm. A number of studies 

4 demonstrate O3-induced changes that are also observed in human neurodegenerative 

5 disorders such as Alzheimer’s and Parkinson’s disease, including signs of oxidative 

6 stress, loss of neurons/neuronal death, reductions in dopamine levels, increased COX-2 

7 expression, and increases in activated microglia in important regions of the brain 

8 (hippocampus, substantia nigra). 

9 Thus, evidence for neurological effects from epidemiologic and controlled human 

10 exposure studies is lacking. However, the toxicological evidence for the impact of O3 on 

11 the brain and behavior is strong, and suggestive of a causal relationship between O3

12 exposure and effects on the central nervous system.

6.5 Effects on Other Organ Systems

6.5.1 Effects on the Liver and Xenobiotic Metabolism

13 Early investigations of the effects of O3 on the liver centered on xenobiotic metabolism, 

14 and the prolongation of drug-induced sleeping time, which was observed at 0.1 ppm O3

15 (Graham et al., 1981). In some species, only adults and especially females were affected. 

16 In rats, high (1.0-2.0 ppm for 3 hours) acute O3 exposures caused increased production of 

17 NO by hepatocytes and enhanced protein synthesis (Laskin et al., 1996; Laskin et al., 

18 1994). Except for the earlier work on xenobiotic metabolism, the responses occurred only 

19 after very high acute O3 exposures. One study, conducted at 1 ppm O3 exposure, has been 

20 identified (Last et al., 2005) in which alterations in gene expression underlying 

21 O3-induced cachexia and downregulation of xenobiotic metabolism were examined. A 

22 number of the downregulated genes are known to be interferon (IFN) dependent, 

23 suggesting a role for circulating IFN. A more recent study by Aibo et al. (2010)

24 demonstrates exacerbation of acetaminophen-induced liver injury in mice after a single 

25 6-hour exposure to 0.25 or 0.5 ppm O3. Data indicate that O3 may worsen drug-induced 

26 liver injury by inhibiting hepatic repair. The O3-associated effects shown in the liver are 

27 thought to be mediated by inflammatory cytokines or other cytotoxic mediators released 

28 by activated macrophages or other cells in the lungs (Laskin and Laskin, 2001; Laskin et 

29 al., 1998; Vincent et al., 1996a). Recently, increased peroxidated lipids were detected in 

30 the plasma of O3 exposed animals (Santiago-López et al., 2010).

31 In summary, mediators generated by O3 exposure may cause effects on the liver in 

32 laboratory rodents. Ozone exposures as low as 0.1 ppm have been shown to affect 
Draft – Do Not Cite or Quote 6-228 June 2012

1 drug-induced sleeping time, and exposure to 0.25 ppm can exacerbate liver injury 

2 induced by a common analgesic. However, very few studies at relevant concentrations 

3 have been conducted, and no data from controlled human exposure or epidemiologic 

4 studies are currently available. Therefore the collective evidence is inadequate to 

5 determine if a causal relationship exists between short-term O3 exposure and 

6 effects on the liver and metabolism.

6.5.2 Effects on Cutaneous and Ocular Tissues

7 In addition to the lungs, the skin is highly exposed to O3 and contains O3 reactive targets 

8 (polyunsaturated fatty acids) that can produce lipid peroxides. The 2006 O3 AQCD (U.S. 

9 EPA, 2006b) reported that although there is evidence of oxidative stress at near ambient 

10 O3 concentrations, skin and eyes are only affected at high concentrations (greater than 

11 1-5 ppm). Ozone exposure (0.8 ppm for 7 days) induces oxidative stress in the skin of 

12 hairless mice, along with proinflammatory cytokines (Valacchi et al., 2009). A recent 

13 study demonstrated that 0.25 ppm O3 differentially alters expression of 

14 metalloproteinases in the skin of young and aged mice, indicating that age may 

15 potentially increase risk of oxidative stress (Fortino et al., 2007). In young mice, healing 

16 of skin wounds is not significantly affected by O3 exposure (Lim et al., 2006). However, 

17 exposure to 0.5 ppm O3 for 6 h/day significantly delays wound closure in aged mice. As 

18 with effects on the liver described above, the effects of O3 on the skin and eyes have not 

19 been widely studied, and information from controlled human exposure or epidemiologic 

20 studies is not currently available. Therefore the collective evidence is inadequate to 

21 determine if a causal relationship exists between short-term O3 exposure and 

22 effects on cutaneous and ocular tissues.

6.6 Mortality 

6.6.1 Summary of Findings from 2006 Ozone AQCD 

23 The 2006 O3 AQCD reviewed a large number of time-series studies consisting of single24 and multicity studies, and meta-analyses. In the large U.S. multicity studies that 

25 examined all-year data, summary effect estimates corresponding to single-day lags 

26 ranged from a 0.5-1% increase in all-cause (nonaccidental) mortality per a standardized 

27 unit increase in O3 of 20 ppb for 24-h avg, 30 ppb for 8-h max, and 40 ppb for 1-h max as 

28 discussed in Section 2.2. The association between short-term O3 exposure and mortality 

29 was substantiated by a collection of meta-analyses and international multicity studies. 
Draft – Do Not Cite or Quote 6-229 June 2012

1 The studies evaluated found some evidence for heterogeneity in O3 mortality risk 

2 estimates across cities and studies. Studies that conducted seasonal analyses, although 

3 more limited in number, reported larger O3 mortality risk estimates during the warm or 

4 summer season. Overall, the 2006 O3 AQCD identified robust associations between 

5 various measures of daily ambient O3 concentrations and all-cause mortality, with 

6 additional evidence for associations with cardiovascular mortality, which could not be 

7 readily explained by confounding due to time, weather, or copollutants. However, it was 

8 noted that multiple uncertainties remain regarding the O3-mortality relationship 

9 including: the extent of residual confounding by copollutants; factors that modify the 

10 O3-mortality association; the appropriate lag structure for identifying O3-mortality effects 

11 (e.g., single-day lags versus distributed lag model); the shape of the O3-mortality C-R 

12 function and whether a threshold exists; and the identification of susceptible populations. 

13 Collectively, the 2006 O3 AQCD concluded that “the overall body of evidence is highly 

14 suggestive that O3 directly or indirectly contributes to non-accidental and

15 cardiopulmonary-related mortality.”

6.6.2 Associations of Mortality and Short-Term Ozone Exposure 

16 Recent studies that examined the association between short-term O3 exposure and 

17 mortality further confirmed the associations reported in the 2006 O3 AQCD. New 

18 multicontinent and multicity studies reported consistent positive associations between 

19 short-term O3 exposure and all-cause mortality in all-year analyses, with additional 

20 evidence for larger mortality risk estimates during the warm or summer months 

21 (Figure 6-26; Table 6-42). These associations were reported across a range of ambient O3

22 concentrations that were in some cases quite low (Table 6-43).
Draft – Do Not Cite or Quote 6-230 June 2012

Note: Effect estimates are for a 40 ppb increase in 1-h max, 30 ppb increase in 8-h max, and 20 ppb increase in 24-h avg O3

concentrations. An “a” represent multicity studies and meta-analyses from the 2006 O3 AQCD. Bell et al. (2005), Ito et al. (2005), 

and Levy et al. (2005) used a range of lag days in the meta-analysis: Lag 0, 1, 2, or average 0-1 or 1-2; single-day lags from 0 to 3; 

and lag 0 and 1-2; respectively. A “b” represents risk estimates from APHENA-Canada standardized to an approximate IQR of 

5.1 ppb for a 1-h max increase in O3 concentrations (see explanation in Section 6.2.7.2).

Figure 6-26 Summary of mortality risk estimates for short-term ozone exposure 

and all-cause (nonaccidental) mortality from all-year and summer 

season analyses.

Study

Gryparis et al. (2004)

Bell et al. (2007)

Schwartz (2005)

Bell and Dominici (2008)

Bell et al. (2004)a

Levy et al. (2005)a

Katsouyanni et al. (2009)

Bell et al. (2005)a

Ito et al. (2005)a

Wong et al. (2010)

Katsouyanni et al. (2009)

Cakmak et al. (2011)

Katsouyanni et al. (2009)

Katsouyanni et al. (2009)b

Samoli et al. (2009)

Bell et al. (2004)a

Schwartz (2005)

Zanobetti and Schwartz (2008)

Zanobetti and Schwartz (2008)

Franklin and Schwartz (2008)

Gryparis et al. (2004)

Medina-Ramon and Schwartz (2008)

Katsouyanni et al. (2009)

Bell et al. (2005)a

Katsouyanni et al. (2009)

Katsouyanni et al. (2009)b

Levy et al. (2005)a

Ito et al. (2005)a

Katsouyanni et al. (2009)

Stafoggia et al. (2010)

Location

APHEA2 (23 cities)

98 U.S. communities 14 U.S. cities 98 U.S. communities

95 U.S. communities

U.S. and Non-U.S. APHENA-Europe U.S. and Non-U.S. U.S. and Non-U.S. PAPA (4 cities)

APHENA-U.S. 7 Chilean cities

APHENA-Canada APHENA-Canada

21 European cities

95 U.S. communities 14 U.S. cities

48 U.S. cities

48 U.S. cities 18 U.S. communities

APHEA2 (21 cities) 48 U.S. cities APHENA-Europe U.S. and Non-U.S. APHENA-Canada APHENA-Canada

U.S. and Non-U.S. U.S. and Non-U.S. APHENA-U.S. 10 Italian cities

Lag

0-1 0-1

0

0-6 0-6

DL(0-2)

0-1 DL(0-2) DL(0-6) DL(0-2) DL(0-2)

0-1 0-6

0

0

0-3

0

0-1 0-2 DL(0-2)

DL(0-2) DL(0-2)

DL(0-2) DL(0-5) ►

All-Year

Summer

-1 1 3 5 7 9 11

% Increase
Draft – Do Not Cite or Quote 6-231 June 2012

Table 6-42 Corresponding effect estimates for Figure 6-26.

Study* Location Lag Avg Time % Increase (95% CI)

All-year

Gryparis et al. (2004) APHEA2 (23 cities) 0-1 1-h max 0.24 (-0.86, 1.98)

Bell et al. (2007) 98 U.S. communities 0-1 24-h avg 0.64 (0.34, 0.92)

Schwartz (2005a) 14 U.S. cities 0 1-h max 0.76 (0.13, 1.40)

Bell and Dominici (2008) 98 U.S. communities 0-6 24-h avg 1.04 (0.56, 1.55)

Bell et al. (2004)

a 95 U.S. communities 0-6 24-h avg 1.04 (0.54, 1.55)

Levy et al. (2005)

a U.S. and Non-U.S. --- 24-h avg 1.64 (1.25, 2.03)

Katsouyanni et al. (2009) APHENA-europe DL(0-2) 1-h max 1.66 (0.47, 2.94)

Bell et al. (2005)

a U.S. and Non-U.S. --- 24-h avg 1.75 (1.10, 2.37)

(Ito et al., 2005)

a U.S. and Non-U.S. --- 24-h avg 2.20 (0.80, 3.60)

(Wong et al., 2010) PAPA (4 cities) 0-1 8-h avg 2.26 (1.36, 3.16)

Katsouyanni et al. (2009) APHENA-U.S. DL(0-2) 1-h max 3.02 (1.10, 4.89)

Cakmak et al. (2011) 7 Chilean cities DL(0-6) 8-h max 3.35 (1.07, 5.75)

Katsouyanni et al. (2009) APHENA-Canada DL(0-2) 1-h max 5.87 (1.82, 9.81)

Katsouyanni et al. (2009)

b APHENA-Canada DL(0-2) 1-h max 0.73 (0.23, 1.20)

Summer

Samoli et al. (2009) 21 European cities 0-1 8-h max 0.66 (0.24, 1.05)

Bell et al. (2004)

a 95 U.S. communities 0-6 24-h avg 0.78 (0.26, 1.30)

Schwartz (2005a) 14 U.S. cities 0 1-h max 1.00 (0.30, 1.80)

Zanobetti and Schwartz (2008a) 48 U.S. cities 0 8-h max 1.51 (1.14, 1.87)

Zanobetti and Schwartz (2008b) 48 U.S. cities 0-3 8-h max 1.60 (0.84, 2.33)

Franklin and Schwartz (2008) 18 U.S. communities 0 24-h avg 1.79 (0.90, 2.68)

Gryparis et al. (2004) APHEA2 (21 cities) 0-1 8-h max 1.80 (0.99, 3.06)

Medina-Ramón and Schwartz (2008) 48 U.S. cities 0-2 8-h max 1.96 (1.14, 2.82)

Katsouyanni et al. (2009) APHENA-europe DL(0-2) 1-h max 2.38 (0.87, 3.91)

Bell et al. (2005)

a U.S. and Non-U.S. --- 24-h avg 3.02 (1.45, 4.63)

Katsouyanni et al. (2009) APHENA-Canada DL(0-2) 1-h max 3.34 (1.26, 5.38)

Katsouyanni et al. (2009) APHENA-Canada DL(0-2) 1-h max 0.42 (0.16, 0.67)

Levy et al. (2005)

a U.S. and Non-U.S. --- 24-h avg 3.38 (2.27, 4.42)

Ito et al. (2005)

a U.S. and Non-U.S. --- 24-h avg 3.50 (2.10, 4.90)

Katsouyanni et al. (2009) APHENA-U.S. DL(0-2) 1-h max 3.83 (1.90, 5.79)

Stafoggia et al. (2010) 10 Italian cities DL(0-5) 8-h max 9.15 (5.41, 13.0)

*Studies included from Figure 6-26..

a

Multicity studies and meta-analyses from the 2006 O3 AQCD. Bell et al. (2005)

a

, Ito et al. (2005)

a

, and Levy et al. (2005)

a used a 

range of lag days in the meta-analysis: Lag 0, 1, 2, or average 0-1 or 1-2; Single-day lags from 0-3; and Lag 0 and 1-2; respectively. 

b

Risk estimates from APHENA-Canada standardized to an approximate IQR of 5.1 ppb for a 1-h max increase in O3 concentrations 

(see explanation in Section 6.2.7.2).
Draft – Do Not Cite or Quote 6-232 June 2012

Table 6-43 Range of mean and upper percentile ozone concentrations in 

previous and recent multicity studies.

Study Location Years Averaging 

Time

Mean 

Concentration (ppb)a Upper Percentile 

Concentrations (ppb)a

Gryparis et al. 

