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6 INTEGRATED HEALTH EFFECTS OF SHORTTERM 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 of short-term O3 exposure with a range of 

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

6 and mortality (Sections 6.2, 6.3, and 6.6). A smaller number of studies are available to 

7 assess the effects of O3 on other physiological systems such as the central nervous system 

8 (Section 6.4), liver and metabolism (Section 6.5.1), and cutaneous and ocular tissues 

9 (Section 6.5.2). 

10 Evidence for the major health effect categories (e.g., respiratory, cardiovascular, 

11 mortality) is described in individual sections that include a brief summary of conclusions 

12 from the 2006 O3 AQCD and an evaluation of recent evidence that is intended to build 

13 upon evidence from previous reviews. Within each section, results are organized by 

14 health endpoint (e.g., lung function, pulmonary inflammation) then by specific scientific 

15 discipline (e.g., controlled human exposure, epidemiology, and toxicology). Each major 

16 section (e.g., respiratory, cardiovascular, mortality) concludes with an integrated 

17 summary of the findings and a conclusion regarding causality. Based upon the framework 

18 described in the Preamble to this ISA, a determination of causality is made for a broad 

19 health effect category, such as respiratory effects, with coherence and plausibility being 

20 based on the evidence available across disciplines and also across the suite of related 

21 health endpoints, including cause-specific mortality. 

6.2 Respiratory Effects

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

23 toxicological studies, the 2006 O3 AQCD concluded that there was clear, consistent 

24 evidence of a causal relationship between short-term O3 exposure and respiratory effects 

25 (U.S. EPA, 2006b). Contributing to this conclusion were consistent and coherent 

26 observations across scientific disciplines of associations of short-term O3 exposures with 

27 pulmonary function decrements and increases in lung inflammation, lung permeability, 

28 and airway hyperresponsiveness. Collectively, these findings provided biological 
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1 plausibility for associations in epidemiologic studies of short-term ambient O3 exposure 

2 with respiratory symptoms and respiratory-related hospitalizations and emergency 

3 department (ED) visits.

4 Controlled human exposure studies have provided strong and quantifiable exposure5 response data on the human health effects of O3. The most salient observations from 

6 studies reviewed in the 1996 and 2006 O3 AQCDs were that: (1) young healthy adults 

7 exposed to O3 concentrations ≥ 80 ppb develop significant reversible, transient 

8 decrements in pulmonary function if minute ventilation (VE) or duration of exposure is 

9 increased sufficiently; (2) relative to young adults, children experience similar 

10 spirometric responses but lesser symptoms from O3 exposure; (3) relative to young 

11 adults, O3-induced spirometric responses are decreased in older individuals; (4) there is a 

12 large degree of intersubject variability in physiologic and symptomatic responses to O3,

13 but responses tend to be reproducible within a given individual over a period of 

14 several months; (5) subjects exposed repeatedly to O3 for several days experience an 

15 attenuation of spirometric and symptomatic responses on successive exposures, that is 

16 lost after about a week without exposure; and (6) acute O3 exposure initiates an 

17 inflammatory response that may persist for at least 18 to 24 hours postexposure.

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

19 derived from the coherence between toxicological and controlled human exposure studies 

20 examining parallel endpoints. For example, O3-induced decrements in lung function have 

21 also been observed in animals, and as in humans, tolerance or attenuation has been 

22 demonstrated in animal models. Both humans and rodents exhibit increased airway 

23 hyperresponsiveness. This is an important consequence of exposure to ambient O3, 

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

25 ambient stimuli. Additionally, airway hyperresponsiveness tends to resolve more slowly 

26 and appears less subject to attenuation. Increased permeability and inflammation have 

27 been observed in the airways of humans and animals alike after O3 exposure, although 

28 these processes are not necessarily associated with immediate changes in lung function or 

29 hyperresponsiveness. Furthermore, the potential relationship between repetitive bouts of 

30 acute inflammation and the development of chronic respiratory disease is unknown. 

31 Another feature of O3 exposure-related respiratory morbidity is impaired host defense 

32 and reduced resistance to lung infection, which has been strongly supported by 

33 toxicological evidence and to a limited extent by human data. Recurrent respiratory 

34 infection in early life is associated with increased incidence of asthma in humans.

35 In epidemiologic studies, short-term O3-related respiratory morbidity has been assessed 

36 most frequently using lung function. Several studies of healthy children attending camps 

37 as well as studies of outdoor workers, groups exercising outdoors, and children with 
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1 asthma support O3 effects on lung function decrements at ambient levels (U.S. EPA, 

2 2006b, 1996a). In addition to lung function, ambient O3 exposure has been associated 

3 with increases in respiratory symptoms (e.g., cough, wheeze, shortness of breath), 

4 especially in large U.S. panel studies of children with asthma (Gent et al., 2003; 

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

6 respiratory endpoints collectively provides support for epidemiologic studies that have 

7 demonstrated consistent positive associations between O3 exposure and respiratory 

8 hospital admissions and ED visits, specifically during the summer or warm months. In 

9 contrast with other respiratory health endpoints, the association between short-term O3

10 exposure and respiratory mortality is less clearly indicated. Although O3 has been 

11 consistently associated with nonaccidental and cardiopulmonary mortality, the 

12 contribution of respiratory causes to these findings has been uncertain as the few studies 

13 that have examined mortality specifically from respiratory causes have reported 

14 inconsistent associations with ambient O3 exposures. 

15 As discussed throughout this section, consistent with the strong body of evidence 

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

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

18 controlled human exposure studies, airway inflammatory responses in toxicological 

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

20 studies contribute new evidence on at-risk populations and of associations of ambient O3

21 exposures with biological markers of airway inflammation and oxidative stress, which is 

22 consistent with the extensive evidence from human controlled exposure and toxicological 

23 studies. Furthermore, extending the potential range of well-established O3-associated 

24 respiratory effects, new multicity studies and a multicontinent study demonstrate 

25 associations between short-term ambient O3 exposure and respiratory-related mortality.

6.2.1 Lung Function

6.2.1.1 Controlled Human Exposure

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

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

28 ranging from 40 to 500 ppb, while at rest or during exercise of varying intensity. 

29 Responses to acute O3 exposures in the range of ambient concentrations include 

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

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

32 Reflex inhibition of inspiration results in a decrease in forced vital capacity (FVC) and 
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1 total lung capacity (TLC) and, in combination with mild bronchoconstriction, contributes 

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

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

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

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

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

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

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

9 periods. 

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

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

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

13 exposures as FEV1 and respiratory symptom responses appear minimally affected by 

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

15 have been reported for exposures to 80 and 120 ppb O3 (6.6 h, moderate quasi continuous 

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

17 2003a, b, 2002). 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

33 1991) to 2.7% (Adams, 2006a). On average, across ten 6.6-hour exposure studies, there 

34 has been a 1.0% (n=279) increase in FEV1 (Kim et al., 2011; Schelegle et al., 2009; 

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

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

37 reason for small changes in FEV1 over the course of FA exposures, whether biologically 
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1 based or a systematic effect of the experimental procedures, the use of FA responses as a 

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

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

4 the measured responses. 

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

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

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

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

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

10 having their own control exposure to FA to discern relatively small effects with certainty 

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

12 experimental design. The utility of FA control exposures becomes more apparent when 

13 considering individuals with respiratory disease. The occurrence of exercise-induced 

14 bronchospasm is well recognized to in patients with asthma and COPD and may be 

15 experienced during both FA and O3 exposures. Absent correction for FA responses, 

16 exercise-induced changes in FEV1 could be mistaken for responses due to O3. This 

17 biological phenomenon serves as an example to emphasize the need for a proper control 

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

19 influence of other factors on the outcomes of interest. 

Pulmonary Function Effects of Ozone Exposure in Healthy Subjects

Acute Exposure of Healthy Subjects

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

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

22 typically use fixed concentrations of O3 under carefully regulated environmental 

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

24 in spirometry and symptomatic response) in these individuals is a function of O3

25 concentration (C), minute ventilation (VE), and exposure duration (time). Any physical 

26 activity will increase minute ventilation and therefore the dose of inhaled O3. Dose of 

27 inhaled O3 to the lower airways is also increased due to a shift from nasal to oronasal 

28 breathing with a consequential decrease in O3 scrubbing by the upper airways. Thus, the 

29 intensity of physiological response following an acute exposure will be strongly 

30 associated with minute ventilation. 

31 The product of C × VE × time, although actually a measure of exposure, is commonly 

32 used as a surrogate for O3 dose to the respiratory tract in controlled human exposure 

33 studies. The delivery of O3 to the lower respiratory tract varies as a function of breathing 

34 conditions (route and pattern). And, the dose of O3 to the lower respiratory tract can vary 
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1 between similarly exposed individuals. In support of the use of the product (C × VE × 

2 time) as a surrogate for O3 dose, differences in FEV1 responses among young healthy 

3 adults (32 M, 28 F) exposed to O3 (250 ppb, 30 L/min, 2 h) do not appear to be explained 

4 by intersubject differences in the fraction of inhaled O3 retained in the lung (Ultman et 

5 al., 2004). Using the product of C × VE × time as a surrogate for O3 dose is also useful in 

6 distinguishing between the well defined and characterized exposure of subjects in 

7 controlled human exposure studies as opposed to the use of ambient O3 concentration to 

8 characterize exposure in epidemiologic studies. 

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

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

11 decrement of 6.4% (n=10) (Folinsbee et al., 1978) to 6.7% (n=13) (Horvath et al., 1979). 

12 Airway resistance was not clearly affected during at-rest exposure to these 

13 O3 concentrations. When exposed to 200 ppb for 2.25 h during intermittent periods of rest 

14 and brisk walking, young healthy subjects (83 M, 55 F) show a statistically significant 

15 group mean FEV1 decrement of 8.8% following O3 exposure (Que et al.). For exposures 

16 of 1-2 hours to ≥ 120 ppb O3, statistically significant symptomatic responses and effects 

17 on FEV1 are observed when VE is sufficiently increased by exercise (McDonnell et al., 

18 1999). For instance, 5% of young healthy adults exposed to 400 ppb for 2 h during rest 

19 experienced pain on deep inspiration. Respiratory symptoms were not observed at lower 

20 exposure concentrations (120-300 ppb) or with only 1 h of exposure. However, when 

21 exposed to 120 ppb for 2 h during moderate intermittent exercise, 9% of individuals 

22 experienced pain on deep inspiration, 5% experienced cough, and 4% experienced 

23 shortness of breath. With very heavy continuous exercise (VE = 89 L/min), an O3-induced 

24 group mean decrement of 9.7% in FEV1 has been reported for healthy young adults 

25 exposed for 1 hour to 120 ppb O3 (Gong et al., 1986). Symptoms are present and 

26 decrements in forced expiratory volumes and flows occur at 160-240 ppb O3 following 1 

27 hour of continuous heavy exercise (VE ≈ 55 to 90 L/min (Gong et al., 1986; Avol et al., 

28 1984; Folinsbee et al., 1984; Adams and Schelegle, 1983) and following 2 hours of 

29 intermittent heavy exercise (VE ≈ 65-68 L/min) (Linn et al., 1986; Kulle et al., 1985; 

30 McDonnell et al., 1983). With heavy intermittent exercise (15-min intervals of rest and 

31 exercise [VE = 68 L/min]), symptoms of breathing discomfort and a group mean O3-

32 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 33

 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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A

Source: Brown et al. (2008)

B

Studies appearing in the figure legends are: Adams (2006a, 2003a, 2002, 1998), Folinsbee et al. (1988), Horstman et al. (1990), 

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

Top, panel A: all studies exposed subjects to a constant (square-wave) concentration in a chamber, except Adams (1998) where a 

facemask was used. The McDonnell et al. (2007) curve illustrates the predicted FEV1 decrement at 6.6 hours as a function of ozone 

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. 

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

following 6.6 hours of exposure to ozone. 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.

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)

Adams (1998)

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)

8

6

4

2

0

Ozone-Induced

FEV1 decrement (%)

0.03
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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 

3 moderate level of exercise (VE = 40 L/min). The results from studies using 6.6 hours of 

4 constant or square-wave (S-W) exposures to between 40 and 120 ppb are illustrated in 

5 Figure 6-1(A). Figure 6-1(B) focuses on the range from 40 to 80 ppb and includes 

6 triangular exposure protocols as well as facemask exposures. Exposure to 40 ppb for 6.6 

7 hours produces small, statistically insignificant changes in FEV1 that are relatively 

8 similar to responses from FA exposure (Adams, 2002). Volunteers exposed to 60 ppb O3

9 experience group mean O3-induced FEV1 decrements of about 3% (Kim et al., 2011; 

Brown et al., 2008) (Adams, 2006a)

1 10 ; those exposed to 80 ppb have group mean 

11 decrements which range from 6 to 8% (Adams, 2006a, 2003a; McDonnell et al., 1991; 

12 Horstman et al., 1990); at 100 ppb, group mean decrements range from 8 to 14% 

13 (McDonnell et al., 1991; Horstman et al., 1990); and at 120 ppb, group mean decrements 

14 of 13 to 16% are observed (Adams, 2002; Horstman et al., 1990; Folinsbee et al., 1988). 

15 As illustrated in Figure 6-1, there is a smooth dose-response curve without evidence of a 

16 threshold for exposures between 40 and 120 ppb O3. Taken together, these data indicate 

17 that mean FEV1 is clearly decreased by 6.6-h exposures to 60 ppb O3 and higher 

18 concentrations in subjects performing moderate exercise. 

19 As opposed to constant or S-W concentration patterns used in the studies described 

20 above, many studies conducted at the levels of 40-80 ppb have used variable O3

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

22 exposure profile can potentially lead to higher FEV1 responses than S-W profiles despite 

23 having at the same average O3 concentration over the exposure period. Hazucha et al. 

24 (1992) were the first to investigate the effects of variable versus constant concentration 

25 exposures on responsiveness to O3. In their study, volunteers were randomly exposed to a 

26 triangular concentration profile (averaging 120 ppb over the 8-h exposure) that increased 

27 linearly from 0-240 ppb for the first 4 hours of the 8-h exposure, then decreased linearly 

28 from 240 to 0 ppb over the next 4 hours of the 8-h exposure, and to an S-W exposure of 

29 120 ppb O3 for 8 hours. While the total inhaled O3 doses at 4 hours and 8 hours for the S30 W and the triangular concentration profile were almost identical, the FEV1 response was 

31 dissimilar. For the S-W exposure, FEV1 declined ~5% by the fifth hour and then 

32 remained at that level. With the triangular O3 profile, there was minimal FEV1 response 

33 over the first 3 hours followed by a rapid decrease in FEV1 (-10.3%) over the next 3 

 1 Adams (2006a) did not find effects on FEV1 at 60 ppb to be statistically significant. In an analysis of the Adams (2006a) 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. During the seventh and eighth hours, mean FEV1 decrements improved to -6.3% 

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

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

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

5 recovery during the course of an exposure. 

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

7 elicit greater FEV1 and symptomatic responses than do S-W exposures (Adams, 2006a, b, 

8 2003a). Adams (2006b) reproduced the findings of Hazucha et al. (1992) at 120 ppb. 

9 However, Adams (2006a, 2003a) found that responses from an 80 ppb O3 (average) 

10 triangular exposure did not differ significantly from those observed in the 80 ppb O3 S-W 

11 exposure at 6.6 hours. Nevertheless, FEV1 and symptoms were significantly different 

12 from pre-exposure at 4.6 hours (when the O3 concentration was 150 ppb) in the triangular 

13 exposure, but not until 6.6 hours in the S-W exposure. At the lower O3 concentration of 

14 60 ppb, no temporal pattern differences in FEV1 responses between S-W and triangular 

15 exposure profiles could be discerned (Adams, 2006a). However, total symptom scores 

16 were significantly increased for the 60 ppb triangular (but not the S-W) exposure 

17 following 5.6 and 6.6 hours of exposure. At 80 ppb, respiratory symptoms tended to 

18 increase more rapidly during the triangular than S-W exposure protocol, but then 

19 decreased during the last hour of exposure to be less for the triangular than the S-W 

20 exposure at 6.6 h. Both total symptom scores and pain on deep inspiration were 

21 significantly increased following exposures to 80 ppb relative to all other exposure 

22 protocols, i.e., FA, 40, and 60 ppb exposures. Following the 6.6-hour exposures, 

23 respiratory symptoms at 80 ppb were rougly 2-3 times greater than observed at 60 ppb. 

24 At 40 ppb, triangular and S-W patterns produced spirometric and subjective symptom 

25 responses similar to FA exposure (Adams, 2006a, 2002).

26 For exposures of 60 ppb and greater, these studies (Adams, 2006a, b, 2003a; Hazucha et 

27 al., 1992) demonstrate that during triangular exposure protocols, volunteers exposed 

28 during moderate exercise (VE = 40 L/min) may develop greater spirometric and/or 

29 symptomatic responses during and following peak O3 concentrations as compared to 

30 responses over the same time interval of S-W exposures. This observation is not 

31 unexpected since the inhaled dose rate during peaks of the triangular protocols 

32 approached twice that of the S-W protocols, e.g., 150 ppb versus 80 ppb peak 

33 concentration. At time intervals toward the end of an exposure, O3 delivery rates for the 

34 triangular protocols were less than those of S-W. At these later time intervals, there is 

35 some recovery of responses during triangular exposure protocols, whereas there is a 

36 continued development of or a plateau of responses in the S-W exposure protocols. Thus, 

37 responses during triangular protocols relative to S-W protocols may be expected to 

38 diverge and be greater following peak exposures and then converge toward the end of an 
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1 exposure. The ensuing discussion on exposures between 40 and 80 ppb will focus on 

2 postexposure effects where the influence of triangular and S-W concentration patterns are 

3 minimal, i.e., FEV1 pre-to-post effects are similar (although not identical) between 

4 triangular and S-W protocols having equivalent average exposure concentrations.

5 Schelegle et al. (2009) recently investigated the effects of 6.6 hours variable O3 exposure 

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

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

8 during moderate quasi continuous exercise (VE = 40 L/min). The mean FEV1 (±standard 

9 error) decrements at 6.6 hours (end of exposure relative to pre-exposure) were -0.80 ± 

10 0.90%, 2.72 ± 1.48%, 5.34 ± 1.42%, 7.02 ± 1.60%, and 11.42 ± 2.20% for exposure to 

11 FA, 60, 70, 80, and 87 ppb O3, respectively. Statistically significant decrements in FEV1

12 and increases in total subjective symptom scores (p < 0.05) were found following 

13 exposure to mean concentrations of 70, 80, and 87 ppb O3 relative to FA. Statistically 

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

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

16 produces a statistically significant decrement in FEV1 and symptoms in healthy 

17 individuals completing 6.6-h exposure protocols. At 70 ppb, Schelegle et al. (2009)

18 observed a statistically significant O3-induced of 6.1%. At 60 ppb, an O3-induced 3.5% 

19 FEV1 decrement was not found to be statistically significant. However, this effect is 

20 similar in magnitude to the 2.9% FEV1 decrement at 60 ppb observed by Adams (2006a)

21 that was found to be statistically significant by Brown et al. (2008).

22 More recently, Kim et al. (2011) investigated the effects of a 6.6-h exposure to 60 ppb O3

23 during moderate quasi continuous exercise (VE = 40 L/min) on pulmonary function and 

24 respiratory symptoms in young healthy adults (32 F, 27 M; 25.0 ± 0.5 year) that were 

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

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

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

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

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

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

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

32 inflammatory responses.

33 Consideration of the minimal O3 concentration producing statistically significant effects 

34 on FEV1 following 6.6-h exposures warrants additional discussion. As discussed above, 

35 numerous studies have demonstrated statistically significant O3-induced group mean 

36 FEV1 decrements of 6-8% at 80 ppb. Schelegle et al. (2009) have now reported 

37 statistically significant O3-induced group mean FEV1 decrement of 6%, as well as 
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1 respiratory symptoms, at 70 ppb. At 60 ppb, there is information available from 4 

separate studies (Adams, 1998)

1 2 (Kim et al., 2011; Schelegle et al., 2009; Adams, 2006a). 

3 The group mean O3-induced FEV1 decrements observed in these studies were 3.6% by 

Adams (1998)

2 4 , 2.8% (triangular exposure) and 2.9% (S-W exposure) by Adams (2006a), 

5 3.5% by Schelegle et al. (2009), and 1.8% by Kim et al. (2011). Based on data from these 

6 four studies, at 60 ppb, the weighted-average group mean O3-induced FEV1 decrement 

7 (i.e., adjusted for FA responses) is 2.7% (n=150) (Kim et al., 2011; Schelegle et al., 2009; 

8 Adams, 2006a, 1998). Although not consistently statistically significant, these group 

9 mean changes in FEV1 at 60 ppb are consistent between studies, i.e., none observed an 

10 average improvement in lung function following a 6.6-h exposure to 60 ppb O3. Indeed, 

11 as was illustrated in Figure 6-1, the FEV1 responses at 60 ppb fall on a smooth dose12 response curve for exposures between 40 and 120 ppb O3. Furthermore, in a re-analysis 

13 of the 60 ppb S-W data from Adams (2006a), Brown et al. (2008) found the mean effects 

14 on FEV1 to be highly statistically significant (p<0.002) using several common statistical 

15 tests even after removal of 3 potential outliers. The time-course and magnitude of FEV1

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

17 2002). Taken together, the available evidence shows that detectable effects of O3 on 

18 group mean FEV1 persist down to 60 ppb, but not 40 ppb in young healthy adults 

19 exposed for 6.6 hours during moderate exercise. 

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

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

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

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

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

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

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

27 25.4 ± 2 years old) exposed to O3 (350 ppb with moderate intermittent exercise for 2.2 h), 

28 O3 exposure caused a delayed gas washout (Foster et al., 1997). The pronounced slow 

29 phase of gas washout following O3 exposure represented a 24% decrease in the washout 

30 rate. A day following O3 exposure, 50% of the subjects still had (or developed) a delayed 

31 washout relative to the pre- O3 maneuver. These studies suggest a prolonged O3 effect on 

32 the small airways and ventilation distribution in healthy young individuals.

 1 The American Petroleum Institute has declined to provide a copy of this report to EPA. 

2 This information is from page 133 of Adams (2006a). This decrement may be increased due to a target VE of 23 L/min/m2 BSA 

relative to other studies with which it is listed having the target VE of 20 L/min/m2 BSA. It should also be noted that subjects were 

exposed via a facemask in this study. However, Adams (2003a, b, 2002) found very similar FEV1 responses between facemask and 

chamber exposures.
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1 There is a rapid recovery of O3-induced spirometric responses and symptoms; 40 to 65% 

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

3 Hazucha, 1989). For example, following a 2-h exposure to 400 ppb O3 with intermittent 

4 exercise, Nightingale et al. (2000) observed a 13.5% mean decrement in FEV1. By 3 

5 hours postexposure, however, only a 2.7% FEV1 decrement persisted. Partial recovery 

6 also occurs following cessation of exercise despite continued exposure to O3 (Folinsbee 

7 et al., 1977) and at low O3 concentrations during exposure (Hazucha et al., 1992). A 

8 slower recovery phase, especially after exposure to higher O3 concentrations, may take at 

9 least 24 hours to complete (Folinsbee and Hazucha, 2000; Folinsbee et al., 1993). 

10 Repeated daily exposure studies at higher concentrations typically show that FEV1

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

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

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

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

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

Intersubject Variability in Response of Healthy Subjects

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

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

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

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

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

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

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

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

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

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

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

27 An individual’s FEV1 response to a 2-h O3 exposure is generally reproducible over 

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

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

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

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

32 in FEV1 (Weinmann et al., 1995c; Kulle et al., 1985). For 2-h exposures with intermittent 

33 exercise causing a predicted average FEV1 decrement of 10%, individual decrements 

34 ranged from approximately 0 to 40% in white males aged 18-36 years (McDonnell et al., 

35 1997). For an average FEV1 decrement of 13%, Ultman et al. (2004) reported FEV1

36 responses ranging from a 4% improvement to a 56% decrement in young healthy adults 
Draft – Do Not Cite or Quote 6-13 September 2011

1 (32 M, 28 F) exposed for 1 hour to 250 ppb O3. One-third of the subjects had FEV1

2 decrements of >15%, and 7% of the subjects had decrements of >40%. 

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

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 ozone concentration profile having the average ozone 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%. 

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-h 

exposures to ozone or filtered air. 

3 Consistent with the 1- to 2-h studies, the distribution of individual responses following 

4 6.6-h exposure studies becomes skewed with increasing exposure concentration and 

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

6 frequency distributions of individual FEV1 responses observed in 31 young healthy adults 

7 following 6.6-h exposures between 0 and 80 ppb. Schelegle et al. (2009) found >10%

8 FEV1 decrements in 16, 19, 29, and 42% of individuals exposed for 6.6 hours to 60, 70, 

9 80, and 87 ppb, respectively. Just as there are differences in mean decrements between 

10 studies having similar exposure scenarios (Figure 6-1 at 80 and 120 ppb), there are also 

11 differences in the proportion of individuals affected with >10% FEV1 decrements. At 

12 80 ppb, the proportion affected with >10% FEV1 decrements was 17% (n=30) by Adams 

(2006a)

1 13 , 26% (n=60) by McDonnell (1996), and 29%(n=31) by Schelegle et al. (2009). 

14 At 60 ppb, the proportion with >10% FEV1 decrements was 20% (n=30) by Adams 

(1998)

2

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

5 15 , 16% (n=31) by Schelegle et al. (2009), and 5% 

16 (n=59) by Kim et al. (2011). Based on these studies, the weighted average proportion of 

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

2 This information is from page 761 of Adams (2002).
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1 individuals with >10% FEV1 decrements is 10% following exposure to 60 ppb. Due to 

2 limited data within the published papers, these proportions were not corrected for 

3 responses to FA exposure where lung function typically improves in healthy adults. For 

4 example, uncorrected versus O3-induced (i.e., adjusted for response during FA exposure) 

proportions of individuals having >10% FEV1 decrements in the Adams (2006a)

1 5 study 

6 were, respectively, 3% versus 7% at 60 ppb and 17% versus 23% at 80 ppb. Thus, 

7 uncorrected proportions underestimate the actual fraction of healthy individuals affected. 

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

9 biologically small group mean decrements requires careful consideration. Following 

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

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

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

13 2006a, 1998). The data from these studies also yield a weighted-average proportion 

14 (uncorrected for FA responses) of subjects with >10% FEV1 decrements of 10% (n=150) 

15 (Kim et al., 2011; Schelegle et al., 2009; Adams, 2006a, 1998). In an individual with 

16 relatively “normal” lung function, recognizing technical and biological variability in 

17 measurements, confidence can be given that within-day changes in FEV1 of ≥ 5% are 

18 clinically meaningful (Pellegrino et al., 2005; ATS, 1991). Here focus is given to 

19 individuals with >10% decrements in FEV1 since some individuals in the Schelegle et al. 

20 (2009) study experienced 5-10% FEV1 decrements following exposure to FA. A 10% 

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

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

23 2000a). The data are not available in the published papers to determine the O3-induced 

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

25 stated, however, this uncorrected proportion likely underestimates that actual proportion 

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

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

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

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

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

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

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

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

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

35 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).
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Responses in Individuals with Pre-Existing Disease

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

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

3 person with preexisting function impairment and reduced reserve. 

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

5 moderate exercise do not generally experience statistically significant pulmonary 

6 function decrements following 1- and 2-h exposures to ≤ 300 ppb O3 (Kehrl et al., 1985; 

7 Linn et al., 1983; Linn et al., 1982b; Solic et al., 1982). Following a 4-hour exposure to 

8 240 ppb O3 during exercise, Gong et al. (1997b) found an O3-induced FEV1 decrement of 

9 8% in COPD patients which was not statistically different from the decrement of 3% in 

10 healthy subjects. Demonstrating the need for control exposures and presumably due to 

11 exercise, four of the patients in the Gong et al. (1997b) study had FEV1 decrements of 

12 >14% following both the FA and O3 exposures. Although the clinical significance is 

13 uncertain, small transient decreases in arterial blood oxygen saturation have also been 

14 observed in some of these studies. 

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

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

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

18 significantly larger than in healthy subjects (19% versus 10%, respectively) exposed to 

19 160 ppb O3 during exercise for 7.6-h exposure. In asthmatics, a significant positive 

20 correlation between O3-induced spirometric responses and baseline lung function was 

21 observed, i.e., responses increased with severity of disease. Such differences in 

22 pulmonary function between asthmatics and healthy individuals were not found in shorter 

23 duration studies. Alexis et al. (2000) and Jörres et al. (1996) reported a tendency for 

24 slightly greater FEV1 decrements in asthmatics than healthy subjects. Several studies 

25 reported similar responses between asthmatics and healthy individuals (Scannell et al., 

26 1996; Hiltermann et al., 1995; Basha et al., 1994). The lack of differences in the 

27 Hiltermann et al. (1995) and Basha et al. (1994) studies was not surprising, however, 

28 given extremely small sample sizes and corresponding lack of statistical power. One 

29 study reported a tendency for asthmatics to have smaller O3-induced FEV1 decrements 

30 than healthy subjects (3% versus 8%, respectively) when exposed to 200 ppb O3 for 2 

31 hours during exercise (Mudway et al., 2001). However, the asthmatics in that study also 

32 tended to be older than the healthy subjects, which could partially explain their lesser 

33 response since FEV1 responses to O3 diminish with age. 

34 Some, but not all, studies have also reported that asthmatics have a somewhat 

35 exaggerated airway inflammatory response to acute O3 exposure relative to healthy 

36 control subjects (Holz et al., 2002; Peden, 2001; Newson et al., 2000; Hiltermann et al., 
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1 1999; Michelson et al., 1999; Vagaggini et al., 1999; Hiltermann et al., 1997; Peden et 

2 al., 1997; Scannell et al., 1996; Peden et al., 1995; Basha et al., 1994; McBride et al., 

3 1994). For example, at 18 hours post-O3 exposure (200 ppb, 4 hours with exercise) and 

4 corrected for FA responses, Scannell et al. (1996) found significantly increased 

5 neutrophils in 18 asthmatics (12%) compared to 20 healthy subjects (4.5%). This 

6 difference in inflammatory response was observed despite no group differences in 

7 spirometric responses to O3. 

8 Vagaggini et al. (2010) exposed mild-to-moderate asthmatics (n=23; 33 ± 11 years) to 

9 300 ppb O3 for 2 hours with moderate exercise. Although the group mean O3-induced 

10 FEV1 decrement was only 4%, eight subjects were categorized as “responders” with 

11 >10% FEV1 decrements. There were no baseline differences between responders and 

12 nonresponders. At 6 hours post O3 exposure, sputum neutrophils were significantly 

13 increased by 15% relative to FA in responders. The neutrophil increase in responders was 

14 also significantly greater than the 0.2% increase in nonresponders. Across all subjects, 

15 there was a significant (r=0.61, p = 0.015) correlation between changes in FEV1 and 

16 changes in sputum neutrophils. Prior studies have reported that inflammatory responses 

17 do not appear to be correlated with lung function responses in either asthmatic or healthy 

18 subjects (Holz et al., 1999; Balmes et al., 1997; Balmes et al., 1996; Devlin et al., 1991). 

19 Interestingly, the nonresponders in the Vagaggini et al. (2010) study experienced a 

20 significant O3-induced 11.3% increase in sputum eosinophils, while responders had an 

21 nonsignificant 2.6% decrease. Six of the subjects were NQO1 wild type and GSTM1 null, 

22 but this genotype was not found to be associated with the changes in lung function or 

23 inflammatory responses to O3.

24 A few recent studies have evaluated the effects of corticosteroid usage on the response of 

25 asthmatics to O3. Vagaggini et al. (2007) evaluated whether corticosteroid usage would 

26 prevent O3-induced lung function decrements and inflammatory responses in a group of 

27 subjects with mild persistent asthma (n=9; 25 ± 7 years). In this study, asthmatics were 

28 randomly exposed on four occasions to 270 ppb O3 or FA for 2 hours with moderate 

29 exercise. Exposures were preceded by four days of treatment with prednisone or placebo. 

30 Pretreatment with corticosteroids prevented an inflammatory response in induced sputum 

31 at 6 hours postexposure. FEV1 responses were, however, not prevented by corticosteroid 

32 treatment and were roughly equivalent to those observed following placebo. Vagaggini et 

33 al. (2001) also found budesonide to decrease airway neutrophil influx in asthmatics 

34 following O3 exposure. In contrast, inhalation of corticosteroid budesonide failed to 

35 prevent or attenuate O3-induced responses in healthy subjects as assessed by 

36 measurements of lung function, bronchial reactivity and airway inflammation 

37 (Nightingale et al., 2000). High doses of inhaled fluticasone and oral prednisolone have 
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1 each been reported to reduce inflammatory responses to O3 in healthy individuals (Holz 

2 et al., 2005).

3 More recently, Stenfors et al. (2010) exposed persistent asthmatics (n=13; aged 33 years) 

4 receiving chronic inhaled corticosteroid therapy to 200 ppb O3 for 2 hours with moderate 

5 exercise. An average O3-induced FEV1 decrement of 8.4% was observed, whereas, only a 

6 3.0% FEV1 decrement is predicted for similarly exposed age-matched healthy controls 

7 (McDonnell et al., 2007). At 18 hours postexposure, there was a significant O3-induced 

8 increase in bronchioalveolar lavage (BAL) neutrophils, but not eosinophils. Bronchial 

9 biopsy also showed a significant O3-induced increase in mast cells. This study suggests 

10 that the protective effect of acute corticosteroid therapy against inflammatory responses 

11 to O3 in asthmatics demonstrated by Vagaggini et al. (2007) may be lost with continued 

12 treatment regimes. 

Factors Modifying Responsiveness to Ozone

13 Physical activity increases VE and therefore the dose of inhaled O3. Consequently, the 

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

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

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

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

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

19 exposures. 

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

21 nearly equivalent spirometric responses to O3, but have greater responses than middle22 aged and older adults when exposed to comparable O3 doses (U.S. EPA, 1996a). 

23 Symptomatic responses to O3 exposure, however, appear to increase with age until early 

24 adulthood and then gradually decrease with increasing age (U.S. EPA, 1996a). For 

25 example, healthy children (aged 8-11 y) exposed to 120 ppb O3 (2.5 h; heavy intermittent 

26 exercise) experienced similar spirometric responses but lesser symptoms than similarly 

27 exposed young healthy adults (McDonnell et al., 1985b). For subjects aged 18-36 years, 

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

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

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

31 symptoms may result in their not avoiding or ceasing exposure. Once lung growth and 

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

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

34 progressively with age as does O3 sensitivity. 
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1 In healthy individuals, the fastest rate of decline in O3 responsiveness appears between 

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

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

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

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

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

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

8 considerable evidence that spirometric and symptomatic responses to O3 exposure 

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

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

11 Several studies have suggested that physiological differences between sexes may 

12 predispose females to a greater susceptibility to O3. In females, lower plasma and nasal 

13 lavage fluid (NLF) levels of uric acid (the most prevalent antioxidant), the initial defense 

14 mechanism of O3 neutralization in airway surface liquid, may be a contributing factor 

15 (Housley et al., 1996). Consequently, reduced absorption of O3 in the upper airways may 

16 promote its deeper penetration. Dosimetric measurements have shown that the absorption 

17 distribution of O3 is independent of gender when absorption is normalized to anatomical 

18 dead space (Bush et al., 1996). Thus, a gender-related differential removal of O3 by uric 

19 acid seems to be minimal. In general, the physiologic response of young healthy females 

20 to O3 exposure appears comparable to the response of young males (Hazucha et al., 

21 2003). Several studies have investigated the effects of the menstrual cycle on responses to 

22 O3 in healthy young women. In a study of 9 women exposed during exercise to 300 ppb 

23 O3 for an hour, Fox et al. (1993) found lung function responses to O3 significantly 

24 enhanced during the follicular phase relative to the luteal phase. However, Weinmann et 

25 al. (1995a) found no difference in responses between the follicular and luteal phases as 

26 well as no significant differences between 12 males and 12 females exposed during 

27 exercise to 350 ppb O3 for 2.15 h. Seal et al. (1996) also reported no effect of menstrual 

28 cycle phase in their analysis of responses of 150 women (n=25 per exposure group; 0, 

29 120, 240, 300, and 400 ppb O3). Seal et al. (1996) conceded that the methods used by Fox 

30 et al. (1993) more precisely defined menstrual cycle phase.

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

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

33 (93 M, 94 F) and blacks (undefined ancestry; 92 M, 93 F) exposed to a range of O3

34 concentrations (0-400 ppb). The main effects of gender-race group and O3 concentration 

35 were statistically significant (both at p < 0.001), although the interaction between gender36 race group and O3 concentration was not significant (p = 0.13). These findings indicate 

37 some overall difference between the gender-race groups that is independent of O3

38 concentration, i.e., the concentration-response curves for the four gender-race groups are 
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1 parallel. In a multiple comparison procedure on data collapsed across all O3

2 concentrations for each gender-race group, both black men and black women had 

3 significantly larger decrements in FEV1 than did white men. The authors noted that the 

4 O3 dose per unit of lung tissue would be greater in blacks and females than whites and 

5 males, respectively. That this difference in tissue dose might have affected responses to 

6 O3 cannot be ruled out. The college students recruited for the Seal et al. (1993) study are 

7 probably from better educated and SES advantaged families, thus reducing potential 

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

9 that, of three SES categories, individuals in the middle SES category showed greater 

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

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

12 for this finding. 

13 More recently, Que et al. assessed pulmonary responses in blacks of African American 

14 ancestry (22 M, 24 F) and Caucasians (55 M, 28 F) exposed to 220 ppb O3 for 2.25 h 

15 (alternating 15 min periods of rest and brisk treadmill walking). On average, the black 

16 males experienced a 16.8% decrement in FEV1 following O3 exposure which was 

17 significantly larger than mean FEV1 decrements of 6.2, 7.9, and 8.3% in black females 

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

19 (1993), there was potential that the increased FEV1 decrements in blacks relative to 

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

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

22 Que et al. study, however, since exercise rates were normalized to lung volume (viz., 6-8 

23 times FVC). Thus, the increased mean FEV1 decrement in black males is not likely 

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

25 Smokers are less responsive to O3 than nonsmokers. Spirometric and plethysmographic 

26 pulmonary function decline, nonspecific airway hyperreactivity, and inflammatory 

27 response of smokers to O3 were all weaker than data reported for nonsmokers. Although 

28 all of these responses are intrinsically related, the functional association between them, as 

29 in nonsmokers, has been weak. Similarly, the time course of development and recovery 

30 of these effects as well their reproducibility was not different from nonsmokers. Chronic 

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

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

33 relative to nonsmokers (Frampton et al., 1997b; Torres et al., 1997). 

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

35 scavenges free radicals and limit lipid peroxidation. Exposure to O3 depletes the 

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

37 however, the concentration and the activity of antioxidant enzymes either in ELF or 
Draft – Do Not Cite or Quote 6-20 September 2011

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

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

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

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

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

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

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

8 al., 2001). 

9 A number of studies(e.g., Romieu et al., 2004a; David et al., 2003; Corradi et al., 2002; 

10 Bergamaschi et al., 2001) have reported that genetic polymorphisms of antioxidant 

11 enzymes may modulate pulmonary function and inflammatory response to O3 challenge. 

12 It appears that healthy carriers of NQO1 wild type in combination with GSTM1 null 

13 genotype are more responsive to O3. Adults with GSTM1 null only genotype did not 

14 show O3 hyperresponsiveness. In contrast, asthmatic children with GSTM1 null genotype 

15 (Romieu et al., 2004a) were reported to be more responsive to O3. However, in a 

16 controlled exposure of mild-to-moderate asthmatics (n=23; 33 ± 11 years) to 300 ppb O3

17 for 2 hours with moderate exercise, Vagaggini et al. (2010) found that six of the subjects 

18 had a NQO1wt and GSTM1 null, but this genotype was not associated with the changes 

19 in lung function or inflammatory responses to O3. 

20 Kim et al. (2011) also recently reported that GSTM1 genotype was not predictive of 

21 FEV1 responses in young healthy adults (32 F, 27 M; 25.0 ± 0.5 year) that were roughly 

22 half GSTM1-null and half GSTM1-sufficient. Sputum neutrophil levels, measured in a 

23 subset of the subjects (13 F, 11 M), were also not significantly associated with GSTM1 

24 genotype.

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

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

27 (2009) found that inflammatory responses but not lung function responses to O3 were 

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

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

30 GSTM1 sufficient than nulls. At 24 h postexposure, sputum neutrophils had returned to 

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

32 however, sputum neutrophil levels increased from 4 h to 24 h and were significantly 

33 greater than both baseline levels and levels at 24 h in the GSTM1 sufficient individuals. 

34 Since there was no FA control in the Alexis et al. (2009) study, effects of the exposure 

35 other than O3 itself cannot be ruled out. In general, the findings between studies are 

36 inconsistent. Additional studies that include control exposures are needed to clarify the 

37 influence of genetic polymorphisms on O3 responsiveness.
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1 In a retrospective analysis of data from 541 healthy, nonsmoking, white males between 

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

3 Facility in Chapel Hill, North Carolina, McDonnell et al. (2010) found that increased 

4 body mass index (BMI) was associated with enhanced FEV1 responses. The BMI effect 

5 was of the same order of magnitude but in the opposite direction of the age effect where 

6 by FEV1 responses diminish with increasing age. In a similar retrospective analysis, 

7 Bennett et al. (2007) found enhanced FEV1 decrements following O3 exposure with 

8 increasing BMI in a group of 75 healthy, nonsmoking, women (age 24 ± 4 years; BMI 

9 range 15.7 to 33.4), but not 122 healthy, nonsmoking, men (age 25 ± 4 years; BMI range 

10 19.1 to 32.9). In the women, greater O3-induced FEV1 decrements were seen in 

11 overweight (BMI >25) than in normal weight (BMI from 18.5 to 25), and in normal 

12 weight than in underweight (BMI <18.5) (P trend ≤ 0.022). Together, these results 

13 indicate that higher BMI may be a risk factor for pulmonary effects associated with O3

14 exposure.