(2004)

b

23 European 

cities (APHEA2)

1990-1997 1-h max

8-h max

Summer:

1-h max: 44-117

8-h max: 30-99

Winter:

1-h max: 11-57

8-h max: 8-49

Summer:

1-h max: 62-173

8-h max: 57-154 

Winter:

1-h max: 40-88 

8-h max: 25-78 

Schwartz 

(2005a)

b

14 U.S. cities 1986-1993 1-h max 35.1-60 25th: 26.5-52 

75th: 46.3-69 

Bell et al. (2004) 95 U.S. 

communities 

(NMMAPS)

1987-2000 24-h avg 26.0 NR

Bell et al. (2007) 98 U.S. 

communities 

(NMMAPS)

1987-2000 24-h avg 26.0d NR

Bell and

Dominici (2008)

98 U.S. 

communities 

(NMMAPS)

1987-2000

(All year and 

May-September)

24-h avg All year: 26.8

May-September: 30.0

Maximum:

All year: 37.3

May-September: 47.2

Franklin and 

Schwartz (2008)

18 U.S. 

communities

2000-2005 

(May-September)

24-h avg 21.4-48.7 NR

Katsouyanni et 

al. (2009)

b,e

NMMAPS

12 Canadian 

cities

(APHEA2)

1987-1996 (Canada 

and U.S.) varied by city 

for Europe

1-h max

U.S.: 13.3-38.4

Canada: 6.7-8.4 

Europe:18.3-41.9

75th: 

U.S.: 21.0-52.0 

Canada: 8.7-12.5

Europe: 24.0-65.8

Medina-Ramón 

and Schwartz 

(2008)

b

48 U.S. cities 1989-2000 

(May-September)

8-h max 16.1-58.8 NR

Samoli et al. 

(2009)

b

21 European 

cities (APHEA2)

1990-1997

(June-August)

8-h max 20.0-62.8 75th: 27.2-74.8

Stafoggia et al. 

(2010)

10 Italian cities 2001-2005 

(April-September)

8-h max 41.2-58.9 75th: 47.0-71.6

Cakmak et al. 

(2011)

7 Chilean cities 1997-2007 8-h max 59.0-87.6 NR

Wong et al. 

(2010)

PAPA (4 cities) 1999-2003 (Bangkok)

1996-2002 (Hong 

Kong)

2001-2004 (Shanghai)

2001-2004 (Wuhan)

8-h avg 18.7-43.7 75th: 38.4 - 60.4

Max: 92.1 - 131.8

Zanobetti and 

Schwartz 

(2008b)

48 U.S. cities 1989-2000

(June-August)

8-h max 15.1-62.8 Max: 34.3-146.2

75th: 19.8-75.9
Draft – Do Not Cite or Quote 6-233 June 2012

Study Location Years Averaging 

Time

Mean 

Concentration (ppb)a Upper Percentile 

Concentrations (ppb)a

Zanobetti and 

Schwartz 

(2008a)

48 U.S. citiesc 1989-2000

(Winter: Dec-Feb)

(Spring: March-May)

(Summer: June-Aug)

(Autumn: Sept-Nov)

8-h max

Winter: 16.5

Spring: 41.6

Summer: 47.8

Autumn: 33.5

Max:

Winter: 40.6

Spring: 91.4

Summer: 103.0

Autumn: 91.2

a

O3 concentrations were converted to ppb if the study presented them as μg/m3 by using the conversion factor of 0.51 assuming 

standard temperature (25° C) and pressure (1 atm). b

Study only reported median O3 concentrations. c

Cities with less than 75% observations in a season excluded. As a result, 29 cities examined in winter, 32 in spring, 33 in autumn, 

and all 48 in the summer.

d

Bell et al. (2007) did not report mean O3 concentrations, however, it used a similar dataset as Bell et al. (2004) which consisted of 

95 U.S. communities for 1987-2000. For comparison purposes the 24-h avg O3 concentrations for the 95 communities from Bell et 

al. (2004) are reported here. e

Study did not present air quality data for the summer months.

1 In addition to examining the relationship between short-term O3 exposure and all-cause 

2 mortality, recent studies attempted to address the uncertainties that remained upon the 

3 completion of the 2006 O3 AQCD. As a result, given the robust associations between 

4 short-term O3 exposure and mortality presented across studies in the 2006 O3 AQCD and 

5 supported in the new multicity studies (Figure 6-26), the following sections primarily 

6 focus on the examination of previously identified uncertainties in the O3-mortality 

7 relationship, specifically: O3 associations with cause-specific mortality, confounding, lag 

8 structure (e.g., multiday effects and mortality displacement), effect modification 

9 (i.e., sources of heterogeneity in risk estimates across cities); and the O3-mortality C-R 

10 relationship. Focusing specifically on these uncertainties allows for a more detailed 

11 characterization of the relationship between short-term O3 exposure and mortality.

6.6.2.1 Confounding

12 Recent epidemiologic studies examined potential confounders of the O3-mortality 

13 relationship. These studies specifically focused on whether PM and its constituents or 

14 seasonal trends confounded the association between short-term O3 exposure and 

15 mortality. 

Confounding by PM and PM Constituents

16 An important question in the evaluation of the association between short-term O3

17 exposure and mortality is whether the relationship is confounded by particulate matter, 

18 particularly the PM chemical components that are found in the “summer haze” mixture 

19 which also contains O3. However, because of the temporal correlation among these PM 

20 components and O3, and their possible interactions, the interpretation of results from 
Draft – Do Not Cite or Quote 6-234 June 2012

1 copollutant models that attempt to disentangle the health effects associated with each 

2 pollutant is challenging. Further complicating the interpretation of copollutant results, at 

3 times, is the every-3rd or -6th day PM sampling schedule employed in most locations, 

4 which limits the number of days where both PM and O3 data is available.

5 The potential confounding effects of PM10 and PM2.5 on the O3-mortality relationship 

6 were examined by Bell et al. (2007) using data on 98 U.S. urban communities for the 

7 years 1987-2000 from the National Morbidity, Mortality, and Air Pollution Study 

8 (NMMAPS). In this analysis the authors included PM as a covariate in time-series 

9 models, and also examined O3-mortality associations on days when O3 concentrations 

10 were below a specified value. This analysis was limited by the small fraction of days 

11 when both PM and O3 data were available, due to the every-3rd - or 6th -day sampling 

12 schedule for the PM indices, and the limited amount of city-specific data for PM2.5

13 because it was only collected in most cities since 1999. As a result, of the 91 

14 communities with PM2.5 data, only 9.2% of days in the study period had data for both O3

15 and PM2.5, resulting in the use of only 62 communities in the PM2.5 analysis. An 

16 examination of the correlation between PM (PM10 and PM2.5) and O3 across various strata 

17 of daily PM10 and PM2.5 concentrations found that neither PM size fraction was highly 

18 correlated with daily O3 concentrations across any of the strata examined. These results 

19 were also observed when using 8-h max and 1-h max O3 exposure metrics. National and 

20 community-specific effect estimates of the association between short-term O3 exposure 

21 and mortality were robust to inclusion of PM10 or PM2.5 in time-series models through the 

22 range of O3 concentrations (i.e., <10 ppb, 10-20, 20-40, 40-60, 60-80, and >80 ppb). 

23 Even with the small number of days in which both PM2.5 and O3 data was available, the 

24 percent increases in nonaccidental deaths per 10 ppb increase 24-h avg O3 concentrations 

25 at lag 0-1 day were 0.22% (95% CI: -0.22, 0.65) without PM2.5 and 0.21% (95% CI: 

26 -0.22, 0.64) with PM2.5 in 62 communities.

27 Although strong correlations between PM and O3 were not reported by Bell et al. (2007)

28 the patterns observed suggest regional differences in their correlation (Table 6-44). Both 

29 PM10 and PM2.5 show positive correlations with O3 in the Industrial Midwest, Northeast, 

30 Urban Midwest, and Southeast, especially in the summer months, presumably, because of 

31 the summer peaking sulfate. However, the mostly negative or weak correlations between 

32 PM and O3 in the summer in the Southwest, Northwest, and southern California could be 

33 due to winter-peaking nitrate. Thus, the potential confounding effect of PM on the 

34 O3-mortality relationship could be influenced by the relative contribution of sulfate and 

35 nitrate, which varies regionally and seasonally. 
Draft – Do Not Cite or Quote 6-235 June 2012

Table 6-44 Correlations between PM and ozone by season and region.

No. of Communities Winter Spring Summer Fall Yearly

PM10

Industrial Midwest 19 0.37 0.44 0.44 0.39 0.41

Northeast 15 0.34 0.44 0.36 0.44 0.40

Urban Midwest 6 0.24 0.25 0.22 0.26 0.24

Southwest 9 0.00 0.02 -0.02 0.10 0.03

Northwest 11 -0.17 -0.20 -0.13 -0.11 -0.16

Southern California 7 0.19 0.08 0.12 0.19 0.14

Southeast 25 0.33 0.35 0.31 0.31 0.32

U.S. 93 0.23 0.26 0.24 0.26 0.25

PM2.5

Industrial Midwest 19 0.18 0.39 0.43 0.44 0.36

Northeast 13 0.05 0.26 0.16 0.43 0.25

Urban Midwest 4 0.22 0.31 0.15 0.32 0.20

Southwest 9 -0.15 -0.08 -0.17 -0.15 -0.14

Northwest 11 -0.32 -0.34 -0.39 -0.24 -0.31

Southern California 7 -0.25 -0.22 -0.25 -0.15 -0.23

Southeast 26 0.38 0.47 0.30 0.37 0.39

U.S. 90 0.09 0.21 0.12 0.22 0.16

Source: Bell et al. (2007).
Draft – Do Not Cite or Quote 6-236 June 2012

Note: The diagonal line indicates 1:1 ratio.

Source: Reprinted with permission of Informa UK Ltd, (Smith et al., 2009b).

Figure 6-27 Scatter plots of ozone mortality risk estimates with versus without 

adjustment for PM10 in NMMAPS cities.

1 In an attempt to reassess a number of issues associated with the O3-mortality relationship, 

2 including confounding, Smith et al. (2009b) re-analyzed the publicly available NMMAPS 

3 database for the years 1987-2000. Similar to Bell et al. (2007), the PM10 data used in the 

4 Smith et al. (2009b) analysis consisted primarily of every-6th day data. In analyses 

5 conducted to examine the potential confounding effects of PM10, the authors reported 

6 that, in most cases, O3 mortality risk estimates were reduced by between 22% and 33% in 

7 copollutant models. This is further highlighted in Figure 6-27, which shows scatter plots 

8 of O3-mortality risk estimates with adjustment for PM10 versus without adjustment for 

9 PM10. Smith et al. (2009b) point out that a larger fraction (89 out of 93) of the posterior 

10 estimates lie below the diagonal line (i.e., estimates are smaller with PM10 adjustment) 

11 compared to the raw estimates (56 out of 93). This observation could be attributed to both 

12 sets of posterior estimates being calculated by “shrinking towards the mean” along with 

13 the small number of days where both PM10 and O3 data was available. However, the most 
Draft – Do Not Cite or Quote 6-237 June 2012

1 prominent feature of these plots is that the variation of O3-mortality risk estimates across 

2 cities is much larger than the impact of PM10 adjustment on the O3-mortality relationship. 

3 Franklin and Schwartz (2008) examined the sensitivity of O3 mortality risk estimates to 

4 the inclusion of PM2.5 or PM chemical components associated with secondary aerosols 

(e.g., sulfate [SO4

2- 5 ], organic carbon [OC], and nitrate [NO3-]) in copollutant models. 

6 This analysis consisted of between 3 and 6 years of data from May through September 

7 2000-2005 from 18 U.S. communities. The association between O3 and non-accidental 

8 mortality was examined in single-pollutant models and after adjustment for PM2.5, 

9 sulfate, organic carbon, or nitrate concentrations. The single-city effect estimates were 

10 combined into an overall estimate using a random-effects model. In the single-pollutant 

11 model, the authors found a 0.89% (95% CI: 0.45, 1.33%) increase in nonaccidental 

12 mortality with a 10 ppb increase in same-day 24-hour summertime O3 concentrations 

13 across the 18 U.S. communities. Adjustment for PM2.5 mass, which was available for 

14 84% of the days, decreased the O3-mortality risk estimate only slightly (from 0.88% to 

15 0.79%), but the inclusion of sulfate in the model reduced the risk estimate by 31% (from 

16 0.85% to 0.58%). However, sulfate data were only available for 18% of the days. 

17 Therefore, a limitation of this study is the limited amount of data for PM2.5 chemical 

18 components due to the every-3rd-day or every-6th-day sampling schedule. For example, 

19 when using a subset of days when organic carbon measurements were available (i.e., 17% 

20 of the available days), O3 mortality risk estimates were reduced to 0.51% (95% CI: -0.36 

21 to 1.36) in a single-pollutant model. 

22 Consistent with the studies previously discussed, the results from Franklin and Schwartz 

23 (2008) also demonstrate that the interpretation of the potential confounding effects of 

24 copollutants on O3 mortality risk estimates is not straightforward as a result of the PM 

25 sampling schedule employed in most cities. However, Franklin and Schwartz (2008) find 

26 that O3-mortality risk estimates, although attenuated in some cases (i.e., sulfate), remain 

27 positive. As presented in Figure 6-28, the regional and city-to-city variations in O3

28 mortality risk estimates appear greater than the impact of adjusting for copollutants. In 

29 addition, in some cases, a negative O3 mortality risk estimate becomes even more 

30 negative with the inclusion of sulfate (e.g., Seattle) in a copollutant model, or a null O3

31 mortality risk estimate becomes negative when sulfate is included (e.g., Dallas and 

32 Detroit). Thus, the reduction in the overall O3 mortality risk estimate (i.e., across cities) 

33 needs to be assessed in the context of the heterogeneity in the single-city estimates. 
Draft – Do Not Cite or Quote 6-238 June 2012

Source: Franklin and Schwartz (2008).

Figure 6-28 Community-specific ozone-mortality risk estimates for 

nonaccidental mortality per 10 ppb increase in same-day 

24-h average summertime ozone concentrations in single-pollutant 

models and copollutant models with sulfate.

1 In the APHENA study, the investigators from the U.S. (NMMAPS), Canadian, and 

2 European (APHEA2) multicity studies collaborated and conducted a joint analysis of 

3 PM10 and O3 using each of these datasets (Katsouyanni et al., 2009). For mortality, each 

4 dataset consisted of a different number of cities and years of air quality data: U.S. 

5 encompassed 90 cities with daily O3 data from 1987-1996 of which 36 cities had summer 

6 only O3 measurements; Europe included 23 cities with 3-7 years of daily O3 data during 

7 1990-1997; and Canada consisted of 12 cities with daily O3 data from 1987 to 1996. As 

8 discussed in Section 6.2.7.2, the APHENA study conducted extensive sensitivity 

9 analyses, of which the 8 df/year results for both the penalized spline (PS) and natural 

10 spline (NS) models are presented in the text for comparison purposes, but only the NS 
Draft – Do Not Cite or Quote 6-239 June 2012

1 results are presented in figures because alternative spline models have previously been 

2 shown to result in similar effect estimates (HEI, 2003). Additionally, for the Canadian 

3 results, figures contain risk estimates standardized to both a 40 ppb increment for 

4 1-h max O3 concentrations, consistent with the rest of the ISA, but also the approximate 

5 IQR across the Canadian cities as discussed previously (Section 6.2.7.2). 

6 In the three datasets, the authors found generally positive associations between short-term 

7 O3 exposure and all-cause, cardiovascular, and respiratory mortality. The estimated 

8 excess risks for O3 were larger for the Canadian cities than for the U.S. and European 

9 cities. When examining the potential confounding effects of PM10 on O3 mortality risk 

10 estimates, the sensitivity of the estimates varied across the data sets and age groups. In 

11 the Canadian dataset, O3 risk estimates were modestly reduced, but remained positive, 

12 when adjusting for PM10 for all-cause mortality for all ages in the PS (4.5% [95% CI: 2.2, 

13 6.7%]) and NS (4.2% [95% CI: 1.9, 6.5%]) models to 3.8% (95% CI: -1.4, 9.8%) and 

14 3.2% (95% CI: -2.2, 9.0%), respectively, at lag 1 for a 40 ppb increase in 1-h max O3

15 concentrations (Figure 6-29; Table 6-45). However, adjusting for PM10 reduced O3

16 mortality risk estimates in the ≥ 75-year age group, but increased the risk estimates in the 

17 <75-year age group. For cardiovascular and respiratory mortality more variable results 

18 were observed with O3 risk estimates being reduced and increased, respectively, in 

19 copollutant models with PM10 (Figure 6-29; Table 6-45). Unlike the European and U.S. 

20 datasets, the Canadian dataset only conducted copollutant analyses at lag 1; as a result, to 

21 provide a comparison across study locations only the lag 1 results are presented for the 

22 European and U.S. datasets in this section. 

23 In the European data, O3 risk estimates were robust when adjusting for PM10 in the year24 round data for all-cause, cardiovascular and respiratory mortality. When restricting the 

25 analysis to the summer months moderate reductions were observed in O3 risk estimates 

26 for all-cause mortality with more pronounced reductions in respiratory mortality. In the 

27 U.S. data, adjusting for PM10 moderately reduced O3 risk estimates for all-cause mortality 

28 in a year-round analysis at lag 1 (e.g., both the PS and NS models were reduced from 

29 0.18% to 0.13%) (Figure 6-29; Table 6-45). Similar to the European data, when 

30 restricting the analysis to the summer months, in the U.S. O3 mortality risk estimates 

31 were moderately reduced, but remained positive, when adjusting for PM10 for all-cause 

32 mortality. However, when examining cause-specific mortality risk estimates, consistent 

33 with the results from the Canadian dataset, which employed a similar PM sampling 

34 strategy (i.e., every-6th-day sampling), O3 risk estimates for cardiovascular and 

35 respiratory mortality were more variable (i.e., reduced or increased in all-year and 

36 summer analyses). Overall, the estimated O3 risks appeared to be moderately to 

37 substantially sensitive to inclusion of PM10 in copollutant models. Despite the multicity 
Draft – Do Not Cite or Quote 6-240 June 2012

1 approach, the mostly every-6th-day sampling schedule for PM10 in the Canadian and U.S. 

2 datasets greatly reduced the sample size and limits the interpretation of these results. 

Note: Effect estimates are for a 40 ppb increase in 1-h max O3 concentrations at lag 1. All estimates are for the 8 df/year model with 

natural splines. Circles represent all-year analysis results while diamonds represent summer season analysis results. Open circles 

and diamonds represent copollutant models with PM10. Black = all-cause mortality; red = cardiovascular mortality; and 

blue = respiratory mortality.

a

Risk estimates from APHENA-Canada standardized to an approximate IQR of 5.1 ppb for a 1-h max increase in O3 concentrations 

(see explanation in Section 6.2.7.2).

Figure 6-29 Percent increase in all-cause (nonaccidental) and cause-specific 

mortality from natural spline models with 8 df/yr from the APHENA 

study for single- and copollutant models.

All-Year

Summer

All-Year

Summer

All-Year

Summer

All-Year

All-Year

Summer

All-Year

Summer

All-Year

Summer

Ages

All

≥75

<75

≥75

<75

All

All

≥75

<75

All

All

≥75

<75

≥75

<75

All

Location

APHENA-U.S.

APHENA-Canada

APHENA-Europe

All-Cause

Cardiovascular

Respiratory

All-Cause

Cardiovascular

Respiratory

All-Cause

Cardiovascular

Respiratory

►

◄

◄

a

a

a

a

a

a

a

a

-10 -5 0 5 10 15 20 25 30

% Increase
Draft – Do Not Cite or Quote 6-241 June 2012

Table 6-45 Corresponding effect estimates for Figure 6-29.

Location* Mortality Ages Season Copollutant % Increase (95% CI)

APHENA-U.S. All-Cause All All-year 1.42 (0.08, 2.78)

PM10 1.02 (-1.40, 3.50)

Summer 4.31 (2.22, 6.45)

PM10 1.90 (-0.78, 4.64)

Cardiovascular ≥ 75 All-year 1.10 (-1.33, 3.67)

PM10 0.47 (-4.61, 5.79)

<75 All-year -0.16 (-3.02, 2.86)

PM10 1.34 (-3.63, 6.61)

≥ 75 Summer 3.58 (0.87, 6.37)

PM10 -1.17 (-6.18, 4.07)

<75 Summer 3.18 (0.31, 6.12)

PM10 1.26 (-4.46, 7.28)

Respiratory All All-year 2.46 (-1.87, 6.86)

PM10 3.50 (-4.23, 11.8)

Summer 6.04 (1.18, 11.1)

PM10 7.03 (-3.48, 18.5)

APHENA-Canada All-Cause All All-year 4.15 (1.90, 6.45)

0.52 (0.24, 0.80)a

PM10 3.18 (-2.18, 8.96)

PM10 0.40 (-0.28, 1.10)a

Cardiovascular ≥ 75 All-year 5.62 (0.95, 10.7)

0.70 (0.12, 1.30)a

PM10 1.90 (-9.03, 14.1)

PM10 0.24 (-1.20, 1.70)a

<75 All-year 1.10 (-4.08, 6.61)

0.14 (-0.53, 0.82)a

PM10 -2.64 (-14.7, 11.5)

PM10 -0.34 (-2.00, 1.40)a

Respiratory All All-year 0.87 (-6.40, 8.96)

0.11 (-0.84, 1.10)a

PM10 22.3 (-12.6, 71.3)

PM10 2.60 (-1.70, 7.10)a
Draft – Do Not Cite or Quote 6-242 June 2012

Location* Mortality Ages Season Copollutant % Increase (95% CI)

APHENA-Europe All-Cause All All-year 1.02 (0.39, 1.66)

PM10 1.26 (0.47, 1.98)

Summer 2.06 (1.10, 2.94)

PM10 1.26 (0.16, 2.30)

Cardiovascular ≥ 75 All-year 1.10 (-0.47, 2.70)

PM10 1.18 (-0.55, 2.94)

<75 All-year 1.34 (-0.24, 2.94)

PM10 1.74 (-0.31, 3.75)

≥ 75 Summer 2.54 (0.39, 4.80)

PM10 1.58 (-0.70, 3.99)

<75 Summer 1.66 (-0.70, 4.15)

PM10 1.66 (-1.02, 4.40)

Respiratory All All-year 1.42 (-1.02, 3.83)

PM10 1.42 (-1.02, 3.83)

Summer 4.31 (1.66, 7.11)

PM10 1.18 (-1.79, 4.31)

*Effect estimates from Figure 6-29.

a

Risk estimates from APHENA-Canada standardized to an approximate IQR of 5.1 ppb for a 1-h max increase in O3 concentrations 

(see explanation in Section 6.2.7.2).

1 Stafoggia et al. (2010) examined the potential confounding effects of PM10 on the 

2 O3-mortality relationship in individuals 35 years of age and older in 10 Italian cities from 

3 2001 to 2005. In a time-stratified case-crossover analysis, using data for the summer 

4 months (i.e., April-September), the authors examined O3-mortality associations across 

5 each city, and then obtained a pooled estimate through a random-effects meta-analysis. 

6 Stafoggia et al. (2010) found a strong association with nonaccidental mortality (9.2% 

7 [95% CI: 5.4, 13.0%] for a 30 ppb increase in 8-h max O3 concentrations) in an 

8 unconstrained distributed lag model (lag 0-5) that persisted in copollutant models with 

9 PM10 (9.2% [95% CI: 5.4, 13.7%]). Additionally, when examining cause-specific 

10 mortality, the authors found positive associations between short-term O3 exposure and 

11 cardiovascular (14.3% [95% CI: 6.7, 22.4%]), cerebrovascular (8.5% [95% CI: 0.1, 

12 16.3%]), and respiratory (17.6% [95% CI: 1.8, 35.6%]) mortality in single-pollutant 

13 models. In copollutant models, O3-mortality effect estimates for cardiovascular and 

14 cerebrovascular mortality were robust to the inclusion of PM10 (9.2% [95% CI: 5.4, 

15 13.7%]) and 7.3% [95% CI: -1.2, 16.3%], respectively), and attenuated, but remained 

16 positive, for respiratory mortality (9.2% [95% CI: -6.9, 28.8%]). Of note, the correlations 

17 between O3 and PM10 across cities were found to be generally low, ranging from (-0.03 to 

18 0.49). The authors do not specify the sampling strategy used for PM10 in this analysis.
Draft – Do Not Cite or Quote 6-243 June 2012

Confounding by Seasonal Trend

1 The APHENA study (Katsouyanni et al., 2009), mentioned above, also conducted 

2 extensive sensitivity analyses to identify the appropriate: (1) smoothing method and basis 

3 functions to estimate smooth functions of time in city-specific models; and (2) degrees of 

4 freedom to be used in the smooth functions of time, to adjust for seasonal trends. Because 

5 O3 peaks in the summer and mortality peaks in the winter, not adjusting or not 

6 sufficiently adjusting for the seasonal trend would result in an apparent negative 

7 association between the O3 and mortality time-series. Katsouyanni et al. (2009) examined 

8 the effect of the extent of smoothing for seasonal trends by using models with 3 df/year, 

9 8 df/year (the choice for their main model), 12 df/year, and df/year selected using the sum 

10 of absolute values of partial autocorrelation function of the model residuals (PACF) 

11 (i.e., choosing the degrees of freedom that minimizes positive and negative 

12 autocorrelations in the residuals). Table 6-46 presents the results of the degrees of 

13 freedom analysis using alternative methods to calculate a combined estimate: the Berkey 

14 et al. (1998) meta-regression and the two-level normal independent sampling estimation 

15 (TLNISE) hierarchical method. The results show that the methods used to combine 

16 single-city estimates did not influence the overall results, and that neither 3 df/year nor 

17 choosing the df/year by minimizing the sum of absolute values of PACF of regression 

18 residuals was sufficient to adjust for the seasonal negative relationship between O3 and 

19 mortality. However, it should be noted, the majority of studies in the literature that 

20 examined the mortality effects of short-term O3 exposure, particularly the multicity 

21 studies, used 7 or 8 df/year to adjust for seasonal trends, and in both methods a positive 

22 association was observed between O3 exposure and mortality. 
Draft – Do Not Cite or Quote 6-244 June 2012

Table 6-46 Sensitivity of ozone risk estimates per 10 μg/m3 increase in 

24-h average ozone concentrations at lag 0-1 to alternative 

methods for adjustment of seasonal trend, for all-cause mortality 

using Berkey MLE and TLNISE Hierarchical Models.

Seasonality Control Berkey TLNISE

3 df/year -0.54 (-0.88, 0.20) -0.55 (-0.88, -0.22)

8 df/year 0.30 (0.11, 0.50) 0.31 (0.09, 0.52)

12 df/year 0.34 (0.15, 0.53) 0.33 (0.12, 0.54)

PACF -0.62 (-1.01, -0.22) -0.62 (-0.98, -0.27)

Source: Reprinted with permission of Health Effects Institute (Katsouyanni et al., 2009).

6.6.2.2 Effect Modification

1 There have been several multicity studies that examined potential effect modifiers, or 

2 time-invariant factors, which may modify O3 mortality risk estimates. These effect 

3 modifiers can be categorized into either individual-level or community-level

4 characteristics, which are traditionally examined in second stage regression models. The 

5 results from these analyses also inform upon whether certain populations are greater risk 

6 of an O3-related health effects (Chapter 8). In addition to potentially modifying the 

7 association between short-term O3 exposure and mortality, both individual-level and 

8 community-level characteristics may contribute to the geographic pattern of spatial 

9 heterogeneity in O3 mortality risk estimates. As a result, the geographic pattern of O3

10 mortality risk estimates is also evaluated in this section.