Repeated Ozone Exposure Effects

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

16 about repeated 1to 2 h O3 exposures. Repeated exposures to O3 causes enhanced (i.e., 

17 greater decrements) FVC and FEV1 responses on the second day of exposure. The 

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

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

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

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

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

23 fifth days of repeated O3 exposure. This attenuation of responses is lost in 1 week (Kulle 

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

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

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

27 the second exposure day and attenuated with repeated O3 exposure thereafter (Folinsbee 

28 et al., 1998; Foxcroft and Adams, 1986; Linn et al., 1982a; Folinsbee et al., 1980). In 

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

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

31 (Folinsbee et al., 1994). 

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

33 to be significantly attenuated following four consecutive days of exposure to O3 (250 

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

35 of isovolumetric FEF25-75, Vmax50 and Vmax75) showed a persistent functional reduction 

36 from Day 2 through Day 4. Notably, in contrast to FVC and FEV1 which exhibited a 
Draft – Do Not Cite or Quote 6-22 September 2011

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

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

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

4 significantly higher following O3 (24 h after last O3 exposure) compared to FA. 

5 Inflammatory markers from bronchioalveolar lavage fluid (BALF) following 4 

6 consecutive days of both 2-h (Devlin et al., 1997) and 4-h (Jorres et al., 2000; Christian et 

7 al., 1998) exposures have indicated ongoing cellular damage irrespective of the 

8 attenuation of some cellular inflammatory responses of the airways, lung function and 

9 symptoms response. These data suggest that the persistent small airways dysfunction 

10 assessed by Frank et al. (2001) is likely induced by both neurogenic and inflammatory 

11 mediators, since the density of bronchial C-fibers is much lower in the small than large 

12 airways. 

Summary of Controlled Human Exposure Studies on Lung Function 

13 Responses in humans exposed to ambient O3 concentrations include: decreased 

14 inspiratory capacity; mild bronchoconstriction; rapid, shallow breathing pattern during 

15 exercise; and symptoms of cough and pain on deep inspiration (U.S. EPA, 2006b, 1996a). 

16 Discussed in subsequent Sections 6.2.2.1 and 6.2.3.1, exposure to O3 also results in 

17 airway hyperresponsiveness, pulmonary inflammation, immune system activation, and 

18 epithelial injury (Que et al.; Mudway and Kelly, 2004a). Reflex inhibition of inspiration 

19 results in a decrease in forced vital capacity and, in combination with mild 

20 bronchoconstriction, contributes to a decrease in the FEV1. Healthy young adults exposed 

21 to O3 concentrations ≥ 60 ppb develop statistically significant reversible, transient 

22 decrements in lung function if minute ventilation or duration of exposure is increased 

23 sufficiently. With repeated O3 exposures over several days, FEV1 and symptom responses 

24 become attenuated in both healthy individuals and asthmatics, but this tolerance is lost 

25 after about a week without exposure (Gong et al., 1997a; Folinsbee et al., 1994; Kulle et 

26 al., 1982). In contrast to the attention of FEV1 responses, there appear to be persistent O3

27 effects on small airways function as well as ongoing cellular damage during repeated 

28 exposures. 

29 There is a large degree of intersubject variability in lung function decrements 

30 (McDonnell, 1996). However, these lung function responses tend to be reproducible 

31 within a given individual over a period of several months indicating differences in the 

32 intrinsic responsiveness of individuals (Hazucha et al., 2003; McDonnell et al., 1985a). In 

33 healthy young adults, O3-induced decrements in FEV1 do not appear to depend on gender 

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 

36 experience greater O3-induced decrements in FEV1 than age-matched whites (Que et al.; 
Draft – Do Not Cite or Quote 6-23 September 2011

1 Seal et al., 1993). Healthy children experience similar spirometric responses but lesser 

2 symptoms from O3 exposure relative to young adults (McDonnell et al., 1985b). On 

3 average, spirometric and symptom responses to O3 exposure appear to decline with 

4 increasing age beyond about 18 years of age (McDonnell et al., 1999; Seal et al., 1996). 

5 There is a tendency for slightly increased spirometric responses in mild asthmatics and 

6 allergic rhinitics relative to healthy young adults (Jorres et al., 1996). Spirometric 

7 responses in asthmatics appear to be affected by baseline lung function, i.e., responses 

8 increase with disease severity (Horstman et al., 1995). 

9 Available information on recovery of lung function following O3 exposure 

10 indicates that an initial phase of recovery in healthy individuals proceeds relatively 

11 rapidly, with acute spirometric and symptom responses resolving within about 2 to 4 h 

12 (Folinsbee and Hazucha, 1989). Small residual lung function effects are almost 

13 completely resolved within 24 h. One day following O3 exposure, persisting effects on 

14 the small airways assessed by decrements in FEF25-75 and altered ventilation distribution 

15 have been reported (Frank et al., 2001; Foster et al., 1997). 

6.2.1.2 Epidemiology

16 The O3-induced lung function decrements consistently demonstrated in controlled human 

17 exposure studies (Section 6.2.1.1) provide biological plausibility for the epidemiologic 

18 evidence presented in the 1996 and 2006 O3 AQCDs, in which short-term ambient O3

19 exposure was consistently associated with lung function decrements in diverse 

20 populations (U.S. EPA, 2006b, 1996a). Coherence between the two disciplines was found 

21 not only for effects observed in groups with higher expected personal O3 exposures and 

22 higher exertion levels, including children attending summer camps and adults exercising 

23 or working outdoors, but also for effects observed in children and individuals with pre24 existing respiratory disease such as asthma (U.S. EPA, 2006b, 1996a). Recent 

25 epidemiologic studies focused more on children with asthma rather than on groups with 

26 increased outdoor exposures or other healthy populations. Whereas a majority of recent 

27 studies conducted in children with asthma indicated decreases in lung function in 

28 association with increases in ambient O3 exposure, recent studies in adults with asthma 

29 and individuals without asthma found both O3-associated decreases and increases in lung 

30 function. Recent studies also provided additional data to assess whether particular lags of 

31 O3 exposure were more strongly associated with decrements in lung function; whether O3

32 associations were confounded by copollutant exposures; and whether risk was affected by 

33 factors such as corticosteroid (CS) use, genetic polymorphisms, elevated BMI, and diet. 
Draft – Do Not Cite or Quote 6-24 September 2011

Table 6-1 Mean and upper percentile concentrations of ozone in 

epidemiologic studies examining lung function in populations with 

increased outdoor exposures

Study Location Years/Season O3 Averaging Time

Mean/Median 

Concentration 

(ppb)

Upper Percentile Concentrations (ppb)

Korrick et al. 

(1998)

Mt. Washington, 

NH

1991, 1992

Warm season

Hike-time avg

(2-12 h)

40 Max: 74

Thurston et al. 

(1997)

Connecticut 

River Valley, CT

1991-1993

Warm season

1-h max 83.6 Max: 160

Spektor et al. 

(1988b)

Tuxedo, NY 1985

Warm season

1-h avg NR Max: 124

Spektor et al. 

(1988a)

Fairview Lake, 

NJ

1984

Warm season

1-h avga 53 Max (1-h max): 113

Spektor and 

Lippmann (1991)

Fairview Lake, 

NJ 

1988

Warm season

1-h avga 69 Max (1-h max): 137

Berry et al. 

(1991)

Hamilton, NJ July 1988 1-h max NR Max: 204

Neas et al. 

(1999)

Philadelphia, PA 1993

Warm season

12-h avg 

(9:00 a.m.9:00 p.m.)

57.5 (Camp 1)

55.9 (Camp 2)

Max (Camp 1): 106

Girardot et al. 

(2006)

Great Smoky 

Mountain NP, TN

2002-2003

Warm season Hike-time avg(2-9 h)

48.1b Max: 74.2b

Selwyn et al. 

(1985)

Houston, TX 1981

Warm season

15-min max 47 Max: 135

Thaller et al. 

(2008)

Galveston, TX 2002-2004

Warm season

1-h max 35 (median) Max: 118

Higgins et al. 

(1990)

San Bernardino, 

CA

1987

Warm season

1-h avga 123 Max: 245

Avol et al. (1990) Idyllwild, CA 1988

Warm season

1-h avga 94 Max: 161

Burnett et al. 

(1990)

Lake 

Couchiching, 

Ontario, CA

1983

Warm season

1-h avga 59 Max: 95

Raizenne et al. 

(1989)

Lake Erie, 

Ontario, CA

1986

Warm season

1-h avga 71 Max (1-h max): 143

Brauer et al. 

(1996)

British Columbia, 

Canada

1993

Warm season

1-h max 40 Max: 84

Castillejos et al. 

(1995)

Mexico City, 

Mexico

June 1990-

October 1991

1-h max 179 Max: 365

Romieu et al. 

(1998a)

Mexico City, 

Mexico

March-August 

1996

Work shift avg (6-12 h) 67.3 95th: 105.8

Nickmilder et al. 

(2007)

Southern 

Belgium

2002

Warm season

1-h max

8-h max

NR Max (across 6 camps): 24.5-112.7c

Max (across 6 camps): 18.9-81.1c

Brunekreef et al. 

(1994)

Netherlands 1981

Warm season

Exercise-time avg (10- 145 min)42.8c Max: 99.5c

Hoek et al. 

(1993)

Wageningen, 

Netherlands

1989

Warm season

1-h max NR Max: 122c

Braun-Fahrlander 

et al. (1994)

Southern 

Switzerland

1989

Warm season

30-min avg NR Max: 80c

Hoppe et al. 

(1995); Hoppe et 

al. (2003)

Munich, 

Germany

1992

Warm season

30-min max (1:00 p.m.-

4:00 p.m.)

High O3 days: 65.9

Control O3 days: 27.2

Max (high O3 days): 86

Chan et al. 

(2005)

Taichung City, 

Taiwan

2001

Cold season

8-h avg 

(9:00 a.m.-5:00 p.m.)

35.6 Max: 65.1

Max = Maximum; NR = not reported 

a

1-h avg, preceding lung function measurement. b

Individual-level exposure estimates were derived based on time-activity diary data. c

Concentrations were 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 6-25 September 2011

Populations with Increased Outdoor Exposures

1 Few epidemiologic studies characterizing acute O3-related respiratory morbidity have 

2 accounted for time spent outdoors, which may be an important determinant of 

3 interindividual variability in personal O3 exposure. Among epidemiologic studies, studies 

4 of individuals engaged in outdoor recreation, exercise, or work are more comparable to 

5 controlled exposure studies because of improved estimates O3 exposures, measurement of 

6 lung function before and after discrete periods of outdoor activity, and examination of O3

7 effects during exertion when the dose of O3 reaching the lungs may be higher because of 

8 higher ventilation and inhalation of larger volumes of air. Characteristics and ambient O3

9 concentration data from epidemiologic studies of populations with increased outdoor 

10 exposures are presented in Table 6-1. Similar to findings from controlled human 

11 exposure studies, the collective body of epidemiologic evidence clearly demonstrates 

12 decrements in lung function in association with O3 exposures during periods of outdoor 

13 activity or exercise of varying intensity and duration (15 minutes to 12 hours) (Figures 6-

14 3 to 6-5 and Tables 6-2 to 6-4).

Children Attending Summer Camps

15 Studies of children attending summer camps, most of which were discussed in the 1996 

16 O3 AQCD, have provided important understanding of the impact of ambient O3 exposure 

17 on respiratory effects in young, healthy children. These studies were noted for their on18 site measurement of ambient O3 and daily assessment of lung function by trained staff 

19 over 1- to 2-week periods (Thurston et al., 1997; Berry et al., 1991; Spektor and 

20 Lippmann, 1991; Avol et al., 1990; Burnett et al., 1990; Higgins et al., 1990; Raizenne et 

21 al., 1989; Spektor et al., 1988a; Raizenne et al., 1987). 

22 In groups mostly comprising healthy children (ages 7-17 years), decrements in FEV1

23 were found to be associated consistently with ambient O3 exposures averaged over the 

24 1-8 hours preceding lung function measurement (Figure 6-3 and Table 6-2). Kinney et al. 

25 (1996) corroborated this association in a reanalysis combining 5367 lung function 

26 measurements collected from 616 healthy children from six studies (Spektor and 

27 Lippmann, 1991; Avol et al., 1990; Burnett et al., 1990; Higgins et al., 1990; Spektor et 

28 al., 1988a; Raizenne et al., 1987). Based on uniform statistical methods, a 40-ppb 

29 increase in concurrent-hour O3 exposure was associated with a -20 ml (95% CI: -25, -14) 

change in afternoon FEV1

1 30 (Kinney et al., 1996). In these studies conducted in locations 

 1 To facilitate comparisons among epidemiologic studies, for all health endpoints in Chapter 6, effect estimates are presented in 

terms of a standard increment in ambient O3 concentration, one for each of the three commonly examined O3 averaging times (1-h 

max, 8-h max, and 24-h average). These standard increments are 40 ppb, 30 ppb, and 20 ppb for 1-h max, 8-h max, and 24-h avg 

O3, respectively, and are based on annual mean to 95th percentile differences that are representative of measurements from 

nationwide O3 monitors in U.S. Metropolitan Statistical Areas as described in detail in Section 7.1.3.2 of the 2006 O3 AQCD (U.S. 

EPA, 2006b).
Draft – Do Not Cite or Quote 6-26 September 2011

1 across the Northeast U.S. and Canada and California (Table 6-1) with varying pollutant 

2 mix, a wide range in effect estimates was found. Study-specific effect estimates ranged 

3 between a 0.76 and 48 ml decrease or a 0.3% to 2.2% decrease in study mean FEV1.

4 Associations between ambient O3 exposure and peak expiratory flow (PEF) in camp 

5 studies were more variable than were those with FEV1, as indicated by the wider range in 

6 effect estimates and wider 95% CIs (Figure 6-3 and Table 6-2). Nonetheless, most effect 

7 estimates indicated decreases in PEF in association with ambient O3 exposure. The 

8 largest effect (mean 2.8% decline per 40-ppb increase in 1-h max O3) was estimated in a 

9 group of campers with asthma (Thurston et al., 1997). In this study, O3 also was 

10 associated with increases in chest symptoms and bronchodilator use, suggesting that the 

11 observed decreases in PEF may have been indicative of clinically significant effects.

Effect estimates are from single-pollutant models and are standardized to a 40-ppb increase for 1-h avg or 1-h max ozone 

exposures and a 30-ppb increase for 12-h avg ozone exposures.

Figure 6-3 Changes in FEV1 (ml) or PEF (ml/sec) in association with ambient 

ozone exposure in studies of children attending summer camp.

Study

FEV1 (ml)

Spektor et al. (1988a)

Spektor and Lippmann 

(1991)

Raizenne et al. (1987)

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 standardized increment in O3 (95% CI)

PEF (ml/sec)

Spektor et al. (1988a)

Raizenne et al. (1987)

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 standardized increment in O3 (95% CI)
Draft – Do Not Cite or Quote 6-27 September 2011

Table 6-2 Additional characteristics and quantitative data for studies 

represented in Figure 6-3

Study Location Population Standardized percent 

change (95% CI)a Standardized effect estimate (95% CI)a

FEV1 (ml)

Spektor et al. (1988a) Fairview Lake, NJ Campers without asthma -0.93 (-1.5, -0.35) -20.0 (-32.5, -7.5)

Spektor and Lippmann 

(1991) Fairview Lake, NJ Campers without asthma -2.2 (-3.1, -1.3) -51. 6 (-72.8, -30.4)

Raizenne et al. (1989) Lake Erie, Ontario, 

Canada Campers without asthma -0.48 (-0.80, -0.16) -11.6 (-19.4, -3.8)

Burnett et al. (1990) Lake Couchiching, 

Ontario, Canada Campers without asthma -0.32 (-1.8, 1.2) -7.6 (-42.1, 26.9)

Higgins et al. (1990) San Bernardino, CA Campers without asthma -1.6 (-2.4, -0.87) -33.6 (-49.3, -17.9)

Avol et al. (1991) Pine Springs, CA Campers without asthma -0.58 (-1.1, -0.12) -12.8 (-23.0, -2.6)

Kinney et al. (1996) Pooled analysis Campers without asthma -0.90 (-1.2, -0.65) -20.0 (-25.5, -14.5)

Berry et al. (1991) Hamilton, NJ Campers without asthma Data not available 32.8 (6.9, 58.7)

PEF (ml/sec)

Spektor et al. (1988a) Lake Fairview, NJ Campers without asthma -1.8 (-3.3, -0.40) -80.0 (-142.7, -17.3)

Raizenne et al. (1989) Lake Erie, Ontario, 

Canada Campers without asthma -0.07 (-0.56, 0.41) -4.0 (-30.7, 22.7)

Burnett et al. (1990) Lake Couchiching, 

Ontario, Canada Campers without asthma -1.9 (-3.8, -0.05) -106.4 (-209.9, -2.9)

Higgins et al. (1990) San Bernardino, CA Campers without asthma -0.87 (-2.1, -0.34) -44.0 (-105, -17.2)

Avol et al. (1991) Pine Springs, CA Campers without asthma 1.9 (0.71, 3.1) 86.8 (31.9, 142)

Kinney et al. (1996) Pooled analysis Campers without asthma 0.31 (-0.88, 1.5) 6.8 (-19.1, 32.7)

Berry et al. (1991) Hamilton, NJ Campers without asthma Data not available -40.4 (-132.1, 51.3)

Neas et al. (1999) Philadelphia, PA Campers without asthma -0.58 (-1.5, 0.33) -27.5 (-70.8, 15.8)

Thurston et al. (1997) CT River Valley, CT Campers with asthma -2.8 (-4.9, -0.59) -146.7 (-261.7, -31.7)

a

All effect estimates 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 (9:00 a.m.-9:00 p.m.) O3.

1 As has been observed in controlled human exposure studies, FEV1 and PEF responses to 

2 ambient O3 exposure varied among individual campers. Based on separate regression 

3 analyses of data from individual subjects, O3 exposure was associated with a wide range 

4 of changes in lung function across subjects (Berry et al., 1991; Higgins et al., 1990; 

5 Spektor et al., 1988a). For example, in the study of children attending camp in Fairview 

6 Lake, NJ, 36% of subjects had statistically significant O3-associated decreases in FEV1, 

7 and the upper decile of response was a 6.3% decrease in FEV1 per a 40-pbb increase in 1-

8 h avg O3 (Spektor et al., 1988a).

9 In contrast with these previous studies, a recent cross-sectional study of children 

10 attending six different summer camps in Belgium did not find an association between 

11 ambient O3 exposure and lung function. The ambient O3 concentrations in this recent 

12 study was in the range of those in previous studies (Table 6-1); however, this recent study 
Draft – Do Not Cite or Quote 6-28 September 2011

1 differed from previous studies in that each subject was examined only on one day, and 

2 investigators performed between-camp comparisons rather than within-subject 

3 comparisons. Camps with higher daily 1-h max O3 concentrations did not consistently 

4 have larger decreases in mean intraday FEV1 or FEV1/FVC (Nickmilder et al., 2007).

Populations Exercising Outdoors

5 Similar to camp studies, studies of individuals exercising outdoors were noted for the 

6 serial examination of subjects over days with a wide range in ambient O3 concentrations 

7 and onsite assessment of O3 exposures during discrete periods of outdoor exercise. These 

8 studies collectively show that mean O3 exposures ranging from 40 to 66 ppb during 

9 exercise of variable duration and intensity are associated with small (< 1 to 4% per 

standardized increment in O3

1 10 ) decreases in lung function in adults (Figure 6-4 and Table 

11 6-3). Similar observations were made in children exercising outdoors (Table 6-3). For 

12 both adults and children, evidence was provided largely by older studies that were 

13 reviewed in the 1996 and 2006 O3 AQCDs. 

Figure 6-4 Percent change in FEV1 in association with ambient ozone 

exposures of adults exercising outdoors. Studies generally are 

organized in order of decreasing exercise duration. Effect 

estimates are from single-pollutant models and are standardized to 

a 40-ppb increase for ozone exposures averaged over 15 minutes 

to 1 hour and a 30-ppb increase for ozone exposures averaged over 

3 to 8 hours.

 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.

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

-5 -4 -3 -2 -1 0 1 2

Percent change in FEV1 per standardized

increment in O3 (95% CI)
Draft – Do Not Cite or Quote 6-29 September 2011

Table 6-3 Additional characteristics and quantitative data for studies 

represented in Figure 6-4 and results from studies in children 

exercising outdoors

Study Location Population Exercise duration O3 Averaging 

Time Parameter Standardized percent change (95% CI)a

Studies of adults

Korrick et al. (1998) Mt. Washington, 

NH

Adult day hikers 2-12 h Hike duration FEV1 -1.5 (-2.8, -0.24)

Girardot et al. 

(2006)

Great Smoky Mt, 

TN

Adult day hikers 2-9 h Hike duration FEV1 0.72 (-0.46, 1.90)

Hoppe et al. (2003) Munich, Germany Adults exercising 2 h 30-min max (1:00 

p.m.-4:00 p.m.)

FEV1

PEF

-1.3 (-2.6, 0.13)

-2.8 (-5.9, 0.44)

Selwyn et al. 

(1985)

b Houston, TX Adults exercising NR 15-min max FEV1 -16 ml (-31.1, -0.87)c

Spektor et al. 

(1988a)

b Tuxedo, NY Adults exercising 15-55 min 30-min avg FEV1 -1.31 (-2.0, -0.65)

Brunekreef et al. 

(1994)

Netherlands Adults exercising 10 min-1 h Exercise duration FEV1 -0.82 (-1.6, -0.02)

Studies of children not included in Figure 6-4

Braun-Fahrlander 

et al. (1994)

Switzerland Children 

exercising

10 min 30-min avg PEF -3.8 (-6.9, -0.96)

Castillejos et al. 

(1995)

Mexico City, 

Mexico

Children 

exercising

15 min (2 periods) 1-h avg FEV1 -0.48 (-0.72, -0.24)

Hoek et al. (1993) Wageningen, 

Netherlands

Children 

exercising

1 h 1-h avg PEF -2.2 (-4.9, 0.55)

NR = Not reported. 

a

Effect estimates are standardized to a 40-ppb increase for O3 exposures averaged over 15 min to 1 h and a 30-ppb increase for O3 exposures 

averaged over 3 to 8 h.

b

Results not included in the figure because data were not provided to calculate percent change in lung function.

c

The 95% CI was constructed using a standard error that was estimated from the p-value

1 Two studies of adult day-hikers of similar design and ambient O3 concentrations 

2 produced contrasting results (Girardot et al., 2006; Korrick et al., 1998). These studies 

3 mostly comprised white, healthy adults and examined changes in lung function associated 

4 with O3 exposures during multihour (2-12 h) periods of outdoor exercise. Although 

5 analyses of day-hikers were based on a one-time assessment of lung function, they 

6 included much larger sample sizes compared with panel studies of individuals exercising 

7 outdoors. Among 530 hikers on Mt. Washington, NH, Korrick et al. (1998) reported 

8 posthike declines in FEV1 and FVC of approximately 0.7-1.5% per a 30-ppb increase in 

9 2- to 12-h avg O3. In contrast, among 354 hikers in Great Smoky Mountains National 

10 Park, TN, Girardot et al. (2006) more recently found that O3 exposure was associated 

11 with posthike increases in many of the same lung function indices. Several differences in 

12 study characteristics were used by Girardot et al. (2006) to explain discrepant results, 

13 including their use of a larger number of less-well trained technicians, shorter mean 

14 duration of hike (5 hours versus 8 hours), and older mean age of their subjects.

15 As was observed in camp studies, the magnitudes of O3-associated decreases in lung 

16 function varied among individual subjects. Korrick et al. (1998) found larger O3-
Draft – Do Not Cite or Quote 6-30 September 2011

1 associated decreases in FEV1 among hikers who were male, had history of asthma or 

2 wheeze, were never smokers, and hiked greater than 8 hours. Additionally, O3 was 

3 associated with an increased odds of a greater than 10% decline in FEF25-75% among 

4 hikers (OR: 2.3 [95% CI: 1.2, 6.7] per 30-ppb increase in 2- to 12-h avg O3) (Korrick et 

5 al., 1998). Likewise, Hoppe et al. (2003) found that on days with 30-min max (1:00 p.m.-

6 4:00 p.m.) ambient O3 concentrations above 50 ppb, 14% of athletes had at least a 20% 

7 decrease in lung function or 10% increase in airway resistance.

Outdoor Workers

8 The 2006 O3 AQCD indicated that ambient O3 exposure was associated consistently with 

9 decrements in lung function among outdoor workers (U.S. EPA, 2006b), and recent 

10 studies produced similar findings (Thaller et al., 2008; Chan and Wu, 2005) (Figure 6-5 

11 and Table 6-4). Although most of these studies assessed O3 exposures using central site 

12 measurements, they were noteworthy for the long periods of time spent outdoors (6-14 

13 hours across studies). Further, associations between O3 exposure and lung function 

14 decrements were found for time periods during which ambient O3 concentrations did not 

15 exceed 80 ppb (Table 6-1) (Chan and Wu, 2005; Brauer et al., 1996; Hoppe et al., 1995). 

16 In particular, Many studies of outdoor workers found that in addition to same-day 

17 exposures, O3 exposures lagged 1 or 2 days (Chan and Wu, 2005; Brauer et al., 1996) or 

18 exposures averaged over 2 days (Romieu et al., 1998a) were associated with equal or 

19 larger decrements in lung function (Figure 6-5 and Table 6-4).

20 Similar to other populations with increased outdoor exposure, the magnitudes of O3-

21 associated lung function decrements in outdoor workers were small. Per standardized 

increment in O3 concentration1 22 , decreases in lung function ranged between less than 1% 

23 and 3.6%. The magnitude of decrease was not found to depend strongly on duration of 

24 outdoor work or ambient O3 concentration. The largest decrease (6.4% per 40-ppb 

25 increase in 1-h max O3) was observed among berry pickers in British Columbia who were 

26 exposed to relatively low ambient O3 concentrations (work shift mean: 26.0 ppb [SD: 

27 11.8]) but had longer periods of outdoor work (8-14 hours) (Brauer et al., 1996) (Figure 

28 6-5 and Table 6-4). However, a much smaller O3-associated decrease in FEV1 was found 

29 among street workers in Mexico City who were exposed to higher O3 concentrations 

30 (work shift mean: 67.3 ppb [SD: 24]) during a similar duration of outdoor work. Among 

31 studies of outdoor workers, the smallest magnitude of decrease (0.4% decrease (95% CI: 

32 -0.8, 0) in afternoon FEV1/FVC per 40-ppb increase in 1-h max O3) was observed among 

33 lifeguards in Galveston, TX (Thaller et al., 2008) whose outdoor work periods were 

34 shorter than those of the berry pickers but who were exposed to a similar range of 

 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 6-31 September 2011

Figure 6-5 Percent change in lung function in association with ambient ozone 

exposures among outdoor workers. Studies generally are 

organized in order of increasing mean ambient ozone 

concentration. Effect estimates are from single-pollutant models 

and are standardized to a 40-ppb increase for 30-min or 1-h max 

ozone exposures. 

Table 6-4 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 Lifeguards FVC

FEV1/FVC

6-8 h 1-h max 0 0.24 (-0.28, 0.72)

-0.40 (-0.80, 0)

Brauer et al. 

(1996)

British 

Columbia, 

Canada

Berry pickers 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

Forestry 

workers

FEV1 NR 30-min max (1:00 

p.m.-4:00 p.m.)

0 -1.4 (-3.0, 0.16)

Romieu et 

al. (1998a)

Mexico City, 

Mexico

Male street 

workers

FEV1 Mean (SD): 9 h 

(1)

1-h max 0

0-1 

avg

Placebo

Antioxidant

Placebo

Antioxidant

-2.1 (-3.3, -0.85)

-0.52 (-2.0, 0.97)

-3.4 (-6.0, -0.78)

-1.2 (-4.2, 1.8)

Chan et al. 

(2005)

b Taichung City, 

Taiwan

Mail carriers PEF 8 h 8-h avg (9:00 a.m.- 5:00 p.m.)0

1

-1.0 (-1.3, -0.66)

-1.1 (-1.5, -0.78)

NR = Not reported.

a

Effect estimates are standardized to a 40-ppb increase for 30-min or 1-h max O3 and a 30-ppb increase for 8-h max O3. 

a

PEF results not included in figure. 

Study

Thaller et al. (2008)

Brauer et al. (1996)

Hoppe et al. (1995)

Romieu et al. (1998)

Population

Lifeguards

Berry pickers

Forestry workers

Street workers

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 standardized increment

in O3 (95% CI)
Draft – Do Not Cite or Quote 6-32 September 2011

1 ambient O3 concentrations. Few studies provided information on ventilation rate or pulse 

2 rate, thus it was difficult to ascertain whether differences in the magnitudes of O3-

3 associated decreases in lung function were related to differences in workers’ levels of 

4 exertion.

Associations at lower ozone concentrations

5 Studies of populations engaged in outdoor activity examined and found that associations 

6 between O3 and lung function decrements persisted at lower O3 concentrations 

7 (Table 6-5). Among adults exercising outdoors, Spektor et al. (1988b) found that 

8 associations persisted in analyses restricted to 30-min max ambient O3 concentrations 

9 less than 80 ppb, and for most lung function parameters, effect estimates were similar to 

10 those obtained for the full range of O3 concentrations (Table 6-5). In a study of children 

11 attending summer camp, similar effects were estimated for the full range of 1-h avg O3

12 concentrations and those less than 60 ppb (Spektor et al., 1988a). Brunekreef et al. (1994)

13 found ambient O3 exposure (10-min to 1-h) during outdoor exercise to be associated with 

14 decreases in lung function in analyses restricted to concentrations less than 61 (Table 6-5) 

15 and 51 ppb. However, effect estimates were near zero with O3 concentrations less than 

16 41 ppb (Brunekreef et al., 1994). In contrast, Brauer et al. (1996) found associations 

17 persisted with 1-h max O3 concentrations less than 40 ppb. 

Table 6-5 Associations between ambient ozone exposure and lung function 

decrements in different ranges of ambient ozone concentrations

Study Location Population Parameter

O3 

Averaging Time

O3

Concentration 

Range

Standardized percent change (95% CI)a

Brunekreef et al. (1994) Netherlands Adults exercising % change 

FEV1

10-m to 1-h

Lag 0

Full range

O3 < 61 ppb

-0.82 (-1.6, -0.02)

-2.1 (-4.5, 0.32)

Spektor et al. (1988b) Tuxedo, NY Adults exercising FEV1 (ml) 30-min avg

Lag 0

Full range

O3 < 80 ppb

-54 (-84, -27)b

-52 (-101, -3.4)b

Spektor et al. (1988a) Fairview Lake, NJ Campers without 

asthma

% change 

FEV1

1-h avg

Lag 0

Full range

O3 < 80 ppb

O3 < 60 ppb

-2.7 (-3.3, -2.0)

-1.4 (-2.5, -0.34)

-2.2 (-3.7, -0.80)

Korrick et al. (1998) Mt. Washington, 

NH

Adult day hikers % change 

FEV1

Hike duration

(2-12 h)

Lag 0

Full range

O3 > 40 ppb

-1.5 (-2.8, -0.24)

-2.6 (-4.9, -0.32)

a

Effect estimates are standardized to a 40-ppb increase for O3 exposures averaged over 10 min to 1 h and a 30-ppb increase for O3 exposures 

averaged over 2 to12 h.

b

Data were not provided to calculate percent change.

18 Korrick et al. (1998) examined associations with hike-time average O3 exposures (2-12 h) 

19 and found effect estimates that were more negative in analyses restricted to O3

20 concentrations greater than 40 ppb. Based on the results from a nonparametric model in 
Draft – Do Not Cite or Quote 6-33 September 2011

1 Korrick et al. (1998), it appeared that the association between O3 exposure and lung 

2 function decrements in this population was limited to 2- to 12-h avg O3 exposures above 

3 40 ppb. 

Children with Asthma

4 Associations between ambient O3 exposures and lung function decrements in children 

5 with asthma have been examined in epidemiologic studies conducted across diverse 

6 geographical locations and a range of ambient O3 concentrations (Table 6-6). Whereas 

7 studies of populations with increased outdoor exposures monitored O3 exposures at the 

8 site of subjects’ outdoor activities and used trained staff to measure lung function, studies 

9 of children with asthma relied more heavily on O3 measured at central monitoring sites 

10 and lung function measured by subjects. However, studies of children with asthma have 

11 provided more information on factors that may confer increased susceptibility to the 

12 respiratory effects of O3 exposure, confounding by copollutant exposure or meteorology, 

13 and the potential clinical significance of O3-associated changes in lung function with the 

14 concurrent assessment of respiratory symptoms.

15 Collectively, the large body of evidence, which includes large U.S. multicity studies and 

16 several smaller studies conducted in the U.S., Mexico City, and Europe, demonstrates 

17 that increases in ambient O3 exposure (various averaging times and lags) are associated 

18 with decrements in FEV1 (Figure 6-6 and Table 6-7) and PEF (Figure 6-7 and Table 6-8) 

19 in children with asthma. In addition to examining a single lung function measurement per 

20 day, several studies examined associations of O3 exposure with measures of lung function 

21 variability. Although different definitions of variability were used, studies consistently 

22 found that O3-associated changes in lung function variability were indicative of poorer 

23 lung function, whether characterized as a decrease from the individual’s mean lung 

24 function over the study period (Jalaludin et al., 2000), a decrease in lung function over 

25 the course of the day (Lewis et al., 2005), or a decrease in the lowest daily measurement 

26 (Just et al., 2002).

27 Studies of children with asthma that were restricted to winter months provided little 

28 evidence of an association between various single- and multi-day lags of ambient O3

29 exposure and changes in lung function; several studies reported O3-associated increases 

30 in lung function (Dales et al., 2009; Liu et al., 2009a; Rabinovitch et al., 2004). In colder 

31 months, ambient O3 concentrations are low and in many locations, children remain 

32 primarily indoors. Thus, it is less likely that effects will be demonstrated for O3. As noted 

33 in previous AQCDs for lung function and other endpoints such as respiratory hospital 

34 admissions, ED visits, and mortality, associations with O3 generally are greater in the 

35 warm season.
Draft – Do Not Cite or Quote 6-34 September 2011

Table 6-6 Mean and upper percentile concentrations of ozone in 

epidemiologic studies examining lung function in children with 

asthma

Study Location Years/Season O3 Averging 

Time

Mean/Median 

Concentration 

(ppb)

Upper Percentile 

Concentrations 

(ppb)

Mortimer et al. (2002)

Mortimer et al. (2000)

Bronx, East Harlem, NY; Baltimore, 

MD; Washington, DC; Detroit, MI, 

Cleveland, OH; Chicago,IL; St. 

Louis, MO (NCICAS)

1993

Warm season

8-h avg

(10:00a.m.-

6:00 p.m.)

48 NR

O’Connor et al. (2008) Boston, MA; Bronx, Manhattan NY; 

Chicago, IL; Dallas, TX, Seattle, 

WA; Tucson, AZ (ICAS)

1998-2001

All-year

24-h avg NR NR

Thurston et al. (1997) Connecticut River Valley, CT 1991-1993

Warm season

1-h max 83.6a Max: 160

Lewis et al. (2005) Detroit, MI 2001-2002

All-year

8-h max Eastside: 40.4a

Westside: 41.4a

Overall max: 92.0a

Rabinovitch et al. 

(2004)

Denver, CO 1999-2002

Cold season

1-h max 28.2 Max 70.0

Delfino et al. (2004) Alpine, CA SeptemberOctober 1999

April-June 2000

8-h max 62.9 90th: 83.9, Max: 105.9

Dales et al. (2009)

Liu et al. (2009a)

Windsor, ON, Canada 2005

Cold season

24-h avg

1-h max

14.1

27.2

75th: 17.8

75th: 32.8

Romieu et al. (1996) Northern Mexico City, Mexico April-July 1991

November 1991-

February 1992

1-h max 190 Max: 370

Romieu et al. (1997) Southern Mexico City, Mexico April-July 1991

November 1991-

February 1992

1-h max 196 Max: 390

Romieu et al. (2002); 

Romieu et al. (2004a); 

Romieu et al. (2006)

Mexico City, Mexico 1998-2000

All-year

8-h max

1-h max

69

102

Max: 184

Max: 309

Barraza-Villarreal et al. 

(2008); Romieu et al. 

(2009)

Mexico City, Mexico 2003-2005

All-year

8-h max

1-h max

31.6

86.5

Max (8-h): 86.3

Hernández-Cadena et 

al. (2009)

Mexico City, Mexico 2005

Warm season

24-h avg

1-h max

26.3

74.5

75th: 35.3; Max: 62.8

75th: 92.5; Max: 165.0

Gielen et al. (1997) Amsterdam, Netherlands 1995

Warm season

8-h max 34.2 Max: 56.5

Just et al. (2002) Paris, France April-June 1996 24-h avg 30.0 Max: 61.7

Hoppe et al. (2003) Munich, Germany 1992-1995

Warm season

30-min max 

(1:00 p.m.-4:00 

p.m.)

High O3 days: 66.9

Control O3 days: 32.5

Max: 91 (high O3 days)

39 (control O3 days)

Wiwatanadate and 

Trakultivakorn (2010)

Chiang Mai, Thailand August 2005-June 

2006

24-h avg 17.5 90th: 26.82

Max: 34.65

Jalaludin et al. (2000) Sydney, Australia FebruaryDecember 199415-h avg (6:00 

a.m.-9:00 p.m.)

12 Max: 43

NCICAS = National Cooperative Inner-City Asthma Study, NR = Not Reported, ICAS = Inner City Asthma Study, Max = Maximum. a

Measured at sites established by investigators.
Draft – Do Not Cite or Quote 6-35 September 2011

Figure 6-6 Percent change in FEV1 in association with ambient ozone 

exposures among children with asthma. Results generally are 

presented in order of increasing mean ambient ozone

concentration. CS = Corticosteroid, URI = Upper respiratory 

infection. Effect estimates are from single-pollutant models and are 

standardized to a 40-ppb increase for 30-min or 1-h max ozone 

exposures, a 30-ppb increase for 8-h max or 8-h avg ozone 

exposures, and a 20-ppb increase for 24-h avg ozone exposures.

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

2

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 Ile/Val

GSTP1 Val/Val

, moderate/severe asthma

, moderate/severe asthma

◄

◄

-10 -8 -6 -4 -2 0 2 4

Percent change in FEV1 per standardized increment in O3 (95% CI)
Draft – Do Not Cite or Quote 6-36 September 2011

Table 6-7 Additional characteristics and quantitative data for studies 

represented in Figure 6-6

Study Location/ Population

O3

Averaging 

Time

O3 Lag Parameter Subgroup

Standardized 

percent change 

(95% CI)a

Liu et al. (2009a) Windsor, ON, Canada

Children with asthma

24-h avg 0 FEV1 -0.89 (-3.5, 1.8)

Lewis et al. (2005) Detroit, MI

Children with asthma

8-h max 2 Lowest daily FEV1 CS user

With URI

-8.0 (-13.5, -2.1)

-5.4 (-11.3, 1.0)

Hoppe et al. (2003) Munich, Germany

Children

30-min max 

(1:00p.m.-

4:00p.m.)

1 Afternoon FEV1

Afternoon FVC

Without asthma

With asthma

Without asthma

With asthma

0.93 (-0.80, 2.7)

-0.56 (-4.6, 3.7)

-0.09 (-1.7, 1.6)

-3.5 (-5.9, -1.0)

Barraza-Villarreal 

et al. (2008)

Mexico City, Mexico

Children

8-h max 0-4 avg FEV1 Without asthma

With asthma

-1.5 (-4.7, 1.7)b

-0.12 (-2.0, 1.8)b

Romieu et al. 

(2002)

Mexico City, Mexico

Children with asthma

1-h max 1 FEV1 Placebo

Antioxidant

Placebo,moderate/severe

asthma

Antioxidant,

moderate/severe

asthma

-0.21 (-0.78, 0.36)b

0.05 (-0.59, 0.69)b

-1.1 (-2.0, -0.19)b

-0.04 (-0.92, 0.83)b

Romieu et al. 

(2006)

Mexico City, Mexico

Children with asthma

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

Children with asthma

1-h max 0 Evening % 

predicted FEV1

-0.47 (-1.9, 0.95)

Rabinovitch et al. 

(2004)

Denver, CO

Children with asthma

1-h max 0-2 avg Morning FEV1 (ml) 53 (-2.4, 108)

O’Connor et al. 

(2008)

7 U.S. communities

Children with asthma

24-h avg 1-5 avg Change in % 

predicted FEV1

-0.41 (-1.0, 0.21)

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 O3, and a 20-ppb increase for 

24-h avg O3.

c

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 lung function.
Draft – Do Not Cite or Quote 6-37 September 2011

Figure 6-7 Percent change in PEF or FEF25-75% in association with ambient 

ozone exposures among children with asthma. Results generally 

are presented in order of increasing mean ambient ozone

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 ozone exposures and a 30-ppb 

increase for 8-h max or 8-h avg ozone exposures.

Study

Gielen et al. (1997)

Mortimer et al. (2002)

Mortimer et al. (2000)

Thurston et al. (1997)

Romieu et al. (2004)

Romieu et al. (1996)

Romieu et al. (1997)

Parameter

PEF

PEF

PEF

PEF

FEF25-75%

Evening PEF

Evening PEF

O3 Lag

2

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, GSTM1 positive

-10 -8 -6 -4 -2 0 2 4

Percent change in lung function parameter per standardized

increment in O3 (95% CI)
Draft – Do Not Cite or Quote 6-38 September 2011

Table 6-8 Additional characteristics and quantitative data for studies 

represented in Figure 6-7

Study Location/ Population

O3

Averaging 

Time

O3

Lag Parameter Subgroup

Standardized 

percent change 

(95% CI)a

Gielen et al. (1997) Amsterdam, Netherlands

Children w/asthma

8-h max 2 PEF -1.3 (-2.6, -0.10)

Mortimer et al. (2002) 8 U.S. communities

Children w/asthma

8-h avg

(10:00a.m.-

6:00p.m.)