Individual-Level Characteristics

11 Medina-Ramón and Schwartz (2008) conducted a case-only study in 48 U.S. cities to 

12 identify populations potentially at increased risk to O3-related mortality for the period 

13 1989-2000 (May through September of each year [i.e., warm season]). A case-only 

14 design predicts the occurrence of time-invariant characteristics among cases as a function 

15 of the exposure level (Armstrong, 2003). For each potential effect modifier 

16 (time-invariant individual-level characteristics), city-specific logistic regression models 

17 were fitted, and the estimates were pooled across all cities. Furthermore, the authors 

18 examined potential differences in individual effect modifiers according to several city 

19 characteristics (e.g., mean O3 level, mean temperature, households with central air 

20 conditioning, and population density) in a meta-regression. Across cities, the authors 

21 found a 1.96% (95% CI: 1.14-2.82%) increase in mortality at lag 0-2 for a 30 ppb 

22 increase in 8-h max O3 concentrations. Additionally, Medina-Ramón and Schwartz 
Draft – Do Not Cite or Quote 6-245 June 2012

1 (2008) examined a number of individual-level characteristics (e.g., age, race) and chronic 

2 conditions (e.g., secondary causes of death) as effect modifiers of the association between 

3 short-term O3 exposure and mortality. The authors found that older adults (i.e., ≥ 65), 

4 women >60 years of age, black race, and secondary atrial fibrillation showed the greatest 

5 additional percent change in O3-related mortality (Table 6-47). When examining city6 level characteristics, the authors found that older adults, black race, and secondary atrial 

7 fibrillation had a larger effect on O3 mortality risk estimates in cities with lower mean O3

8 concentrations. Of note, a similar case-only study (Schwartz, 2005b) examined potential 

9 effect modifiers of the association between temperature and mortality, which would be 

10 expected to find results consistent with the Medina-Ramón and Schwartz (2008) study 

11 due to the high correlation between temperature and O3. However, when stratifying days 

12 by temperature Schwartz (2005b) found strong evidence that diabetes modified the 

13 temperature-mortality association on hot days, which was not as evident when examining 

14 the O3-mortality association in Medina-Ramón and Schwartz (2008). This difference 

15 could be due to the study design and populations included in both studies, a multicity 

16 study including all ages (Medina-Ramón and Schwartz, 2008) compared to a single-city 

17 study of individuals ≥ 65 years of age (Schwartz, 2005b). However, when examining 

18 results stratified by race, nonwhites were found to have higher mortality risks on both hot 

19 and cold days, which provide some support for the additional risk found for black race in 

20 Medina-Ramón and Schwartz (2008).

21 Individual-level factors that may result in increased risk of O3-related mortality were also 

22 examined by Stafoggia et al. (2010). As discussed above, using a time-stratified case23 crossover analysis, the authors found an association between short-term O3 exposure and 

24 nonaccidental mortality in an unconstrained distributed lag model in 10 Italian cities 

25 (9.2% [95% CI: 5.4, 13.0%; lag 0-5 for a 30 ppb increase in 8-h max O3 concentrations). 

26 Stafoggia et al. (2010) conducted additional analyses to examine whether age, sex, 

27 income level, location of death, and underlying chronic conditions increased the risk of 

28 O3-related mortality, but data were only available for nine of the cities for these analyses. 

29 Of the individual-level factors examined, the authors found the strongest evidence for 

30 increased risk of O3-related mortality in individuals ≥ 85 years of age (22.4% [95% CI: 

31 15.0, 30.2%]), women (13.7% [95% CI: 8.5, 19.7%]), and out-of-hospital deaths (13.0% 

32 [95% CI: 6.0, 20.4%]). When focusing specifically on out-of hospital deaths and the 

33 subset of individuals with chronic conditions, Stafoggia et al. (2010) found the strongest 

34 association for individuals with diabetes, which is consistent with the potentially 

35 increased risk of diabetics on hot days observed in Schwartz (2005b).
Draft – Do Not Cite or Quote 6-246 June 2012

Table 6-47 Additional percent change in ozone-related mortality for individuallevel characteristics.

Percentage (95% CI)

Socio-demographic characteristics

Age 65 yr or older 1.10 0.44, 1.77

Women 0.58 0.18, 0.98

Women <60 yr oldb -0.09 -0.76, 0.58

Women ≥ 60 yr oldb 0.60 0.25, 0.96

Black race 0.53 0.19, 0.87

Low education -0.29 -0.81, 0.23

Chronic conditions (listed as secondary cause)

Respiratory system diseases

Asthma 1.35 -0.31, 3.03

COPD 0.01 -0.49, 0.52

Circulatory system diseases

Atherosclerosis -0.72 -1.89, 0.45

Atherosclerotic CVD 0.74 -0.86, 2.37

Atherosclerotic heart disease -0.38 -1.70, 0.96

Congestive heart disease -0.04 -0.39, 0.30

Atrial fibrillation 1.66 0.03, 3.32

Stroke 0.17 -0.28, 0.62

Other diseases

Diabetes 0.19 -0.46, 0.84

Inflammatory diseases 0.18 -1.09, 1.46

a

These estimates represent the additional percent change in mortality for persons who had the characteristic being examined compared to persons 

who did not have the characteristic, when the mean O3 level of the previous 3 days increased 10 ppb. These values were not standardized 

because they do not represent the actual effect estimate for the characteristic being evaluated, but instead, the difference between effect estimates 

for persons with versus without the condition.

b

Compared with males in the same age group.

Source: Reprinted with permission of Lippincott Williams & Wilkins (Medina-Ramón and Schwartz, 2008).

1 Additionally, Cakmak et al. (2011) examined the effect of individual-level characteristics 

2 that may modify the O3-mortality relationship in 7 Chilean cities. In a time-series analysis 

3 using a constrained distributed lag of 0-6 days, Cakmak et al. (2011) found evidence for 

4 larger O3 mortality effects in individuals >75 years of age compared to younger ages, 

5 which is similar to Medina-Ramón and Schwartz (2008) and Stafoggia et al. (2010). 

6 Unlike the studies discussed above O3-mortality risk estimates were found to be slightly 

7 larger in males (3.71% [95% CI: 0.79, 6.66] for a 40 ppb increase in max 8-h avg O3

8 concentrations), but were not significantly different than those observed for females 

9 (3.00% [95% CI: 0.43, 5.68]). The major focus of Cakmak et al. (2011) is the 
Draft – Do Not Cite or Quote 6-247 June 2012

1 examination of the influence of SES indicators (i.e., educational attainment, income level, 

2 and employment status) on the O3-mortality relationship. The authors found the largest 

3 risk estimates in the lowest SES categories for each of the indicators examined this 

4 includes: primary school not completed when examining educational attainment; the 

5 lowest quartile of income level; and unemployed individuals when comparing 

6 employment status. 

7 Overall, uncertainties exist in the interpretation of the potential effect modifiers identified 

8 in Medina-Ramón and Schwartz (2008), Stafoggia et al. (2010), and Cakmak et al. (2011)

9 of the O3-mortality relationship due to the heterogeneity in O3-mortality risk estimates 

10 across cities as highlighted in Smith et al. (2009b) (Figure 6-27) and Franklin and 

11 Schwartz (2008) (Figure 6-28). In addition, it is likely that individual-level factors 

12 identified in Medina-Ramón and Schwartz (2008), (Stafoggia et al., 2010), and Cakmak 

13 et al. (2011) only modify the O3-mortality relationship and do not entirely explain the 

14 observed regional heterogeneity in O3-mortality risk estimates. 

Community-level Characteristics

15 Several studies also examined city-level (i.e., ecological) variables in an attempt to 

16 explain the observed city-to-city variation in estimated O3-mortality risk estimates. Bell 

17 and Dominici (2008) investigated whether community-level characteristics, such as race, 

18 income, education, urbanization, transportation use, PM and O3 concentrations, number 

19 of O3 monitors, weather, and air conditioning use could explain the heterogeneity in 

20 O3-mortality risk estimates across cities. The authors analyzed 98 U.S. urban 

21 communities from NMMAPS for the period 1987-2000. In the all-year regression model 

22 that included no community-level variables, a 20 ppb increase in 24-h avg O3

23 concentrations during the previous week was associated with a 1.04% (95% CI: 0.56, 

24 1.55) increase in mortality. Bell and Dominici (2008) found that higher O3-mortality 

25 effect estimates were associated with an increase in: percent unemployment, fraction of 

26 the population Black/African-American, percent of the population that take public 

27 transportation to work; and with a reduction in: temperatures and percent of households 

28 with central air conditioning (Figure 6-30). The modification of O3-mortality risk 

29 estimates reported for city-specific temperature and prevalence of central air conditioning 

30 in this analysis confirm the result from the meta-analyses reviewed in the 2006 O3

31 AQCD. 

32 The APHENA project (Katsouyanni et al., 2009) examined potential effect modification 

33 of O3 risk estimates in the Canadian, European, and U.S. data sets using a consistent set 

34 of city-specific variables. Table 6-48 presents the results from all age analyses for all35 cause mortality using all-year O3 data for the average of lag 0-1 day. While there are 
Draft – Do Not Cite or Quote 6-248 June 2012

1 several significant effect modifiers in the U.S. data, the results are mostly inconsistent 

2 with the results from the Canadian and European data sets. The positive effect 

3 modification by percentage unemployed and the negative effect modification by mean 

4 temperature (i.e., a surrogate for air conditioning rate) are consistent with the results 

5 reported by Bell and Dominici (2008) discussed above. However, the lack of consistency 

6 across the data sets, even between the Canadian and U.S. data, makes it difficult to 

7 interpret the results. Some of these associations may be due to coincidental correlations 

8 with other unmeasured factors that vary regionally (e.g., mean SO2 tend to be higher in 

9 the eastern U.S.).
Draft – Do Not Cite or Quote 6-249 June 2012

Note: The size of each circle corresponds to the inverse of the standard error of the community’s maximum likelihood estimate. Risk 

estimates are for a 10 ppb increase in 24-h avg ozone concentrations during the previous week.Source: Reprinted with permission 

of Johns Hopkins Bloomberg School of Public Health (Bell and Dominici, 2008).

Figure 6-30 Ozone mortality risk estimates and community-specific 

characteristics, U.S., 1987-2000.
Draft – Do Not Cite or Quote 6-250 June 2012

Table 6-48 Percent change in all-cause mortality, for all ages, associated with 

a 40ppb increase in 1-h max ozone concentrations at Lag 0–1 at the 

25th and 75th percentile of the center-specific distribution of 

selected effect modifiers.

Canada Europe U.S.

Effect 

Modifier

25th 

Percentile 

Estimate

(95% CI)

75th

Percentile

Estimate

(95% CI)

t 

Value

25th 

Percentile 

Estimate

(95% CI)

75th

Percentile

Estimate

(95% CI)

t 

Value

25th 

Percentile 

Estimate

(95% CI)

75th

Percentile

Estimate

(95% CI)

t 

Value

NO2 CV 3.10

(1.90, 4.40)

3.99

(2.38, 

5.62)

1.33 1.66

(0.71, 2.62)

1.34

(-0.08, 

2.78)

-0.49 1.26

(0.47, 1.98)

0.08

(-0.78, 

0.95)

-2.87

Mean SO2 2.22

(0.71, 3.83)

4.72

(2.94, 

6.61)

2.16 1.58

(0.47, 2.62)

1.66

(0.39, 

2.86)

0.16 0.47

(-0.47, 1.42)

1.98

(1.10, 

2.94)

2.79

O3 CV 2.86

(0.79, 5.05)

3.50

(2.14, 

4.89)

0.60 2.62

(1.50, 3.75)

1.10

(0.24, 

1.98)

-2.65 0.16

(-0.70, 1.10)

1.50

(0.71, 

2.22)

2.68

Mean 

NO2/PM10

3.91

(2.54, 5.29)

2.54

(0.95, 

4.15)

-1.58 1.74

(0.87, 2.70)

1.50

(0.47, 

2.62)

-0.43 -0.08

(-1.02, 0.95)

1.26

(0.47, 

2.06)

2.64

Mean 

Temperature

2.86

(0.95, 4.72)

3.50

(2.22, 

4.89)

0.83 1.58

(0.39, 2.86)

1.58

(0.31, 

2.78)

-0.04 2.14

(1.34, 2.94)

0.00

(-0.78, 

0.79)

-4.40

% ≥ 75 yr 2.22

(0.79, 3.58)

4.23

(3.02, 

5.54)

2.68 1.50

(0.55, 2.46)

1.82

(0.55, 

3.10)

0.52 1.02

(0.24, 1.90)

1.02

(0.31, 

1.74)

-0.02

Agestandardized

Mortality

2.62

(0.79, 4.48)

4.07

(2.22, 

5.87)

1.14 1.10

(-0.16, 2.38)

1.98

(0.79, 

3.26)

1.07 0.00

(-0.94, 0.87)

1.58

(0.87, 

2.38)

3.81

% 

Unemployed

2.78

(1.42, 4.07)

3.75

(2.54, 

4.89)

1.88 1.42

(-0.47, 3.34)

1.34

(-0.47, 

3.18)

-0.07 0.16

(-0.78, 1.18)

1.50

(0.71, 

2.30)

2.45

Source: Adapted with permission of Health Effects Institute Katsouyanni et al. (2009). 

Regional Pattern of Ozone-Mortality Risk Estimates

1 In addition to examining whether individual- and community-level factors modify the 

2 O3-mortality association, studies have also examined whether these associations varied 

3 regionally within the U.S. Bell and Dominici (2008), in the study discussed above, also 

4 noted that O3-mortality risk estimates were higher in the Northeast (1.44% [95% CI: 0.78, 

5 2.10%]) and Industrial Midwest (0.73% [95% CI: 0.11, 1.35%]), while null associations 

6 were observed in the Southwest and Urban Midwest (Table 6-49). The regional 

7 heterogeneity in O3-mortality risk estimates was further reflected by Bell and Dominici 

8 (2008) in a map of community-specific Bayesian O3-mortality risk estimates 
Draft – Do Not Cite or Quote 6-251 June 2012

1 (Figure 6-31). It is worth noting that in the analysis of PM10 using the same data set, Peng 

2 et al. (2005) also found that both the Northeast and Industrial Midwest showed 

3 particularly elevated effects, especially during the summer months. As mentioned above, 

4 although no evidence for confounding of O3 mortality risk estimates by PM10 was 

5 observed, Bell et al. (2007) did find regional differences in the correlation between O3

6 and PM10. Thus, the heterogeneity in O3 mortality risk estimates may need to be 

7 examined as a function of the correlation between PM and O3. 

8 Smith et al. (2009b), as discussed earlier, also examined the regional difference in O3

9 mortality risk estimates across the same seven regions and similarly found evidence for

10 regional heterogeneity. In addition, Smith et al. (2009b) constructed spatial maps of the 

11 risk estimates by an extension of a hierarchical model that allows for spatial auto12 correlation among the city-specific random effects. Figure 6-32 presents the spatial map 

13 of O3 mortality coefficients from the Smith et al. (2009b) analysis that used 8-h max O3

14 concentrations during the summer. The results from the Bell and Dominici (2008)

15 analysis (Figure 6-31) shows much stronger apparent heterogeneity in O3-mortality risk 

16 estimates across cities than the smoothed map from Smith et al. (2009b) (Figure 6-32), 

17 but both maps generally show larger risk estimates in the eastern region of the U.S. 

Table 6-49 Percentage increase in daily mortality for a 10 ppb increase in 

24-h average ozone concentrations during the previous week by 

geographic region in the U.S., 1987-2000.

No. of Communities Regional Estimate 95% PI*

Regional results

Industrial Midwest 20 0.73 0.11, 1.35

Northeast 16 1.44 0.78, 2.10

Northwest 12 0.08 -0.92, 1.09

Southern California 7 0.21 -0.46, 0.88

Southeast 26 0.38 -0.07, 0.85

Southwest 9 -0.06 -0.92, 0.81

Urban Midwest 7 -0.05 -1.28, 1.19

National results

All continental communities 97 0.51 0.27, 076

All communities 98 0.52 0.28, 0.77

Source: Reprinted with permission of Johns Hopkins Bloomberg School of Public Health (Bell and Dominici, 2008).
Draft – Do Not Cite or Quote 6-252 June 2012

Source: Reprinted with permission of Johns Hopkins Bloomberg School of Public Health, (Bell and Dominici, 2008).

Figure 6-31 Community-specific Bayesian ozone-mortality risk estimates in 98 

U.S. communities.

Source: Reprinted with permission of Informa UK Ltd. (Smith et al., 2009b).

Figure 6-32 Map of spatially dependent ozone-mortality coefficients for 8-h max 

ozone concentrations using summer data.
Draft – Do Not Cite or Quote 6-253 June 2012

6.6.2.3 Interaction

1 Interactions can lead to either antagonistic or synergistic effects; however, most studies 

2 attempt to identify potential factors that interact synergistically with O3 to increase the 

3 risk of mortality. Within this section, interactive effects are defined as time-varying 

4 covariates, such as temperature and copollutants that are included in 1st stage time-series 

5 regression models. To date, only a few time-series studies have investigated the potential 

6 interaction between O3 exposure and copollutants or weather variables. This can be 

7 attributed to the moderate to high correlation between O3 and these covariates, which 

8 makes such investigations methodologically challenging. 

9 Ren et al. (2008) examined the possible synergistic effect between O3 and temperature on 

10 mortality in the 60 largest eastern U.S. communities from the NMMAPS data during the 

11 warm months (i.e., April to October) from 1987-2000. This analysis was restricted to the 

12 eastern areas of the U.S. (i.e., Northeast, Industrial Midwest and Southeast) because a 

13 previous study which focused specifically on the eastern U.S. found that 

14 temperature-mortality patterns differ between the northeast and southeast regions 

15 possibly due to climatic differences (Curriero et al., 2002). To examine possible 

16 geographic differences in the interaction between temperature and O3, Ren et al. (2008)

17 further divided the NMMAPS regions into the Northeast, which included the Northeast 

18 and Industrial Midwest regions (34 cities), and the Southeast, which included the 

19 Southeast region (26 cities). The potential synergistic effects between O3 and temperature 

20 were examined using two different models. Model 1 included an interaction term in a 

21 Generalized Additive Model (GAM) for O3 and maximum temperature (3-day avg values 

22 were used for both terms) to examine the bivariate response surface and the pattern of 

23 interaction between the two variables in each community. Model 2 consisted of a 

24 Generalized Linear Model (GLM) that used interaction terms to stratify by “low,” 

25 “moderate,” and “high” temperature days using the first and third quartiles of temperature 

26 as cut-offs to examine the percent increase in mortality in each community. Furthermore, 

27 a two-stage Bayesian hierarchical model was used to estimate the overall percent increase 

28 in all-cause mortality associated with short-term O3 exposure across temperature levels 

29 and each region using model 2. The same covariates were used in both model 1 and 2. 

30 The bivariate response surfaces from model 1 suggest possible interactive effects 

31 between O3 and temperature although the interpretation of these results is not 

32 straightforward due to the high correlation between these terms. The apparent interaction 

33 between temperature and O3 as evaluated in model 2 varied across geographic regions. In 

34 the northeast region, a 20 ppb increase in 24-h avg O3 concentrations at lag 0-2 was 

35 associated with an increase of 4.49% (95% posterior interval [PI]: 2.39, 6.36%), 6.21% 

36 (95% PI: 4.47, 7.66%) and 12.8% (95% PI: 9.77, 15.7%) in mortality at low, moderate 

37 and high temperature levels, respectively. The corresponding percent increases in 
Draft – Do Not Cite or Quote 6-254 June 2012

1 mortality in the southeast region were 2.27% (95% PI: -2.23, 6.46%) for low temperature, 

2 3.02% (95% PI: 0.44, 5.70%) for moderate temperature, and 2.60% (95% PI: -0.66, 

3 6.01%) for high temperature.

4 When examining the relationship between temperature and O3-related mortality, the 

5 results reported by Ren et al. (2008) (i.e., higher O3-mortality risks on days with higher 

6 temperatures) may appear to contradict the results of Bell and Dominici (2008) described 

7 earlier (i.e., communities with higher temperature have lower O3-mortality risk 

8 estimates). However, the observed difference in results can be attributed to the 

9 interpretation of effect modification in a second-stage regression which uses long-term 

10 average temperatures, as was performed by Bell and Dominici (2008), compared to a 

11 first-stage regression that examines the interaction between daily temperature and O3-

12 related mortality. In this case, the second-stage regression results from Bell and Dominici 

13 (2008) indicate that a city with lower temperatures, on average, tend to show a stronger 

14 O3 mortality effect, whereas, in the first-stage regression performed by Ren et al. (2008), 

15 the days with higher temperature tend to show a larger O3-mortality effect. This observed 

16 difference may in part reflect the higher air conditioning use in communities with higher 

17 long-term average temperatures. Therefore, the findings from Ren et al. (2008) indicating 

18 generally lower O3 risk estimates in the southeast region where the average temperature is 

19 higher than in the northeast region is consistent with the regional results reported by Bell 

20 and Dominici (2008). As demonstrated by the results from both Ren et al. (2008) and 

21 Bell and Dominici (2008) caution is required when interpreting results from studies that 

22 examined interactive effects using two different approaches because potential effect 

23 modification as suggested in a second-stage regression generally does not provide 

24 evidence for a short-term interaction examined in a first-stage regression. Overall, further 

25 examination of the potential interactive (synergistic) effects of O3 and covariates in time26 series regression models is required to more clearly understand the factors that may 

27 influence O3 mortality risk estimates.

6.6.2.4 Evaluation of the Ozone-Mortality C-R Relationship and 

Related Issues

28 Evaluation of the O3-mortality C-R relationship is not straightforward because the 

29 evidence from multicity studies (using log-linear models) suggests that O3-mortality 

30 associations are highly heterogeneous across regions. In addition, there are numerous 

31 issues that may influence the shape of the O3-mortality C-R relationship and the observed 

32 association between short-term O3 exposure and mortality that warrant examination 

33 including: multi-day effects (distributed lags), mortality displacement (i.e., hastening of 

34 death by a short period), potential adaptation, and the exposure metric used to compute 
Draft – Do Not Cite or Quote 6-255 June 2012

1 risks (e.g., 1-hour daily max versus 24-h avg). The following section presents the recent 

2 studies identified that conducted an initial examination of these issues.

Multiday Effects, Mortality Displacement, and Adaptation

3 The pattern of positive lagged associations followed by negative associations in a 

4 distributed lag model may be considered an indication of “mortality displacement”

5 (i.e., deaths are occurring in frail individuals and exposure is only moving the day of 

6 death to a day slightly earlier). Zanobetti and Schwartz (2008b) examined this issue in 48 

7 U.S. cities during the warm season (i.e., June-August) for the years 1989-2000. In an 

8 initial analysis, the authors applied a GLM to examine same-day O3-mortality effects, and 

9 in the model included an unconstrained distributed lag for apparent temperature to take 

10 into account the effect of temperature on the day death occurred and the previous 7 days. 

11 To examine mortality displacement Zanobetti and Schwartz (2008b) refit models using 

12 two approaches: an unconstrained and a smooth distributed lag each with 21-day lags for 

13 O3. In this study, all-cause mortality as well as cause-specific mortality 

14 (i.e., cardiovascular, respiratory, and stroke) were examined for evidence of mortality 

15 displacement. The authors found a 0.96% (95% CI: 0.60, 1.30%) increase in all-cause 

16 mortality across all 48 cities for a 30 ppb increase in 8-h max O3 concentrations at lag 0 

17 whereas the combined estimate of the unconstrained distributed lag model (lag 0-20) was 

18 1.54% (95% CI: 0.15, 2.91%). Similarly, when examining the cause-specific mortality 

19 results (Table 6-50), larger risk estimates were observed for the distributed lag model 

20 compared to the lag 0 day estimates. However, for stroke a slightly larger effect was 

21 observed at lags 4-20 compared to lags 0-3 suggesting a larger window for O3-induced 

22 stroke mortality. This is further supported by the sum of lags 0 through 20 days showing 

23 the greatest effect. Overall, these results suggest that estimating the mortality risk using a 

24 single day of O3 exposure may underestimate the public health impact, but the extent of 

25 multi-day effects appear to be limited to a few days. This is further supported by the 

26 shape of the combined smooth distributed lag (Figure 6-33). It should be noted that the 

27 proportion of total variation in the effect estimates due to the between-cities 

heterogeneity, as measured by I2 28 statistic, was relatively low (4% for the lag 0 estimates 

29 and 21% for the distributed lag), but 21 out of the 48 cities exhibited null or negative 

30 estimates. As a result, the estimated shape of the distributed lag cannot be interpreted as a 

31 general form of lag structure of associations applicable to all the cities included in this 

32 analysis. 
Draft – Do Not Cite or Quote 6-256 June 2012

Table 6-50 Estimated effect of a 10 ppb increase in 8-h max ozone 

concentrations on mortality during the summer months for 

single-day and distributed lag models.

% (Percentage) 95% CI

Total mortality

Lag 0 0.32 0.20, 0.43

Sum lags 0-20 0.51 0.05, 0.96

Sum lags 0-3 0.53 0.28, 0.77

Sum lags 4-20 -0.02 -0.35, 0.31

Cardiovascular mortality

Lag 0 0.47 0.30, 0.64

Sum lags 0-20 0.49 -0.01, 1.00

Sum lags 0-3 0.80 0.48, 1.13

Sum lags 4-20 -0.23 -0.67, 0.22

Respiratory mortality

Lag 0 0.54 0.26, 0.81

Sum lags 0-20 0.61 -0.41, 1.65

Sum lags 0-3 0.83 0.38, 1.28

Sum lags 4-20 -0.24 -1.08, 0.60

Stroke

Lag 0 0.37 0.01, 0.74

Sum lags 0-20 2.20 0.76, 3.67

Sum lags 0-3 0.92 0.26, 1.59

Sum lags 4-20 1.26 0.05, 2.49

Source: Reprinted with permission of American Thoracic Society, Zanobetti and Schwartz (2008b).

1 Samoli et al. (2009) also investigated the temporal pattern of mortality effects in response 

2 to short-term exposure to O3 in 21 European cities that were included in the APHEA2 

3 project. Using a method similar to Zanobetti and Schwartz (2008b), the authors applied 

4 unconstrained distributed lag models with lags up to 21 days in each city during the 

5 summer months (i.e., June through August) to examine the effect of O3 on all-cause, 

6 cardiovascular, and respiratory mortality. They also applied a generalized additive 

7 distributed lag model to obtain smoothed distributed lag coefficients. However, unlike 

8 Zanobetti and Schwartz (2008b), Samoli et al. (2009) controlled for temperature using a 

9 linear term for humidity and an unconstrained distributed lag model of temperature at 

10 lags 0-3 days. The choice of 0- through 3-day lags of temperature was based on a 

11 previous European multicity study (Baccini et al., 2008), which suggested that summer 

12 temperature effects last only a few days. Upon combining the individual city estimates 

13 across cities in a second stage regression, Samoli et al. (2009) found that the estimated 
Draft – Do Not Cite or Quote 6-257 June 2012

1 effects on respiratory mortality were extended for a period of two weeks. However, for 

2 all-cause and cardiovascular mortality, the 21-day distributed lag models yielded null or 

3 (non-significant) negative estimates (Table 6-51). Figure 6-34 shows the distributed lag 

4 coefficients for all-cause mortality, which exhibit a declining trend and negative 

5 coefficients beyond 5-day lags. The authors’ interpretation of these results was that 

6 “using single-day exposures may have overestimated the effects on all-cause and 

7 cardiovascular mortality, but underestimated the effects on respiratory mortality.” Thus, 

8 the results in part suggest evidence of mortality displacement for all-cause and 

9 cardiovascular mortality. 

Source: Reprinted with permission of American Thoracic Society (Zanobetti and Schwartz, 2008b). 

Note: The triangles represent the percent increase in all-cause mortality for a 10 ppb increase in 8-h max O3 concentrations at each 

lag while the shaded areas are the 95% point-wise confidence intervals. 

Figure 6-33 Estimated combined smooth distributed lag for 48 U.S. cities 

during the summer months.
Draft – Do Not Cite or Quote 6-258 June 2012

Table 6-51 Estimated percent increase in cause-specific mortality (and 

95% CIs) for a 10-μg/m3 increase in maximum 8-hour ozone during 

June-August.

Fixed effects

% (95% CI)

Random effects

% (95% CI)

Total mortalitya

Lag 0 0.28 (0.11, 0.45) 0.28 (0.07, 0.48)

Average lags 0-1 0.24 (0.15, 0.34) 0.22 (0.08, 0.35)

Sum lags 0-20, unconstrained 0.01 (-0.40, 0.41) -0.54 (-1.28, 0.20)

Sum lags 0-20, penalized 0.01 (-0.41, 0.42) -0.56 (-1.30, 0.19)

Cardiovascular mortalitya

Lag 0 0.43 (0.18, 0.69) 0.37 (0.05, 0.69)

Average lags 0-1 0.33 (0.19, 0.48) 0.25 (0.03, 0.47)

Sum lags 0-20, unconstrained -0.33 (-0.93, 0.29) -0.62 (-1.47, 0.24)

Sum lags 0-20, penalized -0.32 (-0.92, 0.28) -0.57 (-1.39, 0.26)

Respiratory mortalitya

Lag 0 0.36 (-0.21, 0.94) 0.36 (-0.21, 0.94)

Average lags 0-1 0.40 (0.11, 0.70) 0.40 (0.11, 0.70)

Sum lags 0-20, unconstrained 3.35 (1.90, 4.83) 3.35 (1.90, 4.83)

Sum lags 0-20, penalized 3.66 (2.25, 5.08) 3.66 (2.25, 5.08)

a

Analysis for the same day (lag 0), the average of the same and previous day (lag 0-1), the unconstrained distributed lag model for the sum of 

0-20 days and the penalized distributed lag model (lag 0-20)

Source: Used with permission of BMJ Group (Samoli et al., 2009).