1-5 

avg

PEF All subjects -1.2 (-2.1, -0.26)

Mortimer et al. (2000) 8 U.S. communities

Children w/asthma

8-h avg

(10:00a.m.-

6:00p.m.)

1-5 

avg

PEF Normal BW

Low BW

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

Children w/asthma

1-h avg 0 Intraday change 

PEF

-2.8 (-4.9, -0.59)

Romieu et al. (2004a) Mexico City, Mexico

Children w/asthma

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

Children w/asthma

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

Children w/asthma

1-h max 0

2

Evening PEF -0.52 (-1.0, -0.007)

-0.06 (-0.70, 0.58)

Studies not included in Figure 6-7b

Jalaludin et al. (2000) Sydney, Australia

Children w/asthma

24-h avg 0 % variability 

PEF

Wheeze, no asthma

Asthma, no AHR

Asthma, with AHR

3.8 (0.25, 7.38)c

-0.71 (-2.6, 1.2)c

-5.2 (-8.3, -2.2)c

Wiwatanadate and 

Trakultivakorn (2010)

Chiang Mai, Thailand

Children w/asthma

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)

7 U.S. communities

Children w/asthma

24-h avg 1-5 

avg

Change in % 

predicted PEF

-0.22 (-0.86, 0.43)

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 8-h 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 lung function. 

c Outcome defined as the percent deviation from individual mean PEF during the study period. Group-stratified effect estimates 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; 

3 Mortimer et al., 2000) and Inner-City Asthma Study (ICAS) (O'Connor et al., 2008). 

4 Although the two studies differed in the cities, seasons, racial distribution of subjects, and 

5 lung function indices examined, results were fairly similar. In ICAS, which included 

6 children with asthma and atopy (i.e., allergic sensitization) and year-round examinations 

7 of lung function, a 20-ppb increase in the lag 1-5 average of 24-h avg O3 was associated 

8 with a 0.41-point decrease in percent predicted FEV1 (95% CI: -1.0, 0.21) and a 0.22-

9 point decrease in percent predicted PEF (95% CI: -0.86, 0.43).
Draft – Do Not Cite or Quote 6-39 September 2011

1 Lag 1-5 avg O3 (8-h avg, 10:00 a.m.-6:00 p.m.) also was associated with declines in PEF 

2 in NCICAS, which included different U.S. cities, summer-only measurements, larger 

3 proportions of Black and Hispanic children, and fewer subjects with atopy (79%) 

4 (Mortimer et al., 2002). NCICAS additionally identified groups potentially at increased 

5 risk of O3-associated decrements in PEF. Larger effects were estimated in males, children 

6 of Hispanic ethnicity, children living in crowded housing, and as indicated in Figure 6-7 

7 and Table 6-8, children with low birth weight (Mortimer et al., 2000). Somewhat 

8 paradoxically, O3 was associated with a larger decrease in PEF among subjects taking 

9 cromolyn, medication typically used to treat asthma due to allergy, but a smaller decrease 

10 among subjects with positive atopy (as determined by skin prick test). Similar to 

11 observations from studies of populations with increased outdoor exposures, Mortimer et 

12 al. (2002) found that associations persisted at lower ambient O3 concentrations. At 

13 concentrations below 80 ppb, a 30-ppb increase in lag 1-5 of 8-h avg O3 was associated 

14 with a 1.4% decrease (95% CI: -2.6, -0.21) in PEF, which was similar to the effect 

15 estimated for the full range of O3 concentrations (Figure 6-7 and Table 6-8). In a study of 

16 children with asthma in the Netherlands, Gielen et al. (1997) estimated similar effects for 

17 the full range of 8-h max O3 concentrations and concentrations below 51 ppb.

18 The results from studies of children with asthma indicated that factors in addition to 

19 asthma influenced associations between ambient O3 exposure and changes in lung 

20 function. In comparisons between children with and without asthma, Hoppe et al. (2003)

21 and Jalaludin et al. (2000) generally found larger O3-associated lung function decrements 

22 in children with asthma; whereas Raizenne et al. (1987) did not consistently demonstrate 

23 differences between campers with and without asthma. In their study of children in 

24 Mexico City, Barraza-Villarreal et al. (2008) estimated larger O3-associated decreases in 

25 children without asthma; however, 72% of these children had atopy. These findings 

26 indicated that in addition to asthma, atopy, a condition also characterized by airway 

27 inflammation and similar respiratory symptoms, may increase the risk for O3-associated 

28 respiratory effects.

29 As indicated in Figures 6-6 and 6-7 and Tables 6-7 and 6-8, in most studies of children 

with asthma, standardized increments in ambient O3 exposure1 30 were associated with

31 decreases in lung function that ranged from less than 1% to 2%. Larger magnitudes of 

32 decreases (3-8% per standardized increments in O3) were found in children with asthma 

33 who also were using CS, had a concurrent upper respiratory infection (URI), were 

34 GSTM1 null, had low birth weight, or had increased outdoor exposure (Romieu et al., 

35 2006; Lewis et al., 2005; Romieu et al., 2004a; Jalaludin et al., 2000) than among 

36 children with asthma overall (Barraza-Villarreal et al., 2008; Lewis et al., 2005; Delfino 

 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 6-40 September 2011

1 et al., 2004; Romieu et al., 2002). For example, Jalaludin et al. (2000) estimated a -5.2% 

2 deviation from mean FEV1 per a 20-ppb increase in 24-h avg O3 among children with 

3 asthma and airway hyperresponsiveness and a much smaller -0.71% deviation among 

4 children with asthma without airway hyperresponsiveness. In a group of 86 children with 

5 asthma in Detroit, MI, Lewis et al. (2005) also reported that associations between O3

6 exposure and lung function decrements were confined largely to children with asthma 

7 who used CS or had a concurrent URI. These two groups were observed to have the 

8 largest O3-associated decrements in lung function among all studies of children with 

9 asthma. A 30-ppb increase in 8-h max ambient O3 exposure was associated with a 8.0% 

10 decrease in the mean of lowest daily FEV1 among CS users and a 5.4% decrease among 

11 subjects reporting concurrent URI (Lewis et al., 2005) (Figure 6-6 and Table 6-7).

12 Heterogeneity in lung function responses to ambient O3 exposure also has been 

13 demonstrated as inter-individual variability in the magnitude of O3-associated changes in 

14 lung function. Mortimer et al. (2002) found that for a 30-ppb increase in lag 1-5 avg of 8-

15 h avg O3, there was a 30% (95% CI: 4, 61) increase in the incidence of a greater than 

16 10% decline in PEF. Likewise, Hoppe et al. (2003) found that while the percentages of 

17 change in individual lung function parameters were variable and small, 47% of children 

18 with asthma in their study experienced greater than 10% decline in FEV1, FVC, or PEF 

19 or 20% increase in airway resistance on days with 30-min (1:00 p.m.-4:00 p.m.) max 

20 ambient O3 concentrations greater than 50 ppb relative to days with less than 40 ppb O3. 

21 In addition to finding groups of children with asthma with increased sensitivity to O3

22 exposure, epidemiologic studies have indicated that the decreases in lung function 

23 observed in association with increases in ambient O3 exposure may be clinically 

24 significant by finding that the same or similar lag of O3 exposure was associated with 

25 decrements in lung function and increases in concurrently assessed respiratory symptoms 

26 (Just et al., 2002; Mortimer et al., 2002; Gielen et al., 1997; Romieu et al., 1997; 

27 Thurston et al., 1997; Romieu et al., 1996) (see Figure 6-12 and Table 6-19 for symptom 

28 results).

Effect modification by corticosteroid use

29 In controlled human exposure studies, CS treatment of subjects with asthma generally has 

30 not prevented O3-induced FEV1 decrements (Section 6.2.1.1). In epidemiologic studies 

31 reviewed in the 2006 O3 AQCD, evidence was equivocal, as use of inhaled CS showed 

32 both protective (Delfino et al., 2002; Mortimer et al., 2000) and exacerbating (Gent et al., 

33 2003) effects on respiratory endpoints. Among recent studies, evidence for effect 

34 modification of lung function responses by CS use also was mixed. In Lewis et al. 

35 (2005), analyses of interactions between O3 exposure and CS use indicated stronger 

36 associations among CS users than among CS nonusers (quantitative results not reported 
Draft – Do Not Cite or Quote 6-41 September 2011

1 for CS nonusers). Among the 11 (12.8%) CS users, a 30-ppb increase in lag 2 of 8-h max 

2 O3 was associated with an 8.0% decrease (95% CI: -13.5, -2.1) in lowest daily FEV1 and 

3 a 6.7% increase (95% CI: 0.60, 13.2) in diurnal FEV1 variability (indicating a decrease 

4 from morning to evening). Other lags (1 or 3-5 avg) or averaging times (24-h avg) of 

5 exposure were estimated to have less impact. In contrast to Lewis et al. (2005), 

6 Hernández-Cadena et al. (2009) observed greater O3-related decrements in FEV1 among 

7 the 60 CS nonusers than among the 25 CS users. In two winter-only studies, 

8 consideration of CS use did not largely influence associations between ambient O3 and 

9 lung function parameters (Liu et al., 2009a; Rabinovitch et al., 2004).

10 Although studies varied in populations and season examined, the inconsistency in effect 

11 modification by CS use may be explained, at least in part, by differences in the severity 

12 of asthma among CS users and the definition of CS use. Hernández-Cadena et al. (2009)

13 did not define CS use; however, the group of CS nonusers included both children with 

14 intermittent and persistent asthma. In Lewis et al. (2005), most children with moderate to 

15 severe asthma (91%) were included in the group of CS users (use for at least 50% of 

16 study days); however, these subjects had a higher percent predicted FEV1. Liu et al. 

17 (2009a) did not provide information on asthma severity; however, they defined CS use 

18 more stringently as daily use. Differences in asthma severity and definition of CS use 

19 may explain why both CS use and nonuse could serve as indicators of severe or 

20 uncontrolled asthma across studies. Additionally, investigators did not assess adherence 

21 to reported CS regimen, and misclassification of CS use may bias findings.

Effect modification by antioxidant capacity

22 Ozone is a powerful oxidant whose secondary oxidation products are recognized to 

23 initiate the key modes of action, including the activation of neural reflexes that mediate 

24 decreases in lung function (Section 5.3.2). Additionally, O3 exposure of humans and 

25 animals induces changes in the levels of antioxidants in the ELF (Section 5.3.3). These 

26 observations support the biological plausibility for diminished antioxidant capacity 

27 increasing the risk of O3-associated respiratory effects and augmented antioxidant 

28 capacity decreasing risk. Controlled human exposure studies have demonstrated 

29 protective effects of α-tocopherol (vitamin E) and ascorbate (vitamin C) supplementation 

30 on O3-induced lung function decrements (Section 6.2.1.1), and epidemiologic studies of 

31 children with asthma conducted in Mexico City have had similar findings. Particularly 

32 among children with moderate to severe asthma, ambient O3 exposure was associated 

33 with a smaller decrease in FEV1 in the group supplemented with vitamin C and E as 

34 compared with the placebo group (Romieu et al., 2002) (Figure 6-6 and Table 6-7). 

35 Similarly, Romieu et al. (2009) observed protective effect for diets high in vitamins C 

36 and E as well as omega-3 fatty acids. Subjects were assigned to a fruits and vegetables 
Draft – Do Not Cite or Quote 6-42 September 2011

1 index (FVI) that characterized consumption of vitamins C and E and a Mediterranean diet 

2 index (MDI) that additionally represented the intake of omega-3 fatty acids, which have 

3 anti-inflammatory effects. At lag 0-4 avg of 8-h max O3 concentrations ≥ 38 ppb, a 1-unit 

4 increase in FVI was associated with a 137 ml (95% CI: 8, 266) increase in FEV1. This 

5 protective effect of FVI was diminished at O3 concentrations ≤ 25 ppb (65 ml [95% CI: -

6 70, 200] increase in FEV1 per 1-unit increase in FVI). Similar results were obtained for 

7 MDI. 

8 Antioxidant capacity also can be characterized by variants in genes encoding xenobiotic 

9 metabolizing enzymes with different enzymatic activities. Ambient O3 exposure has been 

10 associated with greater decreases in lung function among children with asthma with the 

11 GSTM1 null genotype, which is associated with lack of oxidant metaboilizing activity 

12 (Romieu et al., 2004a). The difference in response between GSTM1 null and positive 

13 subjects was minimal in children supplemented with antioxidant vitamins (Figure 6-7 and 

14 Table 6-8). Although these findings are biologically plausible given the well15 characterized evidence for O3 effects mediated by secondary oxidation products, it is 

16 important to note that a larger body of controlled human exposure studies has not 

17 consistently found larger O3-induced lung function decrements in GSTM1 null subjects 

18 (Section 6.2.1.1). Effect modification by the GSTP1 variant is less clear. Romieu et al. 

19 (2006) observed larger O3-associated decreases in FEV1 in children with asthma with the 

20 GSTP1 Ile/Ile or Ile/Val variant, both of which are associated with normal oxidative 

21 metabolism activity (Figure 6-6 and Table 6-7). Also unexpectedly, O3 exposure was 

22 associated with an increase in FEV1 among children with the GSTP1 Val/Val variant, 

23 which is associated with reduced oxidative metabolism. Rather than reflecting effect 

24 modification by the GSTP1 variant, these results may reflect effect modification by 

25 asthma severity, as 77% of subjects with the GSTP1 Ile/Ile genotype had moderate to 

26 severe asthma. Supporting evidence is provided by an earlier analysis of the same cohort, 

27 in which the effect of antioxidant supplementation was demonstrated more strongly in the 

28 smaller group of children with moderate to severe asthma than among all subjects with 

29 asthma (Romieu et al., 2002).

Adults with Respiratory Disease

30 Relative to studies in children with asthma, studies of adults with asthma or COPD have 

31 been limited in number. Characteristics and ambient O3 concentration data from these 

32 studies are presented in Table 6-9. Studies that included both children and adults with 

33 asthma did not consistently demonstrate associations between ambient O3 exposure and 

34 decrements in lung function (Ross et al., 2002; Delfino et al., 1997). Ross et al. (2002)

35 found that a 20-ppb increase in lag 0 of 24-h avg O3 was associated with a 2.6 L/min 

36 decrease (95% CI: -4.3, -0.90) in evening PEF among subjects ages 5-49 years. This 
Draft – Do Not Cite or Quote 6-43 September 2011

1 decrement may have been indicative of a clinically significant effect, as lag 0 O3

2 exposure also was associated with an increase in symptom score. In another panel study, 

3 neither ambient nor personal O3 12-h avg exposure was reported to be associated with a 

4 decrease in lung function among subjects ages 9-46 years (Delfino et al., 1997).

5 Comparisons of adults with and without asthma did not conclusively demonstrate that 

6 adults with asthma were at increased risk of O3-associated respiratory effects. In the 

7 recent panel study of 16- to 27-year-old lifeguards in Galveston, TX, a larger O3-

8 associated decrement in FEV1/FVC was found among the 16 lifeguards with asthma (-

9 1.6% [95% CI: -2.8, -0.4] per 40 ppb increase in 1-h max O3) than among the 126 

10 lifeguards without asthma (-0.40% [95% CI: -0.80, 0] per 40 ppb increase in 1-h max O3) 

11 (Brooks, 2010). In the studies of day-hikers, Korrick et al. (1998) found that the O3-

12 associated lung function decrements observed among all hikers were driven by 

13 associations observed in hikers with history of asthma or wheeze (-4.4% [95% CI: -7.5, -

14 1.2] in FEV1 per 30-ppb increase in 2-9 hr avg O3). In contrast, Girardot et al. (2006) did 

15 not find ambient O3 exposure to be consistently associated with decrements in lung 

16 function in subjects with or without respiratory disease history. In another cross-sectional 

17 study of 38 adults with asthma and 13 adults without asthma, atopy was observed to be a 

18 stronger susceptibility factor than was asthma (Khatri et al., 2009). Investigators reported 

19 a larger decrease in percent predicted FEV1/FVC per 30-ppb increase in lag 2 of 8-h max 

20 O3 among the 38 subjects with atopy (with or without asthma) (-12 points [95% CI: -21, -

21 3]) than among subjects with asthma (-4.7 points [95% CI: -11, 2.3]). Additionally, 

22 among adults with asthma, O3 was associated with an increase in FEV1. Based on 

23 correlations observed between decreases in lung function and decreases in quality of life 

24 scores, investigators inferred the O3-associated decreases in lung function to be clinically 

25 significant. They suggested that atopy may influence responses to ambient O3 exposure 

26 because during the summer, high ambient O3 concentrations may increase the 

27 allergenicity of pollens.

28 O3 was not found to have a strong effect on the lung function of adults with asthma in 

29 panel studies conducted in Europe and Asia during low ambient O3 periods 

30 (Wiwatanadate and Liwsrisakun, 2011; Lagorio et al., 2006; Park et al., 2005a), including 

31 one study conducted in Korea during a period of dust storms (Park et al., 2005a). In these 

32 studies that examined multiple lags of O3 exposure, O3 generally was associated with 

33 increases in lung function.

34 Controlled human exposure studies demonstrate robust O3-induced spirometric responses 

35 in children and young adults but diminished, statistically nonsignificant responses in 

36 older adults, both healthy and with COPD (Section 6.2.1.1). Similarly, in a recent 

37 epidemiologic study that followed 94 adults with COPD (ages 40-83 years) daily over a 
Draft – Do Not Cite or Quote 6-44 September 2011

1 2-year period, an increase in ambient O3 exposure was not associated consistently with 

2 decreases PEF, FEV1, and FVC (Peacock et al., 2011). For example, in an analysis 

3 restricted to the summer of 1996, a 30-ppb increase in 8-h max O3 was associated with a 

4 1.7 L/min decrease (95% CI: -3.1, -0.39) in PEF. However, during the summer of 1997, 

5 O3 was found to have little effect on PEF (-0.21 L/min [95% CI: -2.4, 2.0] per 30-ppb 

6 increase in 8-h max O3). Further, in this study, an increase in ambient O3 exposure was 

7 associated with a lower odds of a large PEF decrement (OR for a greater than 20% drop 

8 from an individual’s median value: 0.89 [95% CI: 0.72, 1.10] per 30-ppb increase in lag 1 

9 of 8-h max O3) and was not consistently associated with increases in respiratory 

10 symptoms (Peacock et al., 2011). Ozone exposure also was not consistently associated 

11 with decreases in lung function in a smaller panel study of 11 adults with COPD (mean 

12 age 67 years) (Lagorio et al., 2006). Together, these finding do not provide strong 

13 evidence that increases in O3 exposure are associated with lung function decrements in 

14 adults with COPD.

Table 6-9 Mean and upper percentile concentrations of ozone in 

epidemiologic studies examining lung function in adults with 

respiratory disease

Study Location Years/Season O3 Averaging 

Time

Mean/Median 

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

Korrick et al. 

(1998)

Mt. 

Washington, 

NH

1991, 1992

Warm season

Hike-time avg

(2-12 h)

40 Max: 74

Khatri et al. (2009) Atlanta, GA 2003, 2005, 2006

Warm season

8-h max 59 (median)a 75th: 73a

Ross et al. (2002) East Moline, IL April-October 1994 8-h avg 41.5 Max: 78.3

Thaller et al. 

(2008)

Galveston, TX 2002-2004

Warm season

1-h max 35 (median) Max: 118

Delfino et al. 

(1997)

Alpine, CA 1994

Warm season

12-h avg 

personal

(8:00 a.m.-8:00 

p.m.)

18 90th: 38

Max: 80

Lagorio et al. 

(2006)

Rome, Italy 1999

Spring and winter

24-h avg Spring: 36.2b

Winter: 8.0b

Overall max: 48.6b

Peacock et al. 

(2011)

London, 

England

1995-1997

All-year

8-h max 15.5 Autumn/Winter Max: 32

Spring/Summer Max: 74

Wiwatanadate et 

al. (2011)

Chiang Mai, 

Thailand

August 2005 -

June 2006

24-h avg 17.5 90th: 26.82

Max: 34.65

Park et al. (2005a) Incheon, Korea March-June 2002 24-h avg Dust event days: 23.6

Control days: 25.1

NR

NR = Not reported, Max = Maximum. a

Individual-level exposure 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).

Populations Not Restricted to Individuals with Asthma

15 Several studies have examined associations between ambient O3 exposure and lung 

16 function in children; however, a limited number of studies have examined other 
Draft – Do Not Cite or Quote 6-45 September 2011

1 populations not restricted to individuals with asthma or other healthy populations. 

2 Characteristics and ambient O3 concentration data from studies not restricted to 

3 individuals with asthma are presented in Table 6-10.

Table 6-10 Mean and upper percentile concentrations of ozone in 

epidemiologic studies examining lung function in populations not 

restricted to individuals with asthma

Study Location Years/Season Metric Mean/Median 

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

Alexeef et al. (2007)

Alexeef et al. (2008)

Greater Boston, MA 1995-2005

All-year

24-h avg 24.4a NR

Naeher et al. (1999) Vinton, VA 1995-1996

Warm season

8-h max 34.87 Max: 56.63

Avol et al. (1998a) 6 southern CA 

communities 

1994

Spring and summer

24-h avg personal NR NR

Linn et al. (1996) Rubidoux, Upland, 

Torrence, CA

1992-1993, 1993-

1994

Fall and spring

24-h avg 23 Max: 53

Gold et al. (1999) Mexico City, Mexico 1991

Winter, spring, fall

24-h avg 52.0 Max: 103

Scarlett et al. (1996) Surrey, England 1994

Warm season

8-h max 50.7b Max: 128b

Ward et al. (2002) Birmingham and 

Sandwell, England

1997

Winter and summer

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

1994

March-October

30-min max Freudenstadt median: 50.6

Villingen median: 32.1

Freudenstadt 95th: 89.7

Villingen 95th: 70.1

Hoppe et al. (2003) Munich, Germany 1992-1995

Warm season

30-min max (1:00 p.m.-

4:00 p.m.)

High O3 days: 70.4

Control O3 days: 29.8

Max (high O3 days): 99

Max (control O3 days): 39

Neuberger et al. (2004) Vienna, Austria June-October 1999, 

January-April 2000

NR NR NR

Steinvil et al. (2009) Tel Aviv, Israel 2002-2007

All-year

8-h avg

(10:00 a.m. – 6:00 p.m.)

41.1 75th: 48.7

Max: 72.8

Chen et al. (1999) 3 Taiwan 

communities

1995-1996

May-January

1-h max NR Max: 110.3b

Son et al. (2010) Ulsan, Korea 2003-2007

All-year

8-h max 35.86 Max: 59.53

NR = Not Reported, Max = Maximum. 

a

Measured at central monitoring sites established by investigators. Concentations were averaged across all monitors.

b

Measured at subjects’ schools where lung function measurements were performed.

Children

4 The 2006 O3 AQCD identified children as a potentially at-risk population based on 

5 consistent evidence of association between ambient O3 exposure and decrements in FEV1

6 and PEF (U.S. EPA, 2006b) (Figure 6-8 and Table 6-11). No new studies in children 

7 without asthma are available to compare with previous findings. Hoppe et al. (2003) O3

8 exposure to be associated with decreses in healthy children in Munich, Germany (Figure 

9 6-8 and Table 6-11). In another panel study of healthy children in Vienna, Austria, O3

10 was not associated with decrements in total lung capacity (Neuberger et al., 2004). Most 
Draft – Do Not Cite or Quote 6-46 September 2011

1 of the studies in children did not exclusively examine healthy children. However, several 

2 studies of children that included small proportions (4- 10%) of children with history of 

3 respiratory disease or symptoms and found associations between O3 exposure and 

4 decrements in lung function (Chen et al., 1999; Ulmer et al., 1997; Scarlett et al., 1996). 

5 Based on interactions between O3 exposure and asthma/wheeze history, Avol et al. 

6 (1998a) and Ward et al. (2002) did not find lung function responses to ambient O3

7 exposure to differ between children with history of asthma or wheeze and healthy 

8 children. Combined, these lines of evidence indicate that the associations observed 

9 between ambient O3 exposure and decreases in lung function in children are not driven by 

10 effects in children with asthma or respiratory symptoms, and that healthy children also 

11 may represent a population at increased risk of O3-associated respiratory effects. 

Results generally are presented in order of increasing mean ambient ozone concentration. 

a

The 95% CI was constructed using a standard error that was estimated from the p-value. Effect estimates are from singlepollutant models and are standardized to a 40-, 30-, and 20-ppb increase for a 1-h (or 30-min) max, 8-h max, and 24-h avg ozone 

exposures, respectively.

Figure 6-8 Percent change in lung function in association with ambient ozone 

exposures in studies not restricted to children with asthma.

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

FEV1

FVC

FEV1

FEV1

Intraday change FEV1

Intraday change FVC

O3 Lag

0

0

0

1

1

0 (personal)

-10 -8 -6 -4 -2 0 2

Percent change in lung function parameter per standardized

increment in O3 (95% CI)
Draft – Do Not Cite or Quote 6-47 September 2011

Table 6-11 Additional characteristics and quantitative data for studies 

represented in Figure 6-8 and results from other studies in children

Study Location/

Population O3 Lag O3 Averaging Time Parameter Effect Estimate (95% CI)a

Linn et al. (1996)

3 southern CA 

communities

Children

0 1-h avg Intraday change FEV1

Intraday change FVC

-0.56 (-0.99, -0.12)

-0.21 (-0.62, 0.20)

Hoppe et al. (2003) Munich, Germany

Children 0 30-min max (1:00 p.m.-4:00 p.m.)

FEV1

FVC

-1.4 (-4.3, 1.4)

-2.5 (-4.9, -0.10)

Scarlett et al. (1996) Surrey, England

Children 1 8-h max FEV1 -0.04 (-0.32, 0.23)

Chen et al. (1999) 3 Taiwan communities

Children 1 1-h max FEV1 -1.5 (-2.8, -0.12)

Avol et al. (1998a)

3 southern CA 

communities

Children

0 (personal) 24-h avg Intraday change FEV1

Intraday change FVC

-1.4 (-3.8, 0.90)b

-2.0 (-4.0, 0.01)b

Studies of children not included in Figure 6-8c

Ulmer et al. (1997)

Freudenstadt and 

Villingen, Germany

Children

1 1/2-h max FEV1 (ml) -5.9 (-10.4, 1.3)b

Ward et al. (2002)

Birmingham and 

Sandwell, England

Children

0

0-6 avg 24-h avg PEF (L/min) -3.2 (-8.3, 2.0)d

-11.1 (-22.0, -0.18)d

Gold et al. (1999) Mexico City, Mexico

Children

1

1-10 avg 24-h avg Intraday change PEF (% change) -0.54 (-1.1, 0.05)

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 lung function or 

PEF was analyzed.d

Effect estimates are from analyses restricted to summer months.

1 Among the studies of children, the magnitudes of decrease in lung function per 

standardized increment in ambient O3 exposure1 2 ranged from less than 1 to 4%, a range 

3 similar to that estimated in children with asthma. However, in contrast with studies of 

4 children with asthma, studies of children in the general population did not consistently 

5 find that O3-associated decreases in lung function were accompanied by increases in 

6 respiratory symptoms. Gold et al. (1999) found that lag 1 of O3 exposure was associated 

7 with both decreases in PEF and increases in phlegm; however, the increase in phlegm 

8 was associated with O3 exposure lagged one day whereas the PEF decrement was driven 

9 by exposures lagged 2 to 4 days. Ozone was weakly associated with cough and shortness 

10 of breath among children in England (Ward et al., 2002), and O3 was associated with a 

11 decrease in respiratory symptom score among children in California (Linn et al., 1996). 

12 These findings indicate that while the magnitudes of O3-associated decrease in lung 

13 function may be similar in children with and without asthma, because of the higher 

14 overall lung function in healthy children, the decrements may not be large enough to be 

15 clinically significant in healthy children.

 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 6-48 September 2011

Adults

1 In the small body of studies conducted in adults, O3 has been associated with decrements 

2 in lung function in both healthy adults and those with comorbid factors (Table 6-12). In a 

3 cohort of mostly healthy women, ages 19-43 years, followed for one summer season, 

4 Naeher et al. (1999) observed associations between 8-h max ambient O3 exposure and 

5 decreases in PEF. In a large cross-sectional study of 2,380 healthy adults (75th percentile 

6 of age: 52 years) in Tel Aviv, Israel, across several lags of exposure (single day lags 0-7 

7 and 0-6 avg), O3 was associated mostly with increases in FEV1, FVC, and FEV1/FVC

8 (Steinvil et al., 2009). Another large cross-sectional study was conducted in 2,102 

9 children and adults (mean age: 45 years) living near a petrochemical plant in Ulsan, 

10 Korea (Son et al., 2010). Multiple O3 exposure metrics, including concentrations 

11 averaged across 13 city monitors, concentrations from the nearest monitor, inverse 

12 distance-weighted concentrations, and estimates from kriging, were associated with 

13 decrements in lung function; however, no particular metric consistently showed a larger 

14 effect across the various lags of O3 exposure examined. Lag 0-2 avg of 8-h max O3

15 exposure was associated with the largest decrements in percent predicted FEV1 (1.4-point 

16 decrease [95% CI: -2.7, -0.08] per 30-ppb increase in the 8-h max of lag 0-2 avg O3

17 averaged across all monitors). Although the health status of subjects was not reported, the 

18 mean percent predicted FEV1 in the study population was 82.85%, indicating a large 

19 proportion of subjects with underlying airway obstruction. Results from this study were 

20 not adjusted for meteorological factors and thus, confounding cannot be ruled out. 

21 As described in Section 6.2.1.1, controlled human exposure studies have not consistently 

22 found O3-induced decreases in lung function in older adults. In an earlier study of adults 

23 ages 69-95 years, Hoppe et al. (2003) did not find ambient O3 exposure-associated 

24 decreases in lung function. However, recently, the Normative Aging Study found that 

25 ambient O3 exposure was associated with decrements in FEV1 and FVC in a group of 

26 older men (Alexeeff et al., 2008). This study in the Greater Boston area conducted 

27 spirometry once every 3 years for 10 years in 900 older men (mean [SD] age = 68.9 [7.2] 

28 years), most of whom were white and healthy. Among all subjects, several lags of 24-h 

29 avg O3 exposure (1- to 7-day avg) were associated with decreases in FEV1 (Alexeeff et 

30 al., 2008). Additionally, larger effects were estimated in adults with elevated BMI (≥ 30), 

31 airway hyperresponsiveness, and reduced activity in antioxidant enzymes (i.e., GSTP1 

32 Ile/Val or Val/Val variant) (Alexeeff et al., 2008; Alexeeff et al., 2007) (Table 6-12). 

33 Larger O3-related decrements in FEV1 and FVC also were observed in subjects with long 

34 GT dinucleotide repeats in the promoter region of the antioxidant enzyme heme 

35 oxygenase-1 (Alexeeff et al., 2008), which has been associated with reduced inducibility 

36 (Hiltermann et al., 1998). The largest O3-related percentages of decrease in lung function 

37 were observed in the group of men with airway hyperresponsiveness and elevated BMI (-
Draft – Do Not Cite or Quote 6-49 September 2011

1 5.3% FEV1 [95% CI: -8.3, -2.4] per 20-ppb increase in lag 0-1 avg of 24-h avg O3). In 

2 this cohort, O3 also was associated with decreases in lung function in adults without 

3 airway hyperresponsiveness and BMI < 30, indicating the effects of O3 on lung function 

4 in older adults extends to healthy older adults. However, importantly, the findings may be 

5 generalizable only to older white men.

Table 6-12 Associations between ambient ozone exposure and changes in 

lung function in studies of adults

Study Location/ Population O3 Lag 

O3

Averaging 

Time

Parameter O3 Assessment 

Method/Subgroup

Effect Estimate 

(95% CI)a

Son et al. 

(2010)

Ulsan, Korea

Children and adults, ages 7-

97 yr

0-2 avg 8-h max Change in % 

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

Healthy adults, mean age 43 

yr, 75th %-ile: 52 yr

0

0-6 avg

8-h avg

(10:00 a.m- 6:00 p.m.)FEV1 (ml) 40 (0, 80)

94 (33, 156)

Naeher et al. 

(1999)

Vinton, VA

Healthy women, ages 19-43 

yr

0

0-4 avg 24-h avg Evening PEF (L/min)

-0.06 (-0.11, 0)

-5.1 (-8.7, -1.5)

Hoppe et al. 

(2003)

Munich, Germany

Older adults, ages 69-95 yr

0

1

30-min max 

(1:00p.m.- 4:00p.m.)

% change in 

evening FEV1

0.75 (-2.1, 3.7)

1.2 (-1.3, 3.6)

Alexeeff et al. 

(2008)

Greater Boston, MA

Older adults, mean (SD) age: 

68.8 yr (7.3)

0-1 avg 24-h avg % change in FEV1 GSTP1 Ile/Ile

GSTP1 Ile/Val Val/Val -1.0 (-2.2, 0.19) -2.3 (-3.5, -1.0)

Alexeef et al. 

(2007)

Greater Boston, MA

Older adults, mean (SD) age: 

68.8 yr (7.3)

0-1 avg 24-h avg % change in FEV1

BMI < 30

BMI ≥ 30

No AHR

AHR

BMI ≥ 30 and AHR 

-1.5 (-2.5, -0.52) -3.5 (-5.1, -1.9)

-1.7 (-2.7, -0.73) -4.0 (-6.2, -1.8)

-5.3 (-8.2, -2.3)

IDW = Inverse distance weighting, BMI = Body mass index, AHR = airway hyperresponsiveness. a

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.

Confounding in epidemiologic studies of lung function

6 The 1996 O3 AQCD noted uncertainty regarding confounding by temperature and pollen 

7 (U.S. EPA, 1996a); however, studies collectively do not provide strong evidence of 

8 confounding by these factors. Most studies, whether they involved year-round or 

9 summer-only examinations, included temperature in statistical analyses and found 

10 associations between O3 exposure and decreases in lung function. Across studies, 

11 temperature has shown inconsistent associations with lung function, even among studies 

12 conducted in the summer and in the same geographic region. For example, in studies of 

13 children attending summer camps conducted in the Northeast U.S., temperature was 

14 associated with an increase (Berry et al., 1991) (Thurston et al., 1997) and decrease 

15 (Raizenne et al., 1987) in lung function. In the reanalysis of six camp studies, 

16 investigators did not include temperature in models because temperature within the 

17 normal ambient range had not been shown to affect O3-induced lung function responses 

18 in controlled human exposure studies(Kinney et al., 1996). In two summer camp studies 
Draft – Do Not Cite or Quote 6-50 September 2011

1 conducted in the Northeast U.S., O3 was associated with decreases in lung function in 

2 models without and with temperature (Thurston et al., 1997; Spektor et al., 1988a). In 

3 both studies, temperature and O3 were measured on site of the camps. Spektor et al. 

4 (1988a) estimated similar effects in a model with and without a temperature-humidity 

5 index, and Thurston et al. (1997) found that compared with a univariate model, O3 was 

6 associated with a nearly 2-fold greater decrease in PEF when temperature was added to 

7 the model.

8 Although evaluated in fewer studies, the evidence does not indicate that associations 

9 between ambient O3 exposure and lung function are confounded by pollen. Some camp

10 studies found that pollen independently was not associated with lung function decrements 

11 (Thurston et al., 1997; Avol et al., 1990). A few studies of children with asthma with 

12 follow-up over multiple seasons found O3 to be associated with decrements in lung 

13 function in models that adjusted for pollen counts (Just et al., 2002; Ross et al., 2002; 

14 Jalaludin et al., 2000; Gielen et al., 1997). In these studies, large percentages of subjects 

15 had positive atopy (22-98%), with some studies examining large percentages of subjects 

16 specifically with pollen allergy(Ross et al., 2002; Gielen et al., 1997).

17 A relatively larger number of studies provided information on potential confounding by 

18 copollutants such as PM2.5, PM10, NO2, or SO2. In most cases, investigators indicated that 

19 associations between O3 exposure and lung function were not driven by copollutant

20 confounding; however, studies varied in how they considered confounding. Studies of 

21 subjects exercising outdoors indicated that ambient concentrations of copollutants such as 

22 NO2, sulfur dioxide, or acid aerosol were low and thus, not likely to confound the 

23 observed O3 effects (Hoppe et al., 2003; Brunekreef et al., 1994; Hoek et al., 1993). In 

24 other studies of children with increased outdoor exposures, O3 was consistently 

25 associated with decreases in lung function, whereas other pollutants such as PM2.5, 

26 sulfate, and acid aerosol individually showed variable associations across studies 

27 (Thurston et al., 1997; Castillejos et al., 1995; Berry et al., 1991; Avol et al., 1990; 

28 Spektor et al., 1988a). 

29 Among studies that conducted copollutant modeling, associations between O3 exposure 

30 and lung function decrements were observed to be robust (Figure 6-9 and Table 6-13). In 

31 copollutant models, O3 effect estimates generally fell within the 95% CI of the single32 pollutant model effect estimates. Whereas some studies used the same averaging time for 

33 all pollutants (Lewis et al., 2005; Jalaludin et al., 2000), most examined 1-h max or 8-h 

34 max O3 exposures and 24-h avg copollutant exposures (Son et al., 2010; Chen et al., 

35 1999; Romieu et al., 1997; Romieu et al., 1996). In a Philadelphia-area summer camp 

36 study, Neas et al. (1999) was among the few studies to find that the effect of O3 was 
Draft – Do Not Cite or Quote 6-51 September 2011

1 attenuated in a copollutant model. In a copollutant model with 24-h avg sulfate, the 12-h 

2 avg O3 effect estimate was attenuated to near zero (Figure 6-9 and Table 6-13).

3 In studies with copollutant modeling, ambient O3 concentrations showed a wide range of 

4 correlations with concentrations of copollutants (r=-0.31 to 0.74). Among children with 

5 asthma in Sydney, Australia, Jalaludin et al. (2000) found low correlations of 24-h avg O3

6 with 24-h avg PM10 (r = 0.13) and NO2 (r = -0.31), and in two-pollutant models, PM10

7 and NO2 continued to be associated with increases in PEF, and O3 continued to be 

8 associated with decreases in PEF. In a study of children with asthma in Detroit, MI, 24-h 

9 avg O3 was moderately correlated with 24-h avg PM2.5 (Pearson r= 0.57) and 24-h avg 

10 PM10 (Pearson r=0.59) (Lewis et al., 2005). Inclusion of PM10 or PM2.5 in models resulted 

11 in larger changes in O3 effect estimates than those observed in other studies. As 

12 illustrated in Figure 6-9 and Table 6-13, the magnitude of change was not consistent 

13 between the two subgroups. Among subjects with a concurrent URI, O3-associated 

14 decreases in lowest daily FEV1 were robust to the inclusion of PM10 or PM2.5. Among CS 

15 users, O3 was associated a much larger decrease in FEV1 when PM10 was included in the 

16 model (Lewis et al., 2005). 

17 Studies conducted in Mexico City found small changes in O3-associated lung function 

18 decrements in copollutant models, although different averaging times were used for 

19 different pollutants (Romieu et al., 1997; Romieu et al., 1996) (Figure 6-9 and Table 6-

20 13). In these studies, O3 was moderately correlated with co-pollutants such as NO2 and 

21 PM10 (range of Pearson r = 0.38-0.58). Studies conducted in Asia also found that 

22 associations between O3 and lung function were robust to the inclusion of weakly- to 

23 moderately-correlated copollutants (Son et al., 2010; Chen et al., 1999). Copollutant 

24 effect estimates generally were attenuated, indicating that O3 may confound the results of 

25 copollutants.

26 In a summer camp study conducted in Connecticut, Thurston et al. (1997) found ambient 

27 concentrations of 1-h max O3 and 12-h avg sulfate to be highly correlated (r = 0.74), 

28 making it more difficult to separate their independent effects. With sulfate in the model, a 

29 larger decrease in PEF was estimated for O3; however, the 95% CI was much wider 

30 (Figure 6-9 and Table 6-13). Investigators found that the association between sulfate and 

31 PEF was driven by one day when the ambient concentrations of both pollutants were at 

32 their peak. With the removeal of this influential day, the sulfate effect was attenuated, 

33 whereas O3 effects remained robust (Thurston et al., 1997). Among children with asthma 

34 in Thailand, the O3-associated decrease in PEF was robust to the adjustment of SO2; 

35 however, different lags were examined for O3 (lag 5) and SO2 (lag 4) (Wiwatanadate and 

36 Trakultivakorn, 2010). Some studies did not provide quantitative results but reported that 

37 O3 effects on lung function decrements remained statistically significant in models that 
Draft – Do Not Cite or Quote 6-52 September 2011

1 included copollutants such as PM10, NO2, sulfate, nitrate, or ammonium (Romieu et al., 

2 1998a; Brauer et al., 1996; Linn et al., 1996; Spektor et al., 1988b).

Results are presented for PEF then FEV1 and then in order of increasing mean ambient ozone 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 ozone, respectively. Black circles represent 

ozone effect estimates from single pollutant models, and open circles represent ozone effect estimates from copollutant models.

Figure 6-9 Comparison of ozone-associated changes in lung function in 

single- and copollutant models.

Study

PEF

Jalaludin et al. (2000)

Neas et al. (1999)a

Thurston et al. (1997)

Romieu et al. (1996)

Romieu et al. (1997)

Population

Children with asthma

or wheeze

Children attending camp

Children with asthma

attending camp

Children with asthma

Children with asthma

O3 exposure data

24-h avg, Lag 0

24-h avg, Lag 0

24-h avg, Lag 0

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

O3 with copollutant

None

24-h avg PM10

24-h avg NO2

None

24-h avg sulfate

None

12-h avg sulfate

None

24-h avg PM2.5

None

24-h avg PM10

◄ ►

-15 -13 -11 -9 -7 -5 -3 -1 1 3

Percent change in PEF per standardized increase in O3 (95% CI)

FEV1

Lewis et al. (2005)

Chen et al. (1999)

Children with asthma

using CS

Children with asthma

with URI

Children

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

None

24-h avg PM2.5

24-h avg PM10

None

24-h avg PM2.5

24-h avg PM10

None

24-h avg NO2

◄

►

►

-15 -13 -11 -9 -7 -5 -3 -1 1 3

Percent change in FEV1 per standardized increase in O3 (95% CI)
Draft – Do Not Cite or Quote 6-53 September 2011

Table 6-13 Additional characteristics and quantitative data for studies 

presented in Figure 6-9

Study Location/

Population

O3 Exposure 

Data Parameter

O3-associated 

Percent Change in 

Single-Pollutant 

Model (95% CI)a

O3-associated Percent 

Change in Copollutant Model (95% CI)a

PEF

Jalaludin et al. 

(2000)

Sydney, Australia

Children with asthma or 

wheeze

24-h avg

Lag 0

Intraday change 

PEF

-0.57 (-1.1, -0.06) with 24-h avg PM10,

-0.57 (-1.1, -0.06)

with 24-h avg NO2

-0.55 (-0.1, -0.04)

Neas et al. (1999) Philadelphia, PA

Children attending summer 

camp

12-h avg

Lag 1

Morning PEF

-0.94 (-2.0, 0.08)

with 24-h avg sulfate

-0.02b

Thurston et al. 

(1997)

CT River Valley

Children with asthma attending 

summer camp

1-h max

Lag 0

Intraday change 

PEF -2.8 (-4.9, -0.59)

with 12-h avg sulfate

-11.8 (-31.6, 8.1)

Romieu et al. 

(1996)

Mexico City, Mexico

Children with asthma

1-h max

Lag 0

Evening PEF

-0.55 (-1.3, 0.19)

with 24-h avg PM2.5

-0.24 (-1.2, 0.68) 

Romieu et al. 

(1997)

Mexico City, Mexico

Children with asthma

1-h max

Lag 0

Evening PEF

-0.52 (-1.0, -0.01)

with 24-h avg PM10

-0.79 (-1.4, -0.16) 

FEV1

Lewis et al. 

(2005)

Detroit, MI

Children with asthma using

CS

Children with asthma with

URI

24-h avg

Lag 2

Lowest daily 

FEV1 0.29 (-4.2, 5.0)

-6.0 (-11.2, -0.41)

with 24-h avg PM2.5

-0.18 (-11.0, 11.9)

with 24-h avg PM10

-13.4 (-17.8, -8.8)

with 24-h avg PM2.5

-5.5 (-10.3, -0.42)

with 24-h avg PM10

-7.1 (-11.3, -2.8)

Chen et al. (1999) 3 Taiwan communities

Children

1-h max

Lag 1

FEV1

-1.5 (-2.8, -0.12)

with 24-h avg NO2

-2.0 (-3.5, 0.42) 

Results not included in Figure 6-9

Wiwatanadate 

and 

Trakultivakorn 

(2010)

Chiang Mai, Thailand

Children with asthma

24-h avg

Lag 5

Evening PEF 

(L/min) -2.6 (-5.2, 0) with Lag 4 SO2

-3.2 (-6.2, -0.2) 

Son et al. (2010) Ulsan, Korea

Children and adults

8-h max

Lag 0-2 avg 

(kriging)

Change in % 

predicted FEV1 -1.4 (-2.6, -0.11)

with PM10

-1.8 (-3.4, -0.25) 

CS = Corticosteroid, URI = Upper respiratory infection.

a

Results represent percent changes in lung function parameter per the following standardized increase in ambient O3

concentration: 40 ppb for 1-h max O3, 30 ppb for 8-h max or 12-h avg O3, and 20 ppb for 24-h avg O3.

1 Several studies examined multi-pollutant models that most often included O3, NO2, and 

2 either PM2.5 or PM10. Ozone exposure was associated with similar or larger magnitudes of 

3 decrease lung function in multi-pollutant models (O'Connor et al., 2008; Thaller et al., 

4 2008; Chan and Wu, 2005; Romieu et al., 2002; Korrick et al., 1998; Higgins et al., 

5 1990); however, the independent effects of O3 exposure are more difficult to assess in 

6 relation to incremental changes in more than one copollutant.
Draft – Do Not Cite or Quote 6-54 September 2011

Summary of Epidemiologic Studies of Lung Function

1 The cumulative body of epidemiologic evidence strongly supports associations between 

2 ambient O3 exposure and decrements in lung function in children, particularly, those with 

3 asthma. While little new research is available, previous AQCDs have presented 

4 epidemiologic evidence of heightened effects in children and adults exercising or 

5 working outdoors during periods of relatively low ambient O3 concentrations (Table 6-1). 

6 These epidemiologic results are well-supported by observations from controlled human 

7 exposure studies in which exposures to lower O3 concentrations induce lung function 

8 decrements when combined with exercise as compared with exposures during rest.

9 Recent epidemiologic investigation continued to focus on children with asthma, and most 

10 recent results in this population indicated associations between O3 exposure and 

11 decrements in lung function (Figures 6-6 anf 6-7 and Tables 6-7 and 6-8). Based on a 

12 small number of within-study comparisons of groups with and without asthma, larger 

13 effects were not conclusively estimated for groups with asthma. It is important to note 

14 that most of these studies were not designed to assess between-group differences, and in 

15 some studies, the high prevalence of atopy may have contributed to larger associations in 

16 subjects without asthma (Khatri et al., 2009; Barraza-Villarreal et al., 2008). A large body 

17 of previous studies demonstrated associations in children. Whereas the 2006 O3 AQCD 

18 reported weak evidence, a new study indicates that O3 exposure may be associated with 

19 decrements in lung function in older adults.

20 Across the diverse populations examined in epidemiologic studies, ambient O3 exposure 

21 was associated with 1-8% decreases in lung function per standardized increment in O3

concentration1 22 . Larger decreases (3-8%) usually were observed in children with asthma 

23 or older adults with CS use, concurrent URI, airway hyperresponsiveness, or reduced 

24 activity of antioxidant enzymes. These results indicate that common comorbid and 

25 genetic factors may increase the risk of O3-associated respiratory effects. High dietary 

26 antioxidant intake was found to attenuate O3-associated lung function decrements. Each 

27 of these potential susceptibility or protective factors has been examined in one to two 

28 populations, and further investigation in diverse populations is warranted. Heterogeneity 

29 in response also was demonstrated by observations that increases in ambient O3 exposure 

30 were associated with increased incidence of a greater than 10% decline in lung function 

31 in children with asthma (Hoppe et al., 2003; Mortimer et al., 2002). In considering the 

32 clinical significance of more subtle health outcomes such as lung function changes, it is 

33 important to note that a small shift in the population mean likely will have a 

34 disproportionate effect in the extreme ends of the distribution of lung function where 

35 these small magnitudes of decrease lead to clinically-significant airway resistance or 

 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 6-55 September 2011

1 obstruction and where individuals likely have concurrent symptoms. Several 

2 epidemiologic studies have demonstrated the clinical significance of O3-associated lung 

3 function decrements, primarily in individuals with asthma, by finding concomitant 

4 increases in respiratory symptoms (Khatri et al., 2009; Just et al., 2002; Mortimer et al., 

5 2002; Ross et al., 2002; Gielen et al., 1997; Romieu et al., 1997; Thurston et al., 1997; 

6 Romieu et al., 1996).

7 Collectively, epidemiologic studies have examined and found decreases in lung function 

8 in association with single-day O3 concentrations lagged from 0 to 7 days as well 

9 concentrations averaged over 2-10 days. A large body of evidence indicates decreases in 

10 lung function in association with O3 exposures over the duration of outdoor activity, 

11 same-day, or previous-day O3 exposures (Son et al., 2010; Alexeeff et al., 2008; Lewis et 

12 al., 2005; Ross et al., 2002; Jalaludin et al., 2000; Chen et al., 1999; Romieu et al., 1997; 

13 Brauer et al., 1996; Romieu et al., 1996; Spektor et al., 1988b). Fewer studies find 

14 associations with longer lags of ambient O3 exposures (5-7 days) (Wiwatanadate and 

15 Trakultivakorn, 2010; Hernández-Cadena et al., 2009; Steinvil et al., 2009). However, 

16 associations with multiday averages of exposure (Son et al., 2010; Liu et al., 2009a; 

17 Barraza-Villarreal et al., 2008; O'Connor et al., 2008; Alexeeff et al., 2007; Mortimer et 

18 al., 2002; Ward et al., 2002; Gold et al., 1999; Naeher et al., 1999; Neas et al., 1999)

19 indicate that exposures accumulated over several days may be important. For single- and 

20 multi-day O3 exposures, associations with lung function decrements were observed for 1-

21 h max, 8-h max, and 24-h avg O3, without a clear indication that the strength of evidence 

22 varied among the averaging times. Within studies, O3 exposure for various lag periods 

23 were associated with lung function decrements, possibly indicating that multiple modes 

24 of action may be involved in the responses. Activation of bronchial C-fibers (Section 

25 5.3.2) may lead to decreases in lung function as an immediate response to O3 exposure, 

26 and increased airway hyperresponsiveness resulting from sensitization of airways 

27 (Section 5.3.5) may mediate lung function responses associated with the lagged or 

28 multiday O3 exposures (Peden, 2011).

29 Several studies found that associations with lung function decrements persisted at lower 

30 ambient O3 concentrations. For exposures averaged up to 1 hour during outdoor activity, 

31 multiple studies in individuals engaged in outdoor activities found associations with O3

32 concentrations limited to those below 80 ppb (Spektor et al., 1988a; Spektor et al., 

33 1988b), 60 ppb (Brunekreef et al., 1994; Spektor et al., 1988a), and 50 ppb (Brunekreef et 

34 al., 1994). Among outdoor workers, Brauer et al. (1996) found a robust association with 

35 daily 1-h max O3 concentrations below 40 ppb. For 8-h average O3 exposures, 

36 associations with lung function decrements in children with asthma were found to persist 

37 at concentrations less than 80 ppb in a U.S. multicity study (for lag 1-5 avg) (Mortimer et 
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1 al., 2002) and less than 51 ppb in a study conducted in the Netherlands (for lag 2) (Gielen 

2 et al., 1997).

3 Several studies of lung function evaluated confounding by meterological factors and 

4 copollutant exposures. Most O3 effect estimates remained robust in models that adjusted 

5 for temperature, humidity, and co-pollutants such as PM2.5, PM10, NO2, or SO2. Although 

6 examined in relatively few epidemiologic studies, O3 was associated with decreases in 

7 lung function in models that included pollen or acid aerosols. The consistency of 

8 association in the collective body of evidence with and without adjustment for 

9 copollutant exposures and meterological factors combined with evidence from controlled 

10 human exposure studies for the direct effect of O3 exposure provide substantial evidence 

11 for the independent effects of ambient O3 exposure on lung function decrements.

6.2.1.3 Toxicology

12 The 2006 O3 AQCD concluded that pulmonary function decrements occur in a number of 

13 species with acute exposures (≤ 1 week), ranging from 0.25 to 0.4 ppm O3 (U.S. EPA, 

14 2006b). Early work has demonstrated that during acute exposure of ~0.2 ppm O3 in rats, 

15 the most commonly observed alterations are increased frequency of breathing and 

16 decreased tidal volume (i.e., rapid, shallow breathing). Decreased lung volumes are 

17 observed in rats with acute exposures to 0.5 ppm O3. At concentrations of ≥1 ppm, 

18 breathing mechanics (compliance and resistance) are also affected. Exposures of 6 h/day 

19 for 5 days create a pattern of attenuation of pulmonary function decrements in both rats 

20 and humans without concurrent attenuation of lung injury and morphological changes,

21 indicating that the attenuation did not result in protection against all the effects of O3

22 (Wiester et al., 1996b). A number of studies examining the effects of O3 on pulmonary 

23 function in rats, mice, and dogs are described in Table 6-13 on p. 6-91 of the 1996 O3

24 AQCD and Table AX5-11 on p. AX5-34 of the 2006 O3 AQCD (U.S. EPA, 2006b, 

1996a). Recent lung imaging studies using hyperpolarized 3 25 He provide evidence of 

26 ventilation abnormalities in rats following exposure to 0.5 ppm O3 (Crémillieux et al., 

27 2008). Rats were exposed to 0.5 ppm O3 for 2 or 6 days, either continuously (22 h/day) or 

28 alternating (12 h/day). Dynamic imaging of lung filling (2 mL/s) revealed delayed and 

29 incomplete filling of lung segments and lobes. Abnormalities were mainly found in the 

30 upper regions of the lungs and proposed due to the spatial distribution of O3 exposure 

31 within the lung. Although the small number of animals used in the study (n = 3 to 

32 7/group) makes definitive conclusions difficult, the authors suggest that the delayed 

33 filling of lung lobes or segments is likely a result of an increase in airway resistance 

34 brought about by narrowing of the peripheral small airways. 
Draft – Do Not Cite or Quote 6-57 September 2011

6.2.2 Airway Hyperresponsiveness

1 Airway hyperresponsiveness refers to a condition in which the conducting airways 

2 undergo enhanced bronchoconstriction in response to a variety of stimuli. Airway 

3 responsiveness is typically quantified by measuring changes in pulmonary function (e.g., 

4 FEV1 or specific airway resistance [sRaw]) following the inhalation of an aerosolized 

5 specific (allergen) or nonspecific (e.g., methacholine) bronchoconstricting agent or 

6 another stimulus such as exercise or cold air. Asthmatics are generally more sensitive to 

7 bronchoconstricting agents than nonasthmatics, and the use of an airway challenge to 

8 inhaled bronchoconstricting agents is a diagnostic test in asthma. Standards for airway 

9 responsiveness testing have been developed for the clinical laboratory (ATS, 2000a), 

10 although variation in methodology for administering the bronchoconstricting agent may 

11 affect the results (Cockcroft et al., 2005). There is a wide range of airway responsiveness 

12 in nonasthmatic people, and responsiveness is influenced by wide range of factors, 

13 including cigarette smoke, pollutant exposures, respiratory infections, occupational 

14 exposures, and respiratory irritants. Airways hyperresponsiveness in response to O3

15 exposure has not been examined widely in epidemiologic studies; such evidence is 

16 derived primarily from controlled human exposure and toxicological studies.

6.2.2.1 Controlled Human Exposures

17 Beyond its direct effect on lung function, O3 exposure causes an increase in airway 

18 responsiveness in human subjects as indicated by a reduction in the concentration of 

19 specific (e.g., ragweed) and non-specific (e.g., methacholine) agents required to produce 

20 a given reduction in FEV1 or increase in sRaw. Increased airway responsiveness is an 

21 important consequence of exposure to ambient O3, because the airways are then 

22 predisposed to narrowing upon inhalation of a variety of ambient stimuli including 

23 specific allergens, SO2, and cold air.

24 Increases in airway responsiveness have been reported for exposures to 80 ppb O3 and 

25 above. Horstman et al. (1990) evaluated airway responsiveness to methacholine in young 

26 healthy adults (22 M) exposed to 80, 100, and 120 ppb O3 (6.6 h, quasi continuous 

27 moderate exercise, 39 L/min). Dose-dependent decreases of 33, 47, and 55% in the 

28 cumulative dose of methacholine required to produce a 100% increase in sRaw after 

29 exposure to O3 at 80, 100, and 120 ppb, respectively, were reported. Molfino et al. (1991)

30 reported increased allergen-specific airway responsiveness in mild asthmatics exposed to 

31 120 ppb O3 (1 h resting exposure). Due to safety concerns, however, the exposures in the 

32 Molfino et al. (1991) study were not randomized with FA conducted first and O3

33 exposure second. Attempts to reproduce the findings of Molfino et al. (1991) using a 
Draft – Do Not Cite or Quote 6-58 September 2011

1 randomized exposure design have not found statistically significant changes in airway 

2 responsiveness at such low levels of O3 exposure. At a considerably higher exposure to 

3 250 ppb O3 (3 h, light-to-moderate intermittent exercise, 30 L/min), Jörres et al. (1996)

4 found significant increases in specific and non-specific airway responsiveness of mild 

5 asthmatics 3 h following O3 exposure. Kehrl et al. (1999) found increased reactivity to 

6 house dust mite antigen in mild atopic asthmatics 16-18 h after exposure to 160 ppb O3

7 (7.6 h, light quasi continuous exercise, 25 L/min). Holz et al. (2002) demonstrating that 

8 repeated daily exposure to lower concentrations of 125 ppb O3 (3 h for four consecutive 

9 days; intermittent exercise, 30 L/min) causes an increased response to allergen challenge 

10 at 20 h postexposure in allergic airway disease. 

11 O3 exposure of asthmatic subjects, who characteristically have increased airway 

12 responsiveness at baseline relative to healthy controls (by nearly two orders of 

13 magnitude), can cause further increases in responsiveness (Kreit et al., 1989). Similar 

14 relative changes in airway responsiveness are seen in asthmatics and healthy control 

15 subject exposed to O3 despite their markedly different baseline airway responsiveness. 

16 Several studies (Kehrl et al., 1999; Jorres et al., 1996; Molfino et al., 1991) have 

17 suggested an increase in specific (i.e., allergen-induced) airway reactivity. An important 

18 aspect of increased airway responsiveness after O3 exposure is that this may represent a 

19 plausible link between ambient O3 exposure and increased respiratory symptoms in 

20 asthmatics, and increased hospital admissions and ED visits for asthma. 

21 Changes in airway responsiveness after O3 exposure appear to resolve more slowly than 

22 changes in FEV1 or respiratory symptoms (Folinsbee and Hazucha, 2000). Studies 

23 suggest that O3-induced increases in airway responsiveness usually resolve 18 to 24 h 

24 after exposure, but may persist in some individuals for longer periods (Folinsbee and 

25 Hazucha, 1989). Furthermore, in studies of repeated exposure to O3, changes in airway 

26 responsiveness tend to be somewhat less susceptible to attenuation with consecutive 

27 exposures than changes in FEV1 (Gong et al., 1997a; Folinsbee et al., 1994; Kulle et al., 

28 1982; Dimeo et al., 1981). Increases in airway responsiveness do not appear to be 

29 strongly associated with decrements in lung function or increases in symptoms (Aris et 

30 al., 1995). Recently, Que et al. assessed methacholine responsiveness in healthy young 

31 adults (83M, 55 F) at one day after exposure to 220 ppb O3 and FA for 2.25 h (alternating 

32 15 min periods of rest and brisk treadmill walking). Increases in airways responsiveness 

33 at 1 day post-O3 exposure were not correlated with FEV1 responses immediately 

34 following the O3 exposure nor with changes in epithelial permeability assessed 1 day 

35 post-O3 exposure.
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6.2.2.2 Toxicology

1 In addition to human subjects, a number of species, including nonhuman primates, dogs, 

2 cats, rabbits, and rodents, have been used to examine the effect of O3 exposure on airway 

3 hyperresponsiveness. With a few exceptions, commonly used animal models have been 

4 guinea pigs, rats, or mice acutely exposed to O3 concentrations of 1 to 3 ppm to induce 

5 airway hyperresponsiveness. These animal models are helpful for determining underlying 

6 mechanisms of general airway hyperresponsiveness and are relevant for understanding 

7 airway responses in humans. Although 1-3 ppm may seem like a high exposure 

concentration, based on 18 8 O3 (oxygen-18-labeled ozone) in the BALF of humans and rats, 

9 an exposure of 0.4 ppm O3 in exercising humans appears roughly equivalent to an 

10 exposure of 2 ppm in resting rats (Hatch et al., 1994).

11 A limited number of studies have observed airway hyperresponsiveness in rodents and 

12 guinea pigs after exposure to less than 0.3 ppm O3. As previously reported in the 2006 O3

13 AQCD, one study demonstrated that a very low concentration of O3 (0.05 ppm for 4 h) 

14 induced airway hyperresponsiveness in some of the nine strains of rats tested (Depuydt et 

15 al., 1999). This effect occurred at a concentration of O3 that was much lower than has 

16 been reported to induce airway hyperresponsiveness in any other species. Similar to 

17 ozone’s effects on other endpoints, these observations suggest a genetic component plays 

18 an important role in O3-induced airway hyperresponsiveness in this species and warrants 

19 verification in other species. More recently, Chhabra and colleagues (2010) demonstrated 

20 that exposure of ovalbumin (OVA)-sensitized guinea pigs to 0.12 ppm for 2 h/day for 4 

21 weeks produced specific airway hyperresponsiveness to an inhaled OVA challenge. 

22 Interestingly, in this study , dietary supplementation of the guinea pigs with vitamins C 

23 and E ameliorated a portion of the airway hyperresponsiveness as well as indices of 

24 inflammation and oxidative stress. Larsen and colleagues did an O3 concentration25 response study in mice sensitized by 10 daily inhalation treatments with an OVA aerosol 

26 (Larsen et al., 2010). Although airway responsiveness to methacholine was increased in 

27 non-sensitized animals exposed to a single 3-h exposure to 0.5, but not 0.1 or 0.25, ppm 

28 O3, airway hyperresponsiveness was observed after exposure to 0.1 and 0.25 ppm O3 in 

29 OVA-sensitized mice. Shore and colleagues (Johnston et al., 2005b) have also 

30 demonstrated O3-induced airway hyperresponsiveness in mice after exposure to 0.3 ppm 

31 O3 for 3 hours. Mice that were exposed to the same concentration of O3 for 72 hours 

32 showed no evidence of airway hyperresponsiveness, indicating attenuation of this effect. 

33 Thus, recent toxicological studies have demonstrated that O3-induced airway 

34 hyperresponsiveness occurs in guinea pigs and mice after either acute or repeated 

35 exposure to relevant concentrations of O3.
Draft – Do Not Cite or Quote 6-60 September 2011

1 The mechanisms by which O3 enhances the airway responsiveness to either specific (e.g., 

2 OVA) or non-specific (e.g., methacholine) bronchoprovocation are not clear, but appear 

3 to be associated with complex cellular and biochemical changes in the conducting 

4 airways. Considerable research effort has been directed towards exploring the causes of 

5 O3-induced airway hyperresponsiveness, but the majority of such studies have been 

6 conducted at high concentrations of O3. It is clear that inflammation plays a key role in 

7 O3-induced airway hyperresponsiveness, although the precise mediators and cells that are 

8 involved have not been identified at relevant concentrations of O3. Because inflammation 

9 is likely to play a role in O3-induced airway hyperresponsiveness, the mechanism for this 

10 response may be multifactorial, involving the presence of cytokines, prostanoids, or 

11 neuropeptides; activation of macrophages, eosinophils, or mast cells; and epithelial 

12 damage that increases direct access of mediators to the smooth muscle or receptors in the 

13 airways that are responsible for reflex bronchoconstriction. Johnston et al. (2005b)

14 demonstrated that airway hyperresponsiveness occurred in both wild type and IL-6 

15 knockout mice exposed to 0.3 ppm O3 despite reduction in markers of lung injury and 

16 inflammation in O3-exposed IL-6 knockout mice. This same group of investigators has 

17 demonstrated the involvement of natural killer T cells, obesity, CXCR2, leptin, and IL-17 

18 in O3-induced airway hyperresponsiveness at exposure concentrations of 1-3 ppm O3

19 (Garantziotis et al., 2010; Voynow et al., 2009; Pichavant et al., 2008; Williams et al., 

20 2007b; Lu et al., 2006; Johnston et al., 2005a; Shore et al., 2003). A recent study 

21 demonstrated a role for mindin, an extracellular matrix protein, in the AHR response 

22 resulting from acute exposure to 1 ppm O3 (Frush et al., In Press). Thus, a number of 

23 potential mediators and cells may play a role in O3-induced airway hyperresponsiveness; 

24 mechanistic studies are discussed in greater detail in Chapter 5. 

25 In order to evaluate the ability of O3 to enhance specific and non-specific airway 

26 responsiveness, it is important to take into account the phenomenon of attenuation in 

27 ozone’s effects. Several studies have clearly demonstrated that some effects caused by 

28 acute exposure are absent after repeated exposures to O3. The ability of the pulmonary 

29 system to adapt to repeated insults to O3 is complex, however, and experimental findings 

30 for attenuation to O3-induced airway hyperresponsiveness are inconsistent. As described 

31 above, airway hyperresponsiveness was observed in mice after a 3-h exposure but not in 

32 mice exposed continuously for 72 hours to 0.3 ppm (Johnston et al., 2005b). However, 

33 the Chhabra study demonstrated O3-induced airway hyperresponsiveness in guinea pigs 

34 exposed for 2 h/day for 10 days (Chhabra et al., 2010). Besides the obvious species 

35 disparity, these studies differ in that the mice were exposed continuously for 72 hours, 

36 whereas the guinea pigs were exposed intermittently over 10 days, suggesting that 

37 attenuation might be lost with periods of rest in between O3 exposures. 
Draft – Do Not Cite or Quote 6-61 September 2011

6.2.3 Pulmonary Inflammation, Injury and Oxidative Stress 

1 In addition to physiological pulmonary responses, respiratory symptoms, and airway 

2 hyperresponsiveness, O3 exposure has been shown to result in increased epithelial 

3 permeability and respiratory tract inflammation. In general, inflammation can be 

4 considered as the host response to injury and the induction of inflammation as evidence 

5 that injury has occurred. Inflammation induced by exposure of humans to O3 can have 

6 several potential outcomes: (1) inflammation induced by a single exposure (or several 

7 exposures over the course of a summer) can resolve entirely; (2) continued acute 

8 inflammation can evolve into a chronic inflammatory state; (3) continued inflammation 

9 can alter the structure and function of other pulmonary tissue, leading to diseases such as 

10 fibrosis; (4) inflammation can alter the body’s host defense response to inhaled 

11 microorganisms, particularly in potentially susceptible populations such as the very 

12 young and old; and (5) inflammation can alter the lung’s response to other agents such as 

13 allergens or toxins. Except for outcome (1), the possible chronic responses have only 

14 been directly observed in animals exposed to O3. It is also possible that the profile of 

15 response can be altered in persons with preexisting pulmonary disease (e.g. asthma, 

16 COPD) or smokers. Oxidative stress has been shown to play a key role in initiating and 

17 sustaining O3-induced inflammation. Secondary oxidation products formed as a result of 

18 reactions between O3 and components of the ELF can increase the expression of 

19 cytokines, chemokines, and adhesion molecules and enhance airway epithelium 

20 permeability (Sections 5.3.3. and 5.3.4.).

6.2.3.1 Controlled Human Exposures

21 As reported in studies reviewed in the 1996 and 2006 O3 AQCDs, acute O3 exposure 

22 initiates an acute inflammatory response throughout the respiratory tract which has been 

23 observed to persist for at least 18-24 hours postexposure. A meta-analysis of 21 studies 

24 (Mudway and Kelly, 2004a) showed that neutrophils (PMN) influx in healthy subjects 

25 was linearly associated (p<0.01) with total O3 dose (i.e., the product of O3 concentration, 

26 exposure duration, and VE). As with FEV1 responses to O3, within individual 

27 inflammatory responses to O3 are generally reproducible and correlated between repeat 

28 exposures (Holz et al., 1999). Some individuals also appear to be intrinsically more 

29 susceptible to increased inflammatory responses to O3 exposure (Holz et al., 2005). 

30 The presence of PMNs in the lung has long been accepted as a hallmark of inflammation 

31 and is an important indicator that O3 causes inflammation in the lungs. Neutrophilic 

32 inflammation of tissues indicates activation of the innate immune system and requires a 

33 complex series of events which are normally followed by processes that clear the 
Draft – Do Not Cite or Quote 6-62 September 2011

1 evidence of acute inflammation. Inflammatory effects have been assessed in vivo by 

2 lavage (proximal airway and bronchoalveolar), bronchial biopsy, and more recently, 

3 induced sputum. A single acute exposure (1-4 hours) of humans to moderate 

4 concentrations of O3 (0.2-0.6 ppm) while exercising at moderate to heavy intensities 

5 results in a number of cellular and biochemical changes in the lung, including an 

6 inflammatory response characterized by increased numbers of PMNs, increased 

7 permeability of the epithelial lining of the respiratory tract, cell damage, and production 

8 of proinflammatory cytokines and prostaglandins (U.S. EPA, 2006b). These changes also 

9 occur in humans exposed to 80 and 100 ppb O3 for 6-8 hours (Alexis et al., 2010; Peden 

10 et al., 1997; Devlin et al., 1991). Soluble mediators of inflammation such as the cytokines 

11 (e.g., IL-6, IL-8) and arachidonic acid metabolites (e.g., prostaglandin [PG]E2, PGF2α, 

12 thromboxane, and leukotrienes [LTs] such as LTB4) have been measured in the BALF of 

13 humans exposed to O3. In addition to their role in inflammation, many of these 

14 compounds have bronchoconstrictive properties and may be involved in increased airway 

15 responsiveness following O3 exposure. The possible relationship between repetitive bouts 

16 of acute inflammation in humans caused by O3 and the development of chronic 

17 respiratory disease is unknown. 

18 Studies reviewed in the 2006 O3 AQCD reported that inflammatory responses do not 

19 appear to be correlated with lung function responses in either asthmatic or healthy 

20 subjects. In healthy adults (14 M, 6 F) and asthmatic (12 M, 6 F) volunteers exposed to 

21 200 ppb O3 (4 h with moderate quasi continuous exercise, VE = 44 L/min), percent PMN 

22 and total protein in BAL fluids were significantly increased in the asthmatics relative to 

23 the healthy controls. Spirometric measures of lung function were significantly decreased 

24 following the O3 exposure in both groups, but were not significantly different between 

25 the asthmatic and healthy subjects. Effects of O3 on PMN and total protein were not 

26 correlated with changes in FEV1 or FVC (Balmes et al., 1997; Balmes et al., 1996). 

27 Devlin et al. (1991) exposed healthy adults (18 M) to 80 and 100 ppb O3 (6.6 h with 

28 moderate quasi continuous exercise, 40 L/min). In BAL fluid collected 18 h after 

29 exposure to 100 ppb O3, significant increases in PMNs, protein, PGE2, fibronectin, IL-6, 

30 lactate dehydrogenase, and α-1 antitrypsin compared to FA. Similar but smaller increases 

31 in all mediators were found after exposure to 80 ppb O3 except for protein and 

32 fibronectin. Changes in BAL markers were not correlated with changes in FEV1. Holz et 

33 al. (1999) examined inflammatory responses in healthy (n=21) and asthmatic (n=15) 

34 subjects exposed to 125 and 250 ppb O3 (3 h, light intermittent exercise, 26 L/min). 

35 Significantly increased percent PMN in sputum due to O3 exposure was observed in both 

36 asthmatics and healthy subjects following the 250 ppb exposure. At the lower, 125 ppb 

37 exposure, only the asthmatic group experienced statistically significantly increases in the 

38 percent PMN. Significant decrements in FEV1 were only found following exposure to 

39 250 ppb; these changes in FEV1 did not differ significantly between the asthmatic and 
Draft – Do Not Cite or Quote 6-63 September 2011

1 healthy groups, nor were changes in FEV1 correlated with changes in PMN levels. In 

2 contrast to these earlier findings, Vagaggini et al. (2010) recently reported a significant 

3 (r=0.61, p=0.015) correlation between changes in FEV1 and changes in sputum 

4 neutrophils in mild-to-moderate asthmatics (n=23; 33 ± 11 years) exposed to 300 ppb O3

5 for 2 hours with moderate exercise. 

6 The time course of the inflammatory response to O3 in humans has not been fully 

7 characterized. Different markers exhibit peak responses at different times. Studies in 

8 which lavages were performed 1 hour after O3 exposure (1 h at 0.4 ppm or 4 h at 

9 0.2 ppm) have demonstrated that the inflammatory responses are quickly initiated (Torres 

10 et al., 1997; Devlin et al., 1996; Schelegle et al., 1991). Inflammatory mediators and 

11 cytokines such as IL-8, IL-6, and PGE2 are greater at 1 h than at 18 h post-O3 exposure 

12 (Torres et al., 1997; Devlin et al., 1996). However, IL-8 still remained elevated at 18 h 

13 post-O3 exposure (4 h at 0.2 ppm O3 versus FA) in healthy subjects (Balmes et al., 1996). 

14 Schelegle et al. (1991) found increased PMNs in the “proximal airway” lavage at 1, 6, 

15 and 24 hours after O3 exposure (4 h at 0.2 ppm O3), with a peak response at 6 hours. 

16 However, at 18-24 hours after O3 exposure, PMNs remain elevated relative to 1 hour 

17 postexposure (Torres et al., 1997; Schelegle et al., 1991). 

18 Alexis et al. (2010) recently reported that a 6.6-hour exposure with moderate exercise to 

19 80 ppb O3 caused increased sputum neutrophil levels at 18 hours postexposure in young 

20 healthy adults (n=15; 24 ± 1 years). In a prior study, Alexis et al. (2009) found genotype 

21 effects on inflammatory responses but not lung function responses to a 2 h-exposure to 

22 400 ppb O3. At 4 h post O3 exposure, both GSTM1 genotypes had significant increases in 

23 sputum neutrophils with a tendency for a greater increase in GSTM1-sufficient than null 

24 individuals. At 24 h postexposure, neutrophils had returned to baseline levels in the 

25 GSTM1-sufficient individuals. In the GSTM1-null subjects, however, neutrophil levels 

26 increased further from 4 h to 24 h and were significantly greater than both baseline levels 

27 and 24 h levels in GSTM1-sufficient individuals. Alexis et al. (2009) found that GSTM1-

28 sufficient individuals (n=19; 24 ± 3 years) had a decrease in macrophage levels at 4-

29 -24 hours postexposure to 400 ppb O3 for 2 h with exercise. These studies also provide 

30 evidence for activation of innate immunity and antigen presentation, as discussed in 

31 Section 5.3.6. Effects of the exposure apart from O3 cannot be ruled out in the Alexis et 

32 al. (2010; 2009) studies, however, since no FA exposure was conducted. 

33 Kim et al. (2011) has more recently shown a significant (p < 0.001) increase in sputum 

34 neutrophil levels following a 6.6-hour exposure to 60 ppb O3 relative to FA in young 

35 healthy adults (13 F, 11 M; 25.0 ± 0.5 years). There was no significant effect of GSTM1 

36 genotype (half GSTM1-null) on the inflammatory responses observed in these 
Draft – Do Not Cite or Quote 6-64 September 2011

1 individuals. Previously, inflammatory responses had only been evaluated down to a level 

2 of 80 ppb O3. 

3 Inflammatory responses to O3 exposure have also been studied in asthmatic subjects 

4 (Peden et al., 1997; Scannell et al., 1996; Basha et al., 1994). In these studies, asthmatics 

5 showed significantly more neutrophils in BALF (18 hours postexposure) than did 

6 similarly exposed healthy individuals. In one of these studies (Peden et al., 1997), which 

7 included only allergic asthmatics who tested positive for Dematophagoides farinae 

8 antigen, there was an eosinophilic inflammation (twofold increase), as well as 

9 neutrophilic inflammation (threefold increase). In a study of subjects with intermittent 

10 asthma exposed to 0.4 ppm O3 for 2 hours, increases in eosinophil cationic protein, 

11 neutrophil elastase and IL-8 were found to be significantly increased 16 hours 

12 postexposure and comparable in induced sputum and BALF (Hiltermann et al., 1999). 

13 Scannell et al. (1996) also reported that IL-8 tends to be higher in the BALF of 

14 asthmatics compared to nonasthmatics following O3 exposure, suggesting a possible 

15 mediator for the significantly increased neutrophilic inflammation in those subjects. 

16 Bosson et al. (2003) found significantly greater epithelial expression of IL-5, IL-8, 

17 granulocyte-macrophage colony-stimulating factor and epithelial cell-derived neutrophil18 activating peptide-78 in asthmatics compared to healthy subjects following exposure to 

19 0.2 ppm O3 for 2 h. In contrast, Stenfors et al. (2002) did not detect a difference in the O3-

20 induced increases in neutrophil numbers between 15 mild asthmatic and 15 healthy 

21 subjects by bronchial wash at the 6 h postexposure time point. However, the asthmatics 

22 were on average 5 years older than the healthy subjects in this study, and it is not yet 

23 known how age affects inflammatory responses. It is also possible that the time course of 

24 neutrophil influx differs between healthy and asthmatic individuals. Differences between 

25 asthmatics and healthy subjects in ozone-mediated activation of innate and adaptive 

26 immune responses have been observed in two studies (Hernandez et al., 2010; Bosson et 

27 al., 2003), as discussed in Sections 6.2.5.4 and 5.4.2.2. 

28 Vagaggini et al. (2002) investigated the effect of prior allergen challenge on responses in 

29 mild asthmatics exposed for 2 h to 0.27 ppm O3 or filtered air. At 6 h postexposure, 

30 eosinophil numbers in induced sputum were found to be significantly greater after O3

31 than after air exposures. Studies such as this suggest that the time course of eosinophil 

32 and neutrophil influx following O3 exposure can occur at levels detectable within the 

33 airway lumen by as early as 6 h. They also suggest that the previous or concurrent 

34 activation of proinflammatory pathways within the airway epithelium may enhance the 

35 inflammatory effects of O3. For example, in an in vitro study of primary human nasal 

36 epithelial cells and BEAS-2B cell line, cytokine production induced by rhinovirus 

37 infection was enhanced synergistically by concurrent exposure to O3 at 0.2 ppm for 3 

38 hours (Spannhake et al., 2002). 
Draft – Do Not Cite or Quote 6-65 September 2011

1 Markers from BALF following both 2 hours (Devlin et al., 1997) and 4 hours (Jorres et 

2 al., 2000; Christian et al., 1998) repeated O3 exposures (up to 5 days) indicate that there is 

3 ongoing cellular damage irrespective of the attenuation of some cellular inflammatory 

4 responses of the airways, pulmonary function, and symptom responses. Devlin et al. 

5 (1997) found that several indicators of inflammation (e.g., PMN, IL-6, PGE2, fibronectin) 

6 were attenuated after 5 days of exposure (i.e., values were not different from FA). 

7 However, other markers (LDH, IL-8, total protein, epithelial cells) did not show 

8 attenuation, suggesting that tissue damage probably continues to occur during repeated 

9 exposure. Some cellular responses did not return to baseline levels for more than 10-20 

10 days following O3 exposure. Christian et al. (1998) showed decreased numbers of 

11 neutrophils and a decrease in IL-6 levels in healthy adults after 4 days of exposure versus 

12 the single exposure to 0.2 ppm O3 for 4 h. Jörres et al. (2000) also found both functional 

13 and BALF cellular responses to O3 were abolished at 24 hours postexposure following 

14 the fourth exposure day. However, levels of total protein, IL-6, IL-8, reduced glutathione 

15 and ortho-tyrosine was still increased significantly. In addition, visual scores 

16 (bronchoscopy) for bronchitis and erythema and the numbers of neutrophils in bronchial 

17 mucosal biopsies were increased. Results indicate that, despite an attention of some 

18 markers of inflammation in BALF and pulmonary function decrements, inflammation 

19 within the airways persists following repeated exposure to O3. The continued presence of 

20 cellular injury markers indicates a persistent effect that may not necessarily be recognized 

21 due to the attenuation of spirometric and symptom responses. 

22 A number of studies show that O3 exposures increase epithelial cell permeability through 

direct (technetium-99m labeled diethylene triamine pentaacetic acid, 99m 23 Tc-DTPA, 

24 clearance) and indirect (e.g., increased BALF albumin, protein) techniques. Kehrl et al. 

(1987) showed increased 99m 25 Tc-DTPA clearance in healthy young adults at 75 minutes 

26 postexposure to 0.4 ppm O3 for 2 hours. Foster and Stetkiewicz (1996) have shown that 

increased 99m 27 Tc-DTPA clearance persists for at least 18-20 hours post-O3 exposure (130 

28 minutes to average O3 concentration of 0.24 ppm), and the effect is greater at the lung 

29 apices than at the base. Increased BALF protein, suggesting O3-induced changes in 

30 epithelial permeability, have also been reported at 1 hour and 18 hours postexposure 

31 (Devlin et al., 1997; Balmes et al., 1996). Meta-analysis of results from 21 publications 

32 (Mudway and Kelly, 2004a), showed that increased BALF protein is associated with total 

33 inhaled O3 dose (i.e., the product of O3 concentration, exposure duration, and VE). 

34 It has been postulated that changes in permeability associated with acute inflammation 

35 may provide increased access of inhaled antigens, particles, and other inhaled substances 

36 deposited on lung surfaces to the smooth muscle, interstitial cells, and the blood. Hence, 

37 increases in epithelial permeability following O3 exposure might lead to increases in 

38 airway responsiveness to specific and nonspecific agents. Que et al. investigated this 
Draft – Do Not Cite or Quote 6-66 September 2011

1 hypothesis in healthy young adults (83M, 55 F) exposed to 220 ppb O3 for 2.25 h 

2 (alternating 15 min periods of rest and brisk treadmill walking). As has been observed by 

3 others for FEV1 responses, within individual changes in permeability were correlated 

4 between sequential O3 exposures. This indicates differences in susceptibility to epithelial 

5 damage from O3 exposure among individuals. Increases in epithelial permeability at 1 

6 day post-O3 exposure were not correlated with FEV1 responses immediately following 

7 the O3 exposure nor with changes in airway responsiveness to methacholine in assessed 1 

8 day post-O3 exposure. The authors concluded that changes in FEV1, permeability, and 

9 airway responsiveness following O3 exposure were relatively constant over time in young 

10 healthy adults; although, these responses appear to be mediated by differing physiologic 

11 pathways. 