1 Although the APHENA project (Katsouyanni et al., 2009) did not specifically investigate 

2 mortality displacement and therefore did not consider longer lags (e.g., lag >3 days), the 

3 study did present O3 risk estimates for lag 0-1, lag 1, and a distributed lag model of 0-

4 2 days in the Canadian, European, and U.S. datasets. Katsouyanni et al. (2009) found that 

5 the results vary somewhat across the regions, but, in general, there was no indication that 

6 the distributed lag model with up to a 2-day lag yielded meaningfully larger O3 mortality 

7 risk estimates than the lag 0-1 and lag 1 results. For example, for all-cause mortality, 

8 using the model with natural splines and 8 df/year to adjust for seasonal trends, the 

9 reported percent excess risk for mortality for a 40 ppb increase in 1-h max O3

10 concentrations for lag 0-1, lag 1, and the distributed lag model (lag 0-2) was 2.70% 

11 (95% CI: 1.02, 4.40%), 1.42% (95% CI: 0.08, 2.78%), and 3.02% (95% CI: 1.10, 4.89%), 

12 respectively. Thus, the observed associations appear to occur over a short time period, 

13 (i.e., a few days). Similarly, the Public Health and Air Pollution in Asia (PAPA) study 

14 (Wong et al., 2010) also examined multiple lag days (i.e., lag 0, lag 0-1, and lag 0-4), and 

15 although it did not specifically examine mortality displacement it does provide additional 

16 evidence regarding the timing of mortality effects proceeding O3 exposure. In a combined 
Draft – Do Not Cite or Quote 6-259 June 2012

1 analysis using data from all four cities examined (Bangkok, Hong Kong, Shanghai, and 

2 Wuhan), excess risk estimates at lag 0-4 were larger than those at lag 0 or lag 0-1 in both 

3 fixed and random effect models (results not presented quantitatively). The larger risk 

4 estimates at lag 0-4 can primarily be attributed to the strong associations observed in 

5 Bangkok and Shanghai. However, it is worth noting that Bangkok differs from the three 

6 Chinese cities included in this analysis in that it has a tropical climate and does not 

7 exhibit seasonal patterns of mortality. As a result, Wong et al. (2010) examined the O3-

8 mortality associations at lag 0-1 in only the three Chinese cities and found that risk 

9 estimates were slightly reduced from 2.26% (95% CI: 1.36, 3.16) in the 4 city analysis to 

10 1.84% (0.77, 2.86) in the 3 city analysis for a 30 ppb increase in 8-h max O3

11 concentrations. Overall, the PAPA study further supports the observation of the 

12 APHENA study that associations between O3 and mortality occur over a relatively short13 time period, but also indicates that it may be difficult to interpret O3-mortality 

14 associations across cities with different climates and mortality patterns.

15 When comparing the studies that explicitly examined the potential for mortality 

16 displacement in the O3-mortality relationship, the results from Samoli et al. (2009), which 

17 provide evidence that suggests mortality displacement, are not consistent with those 

18 reported by Zanobetti and Schwartz (2008b). However, the shapes of the estimated 

19 smooth distributed lag associations are similar (Figure 6-33 and Figure 6-34). A closer 

20 examination of these figures shows that in the European data beyond a lag of 5 days the 

21 estimates remain negative whereas in the U.S. data the results remain near zero for the 

22 corresponding lags. These observed difference could be due to the differences in the 

23 model specification between the two studies, specifically the use of: an unconstrained 

24 distributed lag model for apparent temperature up to 7 previous days (Zanobetti and 

25 Schwartz, 2008b) versus a linear term for humidity and an unconstrained distributed lag 

26 model of temperature up to 3 previous days (Samoli et al., 2009); and natural cubic 

27 splines with 2 df per season (Zanobetti and Schwartz, 2008b) versus dummy variables per 

28 month per year to adjust for season (Samoli et al., 2009). It is important to note that these 

29 differences in model specification may have also influenced the city-to-city variation in 

30 risk estimates observed in these two studies (i.e., homogenous estimates across cities in 

31 Zanobetti and Schwartz (2008b) and heterogeneous estimates across cities in Samoli et 

32 al. (2009). Overall, the evidence of mortality displacement remains unclear, but Samoli et 

33 al. (2009), Zanobetti and Schwartz (2008b), and Katsouyanni et al. (2009) all suggest that 

34 the positive associations between O3 and mortality are observed mainly in the first 

35 few days after exposure. 
Draft – Do Not Cite or Quote 6-260 June 2012

Note: The triangles represent the percent increase in all-cause mortality for a 10 μg/m3 increase in 8-h max O3 concentrations at 

each lag; the shaded area represents the 95% CIs.

Source: Reprinted with permission of BMJ Group (Samoli et al., 2009). 

Figure 6-34 Estimated combined smooth distributed lag in 21 European cities 

during the summer (June-August) months.

Adaptation

1 Controlled human exposure studies have demonstrated an adaptive response to O3

2 exposure for respiratory effects, such as lung function decrements, but this issue has not 

3 been examined in the epidemiologic investigation of mortality effects of O3. Zanobetti 

4 and Schwartz (2008a) examined if there was evidence of an adaptive response in the 

5 O3-mortality relationship in 48 U.S. cities from 1989 to 2000 (i.e., the same data analyzed 

6 in Zanobetti and Schwartz (2008b). The authors examined all-cause mortality using a 

7 case-crossover design to estimate the same-day (i.e., lag 0) effect of O3, matched on 

8 referent days from every-3rd-day in the same month and year as the case. Zanobetti and 

9 Schwartz (2008a) examined O3-mortality associations by: season, month in the summer 

10 season (i.e., May through September), and age categories in the summer season 

11 (Table 6-52). The estimated O3 mortality risk estimate at lag 0 was found to be highest in 

12 the summer (1.51% [95% CI: 1.14, 1.87%]; lag 0 for a 30 ppb increase in 8-h max O3

13 concentrations), and, within the warm months, the association was highest in July (1.96% 
Draft – Do Not Cite or Quote 6-261 June 2012

[95% CI: 1.42, 2.48%]; lag 0).1 1 Upon further examination of the summer months, the 

2 authors also observed diminished effects in August (0.84% [95% CI: 0.33, 1.39%]; lag 

3 0). Based on these results, the authors concluded that the mortality effects of O3 appear 

4 diminished later in the O3 season. 

Table 6-52 Percent excess all-cause mortality per 10 ppb increase in daily 

8-h max ozone on the same day, by season, month, and age 

groups.

% 95% CI

By Season

Winter -0.13 -0.56, 0.29

Spring 0.35 0.16, 0.54

Summer 0.50 0.38, 0.62

Fall 0.05 -0.14, 0.24

By Month

May 0.48 0.28, 0.68

June 0.46 0.24, 0.68

July 0.65 0.47, 0.82

August 0.28 0.11, 0.46

September -0.09 -0.35, 0.16

By Age Group

0-20 0.08 -0.42, 0.57

21-30 0.10 -0.67, 0.87

31-40 0.07 -0.38, 0.52

41-50 0.08 -0.27, 0.43

51-60 0.54 0.19, 0.89

61-70 0.38 0.16, 0.61

71-80 0.50 0.32, 0.67

80 0.29 0.13, 0.44

Source: Zanobetti and Schwartz (2008a).

5 To further evaluate the potential adaptive response observed in Zanobetti and Schwartz 

6 (2008a) the distribution of the O3 concentrations across the 48 U.S. cities during July and 

7 August was examined. Both July and August were found to have comparable means of 

8 48.6 and 47.9 ppb with a reported maximum value of 97.9 and 96.0 ppb, respectively. 

9 Thus, the observed reduction in O3-related mortality effect estimates in August (0.84%) 

 1 These values have been standardized to the increment used throughout the ISA for max 8-h avg increase in O3 concentrations of 

30 ppb. These values differ from those presented in Table 6-52 from Zanobetti and Schwartz (2008a) because the authors 

presented values for a 10 ppb increase in max 8-h avg O3 concentrations.
Draft – Do Not Cite or Quote 6-262 June 2012

1 compared to July (1.96%) appears to support the existence of an adaptive response. 

2 However, unlike an individual’s adaptive response to decrements in lung function from 

3 short-term O3 exposure, an examination of mortality prevents a direct observation of 

4 adaptation. Rather, for mortality the adaptation hypothesis is tested with a tacit 

5 assumption that, whatever the mechanism for O3-induced mortality, the risk of death 

6 from short-term O3 exposure is reduced over the course of the summer months through 

7 repeated exposures. This idea would translate to a smaller population that would die from 

8 O3 exposure towards the end of summer. This may complicate the interpretation of the 

9 distributed lag coefficients with long lag periods because the decreased coefficients may 

10 reflect diminished effects of the late summer, rather than diminished effects that are 

11 constant across the summer. These intertwined issues need to be investigated together in 

12 future research. 

Exposure Metric

13 When examining the association between short-term O3 exposure and mortality it is also 

14 important to consider the exposure metric used (i.e., 24-h avg, 8-h max, and 1-h max). To 

15 date, only a few studies have conducted analyses to examine the impact of different 

16 exposure metrics on O3 mortality risk estimates. In Smith et al. (2009b), the authors 

17 examined the effect of different exposure metrics (i.e., 24-h avg , 8-h max, and 1-h max) 

18 on O3-mortality regression coefficients. When examining whether there are differences in 

19 city-specific risk estimates when using different exposure metrics, Smith et al. (2009b)

20 found a rather high correlation (r = 0.7-0.8) between risk estimates calculated using 

21 24-h avg versus 8-h max and 1-h max versus 8-h max averaging times. These results are 

22 consistent with the correlations reported by Darrow et al. (2011a) (Section 6.2.7.3) 

23 between the 8-h max and 24- avg exposure metrics. 

24 In addition to these recent studies published since the 2006 O3 AQCD, Gryparis et al. 

25 (2004) also supports the high correlation between 1-h max and 8-h max O3

26 concentrations reported in Smith et al. (2009b) and Darrow et al. (2011a) and the 

27 subsequent high degree of similarity between mortality risk estimates calculated using 

28 either metric. Although only a limited number of studies have examined the effect of 

29 different exposure metrics on O3-mortality risk estimates, these studies suggest relatively 

30 comparable results across the exposure metrics used. 

Ozone-Mortality C-R Relationship and Threshold Analyses

31 Several of the recent studies evaluated have applied a variety of statistical approaches to 

32 examine the shape of the O3-mortality C-R relationship and whether a threshold exists. 

33 The approach used by Bell et al. (2006) consisted of applying four statistical models to 
Draft – Do Not Cite or Quote 6-263 June 2012

1 the NMMAPS data, which included 98 U.S. communities for the period 1987-2000. 

2 These models included: a linear analysis (i.e., any change in O3 concentration can be 

3 associated with mortality) (Model 1); a subset analysis (i.e., examining O3-mortality 

4 relationship below a specific 24- avg concentration, ranging from 5 to 60 ppb) (Model 2); 

5 a threshold analysis (i.e., assuming that an association between O3 and mortality is 

6 observed above a specific concentration and not below it, using the threshold values set at 

7 an increment of 5 ppb between 0 to 60 ppb and evaluating a presence of a local minima in 

8 AICs computed at each increment) (Model 3); and nonlinear models using natural cubic 

9 splines with boundary knots placed at 0 and 80 ppb, and interior knots placed at 20 and 

10 40 ppb (Model 4). A two-stage Bayesian hierarchical model was used to examine these 

11 models and O3-mortality risk estimates at the city-level in the first stage analysis and 

12 aggregate estimates across cities in the 2nd stage analysis using the average of 0- and 

13 1-day lagged 24-h avg O3 concentrations. The results from all of these models suggest 

14 that if a threshold exists it does so well below the current O3 NAAQS. When restricting 

15 the analysis to all days when the 1997 O3 NAAQS 8-hour standard (i.e., 84 ppb daily 

16 8-h max) is met in each community, Bell et al. (2006) found there was still a 0.60% (95% 

17 PI: 0.30, 0.90%) increase in mortality per 20 ppb increase in 24-h avg O3 concentrations 

18 at lag 0-1. Figure 6-35 shows the combined C-R curve obtained using the nonlinear 

19 model (Model 4). Although these results suggest the lack of threshold in the O3-mortality 

20 relationship, it is difficult to interpret such a curve because: (1) there is uncertainty 

21 around the shape of the C-R curve at 24-h avg O3 concentrations generally below 20 ppb, 

22 and (2) the C-R curve does not take into consideration the heterogeneity in O3-mortality 

23 risk estimates across cities. 
Draft – Do Not Cite or Quote 6-264 June 2012

Source: Bell et al. (2006)

Figure 6-35 Estimated combined C-R curve for nonaccidental mortality and 

24-hour average ozone concentrations at lag 0-1 using the 

nonlinear (spline) model.

1 Using the same NMMAPS dataset as Bell et al. (2006), Smith et al. (2009b) further 

2 examined the O3-mortality C-R relationship. Similar to Bell et al. (2006), Smith et al. 

3 (2009b) conduct a subset analysis, but instead of restricting the analysis to days with O3

4 concentrations below a cutoff the authors only include days above a defined cutoff in the 

5 analysis. The results of this “reversed subset” approach are in line with those reported by 

6 Bell et al. (2006); consistent positive associations at all cutoff points up to a defined 

7 concentration where the total number of days with 24-h avg O3 concentrations above a 

8 value are so limited that the variability around the central estimate is increased. In the 

9 Smith et al. (2009b) analysis this observation was initially observed at 45 ppb, with the 

10 largest variability at 60 ppb; however, unlike Bell et al. (2006) where 73% of days are 

11 excluded when subsetting the data to less than 20 ppb, the authors do not detail the 

12 number of days of data included in the subset analyses at higher concentrations. In 

13 addition to the subset analysis, Smith et al. (2009b) examined the shape of the C-R curve 

14 using a piecewise linear approach with cutpoints at 8-h avg concentrations of 40 ppb, 

15 60 ppb, and 80 ppb. Smith et al. (2009b) found that the shape of the C-R curve is similar 
Draft – Do Not Cite or Quote 6-265 June 2012

1 to that reported by Bell et al. (2006) (Figure 6-35), but argue that slopes of the β for each 

2 piece of the curve are highly variable with the largest variation in the 60-80 ppb range. 