6.2.3.2 Epidemiology

12 In the 2006 O3 AQCD, epidemiologic evidence of changes in pulmonary inflammation in 

13 association with short-term ambient O3 exposure (30-min or 1-h max) was limited to 

14 observations of increases in nasal lavage levels of inflammatory cell counts, eosinophilic 

15 cationic protein, and myeloperoxidases (U.S. EPA, 2006b). As a result of the 

16 development of less invasive methods to collect exhaled breath samples repeatedly from 

17 individuals in the field, the number of studies assessing ambient O3-related changes in 

18 lower airway inflammation and oxidative stress in recent years has increased 

19 dramatically. Although most of the biomarkers examined in these studies were not 

20 specific to the lung, most studies collected exhaled breath, exhaled breath condensate 

21 (EBC), nasal lavage fluid, or induced sputum with the aim of monitoring inflammatory 

22 responses in airways, as opposed to monitoring systemic responses in blood. These recent 

23 studies form a larger base to establish coherence with findings from human experimental 

24 and animal toxicological studies that have measured similar or related endpoints and

25 provide further biological plausibility for associations of ambient O3 exposure with

26 respiratory symptoms and lung function decrements. These biological markers also allow 

27 the assessment of short-term O3-related acute respiratory effects in populations that are 

28 less likely to experience respiratory symptoms, including healthy populations and groups 

29 with increased outdoor exposures. 
Draft – Do Not Cite or Quote 6-67 September 2011

Table 6-14 Mean and upper percentile ozone concentrations in studies 

examining biological markers of pulmonary inflammation and 

oxidative stress

Study Location Years

O3

Averaging 

Time

Mean/Median

Concentration (ppb)

Upper Percentile 

Concentrations (ppb)

Qian et al. 

(2009)

Boston, MA; New York, NY; 

Denver, CO; Philadelphia, PA; 

San Francisco, CA; Madison, WI 

(SOCS)

1997-1999

All-year

8-h max 33.6 75th: 44.4, Max: 91.5

Khatri et al. 

(2009)

Atlanta, GA 2003, 2005, 

2006

Warm season

8-h max 59a Max: 73a

Ferdinands et al. 

(2008)

Atlanta, GA 2004

Warm season

1-h max 61 (median) 75th: 67

Adamkiewicz et 

al. (2007)

Steubenville, OH 2000

Cold season

24-h avg

1-h avgb

15.3

19.8

75th: 20.2, Max: 32.2

75th: 27.5, Max: 61.6

Berhane et al. 

(2011)

13 Southern California 

Communities

September 

2004- June 

2005

8-h avg

(10:00 a.m. -

6:00 p.m.)

NR NR

Delfino et al. 

(2010a)

Los Angeles, CA 2005-2007

All-year

24-h avg Warm season: 33.3

Cool season: 20.6

Max: 76.4

Max: 44.9

Liu et al. (2009a) Windsor, ON, Canada 2005

Cold season

24-h avg 13.0 95th: 26.5

Sienra-Monge et 

al. (2004)

Mexico City, Mexico 1999-2000

All-year

8-h max 66.2 Max: 142.5

BarrazaVillarreal et al. 

(2008)

Mexico City, Mexico 2003-2005

All-year

8-h max 31.6 Max (8-h max): 86.3

Romieu et al. 

(2008)

Mexico City, Mexico 2004

All-year

8-h max 31.1 75th: 38.3

Max: 60.7

Nickmilder et al. 

(2007)

southern Belgium 2002

Warm season

1-h max

8-h max

NR

NR

Max (across 6 camps):

24.5-112.7c

Max (across 6 camps):

18.9-81.1c

Chimenti et al. 

(2009)

Sicily, Italy NR

All-year

8-h avg 

(7:00 a.m.-

3:00 p.m.)

Fall: 32.7 (pre-race), 35.1 

(race)c

Winter: 37.0 (pre-race), 

30.8 (race)c

Summer: 51.2 (pre-race), 

46.1 (race)c

NR

Max = Maximum, NR = Not Reported.

a

Individual-level exposure estimates were derived based on time spent in the vicinity of various O3 monitors.

b

Average O3 oncentration in the 1 h preceding eNO collection.

c

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 6-68 September 2011

Results are presented first for children with asthma followed by results for adults with asthma and older adults. Effect estimates 

are from single-pollutant models and are standardized to a 30-ppb increase for 8-h max or 8-h avg ozone exposures and a 20-ppb 

increase for 24-h avg ozone exposures.

Figure 6-10 Percent change in exhaled nitric oxide (eNO) per standardized 

increment in ambient ozone exposure in studies of individuals with 

and without asthma.

Study

Individuals with asthma

Liu et al. (2009)

Barraza-Villarreal et al. 

(2008)

Qian et al. (2009)

Berhane et al. (2011)

Khatri et al. (2009)

Older adults

Adamkiewicz et al. (2004)

Delfino et al. (2010)

Population

Children with asthma

Children

Children and adults

with asthma

Children

Adults with asthma

Older adults

Older adults

O3 Lag

0

0

0

0-22 cum avg

2

0

0-4 avg

Subgroup

Without asthma

With asthma

Without asthma

With asthma

Without allergy

With allergy

Cool season

Warm season

◄

◄

►

►

►

►

-20 -10 0 10 20 30 40 50

Percent change in eNO per standardized increment in O3

(95% CI)
Draft – Do Not Cite or Quote 6-69 September 2011

Table 6-15 Additional characteristics and quantitative data for studies 

represented in Figure 6-10

Study Location/

Population O3 Lag O3 Averaging Time Subgroup

Standardized 

Percent Change 

(95% CI)a

Studies in individuals with asthma

Liu et al. (2009a) Windsor, ON, Canada

Children with asthma

0 24-h avg -17.0 (-30.3, -1.1)

Barraza-Villarreal et al. (2008) Mexico City, Mexico

Children

0 8-h max Without asthma

With asthma

13.5 (11.2, 15.8)

6.2 (6.0, 6.5)

Berhane et al. (2011) 12 Southern California communities

Children

0-22 cum avg 8-h avg

(10:00 a.m.-6:00 p.m.)

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) 6 U.S. communities 

Children and adults with asthma

0 8-h max -1.2 (-1.7, -0.64)

Khatri et al. (2009) Atlanta, GA

Adults with asthma

2 8-h max 36.6 (1.2, 71.9)

Studies in older adults

Adamkiewicz et al. (2007) Steubenville, Ohio

Older adults

0 24-h avg -5.7 (-25.9, 14.5)

Delfino et al. (2010a) Los Angeles, CA

Older adults

0-4 avg 24-h avg Cool season

Warm season

23.6 (7.3, 39.9)

-0.58 (-13.4, 12.3)

a

Effect estimates are standardized to a 30-ppb increase for 8-h max or 8-h avg O3 and a 20-ppb increase for 24-h avg O3.

Table 6-16 Associations between short-term ambient ozone exposure and 

biological markers of pulmonary inflammation and oxidative stress

Study Location/

Population

O3

Lag

O3 Averaging 

Time Biological Marker Subgroup Effect Estimate 

(95% CI)a

Liu et al. (2009a) Windsor, ON, Canada

Children with asthma

0 24-h avg EBC 8-isoprostane (%

change)

EBC TBARS (% 

change)

10.2 (-9.2, 33.5)

7.2 (-18.3, 40.7)

Romieu et al. (2008) Mexico City, Mexico

Children with asthma

0 8-h max EBC MDAb 1.3 (1.0, 1.7)

Barraza-Villarreal et al. 

(2008)

Mexico City, Mexico

Children

0 8-h max Nasal lavage IL-8 

(pg/ml)

EBC pH

Without asthma

With asthma

Without asthma

With asthma

1.6 (1.4, 1.8)

1.6 (1.4, 1.9)

-0.10 (-0.27, 0.08)c

-0.10 (-0.20, 0.01)c

Sienra-Monge et al. 

(2004)

Mexico City, Mexico

Children with asthma

0-2 avg 8-h max Nasal lavage IL-8b

Nasal lavage IL-6b

Nasal lavage Uric acidb

Nasal lavage GSxb

Placebo

Antioxidant

Placebo

Antioxidant

Placebo

Antioxidant

Placebo

Antioxidant

1.4 (1.0, 2.0)

1.0 (0.70, 1.5)

1.5 (1.2, 2.0)

1.0 (0.76, 1.4)

0.88 (0.70, 1.1)

1.1 (0.84, 1.5)

0.90 (0.82, 0.99)

0.91 (0.83, 0.98)

Khatri et al. (2009) Atlanta, GA

Adults with asthma

2 8-h max Blood eosinophils (% 

change)

2.4 (0.62, 4.2)

Ferdinands et al. 

(2008)

Atlanta, GA

Children exercising 

outdoors

0 1-h max EBC pH 2.5 (-0.20, 5.1)c

EBC = exhaled breath condensate, TBARS = thiobarbituric acid reactive substances, MDA = malondialdehyde, IL-8 = interleukin 8, IL-6 = 

interleukin 6, Antioxidant=group supplemented with vitamins C and E, GSx = glutathione.

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

Models analyzed log-transformed biological markers. Therefore, effect estimates represent the ratio of the geometric means of biological 

markers for a standardized increase in O3 exposure. An estimate less than 1 indicates a decrease in pulmonary inflammation or oxidative stress for 

an increase in O3 exposure, and an estimate greater than 1 indicates an increase in pulmonary inflammation or oxidative stress for an increase in 

O3 exposure.

c

Negative and positive effect estimates indicate increases and decreases in pulmonary inflammation, respectively.
Draft – Do Not Cite or Quote 6-70 September 2011

1 Despite the strengths of biomarker studies, it is important to note that research in this 

2 field continues to develop, and several uncertainties are recognized that may limit the 

3 interpretations of associations between ambient O3 exposure and changes in biomarker 

4 levels. Current areas of development include examination of the clinical relevance of the 

5 observed magnitudes of changes in biological markers of pulmonary inflammation 

6 (Murugan et al., 2009; Duramad et al., 2007), characterization of the time course of 

7 changes between biomarker levels and other endpoints of respiratory morbidity, 

8 development of standardized methodologies for collection, improvement of the 

9 sensitivity and specificity of assay methods, and characterization of subject factors (e.g., 

10 asthma severity and recent medication use) that contribute to inter-individual variability. 

11 These sources of uncertainty may contribute to differences in findings among studies.

12 In recent epidemiologic studies, the biomarker most frequently measured was exhaled 

13 nitric oxide (eNO), likely related to its ease of collection in the field and automated 

14 measurement. Other biological media analyzed included EBC, induced sputum, and nasal 

15 lavage fluid, all of which are hypothesized to contain aerosolized particles and/or cells 

16 from fluid lining the lower and upper airways (Balbi et al., 2007; Howarth et al., 2005; 

17 Hunt, 2002). These fluids contain cytokines, cells, and markers of oxidative stress that 

18 mediate inflammatory responses. In particular, several of the cytokines, cells, and 

19 markers of oxidative stress examined in epidemiologic studies also have been examined 

20 in controlled human exposure and toxicological studies.Table 6-14 presents the 

21 characteristics and ambient O3 concentration data from recent studies assessing 

22 associations between O3 exposure and biological markers of pulmonary inflammation and 

23 oxidative stress. Many recent studies reported positive associations between short-term 

24 ambient O3 exposure and increases in pulmonary inflammation and oxidative stress, in 

25 particular, studies of children with asthma conducted in Mexico City (Figure 6-10 and 

26 Tables 6-15 and 6-16).

Populations with Asthma

Exhaled Nitric Oxide

27 Nitric oxide or eNO has not been examined in controlled human exposure or 

28 toxicological studies of O3 exposure. However, several lines of evidence support its 

29 analysis as an indicator of pulmonary inflammation in epidemiologic studies. Inducible 

30 nitric oxide synthase can be activated by pro-inflammatory cytokines, and NO can be 

31 produced by cells such as neutrophils, eosinophils, and epithelial cells in the lung during 

32 an inflammatory response (Barnes and Liew, 1995). Additional support is provided by 

33 observations of higher eNO in individuals with asthma, and increases in the levels during 

34 acute exacerbations (Jones et al., 2001; Kharitonov and Barnes, 2000).
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1 As indicated in Figure 6-10 and Table 6-15, several studies found that short-term ambient 

2 O3 exposure (8-h max or avg) was associated with increases in eNO in children with 

3 asthma. Liu et al. (2009a) (described in Section 6.2.1.2) reported O3-associated decreases 

4 in eNO; however, this study was restricted to winter months. In this study, results for 

5 EBC levels of TBARS and 8-isoprostane as well as lung function did not provide strong 

6 evidence of O3 effects on airway oxidative stress. 

7 The two studies that compared children with and without asthma did not find larger O3-

8 associated increases in eNO in children with asthma (Figure 6-10 and Table 6-15). 

9 Among children in Southern California, Berhane et al. (2011) examined a 0-22 day 

10 cumulative average of 8-h avg (10:00 a.m.-6:00 p.m.) O3 and estimated similar effects for 

11 children with and without asthma and children with and without allergy. Among children 

12 in Mexico City, Barraza-Villarreal et al. (2008) examined lag 0 of 8-h max O3 and 

13 estimated larger effects for children without asthma. 

14 In the two studies that included adults with asthma, ambient O3 exposure was associated 

15 with both decreases and increases in eNO (Khatri et al., 2009; Qian et al., 2009). In the 

16 multicity salmeterol (β-2 adrenergic agonist) trial (Boston, MA; New York, NY; Denver, 

17 CO; Philadelphia, PA; San Francisco, CA; and Madison, WI), eNO was collected every 

18 2-4 weeks over a 16-week period from 119 subjects with persistent asthma, 87% of 

19 whom were 20-65 years of age (Qian et al., 2009). Among all subjects, lag 0 of 8-h max 

20 O3 was associated with a decrease in eNO as were exposures lagged 1 to 3 days and 

21 averaged over 5 days. Results did not vary among the salmeterol, CS, and placebo 

22 groups, indicating that the counterintuitive findings for O3 were not simply due to the 

23 reduction of inflammatory responses by medication use. The authors suggested that at 

24 higher O3 exposures, O3 may rapidly react with NO in airways to form reactive nitrogen 

25 species such as peroxynitrite. However, in the other study of adults with asthma, ambient 

26 concentrations of 8-h max O3 were higher, and a positive association was found with 

27 eNO (Khatri et al., 2009). In this study conducted during a summer season in Atlanta, 

28 GA, a 30-ppb increase in lag 2 of 8-h max O3 was associated with a 36.6% increase in 

29 eNO (95% CI: 1.2, 71.9). These findings should be interpreted with caution as they were 

30 based on a single eNO measurement per subject and were not adjusted for any 

31 meteorological factors.

Other biological markers of pulmonary inflammation and oxidative stress

32 As indicated in Table 6-16, studies have found associations between short-term ambient 

33 O3 exposure and changes in the levels of proinflammatory cytokines and cells, indicators 

34 of oxidative stress, and antioxidants. Importantly, any particular endpoint was examined 

35 only in one to two studies, and the evidence in individuals with asthma is derived 

36 primarily from studies conducted in Mexico City (Romieu et al., 2009; Barraza-Villarreal 
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1 et al., 2008; Romieu et al., 2008; Sienra-Monge et al., 2004). Despite the limited 

2 evidence, the epidemiologic observations are well-supported by controlled human 

3 exposure and toxicological studies that have measured analogous endpoints. 

4 Several of the modes of action of O3 are mediated by secondary oxidation products 

5 produced in the airways by O3 (Section 5.3.3). Reactive oxygen species (ROS) are 

6 involved in the regulation of inflammation via regulation of the expression of cytokines 

7 and activity of inflammatory cells in airways (Heidenfelder et al., 2009). In controlled 

8 human exposure and toxicological studies, prostaglandins have been frequently measured 

9 to indicate O3-induced increases in oxidative stress (Sections 5.3.3 and 6.2.3.1). 

10 Prostaglandins are produced by the peroxidation of arachidonic acid in cell membranes 

11 (Morrow et al., 1990). Romieu et al. (2008) analyzed biweekly samples of EBC 

12 malondialdehyde (MDA), a thiobarbituric acid reactive substance, which like 

13 prostaglandins, is derived from oxidative degradation of lipids (Janero, 1990). The ratio 

14 of the geometric means of MDA was 1.3 (1.0, 1.7) per a 30-ppb increase in lag 0 of 8-h 

15 max O3. Similar results were reported for lags 1 and 0-1 average exposures. An important 

16 limitation of the study was that 25% of EBC samples had nondetectable levels of MDA. 

17 Thus, the random assignment of concentrations between 0 and 4.1 nmol may have 

18 contributed random measurement error to the estimated O3 effects. Because MDA 

19 represents less than 1% of lipid peroxides and is present at low concentrations, its 

20 reliability as a marker of oxidative stress in vivo has been questioned. However, Romieu 

21 et al. (2008) pointed to their observations of statistically significant associations of EBC 

22 MDA levels with nasal lavage IL-8 levels to support its analysis as a biologically23 relevant indicator of pulmonary inflammation.

24 Uric acid and glutathione are ROS scavengers that are present in the airway ELF. While 

25 the roles of these markers in the inflammatory cascade of asthma are not well 

26 characterized, they are observed to be consumed in response to short-term O3 exposure in 

27 controlled human exposure and animal studies (Section 5.3.3). Results from an 

28 epidemiologic study also indicate that ambient O3 exposure may stimulate an antioxidant 

29 response. In a panel study with three measurements of nasal lavage at 3-week intervals, 

30 Sienra-Monge et al. (2004) found O3-associated decreases in nasal lavage levels of uric 

31 acid and glutathione in children with asthma not supplemented with antioxidant vitamins 

32 (Table 6-16). The magnitude of association was similar for O3 exposures lagged 2 or 3 

33 days and averaged over 3 days.

34 Both controlled human exposure and toxicological studies find O3-induced increases in 

35 the cytokines IL-6 and IL-8 (Sections 5.3.3, 6.2.3.1, and 6.3.3.3), which are involved in 

36 initiating an influx of neutrophils, a hallmark of inflammation induced by short-term O3

37 exposure. Recent epidemiologic studies produced similar findings. Barraza-Villarreal 
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1 et al. (2008) observed that a 30-ppb increase in lag 0 of 8-h max O3 was associated with a 

2 1.61 pg/ml increase (95% CI: 1.4, 1.8) in IL-8. In another study of children with asthma 

3 in Mexico City, Sienra-Monge et al. (2004) found that lags 2, 3, and 0-2 avg of 8-h max 

4 O3 were associated with increases in nasal lavage levels of IL-6 and IL-8 (placebo group), 

5 with the largest effects estimated for lag 0-2 average exposure (Table 6-16).

6 Neutrophil influx has been a prominent characterisitc of O3-induced inflammation; 

7 however, controlled human exposure studies also have found O3-induced increases in 

8 eosinophils in adults with asthma (Section 6.2.3.1). Eosinophils are believed to be the 

9 main effector cells that initiate and sustain inflammation in asthma and allergy (Schmekel 

10 et al., 2001). Consistent with these findings, in a cross-sectional study of adults with 

11 asthma in Atlanta, GA, a 30-ppb increase in lag 0 of 8-h max O3 was associated with a 

12 2.4% increase (0.62, 4.2) in blood eosinophils (Khatri et al., 2009). These results were 

13 not adjusted for meteorological factors.

14 The pH of EBC also was analyzed as an indicator of pulmonary inflammation. EBC pH is 

15 thought to reflect the proton-buffering capacity of ammonium in airways. It has been 

16 widely used in the clinical assessment of asthma, is consistently lower in subjects with 

17 asthma, decreases upon acute asthma exacerbation (on the order of 2 units), and is 

18 negatively correlated with airway levels of proinflammatory cytokines (Carpagnano et 

19 al., 2005; Kostikas et al., 2002; Hunt et al., 2000). In addition to finding O3-associated 

20 increases in eNO and nasal lavage IL-8, Barraza-Villarreal et al. (2008) found small O3-

21 associated decreases in EBC pH (Table 6-16).

22 The prominent influences of ROS and antioxidants in mediating the effects of O3 provide 

23 biological plausibility for the effect modification by antioxidant supplementation. The 

24 modulation of O3-associated lung function by antioxidant capacity has been described in 

25 controlled human exposure and epidemiologic studies (Sections 6.2.1.1 and 6.2.1.2). 

26 Epidemiologic studies also found that higher levels of dietary or supplemented 

27 antioxidants attenuated inflammation and oxidative stress. Sienra-Monge et al. (2004)

28 conducted a 12 week-trial with daily vitamin C and E supplements. In the antioxidant 

29 group, the ratios of the geometric means of nasal lavage IL-6 and IL-8 per 30-ppb 

30 increases in lag 0-2 avg of 8-h max O3 were 1.0, reflecting no increases with increases in 

31 O3 exposure (Table 6-16). Effect modification by antioxidant supplementation was not 

32 consistent for uric acid and glutathione (Table 6-16). Ozone was associated with 

33 increases in uric acid in the antioxidant group and decreases in the placebo group across 

34 O3 lags of exposure. Associations with glutathione were similar in both groups. 

35 Therefore, the results do not clearly delineate the interactions among inhaled O3, 

36 endogenous antioxidants, and dietary supplementations of antioxidants. In another cohort 

37 of children with asthma in Mexico City, a diet high in fruits and vegetables was found to 
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1 protect against O3-related increases in nasal lavage IL-8 (Romieu et al., 2009). At high 

2 ambient O3 levels (≥ 38 ppb, 8-h max), a 1-unit increase in FVI was associated with a 

3 0.219 pg/ml decrease (95% CI: -0.38, -0.05) in IL-8. The protective effect was 

4 diminished by about 49% at O3 levels of 25 ppb or lower. Results from these two studies 

5 indicate that augmenting the circulating levels of antioxidants, through diet or vitamin 

6 supplements, may reduce nasal inflammation associated with high ambient O3 exposures.

Clinical significance of ozone-associated changes in pulmonary 

inflammation and oxidative stress in children with asthma

7 While the results of epidemiologic studies in children with asthma were consistent with 

8 the known modes of action of O3 in consuming antioxidants and inducing oxidative stress 

9 and pulmonary inflammation (Section 5.3.3), the clinical significance of these changes 

10 has not been well-characterized. The levels of several of the biological markers such as 

11 eNO, EBC pH, and MDA have been shown to differ between subjects with and without 

12 asthma and change acutely during an acute asthma exacerbation (Corradi et al., 2003; 

13 Hunt et al., 2000); however, the magnitudes of change for these conditions are not well14 defined. Several studies conducted in individuals with asthma found large O3-associated 

15 increases in eNO; effect estimates ranged between a 6 and 36% increase per standardized 

increment in ambient O3 concentration1 16 (Figure 6-10 and Table 6-15). Standardized 

17 increments in ambient O3 exposure were associated with smaller (1-2%) increases in 

18 interleukins or indicators of oxidative stress (Khatri et al., 2009; Barraza-Villarreal et al., 

19 2008) (Romieu et al., 2008; Sienra-Monge et al., 2004). 

20 Some studies permitted the evaluation of the potential clinical relevance of these changes 

21 in eNO through the concurrent assessment of respiratory symptoms. Among children 

22 with asthma in Mexico City, O3 exposure was associated with increases in eNO and nasal 

23 lavage IL-8 and concurrently assessed cough but not wheeze (Barraza-Villarreal et al., 

24 2008). Among adults with asthma in Atlanta, O3 was associated with increases in eNO, 

25 blood eosinophils, and a decrease in quality of life score, which incorporates indices for 

26 symptoms, mood, and activity limitations (Khatri et al., 2009). These findings suggest 

27 that the more subtle O3-associated increases in biological markers of airway 

28 inflammation may be sufficient to result in respiratory symptoms or activity limitations.

Children without Asthma 

29 Recent studies found that short-term O3 exposure (8-h max or avg) was associated with 

30 indicators of airway inflammation in children without asthma (Berhane et al., 2011; 

31 Barraza-Villarreal et al., 2008) (Figure 6-10 and Tables 6-15 and 6-16). In the panel 

 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.
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1 study of children in Mexico City, O3 exposure was associated with a larger increase in 

2 eNO in the children without asthma than with asthma (13.5% versus 6.2% increase per 

3 30-ppb increase in lag 0 of 8-h max O3). Ozone was associated with similar magnitudes 

4 of changes in IL-8 and EBC pH in children with and without asthma. A distinguishing 

5 feature of this study was that most of the children without asthma were atopic (72%) as 

6 indicated by positive skin prick tests, which may have contributed to the similar effects of 

7 O3 exposure observed in children with and without asthma.

8 However, the Southern California Children’s Health Study estimated similar effects for 

9 8-h avg (10:00 a.m.-6:00 p.m.) ambient O3 exposure on eNO in children with and without 

10 respiratory allergy (Berhane et al., 2011). Results from this large study (n = 2240 

11 children) provided evidence that ambient O3 exposure increases airway inflammation in 

12 healthy children. In comparison with other studies, this analysis from the Children’s 

13 Health Study provided detailed information on differences in association among various 

14 lags of 8-h avg (10:00 a.m.-6:00 p.m.) O3 exposure. Consistent with other studies 

15 examining pulmonary inflammation and oxidative stress, Berhane et al. (2011) found that 

16 relatively shorter lags of exposure, including 1 to 5 days, were associated with increases 

17 in eNO. However, in an examination of several types of lag-based models, including 

18 unconstrained lag models, polynomial distributed lag models, spline-based distributed lag 

19 models, and cumulative lag models, investigators found that a 23-day cumulative lag 

20 model best fit the data. Among the studies evaluated in the current assessment, Berhane 

21 et al. (2011) was unique in evaluating and finding larger effects for cumulative average 

22 O3 exposures over multiple weeks (e.g., 13-30 days). O3 exposures averaged over the 

23 several hours preceding eNO collection were not significantly associated with eNO. The 

24 mechanism for the effects of O3 peaking with a 23-day cumulative lag of exposure is not 

25 known.

Populations with Increased Outdoor Exposures

26 In a limited number of available studies, ambient O3 exposure was not consistently 

27 associated with pulmonary inflammation in populations with increased outdoor 

28 exposures. Important limitations of these studies include small numbers of subjects and 

29 repeated measurements. In a cross-sectional study of children at camps in south Belgium, 

30 although O3 was not associated with lung function, an association was found for eNO 

31 (Nickmilder et al., 2007). Children at camps with lag 0 1-h max O3 concentrations above 

32 85.2 ppb had greater increases in intraday eNO compared with children at camps with O3

33 concentrations below 51 ppb. A benchmark dose analysis indicated that the threshold for 

34 an O3-induced increase of 4.3 ppb eNO (their definition of increased pulmonary 

35 inflammation) was 68.6 ppb for 1-h max O3 and 56.3 ppb for 8-hr max O3. While these 

36 results provide additional evidence for O3-associated increases in airway inflammation in 
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1 healthy children, they should be interpreted with caution since they were not adjusted for 

2 any potential confounding factors. 

3 Recent studies examined associations of O3 exposure with biological markers of airway 

4 inflammation in populations exercising outdoors. In a panel study of 16 adolescent long5 distance runners in Atlanta, GA, lags 0, 1, and 2 of 1-h max O3 were associated with 

6 increases in EBC pH, indicating O3-associated decreases in pulmonary inflammation 

7 (Ferdinands et al., 2008). Among 9 adult male runners in Sicily, Italy examined 3 days 

8 before and 20 hours after 3 races in fall, winter, and summer, weekly average O3

9 concentrations (8-h avg, 7:00 a.m.-3:00 p.m.) were positively correlated with apoptosis of 

10 airway cells (Spearman’s r = 0.76, p < 0.0005) and bronchial epithelial cell differential 

11 counts (Spearman’s r = 0.467, p < 0.05) but not with neutrophil or macrophage cell 

12 counts or levels of the proinflammatory cytokines TNF-α and IL-8 (Chimenti et al., 

13 2009). Although this study provides evidence for some new endpoints, the implications 

14 of the findings are limited since they were not based on a rigorous statistical analysis.

Older Adults

15 Two panel studies examining O3-associated changes in eNO in older adults produced 

16 contrasting findings (Figure 6-10 and Table 6-15). Both studies were similar in that 

17 outdoor O3 was monitored by investigators in the vicinity of subjects’ residences, and 

18 cool season-specific results were presented. However, several differences were 

19 noteworthy, including geographic location, inclusion of healthy subjects, and lags of O3

20 exposure examined. Delfino et al. (2010a) followed 60 elderly subjects with coronary 

21 artery disease in the Los Angeles, CA area for two 6-week periods, one in the warm 

22 season and one in the cool season, although the exact months were not specified. 

23 Multiday averages of O3 (3- to 9-day) were associated with increases in eNO, with effect 

24 estimates increasing with increasing number of averaging days. In contrast with most 

25 other studies, a strong positive effect was estimated for the cooler season (4.06 ppb [95% 

26 CI: 1.25, 6.87]) increase in eNO per 20-ppb increase in lag 0-4 of 24-h avg O3), whereas 

27 no association was observed for the warm season (-0.01 ppb change in eNO [95% CI: -

28 2.31, 2.11]). Despite these unusual findings for the cool season, they were similar to 

29 findings from another study of Los Angeles area adults with asthma that found O3 effects 

30 (i.e., decrease in indoor activity) during the fall season (Eiswerth et al., 2005).

31 Adamkiewicz et al. (2004) did not find a positive association between O3 exposure and 

32 eNO in a group of older adults (ages 54-91 years) comprising healthy subjects and those 

33 with asthma or COPD. The study was conducted in Steubenville, OH between September 

34 and December, and as was observed in most other studies conducted during winter 

35 months, O3 (concurrent 1 hour and 24 hours preceding eNO collection) was associated 
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1 with decreases in eNO, indicating a decrease in pulmonary inflammation (Figure 6-10 

2 and Table 6-16).

Confounding in Epidemiologic Studies of Pulmonary Inflammation and 

Oxidative Stress

3 Except where noted in the preceding text, most epidemiologic studies of pulmonary 

4 inflammation and oxidative stress accounted for the potential for confounding by 

5 meteorological factors. Ambient O3 exposure was associated with pulmonary 

6 inflammation or oxidative stress in models that adjusted for temperature and/or humidity 

7 (Delfino et al., 2010a; Barraza-Villarreal et al., 2008; Romieu et al., 2008). Most studies 

8 conducted over multiple seasons adjusted for season or time trend. Sienra-Monge et al. 

9 (2004) and Berhane et al. (2011) did not adjust for temperature in their final results after 

10 finding that the inclusion of temperature did not change results.

11 Although information is limited to a small number of studies conducted in Mexico City, 

12 the evidence does not indicate the confounding of O3 associations by PM2.5 or PM10

13 exposure. In these studies, which analyzed 8-h averages for both O3 and PM and reported 

14 moderate correlations between pollutants (r=0.46-0.54), robust associations were found 

15 for O3 (Barraza-Villarreal et al., 2008; Romieu et al., 2008; Sienra-Monge et al., 2004). 

16 Only Romieu et al. (2008) provided quantitative results. Lag 0 of 8-h max O3 was 

17 associated with the same magnitude of increase in MDA with and without lag 0 of 8-h 

18 max PM2.5 in the model (ratio of geometric means per 30-ppb increase: 1.3 [95% CI: 1.0, 

19 1.7]). In the copollutant model, the effect estimate for PM2.5 was cut in half.

Summary of Epidemiologic Studies of Pulmonary Inflammation and 

Oxidative Stress

20 Many recent epidemiologic studies reported positive associations between short-term 

21 ambient O3 exposure and increases in pulmonary inflammation and oxidative stress, 

22 particularly, studies of children with asthma in Mexico City. By also finding that O3-

23 associated increases in pulmonary inflammation were attenuated with higher antioxidant 

24 intake, these studies, as a whole, provided evidence that inhaled O3 may be an important 

25 source of ROS in airways and/or may increase airway inflammation via oxidative stress26 mediated mechanisms. Studies also indicated that ambient O3 exposure may increase 

27 airway inflammation in healthy children (Berhane et al., 2011; Nickmilder et al., 2007). 

28 The limited available evidence in subjects exercising outdoors and older adults was 

29 inconclusive. Temperature and humidity were not found to confound O3 associations, and 

30 in the few studies that evaluated copollutant models, O3 effect estimates were robust to 
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1 inclusion of PM2.5 or PM10 (Barraza-Villarreal et al., 2008; Romieu et al., 2008; Sienra2 Monge et al., 2004).

3 Most studies examined associations with daily 8-h max or daytime 8-h avg O3 exposures, 

4 although associations were observed for 1-h max (Nickmilder et al., 2007) and 24-h avg 

5 O3 exposures (Delfino et al., 2010a). Collectively, studies examined associations with 

6 single-day O3 exposures lagged from 0 to 5 days, and exposures averaged over 2 to 9 

7 days. Lag 0 of 8-h max O3 exposure was most frequently examined and consistently 

8 associated with increased airway inflammation and oxidative stress. However, in the few 

9 studies that examined multiple lags of exposure, multiday cumulative O3 exposures, 

10 primarily based on 8-h max or 8-h avg, were associated with greater increases in airway 

11 inflammation and oxidative stress (Berhane et al., 2011; Delfino et al., 2010a; Sienra12 Monge et al., 2004). These findings for longer lags of exposure are supported by 

13 controlled human exposure studies that similarly have found that indicators of airway 

14 inflammation remain elevated following exposures to O3 repeated over multiple days 

15 (Section 6.2.3.1).

16 Several epidemiologic studies simultaneously examined associations of ambient O3

17 exposure with biological markers of airway inflammation and oxidative stress, lung 

18 function, and respiratory symptoms. In most cases, the results differed between the 

19 various biomarkers and lung function. Whether evaluated at the same or different lags of 

20 O3 exposure, associations generally were stronger for biological markers of airway 

21 inflammation than for lung function (Barraza-Villarreal et al., 2008; Nickmilder et al., 

22 2007). Controlled human exposure studies also have demonstrated a lack of correlation 

23 between inflammatory and spirometric responses induced by O3 exposure. Studies have 

24 suggested that O3-related respiratory morbidity may occur via multiple mechanisms with 

25 varying time courses of action, and the examination of a limited number of O3 exposure 

26 lags in these aforementioned studies may explain some of the inconsistencies in 

27 associations of O3 with different respiratory health endpoints.

28 The clinical significance of changes in biological markers of airway inflammation and 

29 oxidative stress are not well-characterized. However, the simultaneous examination of 

30 associations of O3 with respiratory symptoms has permitted the assessment of the clinical 

31 significance of the changes observed in biomarkers. In subjects with asthma, ambient O3

32 exposure was associated with increases in eNO and IL-6 that were accompanied by a 

33 concomitant increase in cough (Barraza-Villarreal et al., 2008) and increases in eNO and 

34 blood eosinophils that were accompanied by a decrease in quality of life score (Khatri et 

35 al., 2009). These findings support clinically-important increases in O3-associated airway 

36 inflammation in individuals with asthma. Similar data are limited to assess the clinical 
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1 significance of changes in other biological markers of airway inflammation and oxidative 

2 stress and in other populations. 

6.2.3.3 Toxicology

3 The 2006 O3 AQCD states that the “extensive human clinical and animal toxicological 

4 evidence, together with the limited available epidemiologic evidence, is clearly indicative 

5 of a causal role for O3 in inflammatory responses in the airways” (U.S. EPA, 2006b). 

6 Airway ciliated epithelial cells and Type 1 cells are the most O3-sensitive cells and are 

7 initial targets of O3. These cells are damaged by O3 and produce a number of 

8 proinflammatory mediators (e.g., interleukins [IL-6, IL-8], PGE2) capable of initiating a 

9 cascade of events leading to PMN influx into the lung, activation of alveolar 

10 macrophages, inflammation, and increased permeability across the epithelial barrier. One 

11 critical aspect of inflammation is the potential for metaplasia and alterations in 

12 pulmonary morphology. Studies have observed increased thickness of the alveolar septa, 

13 presumably due to increased cellularity after acute exposure to O3. Epithelial hyperplasia 

14 starts early in exposure and increases in magnitude for several weeks, after which it 

15 plateaus until exposure ceases. When exposure persists for a month and longer, excess 

16 collagen and interstitial fibrosis are observed. This response, discussed in Chapter 7, 

17 continues to increase in magnitude throughout exposure and can even continue to 

18 increase after exposure ends (Last et al., 1984). Previously published toxicological 

19 studies of the ability of O3 to cause inflammation, injury, and morphological changes are 

20 described in Table 6-5 on p. 6-25 and Tables 6-10 and 6-11 beginning on p. 6-61 of the 

21 1996 O3 AQCD, and Tables AX5-8 and AX5-9, beginning on p. AX5-17 of the 2006 O3

22 AQCD. Numerous recent in vitro and in vivo studies add to this very large body of 

23 evidence for O3-induced inflammation and injury, and provide new information regarding 

24 the underlying mechanisms (Bauer et al., 2011; Aibo et al., 2010; Farraj et al., 2010; 

25 Garantziotis et al., 2010; Hicks et al., 2010b; Castagna et al., 2009; Damera et al., 2009; 

26 Oslund et al., 2009; Vancza et al., 2009; Voynow et al., 2009; Fakhrzadeh et al., 2008; 

27 Han et al., 2008; Inoue et al., 2008; Oslund et al., 2008; Carey et al., 2007; Cho et al., 

28 2007; Dahl et al., 2007; Johnston et al., 2007; Kooter et al., 2007; Wagner et al., 2007; 

29 Wang et al., 2007; Yoon et al., 2007; Huffman et al., 2006; Johnston et al., 2006; Kenyon 

30 et al., 2006; Manzer et al., 2006; Plopper et al., 2006; Jang et al., 2005; Janic et al., 2005; 

31 Johnston et al., 2005a; Johnston et al., 2005b; Oyarzún et al., 2005; Servais et al., 2005; 

32 Frush et al., In Press). 

33 A number of species, including dogs, rabbits, guinea pigs, rats, and mice have been used 

34 as models to study the pulmonary effects of O3, but the similarity of non-human primates 

35 to humans makes them an attractive model in which to study the pulmonary response to 
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1 O3. As reviewed in the 1996 and 2006 O3 AQCDs, several pulmonary effects, including 

2 inflammation, changes in morphometry, and airway hyperresponsiveness, have been 

3 observed in macaque and rhesus monkeys after acute exposure to O3 (Table 6-17 presents 

4 a highlight of these studies). Increases in inflammatory cells were observed after a single 

5 8-hr exposure of adult rhesus monkeys to 1 ppm O3 (Hyde et al., 1992). Inflammation 

6 was linked to morphometric changes, such as increases in necrotic cells, smooth muscle, 

7 fibroblasts, and nonciliated bronchiolar cells, which were observed in the trachea, 

8 bronchi, or respiratory bronchioles. Effects have also been observed after short-term 

repeated exposure to O3 at concentrations that are more relevant to ambient O3 9 levels. 

10 Morphometry changes in the lung, nose, and vocal cords were observed after exposure to 

11 0.15 ppm O3 for 8-h/day for 6 days (Harkema et al., 1993; Dimitriadis, 1992; Harkema et 

12 al., 1987a). Since 2006, however, only one study has been published regarding acute 

13 exposure of non-human primates to O3 (a number of recent chronic studies in non-human 

14 primates are described in Chapter 7). In this study, a single 6-h exposure of adult male 

15 cynomolgus monkeys to 1 ppm O3 induced significant increases in inflammatory and 

16 injury markers, including BAL neutrophils, total protein, alkaline phosphatase, IL-6, IL17 8, and G-CSF (Hicks et al., 2010b). Gene expression analysis confirmed the increases in 

18 the pro-inflammatory cytokine IL-8, which had been previously described in O3 exposed 

19 rhesus monkeys (Chang et al., 1998). The anti-inflammatory cytokine IL-10 was also 

20 elevated, but the fold changes in IL-10 and G-CSF were relatively low and highly 

21 variable. The single exposure also caused necrosis and sloughing of the epithelial lining 

22 of the most distal portions of the terminal bronchioles and the respiratory bronchioles. 

23 Bronchiolitis, alveolitis, parenchymal and centriacinar inflammation were also observed. 

24 A second exposure protocol (two exposures with a 2-week inter-exposure interval) 

25 resulted in similar inflammatory responses, with the exception of total protein and 

26 alkaline phosphatase levels which were attenuated, indicating that attenuation of some 

27 but not all lavage parameters occurred upon repeated exposure of non-human primates to 

28 O3 (Hicks et al., 2010b). This variability in adaptation is similar to the findings of earlier 

29 reports in rodents (Wiester et al., 1996b) and non-human primates (Tyler et al., 1988). 

30 Table 6-17 describes morphometric studies conducted in non-human primates exposed 

31 to O3. 
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Table 6-17 Morphometric observations in non-human primates after acute O3

exposure

Reference O3 concentration Exposure 

duration Species, Sex, Age Observation

Harkema et al. 

(1993)

0.15 8 h/day for 6 

days

Macaca radiata Several fold increase in thickness of surface 

epithelium in respiratory bronchioles

Harkema et al. 

(1987a; 1987b)

Dimitriadis (1992)

0.15

0.3

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

Leonard et al. (1991) 0.25 8 h/day for 7 

days

Macaca radiata 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 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

Hicks et al. (2010a) 1.0 6 h Cynomolgus, M

5-7 kg

Increase in PMNs and IL-8 in lavage fluid

1 Confirmation of pulmonary changes observed in non-human primates, at near ambient 

2 O3concentrations, has been done in a large number of studies in guinea pigs and rodents 

3 (see 1996 and 2006 O3 AQCDs) (U.S. EPA, 2006b, 1996a). Mechanistic studies 

4 completed more recently have extended these findings. Exposure of adult BALB/c mice 

5 to 0.1 ppm O3 for 4 hours increased BAL levels of keratinocyte chemoattractant (KC; IL6 8 homologue) (~ sixfold), IL-6 (~12-fold), and TNF-α (~ twofold) (Damera et al., 2010). 

7 Additionally, O3 increased BAL neutrophils by 21% without changes in other cell types. 

8 A trend of increased neutrophils with increased O3 concentration (0.12-2 ppm) was 

9 observed in BALB/c mice exposed for 3 hours (Jang et al., 2005). Although alterations in 

10 the epithelium of the airways were not evident in 129J mice after 4 hours of exposure to 

11 0.2 ppm O3 (Plopper et al., 2006), detachment of the bronchiolar epithelium was 

12 observed in SD rats after 5 days or 60 days of exposure to 0.25 ppm O3 (Oyarzún et al., 

13 2005). Subacute (65 hours) exposure to 0.3 ppm O3 induced pulmonary inflammation, 

14 cytokine induction, and enhanced vascular permeability in wild type mice of a mixed 

15 background (129/Ola and C57BL/6) and these effects were exacerbated in 

16 metallothionein I/II knockout mice (Inoue et al., 2008). Three hours or 72 hours of 

17 exposure to 0.3 ppm O3 resulted in similar levels of IL-6 expression in the lungs of 

18 C57BL/6 mice (Johnston et al., 2005b), along with increases in BAL protein, sTNFR1, 

19 and sTNFR2. Increased neutrophils were observed only after the 72-h exposure, and 

20 neither exposure resulted in detectable levels of IL-6 or KC protein. Levels of BAL 
Draft – Do Not Cite or Quote 6-82 September 2011

1 protein, sTNFR1, and sTNFR2 were higher in the 72-h exposure group than in the 3-h 

2 exposure group. In another study, the same subacute (72 hours) exposure protocol elicited 

3 increases in BALF protein, IP-10, sTNFR1, macrophages, neutrophils, and IL-6, IL-1α, 

4 and IL-1β expression (Johnston et al., 2007). Yoon et al. (2007) exposed C57BL/6J mice 

5 continuously to 0.3 ppm O3 for 6, 24, 48, or 72 hours, and observed elevated levels of 

6 KC, MIP-2, metalloproteinases, and inflammatory cells in the lungs at various time 

7 points. A similar exposure protocol using C3H/HeJ and C3H/OuJ mice demonstrated 

8 elevations in protein, PMNs, and KC, which were predominantly TLR 4 pathway 

9 dependent based on their prominence in the TLR 4 sufficient C3H/OuJ strain (Bauer et 

10 al., 2011). C3H/OuJ mice also had elevated levels of the heat-shock protein HSP70, and 

11 further experiments in HSP70 deficient mice indicated a role for this particular pathway 

12 in O3-related injury, discussed in more detail in Chapter 5.

13 As reviewed in the 2006 O3 AQCD, the time course for changes in BAL depends on the 

14 parameters being studied. Similarly, after exposing adult C57BL mice to 0.5 ppm O3 for 

15 3 hours, Han et al. (2008) observed early (5 hours postexposure) increases in BAL TNF-α 

16 and IL-1β, which diminished by 24 hours postexposure. Total BAL protein was elevated 

17 at 24 hours, but there were only minimal or negligible changes in LDH, total cells, or 

18 PMNs. Ozone increased BAL mucin levels (with statistical significance by 24 hours 

19 postexposure), and significantly elevated surfactant protein D at both time points. Prior 

20 intratracheal (IT) exposure to multiwall carbon nanotubes enhanced most of these effects, 

21 but the majority of responses to the combined exposure were not greater than those to 

22 nanotubes alone. Ozone exposure did not induce markers of oxidative stress in lung 

23 tissue, BAL, or serum. Consistent with this study, Aibo et al. (2010) did not detect 

24 changes in BAL inflammatory cell numbers in the same mouse strain after a 6-h exposure 

25 to 0.25 or 0.5 ppm. The majority of inflammatory cytokines (pulmonary or circulating) 

26 were not significantly changed (as assessed 9 hours post O3 exposure).

27 Animal toxicology studies have also examined susceptibility factors and the findings 

28 complement research in both controlled human exposure and epidemiologic studies. In a 

29 study examining age, strain, and gender as factors for susceptibility to O3 in mice, 

30 increased BAL neutrophils were observed in all 8 strains of neonates and adults but 

31 statistical significance was found in only 4 strains of neonates and 2 strains of adults at 

32 24 hours after exposure to 0.8 ppm O3 for 5 hours (Vancza et al., 2009). Lung injury, as 

33 measured by BAL protein, was significantly increased in 5 and 8 strains of neonates and 

34 adults, respectively. Interestingly, the observed age-dependent differences in response to 

35 O3 occurred in only certain strains. For example, the fold-increase in neutrophils was 

36 significantly higher, in neonates compared to adults, in the SJL and C3H/HeJ strains and 

lower in BALB/c mice. Measurement of 18 37 O determined that the observed strain- and 

38 age-dependent differences were not due to absorbed O3 dose. Subanalysis of the adult 
Draft – Do Not Cite or Quote 6-83 September 2011

1 mice demonstrated that gender also played a small, but statistically significant, role in the 

2 effect of O3 on BAL neutrophils and protein. These findings suggest that the response to 

3 O3, in mice, may consist of a complex interaction of age, gender, and genetic factors.

4 A study assessing NQO1 as a susceptibility factor was conducted by Voynow et al. 

5 (2009). Specific effects of this gene on O3 responses are discussed in Chapter 8; only 

6 ozone’s effects in wild type C57BL/6 mice are described here. Exposure to 1 ppm for 

7 3 hours increased BAL total cells, neutrophils, and KC; these responses were greatest at 

8 24 hours postexposure. F2-isoprostane (8-isoprostane), a marker of oxidative stress, was 

9 also elevated by O3, peaking at 48 hours postexposure.

10 Atopic asthma appears to be a risk factor for more severe O3 induced airway 

11 inflammation in humans (Balmes et al., 1997; Scannell et al., 1996), and allergic animal 

12 models are often used to investigate the effects of O3 on this susceptible population. 

13 Farraj et al. (2010) exposed allergen-sensitized adult male BALB/c mice to 0.5 ppm O3

14 for 5 hours once per week for 4 weeks. Ovalbumin-sensitized mice exposed to O3 had 

15 significantly increased BAL eosinophils by 85% and neutrophils by 103% relative to 

16 OVA sensitized mice exposed to air, but these changes were not evident upon 

17 histopathological evaluation of the lung, and no O3 induced lesions were evident in the 

18 nasal passages. Ozone increased BAL levels of N-acetyl-glucosaminidase (NAG; a 

marker of injury) and protein. DEP co-exposure (2.0 mg/m3 19 , nose only) inhibited these 

20 responses. These pro-inflammatory effects in an allergic mouse model have also been 

21 observed in rats. Wagner et al. (2007) exposed the relatively O3-resistant Brown Norway 

22 rat strain to 1 ppm O3 after sensitizing and challenging with OVA. Rats were exposed for 

23 2 days, and airway inflammation was assessed one day later. Filtered air for controls 

24 contained less than 0.02 ppm O3. Histopathology indicated O3 induced site-specific lung 

25 lesions in the centriacinar regions, characterized by wall thickening partly due to 

26 inflammatory cells influx. BAL neutrophils were elevated by O3 in allergic rats, and 

27 modestly increased in non-allergic animals (not significant). A slight (but not significant) 

28 increase in macrophages was observed, but eosinophil numbers were not affected by O3. 

29 Soluble mediators of inflammation (Cys-LT, MCP-1, and IL-6) were elevated by O3 in 

30 allergic animals but not non-allergic rats. Treatment with γT, which neutralizes oxidized 

31 lipid radicals and protects lipids and proteins from nitrosative damage, did not alter the 

32 morphologic character or severity of the centriacinar lesions caused by O3, nor did it 

33 reduce neutrophil influx. It did, however, significantly reduce O3-induced soluble 

34 inflammatory mediators in allergic rats. The effects of O3 in animal models of allergic 

35 asthma are discussed in section 6.2.6. 

36 In summary, a large number of toxicology studies have demonstrated that acute exposure 

37 to O3 produces injury and inflammation in the mammalian lung, supporting the 
Draft – Do Not Cite or Quote 6-84 September 2011

1 observations in controlled human exposure studies (Section 6.2.3.1). These acute 

2 changes, both in inflammation and morphology, provide a modicum of evidence for long 

3 term sequelae of exposure to O3. Related alterations resulting from long term exposure, 

4 such as fibrotic changes, are discussed in Chapter 7.

Mechanisms of Injury

5 Since O3 has been well established as a causative agent of airway inflammation and 

6 injury, which may contribute to functional changes observed in human subjects, the 

7 majority of recent research has focused on the underlying mechanisms. A brief 

8 description of some of the recent contributions to this area of research is provided here; 

9 more detailed descriptions of the mechanisms behind O3-mediated injury and 

10 inflammation can be found in the mode of action chapter (Chapter 5). There are several 

11 signaling pathways responsive to changes in oxidation status, which tend to be influenced 

12 at different levels in different host backgrounds. The molecular mechanisms of TNF 

13 receptor-mediated lung injury induced by O3 and associated signaling pathways (NF-κB, 

14 MAPK/AP-1) have been examined (Fakhrzadeh et al., 2008; Cho et al., 2007), along with 

15 the changes in gene expression which characterize O3-induced stress and inflammation 

16 (Wang et al., 2007). Other contributors to injury and inflammation include the IL-1 and 

17 neurokinin receptors (Oslund et al., 2008; Johnston et al., 2007), calcitonin gene-related 

18 peptide receptor activation (Oslund et al., 2009), CXCR2, a receptor for neutrophil 

19 chemokines (Johnston et al., 2005a), mindin, an extracellular matrix protein (Frush et al., 

20 In Press), and NQO1 (Voynow et al., 2009), an enzyme involved in oxidative stress. 

21 Studies indicate a role for oxidative stress in mediating inflammation (Wagner et al., 

22 2007; Jang et al., 2005). Protective roles have been identified for nitric oxide synthase 

23 (Kenyon et al., 2006), metallothionein (Inoue et al., 2008), matrix metalloproteinases 

24 (Yoon et al., 2007), Clara cell secretory protein (Plopper et al., 2006), and the recognition 

25 of oxidized lipids by alveolar macrophages (Dahl et al., 2007).

6.2.4 Respiratory Symptoms and Medication Use

26 Controlled human exposure and toxicological studies have described the modes of action 

27 through which short-term O3 exposure may lead to increases in respiratory symptoms by 

28 demonstrating O3-induced increases in airway hyperresponsiveness, bronchoconstriction 

29 (Section 6.2.2), and pulmonary inflammation (Sections 6.2.3.1 and 6.2.3.3). While 

30 epidemiologic studies have not widely examined associations between ambient O3

31 exposure and airway hyperresponsiveness, they have found O3-associated increases in 

32 pulmonary inflammation and oxidative stress (Section 6.3.2.2). In addition to decreases 
Draft – Do Not Cite or Quote 6-85 September 2011

1 in lung function, controlled human exposure studies clearly demonstrate increases in 

2 subjective respiratory symptoms including cough, pain on deep inspiration, and shortness 

3 of breath (described in detail in Section 6.2.1.1). Similar to lung function responses, these 

4 respiratory symptoms increase with exposure concentration, activity level of the exposed 

5 individual, and duration of exposure (McDonnell et al., 1999). Increases in subjective 

6 respiratory symptoms have been reported following 5.6 and 6.6 h of exposure to 60 ppb 

7 O3. However, the severity of respiratory symptoms following 6.6 h of exposure to 80 ppb 

8 O3 during moderate exercise is roughly 2-3 times greater than that at 60 ppb O3 (Adams, 

9 2006a). These findings integrated across disciplines provide biological plausibility for 

10 epidemiologic associations between increases in short-term ambient O3 exposure and 

11 increases in respiratory symptoms.

12 In epidemiologic studies, respiratory symptom data typically are collected by having 

13 subjects or their parents record symptoms such as wheeze, cough, and shortness of breath 

14 and medication use in a diary without direct supervision by study staff. Several 

15 limitations of symptom reports are well-recognized: recall error if not recorded daily, 

16 differences among subjects in the interpretation of symptoms, biased reporting between 

17 participants with and without asthma, and occurrence in a smaller percentage of the 

18 population compared with changes in lung function and biological markers of pulmonary 

19 inflammation. Nonetheless, symptom diaries remain a convenient and useful tool to 

20 collect individual-level data from a large number of subjects and allow the modeling of 

21 associations between daily changes in O3 exposure and daily changes in respiratory 

22 morbidity. Importantly, most of the limitations described above are sources of random 

23 measurement error that can bias effect estimates to the null or increase the uncertainty 

24 around effect estimates. Furthermore, because respiratory symptoms are associated with 

25 limitations in activity and function and are the primary reason for using medication and 

26 seeking medical care, they provide an assessment of the clinical and public health 

27 significance of ambient O3 exposure. 

28 Most studies have been conducted in individuals with asthma, and as was concluded in 

29 previous O3 AQCD, the collective body of epidemiologic evidence strongly supports 

30 associations between increases in short-term ambient O3 exposure and increases in 

31 respiratory symptoms in children with asthma (U.S. EPA, 2006b, 1996a) (Figure 6-11 

32 and Table 6-19). Evidence also indicates that O3 exposure likely is associated with 

33 increased use of asthma medication (Figure 6-12 and Table 6-20). Studies also find O3

34 exposure to be associated with respiratory symptoms in adults with asthma. The effects of 

35 O3 exposure on respiratory symptoms in healthy populations are not as clearly indicated 

36 (Figure 6-13 and Table 6-23)
Draft – Do Not Cite or Quote 6-86 September 2011

6.2.4.1 Children with Asthma

Respiratory Symptoms

1 Table 6-18 presents the characteristics and ambient O3 concentration data from studies 

2 assessing associations of short-term O3 exposure with respiratory symptoms and 

3 medication use in children with asthma. The strong evidence for associations between 

4 ambient O3 exposure and respiratory symptoms among children with asthma is derived 

5 mostly from several single-region or single-city studies (Figure 6-11 and Table 6-19). 

6 Most studies of children with asthma examined 1-h max, 8-h max, or 8-h average O3

7 exposures. In U.S. multicity studies, O3 was associated with both increases and decreases 

8 in respiratory symptoms among children with asthma (O'Connor et al., 2008; Schildcrout 

9 et al., 2006; Mortimer et al., 2002). In the NCICAS cohort (described in Section 6.2.1.2), 

10 a 30-ppb increase in lag 1-4 avg of 8-h avg (10:00 a.m.-6:00 p.m.) O3 was associated with 

11 an increase in morning asthma symptoms with an OR (95% CI) of 1.35 (95% CI: 1.04, 

12 1.69) (Mortimer et al., 2002). This association did not change (OR: 1.37 [95% CI: 1.02, 

13 1.84]) in an analysis restricted to O3 concentrations below 80 ppb. Odds ratios for lags 2 

14 and 4 of O3 exposure were similar in magntiude. In the ICAS cohort (described in Section 

15 6.2.1.2), associations of 19-day avg of 24-h avg O3 with wheeze and nighttime asthma 

16 were positive and negative, respectively (O'Connor et al., 2008). NCICAS was conducted 

17 during the warm season, and symptom data were collected daily (Mortimer et al., 2002; 

18 Mortimer et al., 2000), whereas in ICAS, every 2 months, parents reported the number of 

19 days with respiratory symptoms over the previous 2 weeks (O'Connor et al., 2008). 

20 Because of the two-week symptom reporting period, ICAS investigators were precluded 

21 from examining associations with single-day and shorter-duration O3 exposure periods.

22 Evidence of O3-associated respiratory symptoms also was weak in another recent U.S. 

23 multicity study (with cities in common with NCICAS and ICAS, Table 6-18) of 990 

24 children with asthma (Schildcrout et al., 2006). As part of the Childhood Asthma 

25 Management Program, symptom data were collected daily, and analyses were restricted 

26 to peak O3 periods between May and September. In meta-analyses that combined city27 specific estimates, a 40-ppb increase in lag 0 of 1-h max O3 was associated with any 

28 asthma symptom with an OR (95% CI) of 1.08 (0.89, 1.31). Odds ratios for lags 1 and 2 

29 and the 3-day sum of O3 were near 1.0. In this study, data were available from an average 

30 of 12 subjects per day per city, and fewer data were collected in summer months. 

31 Because O3 analyses were restricted to summer months, the fewer number of 

32 observations reduced the power to detect associations for O3 relative to other pollutants, 

33 which were analyzed using year-round data. 
Draft – Do Not Cite or Quote 6-87 September 2011

Table 6-18 Mean and upper percentile ozone concentrations in epidemiologic 

studies examining respiratory symptoms, medication use, and 

activity levels in children with asthma

Study Location Years/Season

O3

Averaging Time

Mean/Median

Concentration (ppb) Upper Percentile Concentrations (ppb)

Mortimer et al. 

(2000)

Mortimer et al. 

(2002)

Bronx, East Harlem, NY; 

Baltimore, MD; Washington, DC; 

Detroit, MI, Cleveland, OH; 

Chicago, IL; St. Louis, MO 

(NCICAS)

1993

Warm season

8-h avg

(10:00 a.m.- 6:00 p.m.)

48 NR

O’Connor et al. 

(2008)

Boston, MA; Bronx, Manhattan NY; 

Chicago, IL; Dallas, TX, Seattle, 

WA; Tucson, AZ

(ICAS)

1998-2001

All-year

24-h avg NR NR

Schildcrout et al. 

(2006)

Albuquerque, NM; Baltimore, MD; 

Boston, MA; Denver, CO; San 

Diego, CA; Seattle, WA; St. Louis, 

MO; Toronto, ON, Canada (CAMP)

1994-1995

Warm season

1-h max Range in medians 

across cities: 43.0-65.8 

Range in 90th across 

cities: 61.5-94.7

Gent et al. 

(2003)

CT, southern MA 2001

April-September

1-h max

8-h rolling avg

58.6

51.3

Max: 125.5

Max: 99.6

Thurston et al. 

(1997)

Connecticut River Valley, CT 1991-1993

Warm season

1-h max 83.6 Max: 160

Rabinovitch et 

al. (2004)

Denver, CO 1999-2002

Cold season

1-h max 28.2 Max: 70.0

Mann et al. 

(2010)

Fresno/Clovia, California 2000-2005

All-year

8-h max 49.4 (median) 75th: 69.5, Max: 120.0

Ostro et al. 

(2001)

Los Angeles, CA 1993

August-October

1-h max Los Angeles: 59.5

Pasadena: 95.8

Max: 130

Max: 220

Delfino et al. 

(2003)

Los Angeles, CA 1999-2000

Cold season

1-h max

8-h max

25.4

17.1

90th: 38.0, Max: 52

90th: 26.1, Max: 37

Romieu et al. 

(1996)

northern Mexico City, Mexico April-July 1991

November 1991-

February 1992

1-h max 190 Max: 370

Romieu et al. 

(1997)

southern Mexico City, Mexico April-July 1991

November 1991-

February 1992

1-h max 196 Max: 390

Romieu et al. 

(2006)

Mexico City, Mexico 1998-2000

All-year

1-h max

8-h max

102

69

Max: 309

Max: 184 

Escamilla-Nunez 

et al. (2008)

Mexico City, Mexico 2003-2005

All-year

1-h max

8-h max

86.5

31.6

Max: 86.3 (8-h max)

Gielen et al. 

(1997)

Amsterdam, Netherlands 1995

Warm season

8-h max 34.2 Max: 56.5

Just et al. (2002) Paris, France 1996

April-June

24-h avg 30.0 Max: 61.7

Jalaludin et al. 

(2004)

Sydney, Australia 1994

All-year

15-h avg (6:00 

a.m.-9:00 

p.m.)

12 Max: 43

NCICAS = National Cooperative Inner-City Asthma Study, NR = Not Reported, ICAS = Inner City Asthma Study, NR = Not Reported, CAMP = 

Childhood Asthma Management Program, Max = Maximum. 
Draft – Do Not Cite or Quote 6-88 September 2011

Figure 6-11 Associations of ambient ozone exposure with respiratory 

symptoms in children with asthma. 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. Effect estimates 

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, and 15-h avg 

or 24-h avg ozone exposures, respectively.

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

Wheeze

Cough

Wheeze

Chest symptoms

Difficulty breathing

O3 Lag

0-2 avg

0

0

0

1-4 avg

0

0

2

1-19 avg

3

0

0

0

0-5 avg

Subgroup

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 Ile/Val

GSTP1 Val/Val

►

►

►

0 0.5 1 1.5 2 2.5

Odds ratio (95% CI)
Draft – Do Not Cite or Quote 6-89 September 2011

Table 6-19 Additional characteristics and quantitative data for studies 

presented in Figure 6-11

Study Location/ Population O3

Lag

O3

Averagin

g Time

Symptom Subgroup Odds Ratio 

(95% CI)a

Studies examining aggregates of symptoms

Rabinovitch et al. (2004) Denver, CO

Children with asthma

0-2 

avg

1-h max Daytime 

symptoms

1.34 (1.01, 1.77)

Delfino et al. (2003) Los Angeles, CA

Children with asthma

0 1-h max Bothersome 

symptoms

1.09 (0.39, 3.03)

Schildcrout et al. (2006) 8 U.S. communities

Children with asthma

0 1-h max Asthma symptoms 1.08 (0.89, 1.31)

Gielen et al. (1997) Amsterdam, Netherlands

Children with asthma

0 8-h max LRS

URS

1.04 (0.75, 1.45)

1.16 (1.02, 1.32)

Mortimer et al. (2002)

Mortimer et al. (2000)

8 U.S. communities

Children with asthma

1-4 

avg

8-h avg

(10:00 a.m.-

6:00 p.m.)

Morning 

symptoms

All subjects

No medication use

Cromolyn use

β-agonist/xanthine use

Steroid use

Without allergy

With allergy

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

Children with asthma

0 1-h max LRS 1.07 (1.02, 1.12)

Romieu et al. (1997) southern Mexico City, 

Mexico

Children with asthma

0 1-h max LRS 1.09 (1.04, 1.14) 

Studies examining individual symptoms

Jalaludin et al. (2004) Sydney, Australia

Children with asthma

2 15-h avg 

(6:00 a.m.- 9:00 p.m.)

Wheeze 1.21 (0.92, 1.59)

O’Connor et al. (2008) 7 U.S. communities

Children with asthma

1-19 

avg

24-h avg Wheeze/cough 1.02 (0.86, 1.21)

Ostro et al. (2001) Los Angeles, CA

Children with asthma

3 1-h max Wheeze 0.94 (0.88, 1.00)

Escamilla-Nunez et al. 

(2008)

Mexico City, Mexico

Children with asthma

0 1-h max Wheeze 1.08 (1.03, 1.14)

Mann et al. (2010) Fresno/Clovia, California

Children with asthma

0 8-h max Wheeze All

Fungi allergic

1.00 (0.84, 1.19)

1.06 (0.84, 1.34)

Thurston et al. (1997) CT River Valley, CT

Children with asthma

0 1-h max Chest symptoms 1.28 (1.10, 1.50)

Romieu et al. (2006) Mexico City, Mexico

Children with asthma

0-5 

avg

1-h max Difficulty breathing GSTM1 sufficient

GSTM1 null

GSTP1 Ile/Ile 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)

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, and 15-h avg or 24-h avg O3, respectively.

1

2 Several longitudinal studies conducted in multiple cohorts of children with asthma in 

3 Mexico City, Mexico examined 1-h max O3 exposures and found associations with 

4 increases in respiratory symptoms (Escamilla-Nuñez et al., 2008; Romieu et al., 2006; 

5 Romieu et al., 1997; Romieu et al., 1996). Recent studies expanded on earlier evidence 
Draft – Do Not Cite or Quote 6-90 September 2011

1 by indicating associations with multiday averages of O3 exposure. Both Romieu et al. 

2 (1996) and Romieu et al. (1997) found that among single-day 1-h max O3 exposures 

3 lagged 0 to 2 days, lag 0 had the greatest estimated effect on respiratory symptoms. 

4 Romieu et al. (2006) and Escamilla-Nunez et al. (2008) found that the magnitudes of 

5 association of ambient 1-h max O3 exposure with respiratory symptoms and medication 

6 use increased with increasing number of days over which O3 exposure was averaged. 

7 Studies of children with asthma also identified factors that may contribute to 

8 heterogeneity in symptom responses to ambient O3 exposure. Multiple studies, all of 

9 which examined 8-h avg (10:00 a.m.-6:00 p.m.) or 8-h max O3 exposures, found larger 

10 associations among subjects taking asthma medication; however, the medications varied 

11 among studies. Consistent with findings for lung function, in the NCICAS multicity 

12 cohort, larger associations for morning symptoms were observed in children taking 

13 cromolyn (used to treat asthma with allergy) or beta-agonists/xanthines than in children 

14 taking no medication. Odds ratios did not differ as much between children taking steroids 

15 and children taking no medication (Figure 6-11 and Table 6-19) (Mortimer et al., 2000). 

16 In a cohort of children with asthma in Southern New England, O3 exposures were 

17 associated with larger increases in chest tightness among children taking maintenance 

18 medication (i.e., steroids, cromolyn, or leukotriene inhibitors). 

19 Most studies of children with asthma reported that a majority of subjects (52 to 100%) 

20 were atopic as determined by a positive skin prick test to any examined allergen; 

21 however, results did not conclusively indicate that children with asthma and atopy were 

22 more susceptible to the effects of O3 exposure. In the multicity NCICAS cohort, 

23 Mortimer et al. (2000) found that O3 was associated with a similar incidence of asthma 

24 symptoms among the 79% of subjects with atopy and the 21% of subjects without atopy 

25 (Figure 6-11 and Table 6-19). Odds ratios did not differ by residential levels of allergens. 

26 In a recent study of children with asthma in Fresno, CA, most associations of single- and 

27 multiday lags of 8-h max O3 exposure (0-14 days) with wheeze were near or below 1.0 

28 (Mann et al., 2010). The estimated effects did not differ in fungi allergic subjects, A 

29 larger association was found for cat allergic subjects; however, this finding was limited to 

30 O3 exposure lagged 14 days. In this study, many subjects were allergic to multiple

31 allergens; however, associations were not compared between subjects with any versus no 

32 allergic sensitization. 

33 Although Romieu et al. (2006) did not observe differences in associations between O3

34 and lung function by GST genetic polymorphisms (Section 6.2.1.2), they did observe 

35 effect modification for respiratory symptoms. Compared with GSTM1 positive subjects 

36 and GSTP1 Ile/Ile or Ile/Val subjects, larger effects were estimated for GSTM1 null 

37 subjects and for GSTP1 Val/Val subjects, respectively (Figure 6-11 and Table 6-19). 
Draft – Do Not Cite or Quote 6-91 September 2011

1 Ozone had the greatest estimated effect on difficulty breathing in children with asthma 

2 who were both GSTM1 null and GSTP1 Val/Val (OR: 1.49 [95% CI: 1.14, 1.93] per 30-

3 ppb increase in lag 0-5 avg of 8-h max O3). In the same cohort of children, antioxidant 

4 supplementation reduced O3-associated increases in airway inflammation (Sienra-Monge 

5 et al., 2004). These results add to the body of epidemiologic evidence that antioxidant

6 capacity influences risk of O3-related respiratory morbidity. As was discussed in Section 

7 6.2.1.2, compared with the GSTM1 genotype, evidence for effect modification by GSTP1 

8 genetic polymorphisms is less certain. Romieu et al. (2006) found that the GSTP1 

9 Val/Val variant was associated with a lesser O3-associated decrement in lung function but 

10 greater risk of respiratory symptoms. Whereas some studies have reported greater risk of 

11 asthma among GSTP1 Ile/Ile or Ile/Val subjects (Mapp et al., 2002; Hemmingsen et al., 

12 2001), others have reported greater risk among GSTP1 Val/Val subjects (Tamer et al., 

13 2004). In Romieu et al. (2006), GSTP1 Ile/Ile was associated with greater severity of 

14 asthma, and Lee et al. (2004b) also reported greater risk of air pollution-associated 

15 asthma among GSTP1 Ile/Ile children in the Southern California Children’s Health 

16 Study.

Asthma Medication Use

17 The 2006 O3 AQCD concluded that ambient O3 likely was associated with increased 

18 asthma medication use based on the positive associations found in several studies of 

19 children with asthma (Figure 6-12 and Table 6-20). Among the few newly available 

20 studies on asthma medication use, evidence generally supported the previous conclusion 

21 (Escamilla-Nuñez et al., 2008; Romieu et al., 2006). Most of these studies examined lags 

22 0 or 1 of 1-h max O3 exposures; however, Romieu et al. (2006) found that lag 0-5 avg of 

23 1-h max O3 was associated with a larger increase in bronchodilator use than were lags 1 

24 or 0-1 avg. As compared with respiratory symptoms, effects on medication use were 

25 estimated with greater uncertainty as indicated by the wide 95% CIs. The wide 95% CIs 

26 have been attributed to a smaller number of study subjects reporting medication use and 

27 the low frequency of use over the study period. However, within most studies, findings 

28 were similar for respiratory symptoms and asthma medication use. Among recent studies, 

29 Romieu et al. (2006) and Escamilla-Nunez et al. (2008) observed O3-associated increases 

30 in both respiratory symptoms and bronchodilator use. Schildcrout et al. (2006) did not 

31 observe O3-associated increases in either respiratory symptoms or rescue inhaler use. In 

32 contrast, Romieu et al. (1996) and Rabinovitch et al. (2004) observed that O3 was 

33 positively associated with daytime respiratory symptoms but not with bronchodilator use. 
Draft – Do Not Cite or Quote 6-92 September 2011

CS = corticosteroid. Results are presented in increasing order of ambient ozone concentration. Effect estimates are from singlepollutant models and are standardized to a 40- and 30-ppb increase for 1-h max and 8-h max ozone, respectively

Figure 6-12 Associations of ambient ozone exposure with asthma medication 

use.

Table 6-20 Additional characteristics and quantitative data for studies 

presented in Figure 6-12

Study Location/

Population O3 Lag

O3

Averaging 

Time

Medication Subgroup Odds Ratio 

(95% CI)a

Schildcrout et al. 

(2006)

8 U.S. communities

Children with asthma

0 1-h max Rescue inhaler use 1.01 (0.89, 1.15)

Thurston et al. 

(1997)

CT River Valley, CT

Asthmatic campers

0 1-h max Beta-agonist use 1.17 (0.96, 1.44)

Ostro et al. (2001) Los Angeles, CA

Children with asthma

1 1-h max Extra medication use 1.10 (1.03, 1.19)

Romieu et al. (1996) northern Mexico City, Mexico

Children with asthma

0 1-h max Bronchodilator use 0.97 (0.93, 1.01)

Romieu et al. (1997) southern Mexico City, Mexico

Children with asthma

0 1-h max Bronchodilator use 1.02 (1.00, 1.05)

Romieu et al. (2006) Mexico City, Mexico

Children with asthma

0-5 avg 1-h max Bronchodilator use GSTP1 Ile/Ile

Ile/Val

GSTP1 Val/Val

0.96 (0.90, 1.02)

1.10 (1.02, 1.19)

Gielen et al. (1997) Amsterdam, Netherlands

Children with asthma

0 8-h max Bronchodilator use 1.10 (0.78, 1.55)

Jalaludin et al. 

(2004)

Sydney, Australia

Children with asthma

1 1-h max Beta-agonist use/no 

steroid

ICS use

1.08 (0.89, 1.32)

1.08 (0.96, 1.21)

CS= Corticosteroid. a

Effect estimates are standardized to a 40- and 30-ppb increase for 1-h max and 8-h max O3, respectively.

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)

Outcome

Rescue inhaler use

Beta-agonist use

Extra medication use

Bronchodilator use

Bronchodilator use

Bronchodilator use

Bronchodilator use

Beta-agonist use/no steroid

CS use

Lag

0

0

1

0

0

0-5 avg

0

1

Subgroup

GSTP1 Ile/Ile Ile/Val

GSTP1 Val/Val

0 0.5 1 1.5 2

Odds ratio (95% CI)
Draft – Do Not Cite or Quote 6-93 September 2011

Changes in Activity

1 While investigation has been limited, evidence has not consistently indicated associations 

2 between O3 exposure and diminished activity level in children with asthma (O'Connor et 

3 al., 2008; Delfino et al., 2003). These studies have examined a range of O3 averaging 

4 times and lags of exposure. In the large ICAS cohort, O’Connor et al. (O'Connor et al., 

5 2008) found that a 20-ppb increase in lag 1-19 avg of 24-h O3 ambeint was associated 

6 with a 10% lower odds (95% CI: -26, 10) of slow play. In a small (n = 22) panel study 

7 conducted in children with asthma in Los Angeles CA, Delfino et al. (2003) found that a 

8 40-ppb increase in lag 0 of 1-h max O3 was associated with an increase in symptoms that 

9 interfered with daily activity with an OR (95% CI) of 7.41 (1.18, 43.2). Several studies 

10 reported increases in school absenteeism in children with asthma in association with long 

11 lags of O3 exposure (14-day and 30-day distributed lags or 19-day avg) (O'Connor et al., 

12 2008; Gilliland et al., 2001; Chen et al., 2000). Whereas Chen et al. (2000) and O’Connor 

13 et al. (2008) examined absences for any reason, Gilliland et al. (2001) found associations 

14 with absences for respiratory illnesses. Despite this evidence, several limitations have 

15 been noted, including the uncertain biological relevance of long lag periods of O3

16 exposure and the potential for residual seasonal confounding when examining long lag 

17 periods of exposure. In analyses of single-day lags, Gilliland et al. (2001) found that 8-h 

18 avg (10:00 a.m.-6:00 p.m.) O3 exposure was associated with increases in respiratory19 related absences from lag day 1 to lag day 5, indicating an effect of exposures with 

20 shorter lag periods.

6.2.4.2 Adults with Respiratory Disease

21 Characteristics and ambient O3 concentration data from studies of adults with respiratory 

22 disease are presented in Table 6-21. In this relatively small body of literature, several 

23 studies found ambient O3 exposure (1-h max or 8-h max) to be associated with increases 

24 respiratory symptoms and decreases in activity levels in adults with asthma (Khatri et al., 

25 2009; Feo Brito et al., 2007; Eiswerth et al., 2005; Ross et al., 2002). In a recent panel 

26 study of adults with COPD, investigators found lag 1 of 8-h max O3 to be associated with 

27 increased odds of dyspnea and sputum changes but decreased odds of nasal discharge, 

28 wheeze, or upper respiratory symptoms (Peacock et al., 2011).

29 In a panel study of children and adults with asthma, lag 1-3 avg of 8-h max O3 exposure 

30 was associated with increases in morning and evening symptom scores and frequency of 

31 asthma medication use (Ross et al., 2002). During one pollen season (May-June 2000 or 

32 2001), Feo Brito et al. (2007) specifically followed a group of 137 adults who had asthma 

33 and pollen allergy in central Spain. In the industrial Puertollano, a 40-ppb increase in lag 
Draft – Do Not Cite or Quote 6-94 September 2011

1 3 of 1-h max O3 was associated with a 14.3% increase (95% CI: 3.6, 26.0) in the number 

2 of subjects reporting respiratory symptoms, adjusting only for time trend. There was a 

3 much weaker association in the less industrialized Ciudad Real with lower ambient air 

4 pollution concentrations and a narrower range of ambient O3 concentrations (2.3% [95% 

5 CI: -14, 21%] per 40-ppb increase in lag 4 of 1-h max O3). Park et al. (2005a) followed 

6 adults with asthma in Korea during a period that included dust storms and found that a 

7 20-ppb increase in lag 0 of 24-h avg O3 was associated with an increased odds of night 

8 symptoms (OR: 1.11 [95% CI: 0.96, 1.29]) but not cough (OR: 1.00 [95% CI: 0.94, 

9 1.06]) or rescue inhaler use (OR: 0.99 [95% CI: 0.94, 1.05]).

Table 6-21 Mean and upper percentile ozone concentrations in epidemiologic 

studies examining respiratory symptoms and medication use in 

adults with respiratory disease

Study Location Years/Season

O3 Averaging Time

Mean/Median 

Concentration (ppb) Upper Percentile Concentrations (ppb)

Khatri et al. 

(2009)

Atlanta, GA 2003, 2005, 2006

Warm season

8-h max 59a Max: 73a

Ross et al. 

(2002)

East Moline, IL April-October 1994 8-h avg 41.5 Max: 78.3

Eiswerth et al. 

(2005)

Glendora, CA 1983

Cold season

1-h max NR NR

Peacock et al. 

(2011) London, England 1995-1997

All-year

8-h max 15.5 Autumn/Winter Max: 32

Spring/Summer Max: 74

Feo Brito et al. 

(2007)

Ciudad Real and 

Puertollano, Spain

2000-2001

Warm season

1-h max 65.9 (Ciudad Real)b

56.8 (Puertollano)b

Max: 101.5b (Ciudad Real); 

70.5b (Puertollano)

Wiwatanadate et 

al. (2011) Chiang Mai, Thailand August 2005-June 

2006

24-h avg 17.5 90th: 26.82

Max: 34.65

Park et al. 

(2005a)

Incheon, Korea March-June 2002 24-h avg Dust event days: 23.6

Control days: 25.1

NR

NR = Not Reported, Max = Maximum. a

Individual-level exposure 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).

10 Studies also indicated that ambient O3 exposure may result in decreases in activity levels 

11 in adults with asthma. Notably, although conducted over single seasons, these studies did 

12 not consider confounding by meteorological factors. In a cross-sectional summer study in 

13 Atlanta, GA (described in Section 6.2.1.2), Khatri et al. (2009) observed that a 30-ppb 

14 increase in lag 2 of 8-h max O3 was associated with a 0.69-point decrease (95% CI: -1.28, 

15 -0.11) in the Juniper quality of life score, which incorporates indices for symptoms, 

16 mood, and activity limitations (7-point scale). In a fall study conducted in the Los 

17 Angeles, CA area, Eiswerth et al. (2005) examined the activities of 64 individuals with 

18 asthma (age 16 years and older). A 40-ppb increase in 1-h max O3 was associated with a 

19 0.24% (95% CI: 0.08, 0.40%) lower probability of participation in indoor activities. The 

20 association with outdoor activities was positive but not statistically significant. Although 
Draft – Do Not Cite or Quote 6-95 September 2011

1 the authors acknowledged that their findings were unexpected and may have been 

2 influenced by lack of control for potential confounders, they interpreted the decrease in 

3 indoor activities as rest replacing chores. In contrast, in a panel study of individuals with 

4 asthma (ages 13-78 years) in Thailand, O3 exposure was associated with a lower odds of 

5 symptoms that interfered with activities (OR: 0.74 [95% CI: 0.57, 0.96] per 20-ppb 

6 increase in lag 4 of 24-h avg O3) (Wiwatanadate and Liwsrisakun, 2011).

6.2.4.3 Populations not Restricted to Individuals with Asthma

7 Characteristics and ambient O3 concentration data from studies of populations not 

8 restricted to individuals with asthma are presented in Table 6-22. In contrast with 

9 findings for lung function (Section 6.2.1.2), epidemiologic studies do not provide 

10 consistent evidence of associations between short-term ambient O3 exposure and 

11 increases in respiratory symptoms in children without asthma (Figure 6-13 and 

12 Table 6-23).

Table 6-22 Mean and upper percentile ozone concentrations in epidemiologic 

studies examining respiratory symptoms in populations not 

restricted to individuals with asthma

Study Location Years/Season O3 Averaging 

Time

Mean/Median 

Concentration (ppb) Upper Percentile Concentrations (ppb)

Apte et al. 

(2008)

Multiple U.S. cities (NR) 1994-1998

Winter or summer

Workday avg

(8:00 a.m. -

5:00 p.m.)

24-h avg

34.2a

25.5a

Max: 86.2a

Max: 67.3a

Neas et al. 

(1995)

Uniontown, PA June-August 1990 12-h avg (8:00 

a.m.-8:00 p.m.)

37.2 Max: 44.9

Triche et al. 

(2006)

Southwestern VA 1995-1996

Warm season

1-h max

8-h max

24-h avg

60.8

54.5

35.2

75th: 70.0, Max: 95.0

75th: 64.1, Max: 87.6

75th: 40.6, Max: 56.6

Linn et al. (1996) Rubidoux, Upland, 

Torrence, CA

1992-1993, 1993-1994

Fall and spring

24-h avg 23 Max: 53

Gold et al. 

(1999)

Mexico City, Mexico 1991

Winter, spring, fall

24-h avg 52.0 Max: 103

Ward et al. 

(2002)

Birmingham and Sandwell, 

England

1997

Winter and summer

24-h avg Winter median: 13.0

Summer median: 22.0

Winter Max: 33

Summer Max: 41

Hoek and 

Brunekreef 

(1995)

Deurne and Enkhuizen, 

Netherlands

1989

March-July

1-h max Deurne: 57

Enkhuizen: 59

Max: 107

Max: 114

Moon et al. 

(2009)

4 cities, South Korea April-May 2003 8-h avg (10:00 a.m.-6:00 p.m.)NR NR

Rodriguez et al. 

(2007)

Perth, Australia 1996-2003

All-year

1-h max

24-h avg

33

28

Max: 95

Max: 74

NR = Not Reported, Max = Maximum. a

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 6-96 September 2011

1 Among healthy children in Uniontown, PA, Neas et al. (1995) found a stronger 

2 association between O3 exposure and evening cough using ambient concentrations 

3 weighted by time spent outdoors (OR: 2.20 [95% CI: 1.02, 4.75] per 30-ppb increase in 

4 lag 0 of 12-h avg [8:00 a.m.-8:00 p.m.]) than using unweighted concentrations (OR: 1.36 

5 [95% CI: 0.86, 2.13] per 30-ppb increase in lag 0 of 12-h avg [8:00 a.m.-8:00 p.m.]). 

6 Several other panel studies of school-aged children, in which asthma prevalence ranged 

7 between 0 to 50%, reported null or negative associations between various averaging 

8 times and lags of ambient O3 exposure and respiratory symptoms (Moon et al., 2009; 

9 Rodriguez et al., 2007; Ward et al., 2002; Linn et al., 1996; Hoek and Brunekreef, 1995). 

10 For example, a large study of 696 children in four regions in South Korea, Moon et al. 

11 (2009) observed that among all subjects, ORs of lag 0 8-h avg O3 with most respiratory 

12 symptoms were close to 1.0. In city-specific analyses, O3 exposure was only consistently 

13 associated with increases in URS (runny nose or sneezing), with the largest magnitude of 

14 association observed in Jeju island (OR: 1.08 [95% CI: 0.96, 1.21] per a 30-ppb increase 

15 in lag 0 8-h avg O3). Consistent with other studies conducted in Mexico City, Gold et al. 

16 (1999) reported a positive association between lag 1 of 24-h avg O3 exposure and phlegm 

17 in children; however, investigators acknowledged being unable to distinguish between 

18 the effects of the highly-correlated O3 and PM10 (r = 0.75).

19 In a recent study, O3 exposure was associated with increased odds of respiratory 

20 symptoms in a group of infants who have mothers with asthma (Triche et al., 2006). 