3 However, the larger variability around the β between 60-80 would be expected due to the 

4 small number of days with O3 concentrations within that range in an all-year analysis. 

5 This result is consistent with that observed by Bell et al. (2006), which is presented in 

6 Figure 6-35.

7 The APHENA project (Katsouyanni et al., 2009) also analyzed the Canadian and 

8 European datasets (the U.S. data were analyzed for PM10 only) for evidence of a 

9 threshold, using the threshold analysis method (Model 3) applied in Bell et al. (2006)

10 study described above. There was no evidence of a threshold in the Canadian data 

11 (i.e., the pattern of AIC values for each increment of a potential threshold value varied 

12 across cities, most of which showed no local minima). Likewise, the threshold analysis 

13 conducted using the European data also showed no evidence of a threshold. 

14 The PAPA study, did not examine whether a threshold exists in the O3-mortality C-R 

15 relationship, but instead the shape of the C-R curve individually for each city (Bangkok, 

16 Hong Kong, Shanghai, and Wuhan) (Wong et al., 2010). Using a natural spline smoother 

17 with 3df for the O3 term, Wong et al. (2010) examined whether non-linearity was present 

18 by testing the change in deviance between the smoothed, non-linear, model and an 

19 unsmoothed, linear, model with 1 df. For each of the cities, both across the full range of 

20 the O3 distribution and specifically within the range of the 25th to 75th percentile of each 

21 city’s O3 24-h avg concentrations (i.e., a range of 9.7 ppb to 60.4 ppb across the cities) 

22 there was no evidence of a non-linear relationship in the O3-mortality C-R curve. It 

23 should be noted that the range of the 25th to 75th percentiles in all of the cities, except 

24 Wuhan, was lower than that observed in the U.S. using all-year data where the range 

25 from the 25th to 75th percentiles is 30 ppb to 50 ppb (Table 3-6). 

26 Additional threshold analyses were conducted using NMMAPS data, by Xia and Tong 

27 (2006) and Stylianou and Nicolich (2009). Both studies used a new statistical approach 

28 developed by Xia and Tong (2006) to examine thresholds in the O3 mortality C-R 

29 relationship. The approach consisted of an extended GAM model, which accounted for 

30 the cumulative and nonlinear effects of air pollution using a weighted cumulative sum for 

31 each pollutant, with the weights (non-increasing further into the past) derived by a 

32 restricted minimization method. The authors did not use the term distributed lag model, 

33 but their model has the form of distributed lag model, except that it allows for nonlinear 

34 functional forms. Using NMMAPS data for 1987-1994 for 3 U.S. cities (Chicago, 

35 Pittsburgh, and El Paso), Xia and Tong (2006) found that the extent of cumulative effects 

36 of O3 on mortality were relatively short. While the authors also note that there was 

37 evidence of a threshold effect around 24-h avg concentrations of 25 ppb, the threshold 
Draft – Do Not Cite or Quote 6-266 June 2012

1 values estimated in the analysis were sometimes in the range where data density was low. 

2 Thus, this threshold analysis needs to be replicated in a larger number of cities to confirm 

3 this observation. It should be noted that the model used in this analysis did not include a 

4 smooth function of days to adjust for unmeasured temporal confounders, and instead 

5 adjusted for season using a temperature term. As a result, these results need to be viewed 

6 with caution because some potential temporal confounders (e.g., influenza) do not always 

7 follow seasonal patterns of temperature. 

8 Stylianou and Nicolich (2009) examined the existence of thresholds following an 

9 approach similar to Xia and Tong (2006) for all-cause, cardiovascular, and respiratory 

10 mortality using data from NMMAPS for nine major U.S. cities (i.e., Baltimore, Chicago, 

11 Dallas/Fort Worth, Los Angeles, Miami, New York, Philadelphia, Pittsburgh, and 

12 Seattle) for the years 1987-2000. The authors found that PM10 and O3 were the two 

13 important predictors of mortality. Stylianou and Nicolich (2009) found that the estimated 

14 O3-mortality risks varied across the nine cities with the models exhibiting apparent 

15 thresholds, in the 10-45 ppb range for O3 (3-day accumulation). However, given the city16 to-city variation in risk estimates, combining the city-specific estimates into an overall 

17 estimate complicates the interpretation of a threshold. Unlike the Xia and Tong (2006)

18 analysis, Stylianou and Nicolich (2009) included a smooth function of time to adjust for 

19 seasonal/temporal confounding, which could explain the difference in results between the 

20 two studies. 

21 In conclusion, the evaluation of the O3-mortality C-R relationship did not find any 

22 evidence that supports a threshold in the relationship between short-term exposure to O3

23 and mortality within the range of O3 concentrations observed in the U.S. Additionally, 

24 recent evidence suggests that the shape of the O3-mortality C-R curve remains linear 

25 across the full range of O3 concentrations. However, the studies evaluated demonstrated 

26 that the heterogeneity in the O3-mortality relationship across cities (or regions) 

27 complicates the interpretation of a combined C-R curve and threshold analysis. Given the 

28 effect modifiers identified in the mortality analyses that are also expected to vary 

29 regionally (e.g., temperature, air conditioning prevalence), a national or combined 

30 analysis may not be appropriate to identify whether a threshold exists in the O3-mortality 

31 C-R relationship. Overall, the studies evaluated support a linear O3-mortality C-R 

32 relationship and continue to support the conclusions from the 2006 O3 AQCD, which 

33 stated that “if a population threshold level exists in O3 health effects, it is likely near the 

34 lower limit of ambient O3 concentrations in the United States” (U.S. EPA, 2006b).
Draft – Do Not Cite or Quote 6-267 June 2012

6.6.2.5 Associations of Cause-Specific Mortality and Short-term 

Ozone Exposure

1 In the 2006 O3 AQCD, an evaluation of studies that examined cause-specific mortality 

2 found consistent positive associations between short-term O3 exposure and 

3 cardiovascular mortality, with less consistent evidence for associations with respiratory 

4 mortality. The majority of the evidence for associations between O3 exposure and cause5 specific mortality were from single-city studies, which had small daily mortality counts 

6 and subsequently limited statistical power to detect associations. 

7 New multicity studies evaluated in this review build upon and confirm the associations 

8 between short-term O3 exposure and cause-specific mortality identified in the 2006 O3

9 AQCD (U.S. EPA, 2006b) (Figure 6-36; Table 6-53). In APHENA, a multicontinent 

10 study that consisted of the NMMAPS, APHEA2 and Canadian multicity datasets, 

11 consistent positive associations were reported for both cardiovascular and respiratory 

12 mortality in all-year analyses when focusing on the natural spline model with 8 df/year 

13 (Figure 6-36; Table 6-53). The associations between O3 exposure and cardiovascular and 

14 respiratory mortality in all-year analyses were further supported by the multicity PAPA 

15 study (Wong et al., 2010). The magnitude of cardiovascular mortality associations were 

16 primarily larger in analyses restricted to the summer season compared to those observed 

17 in all-year analyses (Figure 6-36; Table 6-53). Additional multicity studies from the U.S. 

18 (Zanobetti and Schwartz, 2008b) and Europe (Stafoggia et al., 2010; Samoli et al., 2009)

19 that conducted summer season analyses provide evidence supporting associations 

20 between O3 exposure and cardiovascular and respiratory mortality that are similar or 

21 larger in magnitude compared to those observed in all-year analyses. 

22 Of the studies evaluated, only the APHENA study (Katsouyanni et al., 2009) and an 

23 Italian multicity study (Stafoggia et al., 2010) conducted an analysis of the potential for 

24 copollutant confounding of the O3 cause-specific mortality relationship. When focusing 

25 on the natural spline model with 8 df/year and lag 1 results (as discussed in 

26 Section 6.6.2.1), the APHENA study found that O3 cause-specific mortality risk estimates 

27 were fairly robust to the inclusion of PM10 in copollutant models in the European dataset 

28 with more variability in the U.S. and Canadian datasets (i.e., copollutant risk estimates 

29 increased and decreased for respiratory and cardiovascular mortality). In summer season 

30 analyses cardiovascular O3 mortality risk estimates were robust in the European dataset 

31 and attenuated but remained positive in the U.S. datasets; whereas, respiratory O3

32 mortality risk estimates were attenuated in the European dataset and robust in the U.S. 

33 dataset. The authors did not examine copollutant models during the summer season in the 

34 Canadian dataset (Figure 6-29; Table 6-45). Interpretation of these results requires 

35 caution; however, due to the different PM sampling schedules employed in each of these 
Draft – Do Not Cite or Quote 6-268 June 2012

1 study locations (i.e., primarily every-6th day in the U.S. and Canadian datasets and 

2 every-day in the European dataset). The results of the summer season analyses from the 

3 APHENA study (Katsouyanni et al., 2009) are consistent with those from a study of 10 

4 Italian cities during the summer months (Stafoggia et al., 2010). Stafoggia et al. (2010)

5 found that cardiovascular (14.3% [95% CI: 6.7, 22.4%]) and cerebrovascular (8.5% 

6 [95% CI: 0.06, 16.3%]) mortality O3 effect estimates were robust to the inclusion of PM10

7 in copollutant models (14.3% [95% CI: 6.7, 23.1%] and 7.3% [95% CI: -1.2, 16.3], 

8 respectively), while respiratory mortality O3 effects estimates (17.6% [95% CI: 1.8, 

9 35.5%]) were attenuated, but remained positive (9.2% [95% CI: -6.9, 28.8%]). 

Effect estimates are for a 20 ppb increase in 24-h avg; 30 in 8-h max; and 40ppb increase in 1-h max O3 concentrations. 

Red = cardiovascular; blue = respiratory; closed circles = all-year analysis; and open circles = summer-only analysis. An “a” 

represents studies from the 2006 O3 AQCD. A “b” represents risk estimates from APHENA-Canada standardized to an approximate 

IQR of 5.1 ppb for a 1-h max increase in O3 concentrations (Section 6.2.7.2).

Figure 6-36 Percent increase in cause-specific mortality.

Study

Bell et al. (2005)a

Wong et al. (2010)

Katsouyanni et al. (2009)

Gryparis et al. (2004)a

Samoli et al. (2009)

Zanobetti and Schwartz (2008)

Stafoggia et al. (2010)

Katsouyanni et al. (2009)

Bell et al. (2005)a

Wong et al. (2010)

Katsouyanni et al. (2009)

Gryparis et al. (2004)a

Zanobetti and Schwartz (2008)

Katsouyanni et al. (2009)

Samoli et al. (2009)

Stafoggia et al. (2010)

Katsouyanni et al. (2009)

Location

U.S. and non-U.S.

PAPA (4 cities)

APHENA-U.S.

APHENA-Canada

APHENA-Canada

APHENA-Europe

APHENA-U.S.

APHENA-Canada

APHENA-Canada

APHENA-Europe

21 European cities

21 European cities

48 U.S. cities

10 Italian cities

APHENA-U.S.

APHENA-Canada

APHENA-Canada

APHENA-Europe

APHENA-U.S.

APHENA-Canada

APHENA-Canada

APHENA-Europe

U.S. and non-U.S.

PAPA (4 cities)

APHENA-U.S.

APHENA-Canada

APHENA-Canada

APHENA-Europe

APHENA-U.S.

APHENA-Canada

APHENA-Canada

APHENA-Europe

21 European cities

48 U.S. cities

APHENA-U.S.

APHENA-Canada

APHENA-Canada

APHENA-Europe

21 European cities

10 Italian cities

APHENA-U.S.

APHENA-Canada

APHENA-Canada

APHENA-Europe

Ages

All

≥75

<75

All

≥35

≥75

<75

All

≥75

All

≥35

≥75

Cardiovascular

Respiratory

All-Year

Summer

All-Year

Summer

Lag

NR

0-1

DL(0-2)

DL(0-2)

DL(0-2)b

DL(0-2)

DL(0-2)

DL(0-2)

DL(0-2)b

DL(0-2)

0-1

0-1

0-3

DL(0-5)

DL(0-2)

DL(0-2)

DL(0-2)b

DL(0-2)

DL(0-2)

DL(0-2)

DL(0-2)b

DL(0-2)

NR

0-1

DL(0-2)

DL(0-2)

DL(0-2)b

DL(0-2)

DL(0-2)

DL(0-2)

DL(0-2)b

DL(0-2)

0-1

0-3

DL(0-2)

DL(0-2)

DL(0-2)b

DL(0-2)

0-1

DL(0-5)

DL(0-2)

DL(0-2)

DL(0-2)b

DL(0-2)

►

►

►

◄

◄

-10 -5 0 5 10 15 20 25 30

% Increase
Draft – Do Not Cite or Quote 6-269 June 2012

Table 6-53 Corresponding effect estimates for Figure 6-36.