21 Triche et al. (2006) followed 691 infants in southwestern VA \for 83 days between June 

22 and August of 1995 and/or 1996 and found that a 20-ppb increase in lag 0 of 24-h avg O3

23 was associated with odds ratios (95% CI) of 2.34 (1.02, 5.37) for wheeze and of 3.63 

24 (1.81, 7.28) for difficulty breathing among the 61 infants who had mothers with asthma. 

25 Investigators estimated smaller magnitudes of association for 1-h and 8-h max O3

26 exposures. Smaller, statistically nonsignificant associations also were found in analyses 

27 that included all subjects (Figure 6-13 and Table 6-23). While these results suggested that 

28 children with mothers with asthma may be at greater risk of O3-related respiratory 

29 morbidity, the authors acknowledged that mothers with asthma may be more likely to 

30 report symptoms in their children and that transient wheeze, which is common in infants, 

31 may not predict respiratory morbidity later in life. In a study of children with parental 

32 history of asthma with follow-up to an older age (5 years), ambient O3 exposure was not 

33 associated with increases in respiratory symptoms (Rodriguez et al., 2007).
Draft – Do Not Cite or Quote 6-97 September 2011

LRS = lower respiratory symptoms, URS = Upper respiratory symptoms. Effect estimates 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 ozone exposures, respectively.

Figure 6-13 Associations of ambient ozone exposure with respiratory 

symptoms in studies not restricted to children with asthma. 

Table 6-23 Additional characteristics and quantitative data for studies 

presented in Figure 6-13

Study Location/ 

Population O3 Lag O3 Averaging Time Symptom Subgroup Odds Ratio(95% CI)a

Ward et al. (2002) Birmingham and 

Sandwell, England

Children

0-6 avg 24-h avg Wheeze

Shortness of breath

0.78 (0.22, 2.79)

1.80 (0.64, 5.06)

Hoek and 

Brunekreef (1995)

Enkhuizen, 

Netherlands

Children

0 1-h max Cough

URS

0.95 (0.71, 1.25)

1.15 (1.00, 1.33)

Moon et al. (2009) 4 cities, South Korea

Children

0 24-h avg URS All subjects

Jeju Island

0.96 (0.90, 1.03)

1.08 (0.96, 1.21)

Neas et al. (1995) Uniontown, PA

Healthy children

0 12-h avg (8:00 

a.m.-8:00 p.m.)

Evening cough 2.20 (1.02, 4.75)b

Triche et al. (2006) southwestern VA

Infants

0 8-h max Wheeze All subjects

Maternal asthma

1.60 (0.85, 3.00)

2.34 (1.02, 5.37)

Gold et al. (1999) Mexico City, Mexico

Children

1 24-h avg Phlegm 1.04 (1.00, 1.07)

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 12-h avg, and 24-h avg O3, respectively. b

O3 exposures were weighted by the proportion of time spent outdoors.

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)

O3 Lag

0-6 avg

0

0

0

0

0

Symptom

Wheeze

Shortness of breath

Cough

URS

URS

Evening cough

Wheeze

Phlegm

Subgroup

All subjects

Jeju Island

All

With asthmatic mothers

►

►

►

0 1 2 3

Odds ratio (95% CI)
Draft – Do Not Cite or Quote 6-98 September 2011

1 A recent cross-sectional study examined 4,200 adult workers from 100 office buildings 

2 across the U.S. and found that a range of ambient O3 exposure metrics, including the 24-

3 h, workday (8:00 a.m.-5:00 p.m.), and late workday (3:00 p.m.-6:00 p.m.) averages, were 

4 associated with increases in building-related URS (nasal congestion or sore throat) and 

5 LRS (wheeze, shortness of breath, or chest tightness) (Apte et al., 2008). Investigators 

6 suggested that the findings may have been attributable to formaldehyde and organic acids 

7 produced from O3-initiated reactions within buildings; however, additional data on indoor 

8 levels of volatile organic compounds, indoor O3, and infiltration rates is warranted to 

9 characterize whether the observed associations were attributable to the formation of these 

10 secondary species by ambient O3 penetrating indoors

6.2.4.4 Confounding in Epidemiologic Studies of Respiratory 

Symptoms and Medication Use

11 Epidemiologic studies did not indicate that associaitons between short-term O3 exposure 

12 and respiratory symptoms were confounded by meteorological factors. Except where 

13 specified in the text, associations between ambient O3 exposure and respiratory 

14 symptoms or medication use were found after adjusting for temperature in models. Some 

15 studies additionally included humidity in models (Triche et al., 2006; Ross et al., 2002) or 

16 found no independent association with respiratory symptoms (Thurston et al., 1997). 

17 Several studies that examined populations with a high prevalence of atopy found O3-

18 associated increases in respiratory symptoms and asthma medication use in copollutant

19 models that included daily pollen counts (Just et al., 2002; Ross et al., 2002; Gielen et al., 

20 1997). Gielen et al. (1997) and Ross et al. (2002) specifically reported a high prevalence 

21 of grass pollen allergy in their study populations (52% and 38%, respectively). Ross et al. 

22 (2002) found similar associations of O3 with morning symptoms and asthma medication 

23 use in a single-pollutant model (e.g., 0.21-point [95% CI: 0.12, 0.30] increase in 

24 symptom score per 30-ppb increase in lag 1-3 avg of 8-h max O3) and in a copollutant

25 model with daily pollen counts (e.g., 0.20-point [95% CI: 0.11, 0.29] increase in 

26 symptom score per 30-ppb increase in lag 1-3 avg of 8-h max O3). Feo Brito et al. (2007)

27 specifically followed a group of adults in central Spain, all of whom had both asthma and 

28 pollen allergy. In one city, O3 was associated with an increase in the number of subjects 

29 reporting symptoms. A smaller, statistically nonsignificant effect estimate was obtained 

30 for pollen. Conversely, in another city, pollen was associated with an increased incidence 

31 of respiratory symptoms, whereas O3 was not. While copollutant modeling was not 

32 conducted, in both locations, O3 and pollen concentrations were weakly correlated, 

33 indicating that the findings for O3 were not likely confounded by pollen. Rather, the 
Draft – Do Not Cite or Quote 6-99 September 2011

1 results suggested that O3 and pollen may have independent effects that vary between 

2 locations, depending on the mix of airborne pollutants.

Table 6-24 Associations between short-term ozone exposure and respiratory 

symptoms in single- and copollutant models

Study Location/

Population O3 Exposure Data Symptom

O3-associated OR 

in Single-Pollutant

Model (95% CI)a

O3-associated OR 

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 (NCICAS)

Children with asthma

8-h avg (10:00 a.m.- 6:00 p.m.)

Lag 1-4 avg

Morning symptoms 8 cities with SO2 data

1.35 (1.04, 1.69)

7 ciites with NO2 data

1.25 (0.94, 1.67)

3 cities with PM10 data

1.21 (0.61, 2.41)

with lag 1-2 avg, 3-h 

avg SO2

1.23 (0.94, 1.61)

with lag 1-6 avg, 24-h 

avg NO2

1.14 (0.85, 1.55)

with lag 1-2 avg, 24-h 

avg PM10

1.08 (0.49, 2.39)

Thurston et al. (1997) CT River Valley

Children with asthma 

attending summer 

camp

1-h max

Lag 0

Chest symptoms

1.21 (1.12, 1.31)b

with lag 0, 12-h avg 

sulfate

1.19 (1.06, 1.35)b

Romieu et al. (1996) Mexico City, Mexico

Children with asthma

1-h max

Lag 0

LRS

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

Children with asthma

1-h max

Lag 0

LRS

1.09 (1.04, 1.14)

with lag 0, 24-h avg 

PM10

1.09 (1.01, 1.19) 

LRS = Lower respiratory symptoms.

a

Effect estimates 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.

3 Robust associations between O3 exposure and respiratory symptoms also were observed 

4 in copollutant models that included PM2.5, PM10, sulfate, SO2, or NO2 (Table 6-24). 

5 Information on confounding in asthma medication use associations was more limited. 

6 The association between O3 and bronchodilator use did not change in Gent et al. (2003)

7 after adjusting for PM2.5 but decreased in magnitude in Thurston et al. (1997) after 

8 adjusting for 12-h avg sulfate. For respiratory symptoms and medication use, copollutant

9 associations remained robust after adjusting for O3. Notably, studies examined different 

10 averaging times for O3 (1-h max or 8-h avg) and co-pollutants (3-h to 24-h avg) and 

11 reported a range of correlations with co-pollutants. Two studies conducted concurrently 

12 in two regions of Mexico City examined lag 0 exposures of 1-h max O3 and 24-h avg 

13 PM10 or PM2.5 and found robust associations with respiratory symptoms for both O3 and 

14 co-pollutants (Romieu et al., 1997; Romieu et al., 1996). Romieu et al. (1997) reported a 

15 moderate correlation between 1-h max O3 and 24-h avg PM10 (r = 0.47). Thurston et al. 

16 (1997) and Gent et al. (2003) found 1-h max O3 concentrations to be highly correlated 

17 with 12-h avg sulfate (r=0.74) and 24-h avg PM2.5 (r=0.77), respectively, thus the 

18 copollutant results should be interpreted with caution. The association between O3

19 exposure and respiratory symptoms observed in NCICAS was robust in two-pollutant 
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1 models with SO2, NO2, and or PM10; however, the interpretation is complicated because 

2 of the different averaging times and lags of exposure examined for O3 and co-pollutants 

3 (Mortimer et al., 2002) (Table 6-24). Also difficult are interpretations of the robust 

4 associations observed between ambient O3 exposure and respiratory symptoms after 

5 adjusting for multiple pollutants (i.e., PM2.5 plus NO2 or PM10-2.5)(Escamilla-Nuñez et al., 

6 2008; Triche et al., 2006).

6.2.4.5 Summary of Epidemiologic Studies of Respiratory 

Symptoms and Asthma Medication Use

7 With a majority of investigation focused on individuals with asthma, the collective 

8 epidemiologic evidence clearly demonstrates that short-term ambient O3 exposure is 

9 associated with increases in respiratory symptoms and asthma medication use in children 

10 with asthma. In a smaller body of literature, several studies find associations in adults 

11 with asthma. In comparison, evidence has not consistently indicated that short-term O3

12 exposure is associated with reduced activity levels in children or adults with asthma. 

13 Although O3 exposure has been associated with school absenteeism among children with 

14 asthma, only Gilliland et al. (2001) examined absences specifically for respiratory causes 

15 and found associations with O3 exposure lag periods shorter than 14 days. Epidemiologic 

16 studies do not provide consistent evidence of association between short-term ambient O3

17 exposure and respiratory symptoms in children without asthma.

18 Collectively, epidemiologic studies most frequently examined 1-h max and 8-h max or 

19 avg O3 exposures, and the few studies that examined both averaging times found similar 

20 magnitudes of associations with respriatory symptoms (Triche et al., 2006; Delfino et al., 

21 2003; Gent et al., 2003). Several studies found increases in respiratory symptoms with O3

22 exposures averaged over 12 to 24 hours (Triche et al., 2006; Jalaludin et al., 2004; Gold 

23 et al., 1999; Neas et al., 1999). Epidemiologic studies examined associations of 

24 respiratory symptoms with single-day O3 concentrations lagged from 0 to 5 days as well 

25 concentrations averaged over 2 to 19 days. While O3 exposures lagged 0 or 1 days were 

26 consistently associated with respiratory symptoms, several studies that examined a range 

27 of exposure lags found larger effect estimates for multiday averages (3- to 6-days) of O3

28 exposure (Escamilla-Nuñez et al., 2008; Romieu et al., 2006; Rabinovitch et al., 2004; 

29 Just et al., 2002; Mortimer et al., 2002; Ross et al., 2002). These epidemiologic findings 

30 are in contrast with those from controlled human exposure studies that find attenuated 

31 symptom responses with O3 exposures repeated over several days (Section 6.2.1.1). The 

32 epidemiologic findings for lagged O3 exposures or those accumulated over several days 

33 are well-supported by the action of O3 to sensitize bronchial smooth muscle to 

34 hyperreactivity, thus acting as a primer for subsequent exposure to antigens such as 
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1 allergens (Section 5.3.5). In several of the studies of individuals with asthma, the 

2 prevalence of atopy was high (50-100%), and sensitization of airways provides a 

3 biologically plausible mode of action by which lagged or multiday average O3 exposures 

4 are associated with increases in respiratory symptoms in these studies of individuals with 

5 asthma.

6 Epidemiologic evidence did not indicate that associations between short-term O3

7 exposure and respiratory symptoms were confounded by temperature or pollen. In the 

8 limited analysis of confounding by co-pollutants (primarily PM), robust associations with 

9 respiratory symptoms were observed for O3; however, disentangling the independent 

10 effects of O3 exposure in many studies is complicated due to the high correlations 

11 observed between O3 and PM, different averaging times and lags of exposure examined 

12 for co-pollutants, and the multiple co-pollutants included in models. Nonetheless, the 

13 consistency of association among individuals with asthma with and without adjustment 

14 for copollutant exposures combined with evidence from controlled human exposure 

15 studies for the direct effect of O3 exposure provide substantial evidence for the 

16 independent effects of ambient O3 exposure on increases in respiratory symptoms

6.2.5 Lung Host Defenses

17 The mammalian respiratory tract has a number of closely integrated defense mechanisms 

18 that, when functioning normally, provide protection from the adverse effects of a wide 

19 variety of inhaled particles and microbes. For simplicity, these interrelated defenses can 

20 be divided into two major parts: (1) nonspecific (transport, phagocytosis, and bactericidal 

21 activity) and (2) specific (immunologic) defense mechanisms. A variety of sensitive and 

22 reliable methods have been used to assess the effects of O3 on these components of the 

23 lung’s defense system to provide a better understanding of the health effects associated 

24 with the inhalation of this pollutant. The previous O3 AQCD states that animal 

25 toxicological studies provide extensive evidence that acute O3 exposures as low as 0.08 to 

26 0.5 ppm can cause increases in susceptibility to infectious diseases due to modulation of 

27 lung host defenses. Tables 6-6 through 6-9, beginning on p. 6-41 of the 1996 O3 AQCD 

28 (U.S. EPA, 1996a), and Table AX5-7, beginning on p. AX5-8 of the 2006 O3 AQCD

29 (U.S. EPA, 2006b), present studies on the effects of O3 on host defense mechanisms. This 

30 section discusses the various components of host defenses, such as the mucociliary 

31 escalator, the phagocytic, bactericidal, and regulatory role of the alveolar macrophages 

32 (AMs), the adaptive immune system, and integrated mechanisms that are studied by 

33 investigating the host’s response to experimental pulmonary infections.
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6.2.5.1 Mucociliary Clearance 

1 The mucociliary system is one of the lung’s primary defense mechanisms. It protects the 

2 conducting airways by trapping and quickly removing material that has been deposited or 

3 is being cleared from the alveolar region by migrating alveolar macrophages. Ciliary 

4 movement directs particles trapped on the overlying mucous layer toward the pharynx, 

5 where the mucus is swallowed or expectorated. 

6 The effectiveness of mucociliary clearance can be determined by measuring such 

7 biological activities as the rate of transport of deposited particles; the frequency of ciliary 

8 beating; structural integrity of the ciliated cells; and the size, number, and distribution of 

9 mucus-secreting cells. Once this defense mechanism has been altered, a buildup of both 

10 viable and nonviable inhaled substances can occur on the epithelium and may jeopardize 

11 the health of the host, depending on the nature of the uncleared substance. Impaired 

12 mucociliary clearance can result in an unwanted accumulation of cellular secretions, 

13 increased infections, chronic bronchitis, and complications associated with chronic 

14 obstructive pulmonary disease. A number of previous studies with various animal species 

15 have examined the effect of O3 exposure on mucociliary clearance and reported 

16 morphological damage to the cells of the tracheobronchial tree from acute and sub17 chronic exposure to O3 0.2 ppm and higher. The cilia were either completely absent or 

18 had become noticeably shorter or blunt. After placing these animals in a clean-air 

19 environment, the structurally damaged cilia regenerated and appeared normal (U.S. EPA, 

20 1986). Based on such morphological observations, related effects such as ciliostasis, 

21 increased mucus secretions, and a slowing of mucociliary transport rates might be 

22 expected. However, no measurable changes in ciliary beating activity have been reported 

23 due to O3 exposure alone. Essentially no data are available on the effects of prolonged 

24 exposure to O3 on ciliary functional activity or on mucociliary transport rates measured in 

25 the intact animal. In general, functional studies of mucociliary transport have observed a 

26 delay in particle clearance soon after acute exposure. Decreased clearance is more 

27 evident at higher doses (1 ppm), and there is some evidence of tolerance/adaptation for 

28 these effects (U.S. EPA, 1986). However, no recent studies have evaluated the effects of 

29 O3 on mucociliary clearance.

6.2.5.2 Alveolobronchiolar Transport Mechanism 

30 In addition to the transport of particles deposited on the mucous surface layer of the 

31 conducting airways, particles deposited in the deep lung may be removed either up the 

32 respiratory tract or through interstitial pathways to the lymphatic system. The pivotal 

33 mechanism of alveolobronchiolar transport involves the movement of AMs with 
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1 phagocytized particles to the bottom of the mucociliary escalator. Failure of the AMs to 

2 phagocytize and sequester the deposited particles from the vulnerable respiratory 

3 membrane can lead to particle entry into the interstitial spaces. Once lodged in the 

4 interstitium, particle removal is more difficult and, depending on the toxic or infectious 

5 nature of the particle, its interstitial location may allow the particle to set up a focus for 

6 pathologic processes. Although some studies show reduced early (tracheobronchial) 

7 clearance after O3 exposure, late (alveolar) clearance of deposited material is accelerated, 

8 presumably due to macrophage influx (which in itself can be damaging due to proteases 

9 and oxidative reactions in these cells). In an important older study investigating the 

10 effects of longer term O3 exposure on alveolobronchiolar clearance, rats were exposed to 

11 an urban pattern of O3 (continuous 0.06 ppm, 7 days/week with a slow rise to a peak of 

12 0.25 ppm and subsequent decrease to 0.06 ppm over a 9 h period for 5 days/week) for 

13 6 weeks and were exposed 3 days later to chrysotile asbestos, which can cause pulmonary 

14 fibrosis and neoplasia (Pinkerton et al., 1989). After 30 days, the lungs of the O3-exposed 

15 animals had twice the number and mass of asbestos fibers as the air-exposed rats. New 

16 evaluations of O3 effects on alveolar clearance have not been performed.

6.2.5.3 Alveolar Macrophages 

17 Within the gaseous exchange region of the lung, the first line of defense against 

18 microorganisms and nonviable particles that reach the alveolar surface is the AM. This 

19 resident phagocyte is responsible for a variety of activities, including the detoxification 

20 and removal of inhaled particles, maintenance of pulmonary sterility via destruction of 

21 microorganisms, and interaction with lymphocytes for immunologic protection. Under 

22 normal conditions, AMs seek out particles deposited on the alveolar surface and ingest 

23 them, thereby sequestering the particles from the vulnerable respiratory membrane. To 

24 adequately fulfill their defense function, the AMs must maintain active mobility, a high 

25 degree of phagocytic activity, and an optimally functioning biochemical and enzyme 

26 system for bactericidal activity and degradation of ingested material. As discussed in 

27 previous AQCDs, short periods of O3 exposure can cause a reduction in the number of 

28 free AMs available for pulmonary defense, and these AMs are more fragile, less 

29 phagocytic, and have decreased lysosomal enzyme activities required for killing 

30 pathogens. For example, in results from earlier work in rabbits, a 2-h exposure to 0.1 ppm 

31 O3 inhibited phagocytosis and a 3-h exposure to 0.25 ppm decreased lysosomal enzyme 

32 activities (Driscoll et al., 1987; Hurst et al., 1970). Similarly, AMs from rats exposed to 

33 0.1 ppm O3 for 1 or 3 weeks exhibited reduced hydrogen peroxide production (Cohen et 

34 al., 2002). A controlled human exposure study reported decrements in the ability of 

35 alveolar macrophages to phagocytize yeast following exposure of healthy volunteers to 
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1 80 to 100 ppb O3 for 6.6-h during moderate exercise (Devlin et al., 1991). Although the 

2 percentage of phagocytosis-capable macrophages was unchanged by O3 exposure, the 

3 number of yeast engulfed was reduced when phagocytosis was complement-dependent. 

4 However, there was no difference in the ability of macrophages to produce superoxide 

5 anion after O3 exposure. These results are consistent with those from another controlled 

6 human exposure study in which no changes in the level of lysosomal enzymes or 

7 superoxide anion production were observed in macrophages lavaged from healthy human 

8 subjects exposed to 400 ppb O3 for 2 h with heavy intermittent exercise (Koren et al., 

9 1989). More recently, Lay et al. (2007) observed no difference in phagocytic activity or 

10 oxidative burst capacity in macrophages or monocytes from sputum or blood collected 

11 from healthy volunteers after a 2-hour exposure to 400 ppb O3 with moderate intermittent 

12 exercise. However, another study found that oxidative burst and phagocytic activity in 

13 macrophages increased in GSTM1 null subjects compared to GSTM1 positive subjects, 

14 who had relatively unchanged macrophage function parameters after an O3 exposure 

15 identical to that of Lay et al. described above (Alexis et al., 2009). Collectively, these 

16 studies demonstrate that O3 can affect multiple steps or aspects required for proper 

17 macrophage function, but any concentration-response relationship appears complex and 

18 genotype may be a consideration. A few other recent studies have evaluated ozone’s 

19 effects on macrophage function, but these are of questionable relevance due to the use of 

20 in vitro exposure systems and amphibian animal models (Mikerov et al., 2008b; Dohm et 

21 al., 2005; Klestadt et al., 2005).

6.2.5.4 Infection and Adaptive Immunity 

General Effects on the Immune System

22 The effects of O3 on the immune system are complex and dependent on the exposure 

23 regimen and the observation period. According to toxicological studies it appears that the 

24 T-cell-dependent functions of the immune system are more affected than B-cell25 dependent functions (U.S. EPA, 2006b). Generally, there is an early immunosuppressive 

26 effect that subsides with continued O3 exposure, resulting in either a return to normal 

27 responses or an enhancement of immune responses. However, this is not always the case 

28 as Aranyi (1983) showed decreased T-cell mitogen reactions in mice after subchronic 

29 (90-day) exposure to 0.1 ppm O3. Earlier studies report changes in cell populations in 

30 lymphatic tissues (U.S. EPA, 2006b). A more recent study in mice demonstrated that 

31 numbers of certain T cell subsets in the spleen were reduced after exposure to 0.6 ppm O3

32 (10h/day x 15d) (Feng et al., 2006).
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1 The inflammatory effects of O3 involve the innate immune system, and as such can affect 

2 adaptive (or acquired) immunity via alterations in antigen presentation and costimulation 

3 by innate immune cells such as macrophages and dendritic cells. Several recent 

4 controlled human exposure studies demonstrate increased expression of molecules 

5 involved in antigen presentation or costimulation. Lay et al. (2007) collected sputum 

6 monocytes from healthy volunteers exposed to 400 ppb O3 for 2 h with moderate 

7 intermittent exercise and detected increases in HLA-DR, used to present antigen to T 

8 cells, and CD86, a costimulatory marker necessary for T cell activation. Upregulation of 

9 HLA-DR was also observed by Alexis et al. (2009) in sputum dendritic cells and 

10 macrophages from GSTM1 null subjects exposed to 400 ppb O3 for 2 h with moderate 

11 intermittent exercise. On airway monocytes from healthy volunteers 24 hours after 

12 exposure to 80 ppb O3 for 6.6 h with moderate intermittent exercise, HLA-DR, CD86, 

13 and CD14 (a molecule involved in bacterial endotoxin reacitivity) were increased, 

14 whereas CD80, a costimulatory molecule of more heterogeneous function, was decreased 

15 (Alexis et al., 2010). Patterns of expression on macrophages were similar, except that 

16 HLA-DR was found to be significantly decreased after O3 exposure and CD86 was not 

17 significantly altered. An increase in IL-12p70, a macrophage and dendritic cell product 

18 that activates T cells, was correlated with increased numbers of dendritic cells. It should 

19 be noted that these results are reported as comparisons to baseline as there was no clean 

20 air control (Alexis et al., 2010; Alexis et al., 2009). Another controlled human exposure 

21 study reported no increase in IL-12p70 in sputum from healthy, atopic, or atopic 

22 asthmatic subjects following a 2-hour exposure to 400 ppb O3 with intermittent moderate 

23 exercise (Hernandez et al., 2010). Levels of HLA-DR, CD14 and CD86 were not 

24 increased on macrophages collected from any of these subjects. It is difficult to compare 

25 these results to those of Lay et al. (2007) and Alexis et al. (2010) due to differences in O3

26 concentration, cell type examined, and timing of postexposure analysis. 

27 Although no controlled human exposure studies have examined the effects of O3 on the 

28 ability to mount antigen-specific responses, upregulation of markers associated with 

29 innate immune activation and antigen presentation could potentially enhance adaptive 

30 immunity and increase immunologic responses to antigen. While this may bolster

31 defenses against infection, it also may enhance allergic responses (Section 6.2.6).

32 In animal models, O3 has been found to alter responses to antigenic stimulation. For 

33 example, antibody responses to a T-cell-dependent antigen were suppressed after a 

34 56-day exposure of mice to 0.8 ppm O3, and a 14-day exposure to 0.5 ppm O3 decreased 

35 the antiviral antibody response following influenza virus infection (Jakab and Hmieleski, 

36 1988); the latter impairment may pave the way for lowered resistance to reinfection. The 

37 immune response is highly influenced by the temporal relationship between O3 exposure 

38 and antigenic stimulation. When O3 exposure preceded Listeria infection, there were no 
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1 effects on delayed-type hypersensitivity or splenic lymphoproliferative responses; 

2 however, when O3 exposure occurred during or after Listeria infection was initiated, 

3 these immune responses were suppressed (Van Loveren et al., 1988). In another study, a 

4 reduction in mitogen activated T-cell proliferation was observed after exposure to 

5 0.6 ppm for 15 days, and could be ameliorated by antioxidant supplementation. Antigen6 specific proliferation decreased by 60%, indicating attenuation of the acquired immunity 

7 needed for subsequent memory responses (Feng et al., 2006). O3 exposure also skewed 

8 the ex-vivo cytokine responses elicited by non-specific stimulation toward inflammation, 

9 decreasing IL-2 and increasing IFN-γ. Modest decreases in immune function assessed in 

10 the offspring of O3-exposed dams (mice) were observed by Sharkhuu et al. (2011). The 

11 ability to mount delayed-type hypersensitivity responses was significantly suppressed in 

12 42 day-old offspring when dams were exposed to 0.8 or 1.2 ppm O3, but not 0.4 ppm, 

13 from gestational day 9-18. Humoral responses to immunization with sheep red blood 

14 cells were unaffected, as were other immune parameters such as splenic populations of 

15 CD45+ T cells, iNKT cells, and levels of IFN-γ, IL-4, and IL-17 in the BALF. Generally, 

16 continuous exposure to O3 impairs immune responses for the first several days of 

17 exposure, followed by an adaptation to O3 that allows a return of normal immune 

18 responses. Most species show little effect of O3 exposures prior to immunization, but 

19 show a suppression of responses to antigen in O3 exposures post-immunization. 

Microbial Infection

Bacterial infection

20 A relatively large body of evidence shows that O3 increases susceptibility to bacterial 

21 infections. The majority of studies in this area were conducted before the 1996 O3 AQCD 

22 was published and many are included in Table 6-9 on p. 6-53 of that document. Known 

23 contributing factors are impaired mucociliary streaming, altered chemotaxis/motility, 

24 defective phagocytosis of bacteria, decreased production of lysosomal enzymes or 

25 superoxide radicals by alveolar macrophages, and decreased IFN-γ levels. In animal 

26 models of bacterial infection, exposure to 0.08 ppm O3 increases streptococcus-induced 

27 mortality, regardless of whether O3 exposure precedes or follows infection (Miller et al., 

28 1978; Coffin and Gardner, 1972; Coffin et al., 1967). Increases in mortality are due to the 

29 infectious agent, thereby reflecting functional impairment of host defenses. Exercise and 

30 copollutants can enhance ozone’s effects in infectivity models. Although both mice and 

31 rats exhibit impaired bactericidal macrophage activity after O3 exposure, mortality due to 

32 infection is only observed in mice. Additionally, although mice and humans share many 

33 host defense mechanisms, there is little compelling evidence from epidemiologic studies 

34 (Section 6.2.7.3). 
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Viral infection

1 Only a few studies, described in previous AQCDs, have examined the effects of O3

2 exposure on the outcome of viral respiratory infection (see Table 6-9 on p. 6-53 of the 

3 1996 O3 AQCD. Some studies show increased mortality, while others show diminished 

4 severity and increased survival time. There is little to no evidence from studies of animals 

5 or humans to suggest that O3 increases the incidence of respiratory viral infection in 

6 humans. In human volunteers infected with rhinovirus prior to O3 exposure (0.3 ppm for 

7 5 consecutive days), no effect on viral titers, IFN-γ production, or blood lymphocyte 

8 proliferative responses to viral antigen was observed (Henderson et al., 1988). In vitro 

9 cell culture studies of human bronchial epithelial cells indicate O3-induced exacerbation 

10 of human rhinovirus infection (Spannhake et al., 2002), but this is of limited relevance. 

11 Newer studies on the interactions of O3 and viral infections have not been published. 

12 Natural killer (NK) cells, which destroy virally infected cells and tumors in the lung, 

13 appear to be inhibited by higher concentrations of O3 and either unaffected or stimulated 

14 at lower concentrations. Several studies show decreases in NK cell activity following 

15 acute exposures ranging from 0.8 to 1 ppm (Gilmour and Jakab, 1991; Van Loveren et 

16 al., 1990; Burleson et al., 1989). However, Van Loveren et al. (1990) showed that a 

17 1-week exposure to 0.2 or 0.4 ppm O3 increased NK cell activity, and an urban pattern of 

18 exposure (base of 0.06 ppm with peaks of 0.25 ppm) had no effect on NK cell activity 

19 after 1, 3, 13, 52, or 78 weeks of exposure (Selgrade et al., 1990). A more recent study 

20 demonstrated a 35% reduction in NK cell activity after exposure of mice to 0.6 ppm O3

21 (10h/day x 15d) (Feng et al., 2006). The defective IL-2 production demonstrated in this 

22 study may impair NK cell activation. Alternatively, NK cell surface charge may be 

23 altered by ROS, decreasing their adherence to target cells (Nakamura and Matsunaga, 

24 1998). 

Summary: Infections

25 Taken as a whole, the data clearly indicate that an acute O3 exposure impairs the host 

26 defense capability of both humans and animals, primarily by depressing alveolar 

27 macrophage function and perhaps also by decreasing mucociliary clearance of inhaled 

28 particles and microorganisms. This suggests that humans exposed to O3 could be 

29 predisposed to bacterial infections in the lower respiratory tract. The seriousness of such 

30 infections may depend on how quickly bacteria develop virulence factors and how 

31 rapidly PMNs are mobilized to compensate for the deficit in alveolar macrophage 

32 function. To date, a limited number of epidemiologic studies have examined associations 

33 between O3 exposure and HA/ED for respiratory infection, pneumonia, or influenza. 

34 Results have been mixed, and in some cases conflicting (see Sections 6.2.7.2 and 

35 6.2.7.3). With the exception of influenza, it is difficult to ascertain whether cases of 

36 respiratory infection or pneumonia are of viral or bacterial etiology. A study that 
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1 examined the association between O3 exposure and respiratory hospital admissions in 

2 response to an increase in influenza intensity did observe an increase in respiratory 

3 hospital admissions (Wong et al., 2009), but information from toxicological studies of O3

4 and viral infections is ambiguous.

6.2.6 Allergic and Asthma-Related Responses

5 Effects resulting from combined exposures to O3 and allergens have been studied in a 

6 variety of animal species, generally as models of experimental asthma. Pulmonary 

7 function and airways hyperresponsiveness in animal models of asthma are discussed in 

8 Sections 6.2.1.7 and 6.2.2.2. Previous evidence indicates that O3 exposure skews immune 

9 responses toward an allergic phenotype. For example, Gershwin et al. (1981) reported 

10 that O3 (0.8 and 0.5 ppm for 4 days) exposure caused a 34-fold increase in the number of 

11 IgE (allergic antibody)-containing cells in the lungs of mice. In general, the number of 

12 IgE-containing cells correlated positively with levels of anaphylactic sensitivity. In 

13 humans, allergic rhinoconjunctivitis symptoms are associated with increases in ambient 

14 O3 concentrations (Riediker et al., 2001). Recent controlled human exposure studies have 

15 observed O3-induced changes indicating allergic skewing. Airway eosinophils, which 

16 participate in allergic disease and inflammation, were observed to increase in atopic, 

17 mildly asthmatic volunteers 18 h following a 7.6-hour exposure to 160 ppb O3 with light 

18 intermittent exercise (Peden et al., 1997). No increase in airway eosinophils was observed 

19 4 h after exposure of healthy, atopic, or atopic asthmatic subjects to 400 ppb O3 for 2 h 

20 with moderate intermittent exercise (Hernandez et al., 2010). However, atopic subjects 

21 did exhibit increased IL-5, a cytokine involved in eosinophil recruitment and activation, 

22 suggesting that perhaps these two studies observed the same effect at different time 

23 points. Several epidemiologic studies discussed in Section 7.2.5 describe an association 

24 between eosinophils and long-term O3 exposure, consistent with chronic exposure studies 

25 in non-human primates. Hernandez et al. (2010) also observed increased expression of 

26 high and low affinity IgE receptors on sputum macrophages from atopic asthmatics, 

27 which may enhance IgE-dependent inflammation. Sputum levels of IL-4 and IL-13, both 

28 pro-allergic cytokines that aid in the production of IgE,were unaltered in any group. The 

29 lack of increase in IL-4 levels in sputum reported by Hernandez et al., along with 

30 increased IL-5, is consistent with results from Bosson et al. (2003), in which IL-5 (but not 

31 IL-4 levels) increased in bronchial epithelial biopsy specimens following exposure of 

32 mild atopic asthmatics to 200 ppb O3 for 2 h with moderate intermittent exercise. IL-5 

33 was not elevated in specimens obtained from healthy (non-asthmatic) O3-exposed 

34 subjects. Collectively, findings from these studies suggest that O3 can induce or enhance 

35 certain components of allergic inflammation in atopic and atopic asthmatic individuals.
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1 Ozone enhances inflammatory and allergic responses to allergen challenge in sensitized 

2 animals. Short-term exposure (2 days) to 1 ppm O3 exacerbated allergic rhinitis and lower 

3 airway allergic inflammation in Brown Norway rats, a rat strain that is comparatively less 

4 sensitive to O3 than other rats or humans (Wagner et al., 2009; Wagner et al., 2007). 

5 OVA-sensitized rats were intranasally challenged with OVA on days 1 and 2, and 

6 exposed to 0 or 1 ppm O3 (8 h/day) on days 4 and 5. Analysis at day 6 indicated that O3

7 exposure enhanced intraepithelial mucosubstances in the nose and airways, induced cys8 LTs, MCP-1, and IL-6 production in BALF, and upregulated expression of the 

9 proallergic cytokines IL-5 and IL-13. These changes were not evident in non-allergic 

10 controls. All of these responses were blunted by gamma-tocopherol (γT; vitamin E) 

11 therapy. γT neutralizes oxidized lipid radicals, and protects lipids and proteins from 

12 nitrosative damage from NO-derived metabolites. Farraj et al. (2010) exposed allergen13 sensitized adult male 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 14 ) co-exposure of OVA-sensitized mice elicited 

15 significantly greater serum IgE levels than in DEP-exposed OVA-sensitized mice (98% 

16 and 89% increases, respectively). Ozone slightly enhanced levels of BAL IL-5, but 

17 despite increases in IgE, caused a significant decrease in BAL IL-4 levels. IL-10, IL-13, 

18 and IFN-γ levels were unaffected. Lung resistance and elastance were unaffected in 

19 allergen sensitized mice exposed solely to 0.5 ppm O3 once a week for 4 weeks (Farraj et 

20 al., 2010). However, co-exposure to O3 and diesel exhaust particles increased lung 

21 resistance. 

22 In addition to exacerbating existing allergic responses, O3 can also act as an adjuvant to 

23 produce sensitization in the respiratory tract. In a model of murine asthma, using OVA 

24 free of detectable endotoxin, inclusion of 1 ppm O3 during the initial exposures to OVA 

25 (2 h, days 1 and 6) enhanced the inflammatory and allergic responses to subsequent 

26 allergen challenge (Hollingsworth et al., 2010). Compared to air exposed animals, O3

27 exposed mice exhibited significantly higher levels of total cells, macrophages, 

28 eosinophils, and PMNs in BALF, and increased total serum IgE. Pro-allergic cytokines 

29 IL-4, and IL-5 were also significantly elevated, along with pleiotropic Th2 cytokine IL-9 

30 (associated with bronchial hyperresponsiveness) and pro-inflammatory IL-17, produced 

31 by activated T cells. Based on lower inflammatory, IgE, and cytokine responses in Toll32 like receptor 4 deficient mice, the effects of O3 seem to be dependent on TLR 4 signaling, 

33 as are a number of other biological responses to O3 according to studies by Hollingsworth 

34 et al. (2004), Kleeberger et al.(2000) and Garanziotis et al. (2010). The involvement of 

35 TLR 4, along with its endogenous ligand, hyaluronan, in O3-induced responses described 

36 in these studies has been corroborated by a controlled human exposure study by 

37 Hernandez et al. (2010), who found increased TLR 4 expression and elevated levels of 

38 hyaluronic acid in atopic and atopic asthmatic volunteers exposed to 400 ppb O3. This 

39 pathway is discussed in more detail in Chapter 5. Examination of dendritic cells (DCs) 
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1 from the draining thoracic lymph nodes indicated that O3 did not enhance the migration 

2 of DCs from the lungs to the lymph nodes, nor did it alter the expression of functional 

3 DC markers such as CD40, MHC class II, or CD83. However, O3 did increase expression 

4 of CD86, which is generally associated with Th2 responses and is detected at higher 

5 levels on DCs from allergic asthmatics compared to those from healthy donors (Chen et 

6 al., 2006b). Increased CD86 has also been observed on airway cells collected from 

7 human subjects following exposure to O3 in studies by Lay et al. (2007) and Alexis et al.

8 (2009), but not Hernandez et al. (2010) (study details described in Section 6.2.5.4).

9 Ozone exposure during gestation has modest effects on allergy and asthma related 

10 endpoints in adult offspring. When dams were exposed to 1.2 ppm O3 (but not 0.8 ppm) 

11 from gestational day 9-18, some allergic and inflammatory responses to OVA 

12 sensitization and challenge were reduced compared to air exposed controls. This included 

13 IgE levels and eosinophils, and was only true of mice that were immunized early in life 

14 (PND 3) as opposed to later (PND 42), perhaps due to the proximity of O3 and antigen 

15 exposure. The effects of gestational O3 exposure on immune function have not been 

16 widely studied, and although reductions in allergic endpoints are not generally observed 

17 in association with O3, other parameters of immune function were found to be reduced, so 

18 a more global immunosuppression may underlie these effects. 

19 In addition to ozone’s pro-allergic effects, it could also make airborne allergens more 

20 allergenic. When combined with NO2, O3 has been shown to enhance nitration of 

21 common protein 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

22 The 2006 O3 AQCD evaluated numerous respiratory ED visits and hospital admissions 

23 studies, which consisted primarily of time-series studies conducted in the U.S., Canada, 

24 Europe, South America, Australia and Asia. Upon collectively evaluating the scientific 

25 evidence, the 2006 O3 AQCD concluded that “the overall evidence supports a causal 

26 relationship between acute ambient O3 exposures and increased respiratory morbidity 

27 resulting in increased ED visits and [hospital admissions] during the warm season” (U.S. 

28 EPA, 2006b). This conclusion is “strongly supported by the human clinical, animal 

29 toxicologic[al], and epidemiologic evidence for [O3-induced] lung function decrements, 

30 increased respiratory symptoms, airway inflammation, and airway hyperreactivity” (U.S. 

31 EPA, 2006b). 
Draft – Do Not Cite or Quote 6-111 September 2011

1 Since the completion of the 2006 O3 AQCD, relatively fewer studies conducted in the 

2 U.S., Canada, and Europe have examined the association between short-term exposure to 

3 ambient O3 and respiratory hospital admissions and ED visits with a growing number of 

4 studies having been conducted in Asia. This section focuses primarily on multicity 

5 studies because they examine the effect of O3 on respiratory-related hospital admissions 

6 and ED visits over a large geographic area using a consistent statistical methodology. 

7 Single-city studies that encompass a large number of hospital admissions or ED visits, or 

8 included a long study-duration were also evaluated because these studies have more 

9 power to detect whether an association exists between short-term O3 exposure and 

10 respiratory hospital admissions and ED visits compared to smaller single-city studies. 

11 Additional single-city studies were also evaluated within this section, if they were 

12 conducted in locations not represented by the larger single-city and multicity studies, or 

13 examined population-specific characteristics not included in the larger studies that may 

14 modify the association between short-term O3 exposure and respiratory-related hospital 

15 admissions or ED visits. The remaining single-city studies identified were not evaluated 

16 in this section due to factors such as inadequate study design or insufficient sample size.

17 It should be mentioned that when examining the association between short-term O3

18 exposure and respiratory health effects that require medical attention, it is important to 

19 distinguish between hospital admissions and ED visits. This is because it is likely that a 

20 small percentage of respiratory ED visits will be admitted to the hospital; therefore, 

21 respiratory ED visits may represent potentially less serious, but more common outcomes. 

22 As a result, in the following sections respiratory hospital admission and ED visit studies 

23 are evaluated individually. Additionally, within each section, results are presented as 

24 either a collection of respiratory diagnoses or as individual diseases (e.g., asthma, COPD, 

25 pneumonia and other respiratory infections) in order to evaluate the potential effect of 

26 short-term O3 exposure on each respiratory-related outcome. The ICD codes (i.e., ICD-9 

27 or ICD-10) that encompass each of these endpoints are presented in Table 6-25 along 

28 with the air quality characteristics of the city, or across all cities, included in each study 

29 evaluated in this section.
Draft – Do Not Cite or Quote 6-112 September 2011

Table 6-25 Mean and upper percentile concentrations of respiratory-related 

hospital admission and emergency department 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: 8.9-12.4

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)

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

Stieb et al. 