Study* Location Ages Lag Avg Time %Increase (95% CI)

Cardiovascular

All-year - Cardiovascular

Bell et al. (2005)

a U.S. and non-U.S. All NR 24-h avg 2.23 (1.36,3.08)

Wong et al. (2010) PAPA (4 cities) 0-1 8-h max 2.20 (0.06, 4.37)

Katsouyanni et al. (2009) APHENA-U.S. ≥ 75 DL(0-2) 1-h max 2.30 (-1.33, 6.04)

APHENA-Canada DL(0-2) 8.96 (0.75,18.6)

APHENA-Canada DL(0-2)b 1.1 (0.10,2.20)

APHENA-europe DL(0-2) 2.06 (-0.24, 4.31)

APHENA-U.S. <75 DL(0-2) 3.83 (-0.16, 7.95)

APHENA-Canada DL(0-2) 7.03 (-2.71, 17.7)

APHENA-Canada DL(0-2)b 0.87 (-0.35, 2.10)

APHENA-europe DL(0-2) 1.98 (-1.09, 5.13)

Summer – Cardiovascular

Gryparis et al. (2004)

a 21 European cities All 0-1 8-h max 2.7 (1.29,4.32)

Samoli et al. (2009) 21 European cities 0-1 8-h max 1.48 (0.18, 2.80)

Zanobetti and Schwartz (2008b) 48 U.S. cities 0-3 8-h max 2.42 (1.45, 3.43)

Stafoggia et al. (2010) 10 Italian cities ≥ 35 DL(0-5) 8-h max 14.3 (6.65, 22.4)

Katsouyanni et al. (2009) APHENA-U.S. ≥ 75 DL(0-2) 1-h max 3.18 (-0.47, 6.95)

APHENA-Canada DL(0-2) 1.50 (-2.79, 5.95)

APHENA-Canada DL(0-2)b 0.19 (-0.36, 0.74)

APHENA-europe DL(0-2) 3.67 (0.95, 6.53)

APHENA-U.S. <75 DL(0-2) 6.78 (2.70, 11.0)

APHENA-Canada DL(0-2) -1.02 (-4.23, 2.30)

APHENA-Canada DL(0-2)b -0.13 (-0.55, 0.29)

APHENA-europe DL(0-2) 2.22 (-1.48, 6.04)

Respiratory

All-years - Respiratory

Bell et al. (2005)

a U.S. and non-U.S. All NR 24-h avg 0.94 (-1.02, 2.96)

Wong et al. (2010) PAPA (4 cities) 0-1 8-h max 2.02 (-0.41, 4.49)

Katsouyanni et al. (2009) APHENA-U.S. DL(0-2) 1-h max 2.54 (-3.32, 8.79)

APHENA-Canada DL(0-2) 1.02 (-11.9, 15.9)

APHENA-Canada DL(0-2)b 0.13 (-1.60, 1.90)

APHENA-europe DL(0-2) 1.82 (-2.18, 6.04)

APHENA-U.S. ≥ 75 DL(0-2) 1.10 (-6.48, 9.21)

APHENA-Canada DL(0-2) -4.61 (-19.3, 13.3)

APHENA-Canada DL(0-2)b -0.60 (-2.70, 1.60)

APHENA-europe DL(0-2) 1.10 (-3.48, 5.95)
Draft – Do Not Cite or Quote 6-270 June 2012

Study* Location Ages Lag Avg Time %Increase (95% CI)

Summer - Respiratory

Gryparis et al. (2004)

a 21 European cities All 0-1 8-h max 6.75 (4.38, 9.10)

Zanobetti and Schwartz (2008b) 48 U.S. cities 0-3 8-h max 2.51 (1.14, 3.89)

Katsouyanni et al. (2009) APHENA-U.S. DL(0-2) 1-h max 4.40 (-2.10, 11.3)

APHENA-Canada DL(0-2) 26.1 (13.3, 41.2)

APHENA-Canada DL(0-2)b 3.00 (1.60, 4.50)

APHENA-europe DL(0-2) 3.83 (-1.33, 9.21)

Samoli et al. (2009) 21 European cities 0-1 8-h max 2.38 (0.65, 4.19)

Stafoggia et al. (2010) 10 Italian cities ≥ 35 DL(0-5) 8-h max 17.6 (1.78, 35.5)

Katsouyanni et al. (2009) APHENA-U.S. ≥ 75 DL(0-2) 1-h max 4.07 (-4.23, 13.0)

APHENA-Canada DL(0-2) 19.5 (2.22, 40.2)

APHENA-Canada DL(0-2)b 2.30 (0.28, 4.40)

APHENA-europe DL(0-2) 2.46 (-3.40, 8.62)

*Studies from Figure 6-36, plus others.

a

Studies from the 2006 O3 AQCD.

b

Risk estimates from APHENA-Canada standardized to an approximate IQR of 5.1 ppb for a 1-h max increase in O3 concentrations 

(Section 6.2.7.2).

1 Collectively, the results from the new multicity studies provide evidence of associations 

2 between short-term O3 exposure and cardiovascular and respiratory mortality with 

3 additional evidence indicating these associations persist, and in some cases the magnitude 

4 of associations are increased, in the summer season. Although copollutant analyses of 

5 cause-specific mortality are limited, the APHENA study found that O3 cause-specific 

6 mortality risk estimates were fairly robust to the inclusion of PM10 in copollutant models 

7 when focusing on the dataset with daily PM10 data (i.e., the European dataset), which is 

8 supported by the results from Stafoggia et al. (2010). Additionally, APHENA found that 

9 O3 cause-specific mortality risk estimates were moderately to substantially sensitive 

10 (e.g., increased or attenuated) to inclusion of PM10 in the U.S. and Canadian datasets. 

11 However, the mostly every-6th-day sampling schedule for PM10 in the U.S. and Canadian 

12 datasets greatly reduced their sample size and limits the interpretation of these results. 

6.6.3 Summary and Causal Determination

13 The evaluation of new multicity studies that examined the association between short-term 

14 O3 exposure and mortality found evidence which supports the conclusions of the 2006 O3

15 AQCD. These new studies reported consistent positive associations between short-term 

16 O3 exposure and all-cause (nonaccidental) mortality, with associations persisting or 

17 increasing in magnitude during the warm season, and provide additional support for 

18 associations between O3 exposure and cardiovascular and respiratory mortality. 
Draft – Do Not Cite or Quote 6-271 June 2012

1 Recent studies further examined potential confounders (e.g., copollutants and seasonality) 

2 of the O3-mortality relationship. Because the PM-O3 correlation varies across regions, 

3 due to the difference in PM chemical constituents, interpretation of the combined effect 

4 of PM on the relationship between O3 and mortality is not straightforward. Unlike 

5 previous studies that were limited to primarily examining the confounding effects of 

6 PM10, the new studies expanded their analyses to include multiple PM indices (e.g., PM10, 

7 PM2.5, and PM components). An examination of copollutant models found evidence that 

8 associations between O3 and all-cause mortality were robust to the inclusion of PM10 or 

9 PM2.5 (Stafoggia et al., 2010; Katsouyanni et al., 2009; Bell et al., 2007), while other 

10 studies found evidence for a modest reduction (~20-30%) when examining PM10 (Smith 

11 et al., 2009b). Additional evidence suggests potential sensitivity (e.g., increases and 

12 attenuation) of O3 mortality risk estimates to copollutants by age group or cause-specific 

13 mortality (e.g., respiratory and cardiovascular) (Stafoggia et al., 2010; Katsouyanni et al., 

14 2009). An examination of PM components, specifically sulfate, found evidence for 

15 reductions in O3-mortality risk estimates in copollutant models (Franklin and Schwartz, 

16 2008). Overall, across studies, the potential impact of PM indices on O3-mortality risk 

17 estimates tended to be much smaller than the variation in O3-mortality risk estimates 

18 across cities suggesting that O3 effects are independent of the relationship between PM 

19 and mortality. However, interpretation of the potential confounding effects of PM on 

20 O3-mortality risk estimates requires caution. This is because the PM-O3 correlation varies 

21 across regions, due to the difference in PM components, complicating the interpretation 

22 of the combined effect of PM on the relationship between O3 and mortality. Additionally, 

23 the limited PM or PM component datasets used as a result of the every-3rd- and 6th-day 

24 PM sampling schedule instituted in most cities limits the overall sample size employed to 

25 examine whether PM or one of its components confounds the O3-mortality relationship. 

26 An examination of potential seasonal confounding of the O3-mortality relationship found 

27 that the extent of smoothing or the methods used for adjustment can influence O3 risk 

28 estimates when not applying enough degrees of freedom to control for temporal/season 

29 trends (Katsouyanni et al., 2009). This is because of the opposing seasonal trends 

30 between O3 and mortality. 

31 The multicity studies evaluated within this section also examined the regional 

32 heterogeneity observed in O3-mortality risk estimates. These studies provide evidence 

33 which suggests generally higher O3-mortality risk estimates in northeastern U.S. cities 

34 with some regions showing no associations between O3 exposure and mortality 

35 (e.g., Southwest, Urban Midwest) (Smith et al., 2009b; Bell and Dominici, 2008). 

36 Multicity studies that examined individual- and community-level characteristics 

37 identified characteristics that may explain the observed regional heterogeneity in 

38 O3-mortality risk estimates as well as characteristics of populations potentially at greatest 
Draft – Do Not Cite or Quote 6-272 June 2012

1 risk for O3-related health effects. An examination of community-level characteristics 

2 found an increase in the O3-mortality risk estimates in cities with higher unemployment, 

3 percentage of the population Black/African-American, percentage of the working 

4 population that uses public transportation, lower temperatures, and lower prevalence of 

5 central air conditioning (Medina-Ramón and Schwartz, 2008). Additionally, a potential 

6 interactive, or synergistic, effect on the O3-mortality relationship was observed when 

7 examining differences in the O3-mortality association across temperature levels (Ren et 

8 al., 2008). An examination of individual-level characteristics found evidence that older 

9 age, female sex, Black race, having atrial fibrillation, SES indicators (i.e., educational 

10 attainment, income level, and employment status), and out-of hospital deaths, specifically 

11 in those individuals with diabetes, modify O3-mortality associations (Cakmak et al., 

12 2011; Stafoggia et al., 2010; Medina-Ramón and Schwartz, 2008), and lead to increased 

13 risk of O3-related mortality. Overall, additional research is warranted to further confirm 

14 whether these characteristics, individually or in combination, can explain the observed 

15 regional heterogeneity. 

16 Additional studies were evaluated that examined factors that may influence the shape of 

17 the O3-mortality C-R curve, such as multi-day effects, mortality displacement, adaptation, 

18 the use of different exposure metrics (i.e., 24-h avg, 8-h max or 1-h max), and whether a 

19 threshold exists in the O3-mortality relationship. An examination of multiday effects in a 

20 U.S. and European multicity study found conflicting evidence for mortality displacement, 

21 but both studies suggest that the positive associations between O3 and mortality are 

22 observed mainly in the first few days after exposure (Samoli et al., 2009; Zanobetti and 

23 Schwartz, 2008b). A U.S. multicity study found evidence of an adaptive response to O3

24 exposure, with the highest risk estimates earlier in the O3 season (i.e., July) and 

25 diminished effects later (i.e., August) (Zanobetti and Schwartz, 2008a). However, the 

26 evidence of adaptive effects has an implication for the interpretation of multi-day effects, 

27 and requires further analysis. The limited number of studies conducted that examined the 

28 effect of using different exposure metrics (i.e., 1-h max, 8-h max, and 24-h avg) when 

29 examining the O3-mortality relationship found relatively comparable O3-mortality risk 

30 estimates across the exposure metrics used (Smith et al., 2009b; Gryparis et al., 2004). 

31 Analyses that specifically focused on the O3-mortality C-R relationship supported a linear 

32 O3-mortality relationship and found no evidence of a threshold within the range of O3

33 concentrations in the U.S., but did observe evidence for potential differences in the C-R 

34 relationship across cities (Katsouyanni et al., 2009; Stylianou and Nicolich, 2009; Bell et 

35 al., 2006). Collectively, these studies support the conclusions of the 2006 O3 AQCD that 

36 “if a population threshold level exists in O3 health effects, it is likely near the lower limit 

37 of ambient O3 concentrations in the U.S.” 
Draft – Do Not Cite or Quote 6-273 June 2012

1 Studies that examined the association between short-term O3 exposure and cause-specific 

2 mortality confirm the associations with both cardiovascular and respiratory mortality 

3 reported in the 2006 O3 AQCD (Stafoggia et al., 2010; Wong et al., 2010; Katsouyanni et

4 al., 2009; Samoli et al., 2009; Zanobetti and Schwartz, 2008b). These associations were 

5 primarily larger in magnitude during the summer season compared to all-year analyses. 

6 Of the studies that examined the potential confounding effects of PM [i.e., Stafoggia et al. 

7 (2010); Katsouyanni et al. (2009)], O3 mortality associations remained relatively robust 

8 in copollutant models, but interpretation of these studies was complicated by the different 

9 PM sampling schedules (e.g., every-6th-day) employed in each study. Overall, the strong 

10 evidence for respiratory effects due to short-term O3 exposure (Section 6.2) are consistent 

11 across disciplines and provides coherence for the respiratory mortality associations 

12 observed across studies. However, the strong evidence for O3-induced cardiovascular 

13 mortality is complicated by toxicological studies that provide initial evidence for a 

14 biologically plausible mechanism for O3-induced cardiovascular mortality, but a lack of 

15 coherence with controlled human exposure and epidemiologic studies of cardiovascular 

16 morbidity that do not demonstrate consistent evidence of O3-induced cardiovascular 

17 effects (Section 6.3).

18 In conclusion, the recent epidemiologic studies build upon and confirm the associations 

19 between short-term O3 exposure and all-cause and cause-specific mortality reported in the 

20 2006 O3 AQCD. However, there is a lack of coherence across disciplines and consistency 

21 across health outcomes for O3-induced cardiovascular morbidity (Section 6.3) which do 

22 not support the relatively strong epidemiologic evidence for O3-related cardiovascular 

23 mortality. Overall, recent studies have provided additional information regarding key 

24 uncertainties (previously identified - including the potential confounding effects of 

25 copollutants and seasonal trend), individual- and community-level factors that may lead 

26 to increased risk of O3-induced mortality and the heterogeneity in O3-mortality risk 

27 estimates, and continued evidence of a linear no-threshold C-R relationship. Although 

28 some uncertainties still remain, the collective body of evidence is sufficient to conclude 

29 that there is likely to be a causal relationship between short-term O3 exposure and 

30 total mortality.

6.7 Overall Summary

31 The evidence reviewed in this chapter describes the recent findings regarding the health 

32 effects of short-term exposure to ambient O3 concentrations. Table 6-54 provides an 

33 overview of the causal determinations for each of the health categories evaluated.
Draft – Do Not Cite or Quote 6-274 June 2012

Table 6-54 Summary of causal determinations for short-term exposures to 

ozone.

Health Category Causal Determination

Respiratory Effects Causal relationship

Cardiovascular Effects Suggestive of a causal relationship

Central Nervous System Effects Suggestive of a causal relationship

Effects on Liver and Xenobiotic Metabolism Inadequate to infer a causal relationship

Effects on Cutaneous and Ocular Tissues Inadequate to infer a causal relationship

Total Mortality Likely to be a causal relationship
Draft – Do Not Cite or Quote 6-275 June 2012

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