(2009)

7 Canadian 

cities

Emergency Department 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 Emergency Department 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. 

(2011b)

Atlanta, GA Emergency Department Visits:

All respiratory (460-466, 477, 

480-486, 491, 492, 493, 496, 

786.09)

8-h max

1-h max

24-h avg

Commute

Day-time

Night-time

Warm 

(March-October):

8-h max: 53

1-h max: 62

24-h avg: 30

Commute: 35i

Day-time: 45i

Night-time: 14i

8-h 

max: 

75th: 67

Max: 

148

1-h 

max: 

75th: 76

Max: 

180

24-h avg: 

75th: 37

Max: 81

Commute: 

75th: 45

Max: 106

Daytime: 

75th: 58

Max: 

123

Nighttime: 

75th: 22

Max: 64

Villeneuve et al. 

(2007)b

Alberta, CAN Emergency Department 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 Emergency Department 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
Draft – Do Not Cite or Quote 6-113 September 2011

Study Location Type of Visit (ICD9/10) Averaging 

Time

Mean 

Concentration (ppb)a Upper Percentile Concentrations (ppb)a

Strickland et al. 

(2010)

Atlanta, GA Emergency Department 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 

et al. (2009)

Seattle, WA Emergency Department 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

Emergency Department Visits: COPD (J40-44)1-h max 48.8 75th: 61.0

Max: 143.8

Orazzo et al. 

(2009)

c 6 Italian cities Emergency Department 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:

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. Newly identified studies 

4 attempt to further examine the effect of O3 exposure on respiratory-related hospital 

5 admissions through a multicity design that examines O3 effects across countries using a 
Draft – Do Not Cite or Quote 6-114 September 2011

1 standardized methodology; multicity studies that examine effects within one country; and 

2 multi- and single-city studies that attempt to examine potential modifiers of the O3-

3 respiratory-related hospital admission relationship. 

4 The Air Pollution and Health: A European and North American Approach (APHENA) 

5 study combined data from existing multicity study databases from Canada, Europe 

6 (APHEA2) (Katsouyanni et al., 2001), and the U.S. (NMMAPS) (Samet et al., 2000) in 

7 order to “develop more reliable estimates of the potential acute effects of air pollution on 

8 human health [and] provide a common basis for [the] comparison of risks across 

9 geographic areas” (Katsouyanni et al., 2009). In an attempt to address both of these 

10 issues, the investigators conducted extensive sensitivity analyses to evaluate the 

11 robustness of the results to different model specifications (e.g., penalized splines [PS] 

12 versus natural splines [NS]) and the extent of smoothing to control for seasonal and 

13 temporal trends. The trend analyses consisted of subjecting the models to varying extent 

14 of smoothing selected either a priori (e.g., 3 df/year, 8 df/year, and 12 df/year) or by 

15 using the absolute sum of the residuals of the partial autocorrelation function (PACF). 

16 However, the investigators did not identify the model they deemed to be the most 

17 appropriate for comparing the results across study locations. As a result, when discussing 

18 the results across the three study locations below, the 8 df/year results are presented for 

19 both the PS and NS models because: (1) 8 df/year is most consistent with the extent of 

20 temporal adjustment used in previous and recent large multicity studies in the U.S. (e.g., 

21 NMMAPS); (2) the risk estimates for 8 df/year and 12 df/year are comparable for all 

22 three locations; (3) the models that used the PACF method did not report the actual 

23 degrees of freedom chosen; and (4) the 3 df/year and the PACF method resulted in 

24 negative O3 risk estimates, which is inconsistent with the results obtained using more 

25 aggressive seasonal adjustments. Additionally, when comparing results across studies in 

26 figures, only the results from one of the spline models (e.g., NS) are presented because it 

27 has been previously demonstrated that alternative spline models result in relatively 

28 similar effect estimates (HEI, 2003). However, it should be noted that the underlying data 

29 and model specifications could result in varying degrees of bias and precision in effect 

30 estimates with different spline models (Ostro et al., 2006).

31 Katsouyanni et al. (2009) examined respiratory hospital admissions for people aged 

32 65 years and older using 1-h max O3 data. The extent of hospital admission and O3 data 

33 varied across the 3 datasets: Canadian dataset included 12 cities with data for 3 years 

34 (1993-1996) per city; European dataset included 8 cities with each city having data for 

35 between 2 and 8 years from 1988-1997; and U.S. dataset included 14 cities with each city 

36 having data for between 4 and 10 years from 1985-1994 and 7 cities having only summer 

37 O3 data. The investigators used a three-stage hierarchical model to account for within38 city, within region, and between region variability. Results were presented individually 
Draft – Do Not Cite or Quote 6-115 September 2011

1 for each region (Figure 6-14; Table 6-26). Ozone and PM10 concentrations were weakly 

2 correlated in all locations in the summer (r=0.27-0.40), but not in the winter. 

3 In the Canadian cities, using all-year data, a 40 ppb increase in 1-h max O3

4 concentrations at lag 0-1 was associated with an increase in respiratory hospital 

5 admissions of 8.9% (95% CI: 0.79, 16.8%) in a PS model and 8.1% (95% CI: 0.24, 

6 16.8%) in a NS model (Katsouyanni et al., 2009). The results were somewhat sensitive to 

7 the lag day selected, reduced when using a single-day lag (e.g., lag 1) (PS: 6.0%; NS: 

8 5.5%) and increased when using a distributed lag model (PS: 18.6%; NS: 20.4%). When 

9 adjusting for PM10, the magnitude of the effect estimate was slightly larger in the NS 

10 model (5.1% [95% CI: -6.6, 18.6%]) compared to the PS model (3.1% [95% CI: -8.3, 

11 15.9%]); however, the copollutant analysis was only conducted using a 1-day lag. The 

12 large confidence intervals for both models could be attributed to the reduction in days 

13 included in the copollutant analyses as a result of the every-6th-day PM sampling 

14 schedule. When restricting the analysis to the summer months, stronger associations were 

15 observed between O3 and respiratory hospital admissions across the lags examined, 

16 ranging from ~22 to 37% (the study does not specify whether these effect estimates are 

17 from a NS or PS model). Because O3 concentrations across the cities included in the 

18 Canadian dataset (Katsouyanni et al. (2009) are low (median concentrations ranging from 

19 6.7-8.3 ppb [Table 6-25]), the standardized increment of 40 ppb for a 1-h max increase in 

20 O3 concentrations does not accurately reflect the observed risk of O3-related respiratory 

21 hospital admissions. Although this increment adequately characterizes the distribution of 

22 1-h max O3 concentrations across the U.S. and European datasets, it misrepresents the 

23 observed O3 concentrations in the Canadian dataset. As a result in summary figures, for 

24 comparability, effect estimates from the Canadian dataset are presented for both a 5.1 ppb 

25 increase in 1-h max O3 concentrations (i.e., an approximate interquartile range [IQR] 

26 increase in O3 concentrations across the Canadian cities) as well as the standardized 

27 increment used throughout the ISA.

28 In Europe, weaker but positive associations were also observed in year round analyses; 

29 2.9% (95% CI: 0.63, 5.0%) in the PS model and 1.6% (95% CI: -1.7, 4.2%) in the NS 

30 model at lag 0-1 for a 40 ppb increase in 1-h max O3 concentrations (Katsouyanni et al., 

31 2009). Additionally, at lag 1, associations between O3 and respiratory hospital admissions 

32 were also reduced, but in contrast to the lag 0-1 analysis, greater effects were observed in 

33 the NS model (2.9% [95% CI: 1.0, 4.9%]) compared to the PS model (1.5% [95% CI: -

34 2.2, 5.4]). Unlike the Canadian analysis, a distributed lag model provided limited 

35 evidence of an association between O3 and respiratory hospital admissions. To compare 

36 with the Canadian results, when adjusting for PM10 at lag 1, effect estimates were 

37 increased in the PS model (2.5% [95% CI: 0.39-4.8%]) and remained robust in the NS 

38 model (2.4% [95% CI: 0.08, 4.6%]). However, the European analysis also examined the 
Draft – Do Not Cite or Quote 6-116 September 2011

1 effect of adjusting for PM10 at lag 0-1 and found results were attenuated in both models 

2 (PS: 0.8% [95% CI: -2.3, 4.0%]; NS: 0.8% [95% CI: -1.8, 3.6%]). Unlike the Canadian 

3 and U.S. datasets, the European dataset consisted of daily PM data. The investigators did 

4 not observe stronger associations in the summer-only analyses for the European cities at 

5 lag 0-1 (PS: 0.4% [95% CI: -3.2, 4.0%]; NS: 0.2% [95% CI: -3.3, 3.9%]), but did observe 

6 some evidence for larger effects during the summer, an ~2.5% increase, at lag 1 in both 

7 models (the study does not present the extent of temporal smoothing used for these 

8 models). 

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 ozone concentrations.

Figure 6-14 Percent increase in respiratory hospital admissions from natural 

spline models 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 6-117 September 2011

Table 6-26 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) 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 

6 dataset with the PS model (1.1% [95% CI: -3.0, 5.3%]), but larger effects in the NS 

7 model (3.3% [95% CI: 0.02, 6.8%]), which is consistent with the Canadian results. When 

8 adjusting for PM10 using the U.S. data (i.e., every-6th-day PM data), results were 

9 attenuated at lag 0-1 (PS: 0.6% [95% CI: -2.0, 3.3%]; NS: 1.4% [95% CI: -1.3, 4.2%]) 

10 which is consistent with the results presented for the European dataset. However, at lag 1, 

11 U.S. risk estimates remained robust to the inclusion of PM10 in copollutant models as was 

12 observed in the Canadian and European datasets. Compared to the all-year analyses, the 

13 investigators did not observe stronger associations in the summer-only analysis at either 

14 lag 0-1 (~2.2%) or lag 1 (~2.8%) in both the PS and NS models (the study does not 

15 present the extent of temporal smoothing used for these models).

16 Several additional multicity studies examined respiratory disease hospital admissions in 

17 Canada and Europe. Cakmak et al. (2006b) evaluated the association between ambient O3
Draft – Do Not Cite or Quote 6-118 September 2011

1 concentrations and respiratory hospital admissions for all ages in 10 Canadian cities from 

2 April 1993 to March 2000. The primary objective of this study was to examine the 

3 potential modification of the effect of ambient air pollution on daily respiratory hospital 

4 admissions by education and income using a time-series analysis conducted at the city5 level. The authors calculated a pooled estimate across cities for each pollutant using a 

6 random effects model by first selecting the lag day with the strongest association from the 

7 city-specific models. For O3, the mean lag day across cities that provided the strongest 

8 association and for which the pooled effect estimate was calculated was 1.2 days. In this 

9 study, all-year O3 concentrations were used in the analysis, and additional seasonal 

10 analyses were not conducted. Cakmak et al. (2006b) reported a 4.4% increase (95% CI: 

11 2.2, 6.5%) in respiratory hospital admissions for a 20 ppb increase in 24-h average O3

12 concentrations. The investigators only examined the potential effect of confounding by 

13 other pollutants through the use of a multipollutant model (i.e., two or more additional 

14 pollutants included in the model), which is difficult to interpret due to the potential 

15 multicollinearity between pollutants. Cakmak et al. (2006b) also conducted an extensive 

16 analysis of potential modifiers, specifically sex, educational attainment, and family 

17 income, on the association between air pollution and respiratory hospital admissions. 

18 When stratifying by sex, the increase in respiratory hospital admissions due to short-term 

19 O3 exposure were similar in males (5.2% [95% CI: 3.0, 7.3%]) and females (4.2% [95% 

20 CI: 1.8, 6.6%]). In addition, the examination of effect modification by income found no 

21 consistent trend across the quartiles of family income. However, there was evidence that 

22 individuals with an education level less than the 9th grade were disproportionately 

23 affected by O3 exposure (4.6% [95% CI: 1.8, 7.5%]) compared to individuals that 

24 completed grades 9-13 (1.7% [95% CI: -1.9, 5.3%]), some university or trade school 

25 (1.4% [95% CI: -2.0, 5.1%]), or have a university diploma (0.66% [95% CI: -3.3, 4.7%]). 

26 The association between O3 and individuals with an education level less than the 9th 

27 grade was the strongest association across all of the pollutants examined. 

28 A multicity study conducted in Europe by Biggeri et al. (2005) examined the association 

29 between short-term O3 exposure and respiratory hospital admissions for all ages in four 

30 Italian cities from 1990 to 1999. In this study, O3 was only measured during the warm 

31 season (May-September). The authors examined associations between daily respiratory 

32 hospital admissions and short-term O3 exposure at the city-level using a time-series 

33 analysis. Pooled estimates were calculated by combining city-specific estimates using 

34 fixed and random effects models. The investigators found no evidence of an association 

35 between O3 exposure and respiratory hospital admissions in the warm season in both the 

36 random (0.1% [95% CI: -5.2, 5.7%]; distributed lag 0-3) and fixed effects (0.1% [95% 

37 CI: -5.2, 5.7%]; distributed lag 0-3) models for a 30 ppb increase in 8-h max O3

38 concentrations. 
Draft – Do Not Cite or Quote 6-119 September 2011

1 Additional studies examined associations between short-term O3 exposure and respiratory 

2 hospital admissions specifically in children. In a multicity study conducted in Canada, 

3 Dales et al. (2006) examined the association between all-year ambient O3 concentrations 

4 and neonatal (ages 0-27 days) respiratory hospital admissions in 11 Canadian cities from 

5 1986 to 2000. The investigators used a statistical analysis approach similar to Cakmak et 

6 al. (2006b) (i.e., time-series analysis to examine city-specific associations, and then a 

7 random effects model to pool estimates across cities). The authors reported that for O3,

8 the mean lag day across cities that provided the strongest association was 2 days. The

9 authors reported a 5.4% (95% CI: 2.9, 8.0%) increase in neonatal respiratory hospital 

10 admissions for a 20 ppb increase in 24-h avg O3 concentrations at lag-2 days. The results 

11 from Dales et al. (2006) provide support for the associations observed in a smaller scale 

12 study that examined O3 exposure and pediatric respiratory hospital admissions in 

13 New York state (Lin et al., 2008a). Lin et al. (2008a) observed a positive association 

14 between O3 and pediatric (i.e., <18 years) respiratory admissions at lag 2 (results not 

15 presented quantitatively) in a two-stage Bayesian hierarchical model analysis of 11 

16 geographic regions of New York from 1991 to 2001. 

17 Overall, the evidence from epidemiologic studies continues to support an association 

18 between short-term O3 exposure and respiratory-related hospital admissions, but it 

19 remains unclear whether certain factors (individual- or population-level) modify this 

20 association. Wong et al. (2009) examined the potential modification of the relationship 

21 between ambient O3 (along with NO2, SO2, and PM10) and respiratory hospital 

22 admissions by influenza intensity in Hong Kong for the period 1996 – 2002. Influenza 

23 intensity was defined as a continuous variable using the proportion of weekly specimens 

24 positive for influenza A or B instead of defining influenza epidemics. This approach was 

25 used to avoid any potential bias associated with the unpredictable seasonality of influenza 

26 in Hong Kong (Wong et al., 2009). In models that examined the baseline effect (i.e., 

27 without taking into consideration influenza intensity) of short-term O3 exposure, the 

28 authors found a 3.6% (95% CI: 1.9, 5.3%) and 3.2% (95% CI: 1.0, 5.4%) increase in 

29 respiratory hospital admissions at lag 0-1 for a 30 ppb increase in 8-h max O3

30 concentrations for the all age and ≥ 65 age groups, respectively. When examining 

31 influenza intensity, Wong et al. (2009) reported that the association between short-term 

32 exposure to O3 and respiratory hospital admissions was stronger with higher levels of 

33 influenza intensity: additional increase in respiratory hospital admissions above baseline 

34 of 1.4% (95% CI: 0.24, 2.6%) for all age groups and 2.4% (95% CI: 0.94, 3.8%) for those 

35 65 and older when influenza activity increased from 0% to 10%. No difference in effects 

36 was observed when stratifying by sex. 
Draft – Do Not Cite or Quote 6-120 September 2011

Cause-Specific Respiratory Outcomes

1 In the 2006 O3 AQCD a limited number of studies were identified that examined the 

2 effect of short-term O3 exposure on cause-specific respiratory hospital admissions. The 

3 limited evidence “reported positive O3 associations with... asthma and COPD, 

4 especially... during the summer or warm season” (U.S. EPA, 2006b). Of the studies 

5 evaluated since the completion of the 2006 O3 AQCD, more have focused on identifying 

6 whether O3 exposure is associated with specific respiratory-related hospital admissions, 

7 including COPD, pneumonia, and asthma, but the overall body of evidence remains 

8 small. 

Chronic Obstructive Pulmonary Disease

9 Medina-Ramon et al. (2006) examined the association between short-term exposure to 

10 ambient O3 and PM10 concentrations and Medicare hospital admissions among 

11 individuals ≥ 65 years of age for COPD in 35 cities in the U.S. for the years 1986-1999. 

12 The cities included in this analysis were selected because they monitored PM10 on a daily 

13 basis. In this study, city-specific results were obtained using a monthly time-stratified 

14 case-crossover analysis. A meta-analysis was then conducted using random effects 

15 models to combine the city-specific results. All cities measured O3 from May through 

16 September, while only 16 of the cities had year-round measurements. The authors 

17 reported a 1.6% increase (95% CI: 0.48, 2.9%) in COPD admissions for lag 0-1 in the 

18 warm season for a 30 ppb increase in 8-h max O3 concentrations. When examining 

19 single-day lags, stronger associations were observed for lag 1 (2.9% [95% CI: 1.8, 4.0%]) 

20 compared to lag 0 (-1.5% [95% CI: -2.7, -0.24%]). The authors found no evidence of 

21 associations in cool season (-1.9% [95% CI: -3.6, -0.06%]; lag 0-1) or year round (0.24% 

22 [95% CI: -0.78, 1.2%]; lag 0-1) analyses. In a copollutant model using warm season data, 

23 the association between O3 and COPD hospital admissions was robust to the inclusion of 

24 PM10 in the model (results not presented quantitatively). The authors conducted 

25 additional analyses to examine potential modification of the warm season estimates for 

26 O3 and COPD admissions by several city-level characteristics: percentage living in 

27 poverty, emphysema mortality rate (as an indication of smoking), daily summer apparent 

28 temperature, and percentage of households using central air conditioning. Of the city29 level characteristics examined, stronger associations were only reported for cities with a 

30 larger variability in daily apparent summer temperature.

31 In a single-city study conducted in Vancouver from 1994-1998, a location with low 

32 ambient O3 concentrations (Table 6-25), Yang et al. (2005b) examined the association 

33 between O3 and COPD. Ozone was moderately inversely correlated with CO (r=-0.56), 

34 NO2 (r=-0.32), and SO2 (r=-0.34), and weakly inversely correlated with PM10 (r=-0.09), 

35 suggesting that the observed O3 effect is likely not only due to a positive correlation with 
Draft – Do Not Cite or Quote 6-121 September 2011

1 other pollutants. Yang et al. (2005b) examined 1- to 7-day (e.g., (0-6 days) lagged 

2 moving averages and observed an 8.8% (95% CI: -12.5, 32.6%) increase in COPD 

3 admissions for lag 0-3 per 20 ppb increase in 24-h avg O3 concentrations. In two4 pollutant models at lag 0-3, O3 effect estimates were robust to the inclusion of NO2, SO2, 

5 and PM10 in the model, but were increased slightly when adding CO (Figure 6-20; Table 

6 6-28). 

Pneumonia

7 In addition to COPD, Medina-Ramon et al. (2006) examined the association between 

8 short-term exposure to ambient O3 and PM10 concentrations and Medicare hospital 

9 admissions among individuals ≥ 65 years of age for pneumonia (ICD-9: 480-487). The 

10 authors reported an increase in pneumonia hospital admissions in the warm season (2.5% 

11 [95% CI: 1.6, 3.5%] for a 30 ppb increase in 8-h max O3 concentrations; lag 0-1). Similar 

12 to the results observed for COPD hospital admissions, pneumonia hospital admissions 

13 associations were stronger at lag 1 (2.6% [95% CI: 1.8, 3.4%]) compared to lag 0 (0.06% 

14 [95% CI: -0.72, 0.78%]), and no evidence of an association was observed in the cool 

15 season or year round. In two-pollutant models, the association between O3 exposure and 

16 pneumonia hospital admissions was robust to the inclusion of PM10 (results not presented 

17 quantitatively). The authors also examined potential effect modification of the warm 

18 season estimates for O3-related pneumonia hospital admissions, as was done for COPD, 

19 by several city-level characteristics. Stronger associations were reported in cities with a 

20 lower percentage of central air conditioning use. Across the cities examined, the 

21 percentage of households having central air conditioning ranged from 6 to 93%. The 

22 authors found no evidence of effect modification of the O3-pneumonia hospital admission 

23 relationship when examining the other city-level characteristics.

24 Results from a single-city study conducted in Boston did not support the results presented 

25 by Medina-Ramon et al. (2006). Zanobetti and Schwartz (2006) examined the association 

26 of O3 and pneumonia Medicare hospital admissions for the period 1995-1999. Ozone was 

27 weakly positively correlated with PM2.5 (r=0.20) and weakly inversely correlated with 

28 black carbon, NO2, and CO (-0.25, -0.14, and -0.30, respectively). In an all-year analysis, 

29 the investigators reported a 3.8% (95% CI: -7.9, -0.1%) decrease in pneumonia 

30 admissions for a 20 ppb increase in 24-h average O3 concentrations at lag 0 and a 6.0% 

31 (95% CI: -11.1, -1.4%) decrease for the average of lags 0 and 1. It should be noted that 

32 the mean daily counts of pneumonia admissions was low for this study, ~14 admissions 

33 per day compared to ~271 admissions per day for Medina-Ramon et al. (2006). However, 

34 in analyses with other pollutants Zanobetti and Schwartz (2006) did observe positive 

35 associations with pneumonia hospital admissions, indicating that the low number of daily 
Draft – Do Not Cite or Quote 6-122 September 2011

1 hospital admission counts probably did not influence the O3-pneumonia hospital 

2 admissions association in this study. .

Asthma

3 There are relatively fewer studies that examined the association between short-term 

4 exposure to O3 and asthma hospital admissions, presumably due to the limited power 

5 given the relative rarity of asthma hospital admissions compared to ED or physician 

6 visits. A study from New York City examined the association of 8-h max O3

7 concentrations with severe acute asthma admissions (i.e., those admitted to the Intensive 

8 Care Unit [ICU]) during the warm season in the years 1999 through 2006 (Silverman and 

9 Ito, 2010). In this study, O3 was moderately correlated with PM10 (r=0.59). When 

10 stratifying by age, the investigators reported positive associations with ICU asthma 

11 admissions for the 6- to 18-year age group (26.8% [95% CI: 1.4, 58.2%] for a 30 ppb 

12 increase in maximum 8-h avg O3 concentrations at lag 0-1), but little evidence of 

13 associations for the other age groups examined (<6 years, 19-49, 50+, and all ages). 

14 However, positive associations were observed for each age-stratified group and all ages 

15 for non-ICU asthma admissions, but again the strongest association was reported for the 

16 6- to 18-years age group (28.2% [95% CI: 15.3, 41.5%]; lag 0-1). In two-pollutant 

17 models, O3 effect estimates for both non-ICU and ICU hospital admissions remained 

18 robust to adjustment for PM2.5. In an additional analysis, using a smooth function, the 

19 authors examined whether the shape of the C-R curve for O3 and asthma hospital 

20 admissions (i.e., both general and ICU for all ages) is linear. To account for the potential 

21 confounding effects of PM2.5, Silverman and Ito (2010) also included a smooth function 

of PM2.5 22 lag 0-1. When comparing the curve to a linear fit line the authors found that the 

23 linear fit is a reasonable approximation of the concentration-response relationship 

24 between O3 and asthma hospital admissions around and below the level of the current 

25 NAAQS (Figure 6-15). 
Draft – Do Not Cite or Quote 6-123 September 2011

Source: Used with permission from American Academy of Allergy, Asthma & Immunology (Silverman and Ito, 2010).

The average of 0 day and 1 day lagged 8-h ozone 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.

Figure 6-15 Estimated relative risks (RRs) of ozone-related asthma hospital 

admissions 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 4.6.4, recent studies by Neidell (2009) and Neidell and 

5 Kinney (2010) conducted in Souther 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 a few epidemiologic studies have examined averting 

10 behavior and these studies are limited to asthma hospital admissions, they do provide 

11 preliminary evidence indicating that epidemiologic studies may underestimate 
Draft – Do Not Cite or Quote 6-124 September 2011

1 associations between O3 exposure and health effects by not accounting for behaviorial 

2 modification when public health alerts are issued.

6.2.7.3 Emergency Department Visit Studies

3 Overall, relatively fewer studies have examined the association between short-term O3 

4 exposure and respiratory-related ED visits, compared to hospital admissions. In the 2006 

5 O3 AQCD, positive, but inconsistent, associations were observed between O3 and 

6 respiratory-related ED visits with effects generally occurring during the warm season. 

7 Since the completion of the previous AQCD, larger studies have been conducted, in 

8 terms of sample size, study duration, and in some cases multiple cities, to examine the 

9 association between O3 and ED visits for all respiratory diseases, COPD, and asthma. 

Respiratory Disease

10 A large single-city study conducted in Atlanta, by Tolbert et al. (2007), and subsequently 

11 reanalyzed by Darrow et al. (2011b), provides evidence for an association between short12 term exposures to ambient O3 concentrations and respiratory ED visits. Tolbert et al. 

13 (2007) examined the association between air pollution, both gaseous pollutants and PM 

14 and its components, and respiratory disease ED visits in all ages from 1993 to 2004. The 

15 correlations between O3 and the other pollutants examined ranged from 0.2 for CO and 

16 SO2 to 0.5-0.6 for the PM measures. Using an a priori average of lags 0-2 for each air 

17 pollutant examined, the authors reported a 3.9% (95% CI: 2.7, 5.2%) increase in 

18 respiratory ED visits for a 30 ppb increase in 8-h max O3 concentrations during the warm 

19 season [defined as March-October in Darrow et al. (2011b)]. In copollutant models, the 

20 O3 associations with respiratory ED visits remained robust with CO, NO2, and PM10

21 (results not presented quantitatively). 

22 Darrow et al. (2011b) examined the same data as Tolbert et al. (2007), but explored 

23 whether differences exist in the association between O3 exposure and respiratory-related 

24 ED visits depending on the exposure metric used (i.e., 8-h max, 1-h max, 24-h average, 

25 commuting period [7:00 a.m. to 10:00 a.m.; 4:00 p.m. to 7:00 p.m.], day-time [8:00 a.m. 

26 to 7:00 p.m.] and night-time [12:00 a.m. to 6:00 a.m.]). To examine the association 

27 between the various O3 exposure metrics and respiratory ED visits, the authors used a 

28 time-stratified case-crossover approach, selecting control days as those days within the 

29 same calendar month and maximum temperature as the case day. Darrow et al. (2011b)

30 found at lag 1, the results were somewhat variable across exposure metrics. The strongest 

31 associations with respiratory ED visits were found when using the 8-h max, 1-h max, and 

32 day-time exposure metrics with weaker associations using the 24-h avg and commuting 
Draft – Do Not Cite or Quote 6-125 September 2011

1 period exposure metrics; a negative association was observed when using the night-time 

2 exposure metric (Figure 6-16).

Source: Used with permission from Nature Publishing Group (Darrow et al., 2011b). 

Figure 6-16 Risk ratio for respiratory ED visits and different ozone exposure 

metrics in Atlanta from 1993-2004. 

3 In an additional study conducted in 6 Italian cities, Orazzo et al. (2009) examined 

4 respiratory ED visits for ages 0-2 years in 6 Italian cities from 1996 to 2000. However, 

5 instead of identifying respiratory ED visits using the traditional approach of selecting 

6 ICD codes as was done by Tolbert et al. (2007) and Darrow et al. (2011b), Orazzo et al. 

7 (2009) used data on wheeze extracted from medical records as an indicator of lower 

8 respiratory disease. This study examined daily counts of wheeze in relation to air 

9 pollution using a time-stratified case-crossover approach in which control days were 

10 matched on day of week in the same month and year as the case day. The authors found 

11 no evidence of an association between 8-h max O3 concentrations and respiratory ED 

12 visits in children aged 0-2 years in models that examined both single-day lags and 

13 moving averages of lags from 0-6 days in year-round and seasonal analyses (i.e., warm 
Draft – Do Not Cite or Quote 6-126 September 2011

1 and cool seasons). In all-year analyses, the percent increase in total wheeze ranged from -

2 1.4% to -3.3% for a 0-1 to 0-6 day lag, respectively. 

COPD

3 Stieb et al. (2009) also examined the association between short-term O3 exposure and 

4 COPD ED visits in 7 Canadian cities. Across cities, in an all-year analysis, O3 was found 

5 to be positively associated with COPD ED visits (4.0% [95% CI: -0.54, 8.6%] at lag 2 for 

6 a 20 ppb increase in 24-h avg O3 concentrations). In seasonal analyses, larger effects 

7 were observed between O3 and COPD ED visits during the warm season (i.e., April8 September) 6.8% [95% CI: 0.11, 13.9%] (lag day not specified); with no associations 

9 observed in the winter season. Stieb et al. (2009) also examined associations between 

10 respiratory-related ED visits, including COPD, and air pollution at sub-daily time scales 

11 (i.e., 3-h avg of ED visits versus 3-h avg pollutant concentrations) and found no evidence 

12 of consistent associations between any pollutant and any respiratory outcome. 

13 In a single-city study, Arbex et al. (2009) examined the association between COPD and 

14 several ambient air pollutants, including O3, in Sao Paulo, Brazil for the years 2001-2003 

15 for individuals over the age of 40. Associations between O3 exposure and COPD ED 

16 visits were examined in both single-day lag (0-6 days) and polynomial distributed lag 

17 models (0-6 days). In all-year analyses, O3 was not found to be associated with an 

18 increase in COPD ED visits (results not presented quantitatively). The authors also 

19 conducted stratified analyses to examine the potential modification of the air pollutant20 COPD ED visits relationship by age (e.g., 40-64, >64) and sex. In these analyses O3 was 

21 found to have an increase in COPD ED visits for women, but not for men or either of the 

22 age groups examined.

Asthma 

23 In a study of 7 Canadian cities, Stieb et al. (2009) also examined the association between 

24 exposure to air pollution (i.e., CO, NO2, O3, SO2, PM10, PM2.5, and O3) and asthma ED 

25 visits. Associations between short-term O3 exposure and asthma ED visits were examined 

26 at the city level and then pooled using either fixed or random effects models depending 

27 on whether heterogeneity among effect estimates was found to be statistically significant. 

28 Across cities, in an all-year analysis, the authors found that short-term O3 exposure was 

29 associated with a positive increase (3.5% [95% CI: 0.33, 6.8%] at lag 2 for a 20 ppb 

30 increase in 24-h avg O3 concentrations) in asthma ED visits. The authors did not present 

31 the results from seasonal analyses for asthma, but state that no associations were 

32 observed between any pollutant and respiratory ED visits in the winter season. As stated 

33 previously, in analyses of 3-h avg O3 concentrations, the authors observed no evidence of 

34 consistent associations between any pollutant and any respiratory outcome, including 
Draft – Do Not Cite or Quote 6-127 September 2011

1 asthma. A single-city study conducted in Alberta, Canada (Villeneuve et al., 2007) from 

2 1992-2002 among individuals two years of age and older provides additional support for 

3 the findings from Stieb et al. (2009), but also attempts to identify those lifestages (i.e., 2-

4 4, 5-14, 15-44, 45-64, 65-74, or 75+) most susceptible to O3-induced asthma ED visits. In 

5 a time-referent case-crossover analysis, Villeneuve et al. found an increase in asthma ED 

6 visits in an all-year analysis across all ages (12.0% [95% CI: 6.8, 17.2] for a 30 ppb 

7 increase in max 8-h avg O3 concentrations at lag 0-2) with associations being stronger 

8 during the warmer months (19.0% [95% CI: 11.9, 28.1]). When stratifying by age, the 

9 strongest associations were observed in the warm season for individuals 5-14 (28.1% 

10 [95% CI: 11.9, 45.1]; lag 0-2) and 15-44 (19.0% [95% CI: 8.5, 31.8]; lag 0-2). These 

11 associations were not found to be confounded by the inclusion of aeroallergens in age12 specific models.

13 Several additional single-city studies have also provided evidence of an association 

14 between asthma ED visits and ambient O3 concentrations. Ito et al. (2007b) examined the 

15 association between short-term exposure to air pollution and asthma ED visits for all ages 

16 in New York City from 1999 to 2002. Ito et al. (2007b) used three different weather 

17 models with varying extent of smoothing to account for temporal relationships and 

18 multicollinearity among pollutants and meteorological variables (i.e., temperature and 

19 dew point) to examine the effect of model selection on the air pollutant-asthma ED visit 

20 relationship. When examining O3, the authors reported a positive association with asthma 

21 ED visits, during the warm season across the models (ranging from 8.6 to 16.9%) and an 

22 inverse association in the cool season (ranging from -23.4 to -25.1%), at lag 0-1 for a 30 

23 ppb increase in 8-h max O3 concentrations. Using a simplified version of the weather 

24 model used in NMMAPS analyses (i.e., terms for same-day temperature and 1-3 day 

25 average temperature), Ito et al. (2007b) found that O3 effects were not substantially 

26 changed in copollutant models with PM2.5, NO2, SO2, and CO during the warm season 

27 (Figure 6-19; Table 6-27).
Draft – Do Not Cite or Quote 6-128 September 2011

Source: Used with permission from American Thoracic Society (Strickland et al., 2010).

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 dose-response estimates at the 

distribution tails.

Figure 6-17 Loess dose-response estimates and twice-standard error estimates 

from generalized additive models for associations between 3-day 

avg 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 the same air 

3 quality data as Darrow et al. (2011b) and Tolbert et al. (2007). However, unlike Darrow 

4 et al. (2011b) and Tolbert et al. (2007), which used single centrally located monitors or an 

5 average of monitors, respectively, Strickland et al. (2010) used population-weighting to 

6 combine daily pollutant concentrations across monitors. In this study, the authors 

7 developed a statistical model using hospital-specific time-series data that is essentially 

8 equivalent to a time-stratified case-crossover analysis (i.e., using interaction terms 

9 between year, month, and day-of-week to mimic the approach of selecting referent days 

10 within the same month and year as the case day). The authors observed a 6.4% (95% CI: 

11 3.2, 9.6%) increase in ED visits for a 30 ppb increase in 8-h max O3 concentrations at lag 

12 0-2 in an all-year analysis. In seasonal analyses, stronger associations were observed 

13 during the warm season (i.e., May-October) (8.4% [95% CI: 4.4, 12.7%]; lag 0-2) than 

14 the cold season (4.5% [95% CI: -0.82, 10.0%]; lag 0-2). Strickland et al. (2011)

15 confirmed these findings in an additional analysis using the same dataset, and found that 

16 the metric used to assign exposure (i.e., centrally located monitor, unweighted average 
Draft – Do Not Cite or Quote 6-129 September 2011

1 across monitors, and population-weighted average across monitors) did not influence 

2 pediatric asthma ED visit risk estimates for spatially homogeneous pollutants such as O3.

3 In copollutant analyses, Strickland et al. (2010) found that O3 effect estimates were not 

4 substantially changed when controlling for other pollutants (CO, NO2, PM2.5 elemental 

5 carbon, PM2.5 sulfate) (results not presented quantitatively). The authors also examined 

6 the C-R relationship between O3 exposure and pediatric asthma ED visits and found that 

7 both quintile and loess dose-response analyses (Figure 6-17) suggest that there are 

8 elevated associations with O3 at concentrations as low as 30 ppb. These dose-response 

9 analyses do not provide evidence of a threshold level.

10 In a single-city study conducted on the West coast, Mar and Koenig (2009) examined the 

11 association between O3 exposure and asthma ED visits (ICD-9 codes_ 493-493.9) for 

12 children (< 18) and adults (≥ 18) in Seattle, WA from 1998 to 2002. Of the total number 

13 of visits over the study duration, 64% of visits in the age group < 18 comprised boys, and 

14 70% of visits in the ≥ 18 age group comprised females. Mar and Koenig (2009)

15 conducted a time-series analysis using both 1-h max and max 8-h avg O3 concentrations. 

16 Although a similar pattern of associations was observed using both metrics, only those 

17 results using the max 8-h avg O3 metric are discussed here since they are more applicable 

18 to the current O3 NAAQS. Mar and Koenig (2009) presented results for single day lags of 

19 0 to 5 days, but found consistent positive associations across individual lag days which 

20 supports the findings from the studies discussed above that examined multi-day 

21 exposures. For children, consistent positive associations were observed across all lags, 

22 ranging from a 19.1-36.8% increase in asthma ED visits for a 30 ppb increase in 8-h max 

23 O3 concentrations with the strongest associations observed at lag 0 (33.1% [95% CI: 3.0, 

24 68.5]) and lag 3 (36.8% [95% CI: 6.1, 77.2]) (Figure x). O3 was also found to be 

25 positively associated with asthma ED visits for adults at all lags, ranging from 9.3-26.0%, 

26 except at lag 0 (Figure 6-18). The slightly different lag times for children and adults 

27 suggest that children may be more immediately responsive to O3 exposures than adults 

28 (Mar and Koenig, 2009). 
Draft – Do Not Cite or Quote 6-130 September 2011

Adapted from Mar and Koenig (2009).

Figure 6-18 Relative risk of asthma ED visits children and adults for a 30 ppb 

increase in max 8-h avg O3 concentrations in Seattle, WA, 1998-

2002. 

Respiratory Infection

1 Although an increasing number of studies have examined the association between O3

2 exposure and cause-specific respiratory ED visits this trend has not included an extensive 

3 examination of the association between O3 exposure and respiratory infection ED visits. 

4 Stieb et al. (2009) also examined the association between short-term O3 exposure and 

5 respiratory infection ED visits in 7 Canadian cities. In an all-year analysis, there was no 

6 evidence of an association between O3 exposure and respiratory infection ED visits at all 

7 lags examined (i.e., 0, 1, and 2). Across cities, respiratory infections comprised the single 

8 largest diagnostic category, approximately 32%, of all the ED visits examined, which 

9 also included myocardial infarction, heart failure, dysrhythmia, asthma, and COPD.

Lag 0

Lag 1

Lag 2

Lag 3

Lag 4

Lag 5

0.80 1.00 1.20 1.40 1.60 1.80

Relative Risk

Black = Children

Red = Adults
Draft – Do Not Cite or Quote 6-131 September 2011

6.2.7.4 Outpatient and Physician Visit Studies

1 Several studies have examined the association between ambient O3 concentrations and 

2 physician or outpatient (non-hospital, non-ED) visits for acute conditions in various 

3 geographic locations. Burra et al. (2009) examined asthma physician visits among 

4 patients aged 1-17 and 18-64 years in Toronto, Canada from 1992 to 2001. The authors 

5 found little or no evidence of an association between asthma physician visits and O3; 

6 however, seasonal analyses were not conducted. It should be noted that in this study, 

7 most of the relative risks for O3 were less than one and statistically significant, perhaps 

8 indicating an inverse correlation with another pollutant or an artifact of the strong 

9 seasonality of asthma visits. Villeneuve et al. (2006b) also focused on physician visits to 

10 examine the effect of short-term O3 exposure on allergic rhinitis among individuals aged 

11 65 or older in Toronto from 1995 to 2000. The authors did not observe any evidence of 

12 an association between allergic rhinitis physician visits and ambient O3 concentrations in 

13 single-day lag models in an all-year analysis (results not presented quantitatively). 

14 In a study conducted in Atlanta, Sinclair et al. (2010) examined the association of acute 

15 asthma and respiratory infection (e.g., upper respiratory infections and lower respiratory 

16 infections) outpatient visits from a managed care organization with ambient O3

17 concentrations as well as multiple PM size fractions and species from August 1998 

18 through December 2002. The authors separated the analysis into two time periods (the

19 first 25 months of the study period and the second 28 months of the study period), in 

20 order to compare the air pollutant concentrations and relationships between air pollutants 

21 and acute respiratory visits for the 25-month time-period examined in Sinclair et al. 

22 (2004) to an additional 28-month time-period of available data from the Atlanta Aerosol 

23 Research Inhalation Epidemiology Study (ARIES). The authors found little evidence of 

24 an association between O3 and asthma visits, for both children and adults, or respiratory 

25 infection visits in all-year analyses and seasonal analyses. For example, a slightly 

26 elevated relative risk (RR) for childhood asthma visits was observed during the 25-month 

27 period in the cold season (RR: 1.12 [95% CI: 0.86, 1.41]; lag 0-2 for a 30 ppb increase in 

28 8-h max O3), but not in the warm season (RR: 0.97 [95% CI: 0.86, 1.10]; lag 0-2). During 

29 the 28-month period at lag 0-2, a slightly larger positive effect was observed during the 

30 warm season (RR: 1.06 [95% CI: 0.97, 1.17]), compared to the cold season (RR: 1.03 

31 [95% CI: 0.87, 1.21]). Overall, these results contradict those from Strickland et al. (2010)

32 discussed above. Although the mean number of asthma visits and O3 concentrations in 

33 Sinclair et al. (2010) and Strickland et al. (2010) are similar the difference in results 

34 between the two studies could be attributed to the severity of O3-induced asthma 

35 exacerbations (i.e., more severe symptoms requiring a visit to a hospital) and behavior, 

36 such as delaying a visit to the doctor for less severe symptoms. 
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6.2.7.5 Summary

1 The results of the recent studies evaluated largely support the conclusion of the 2006 O3

2 AQCD. While fewer studies were published overall since the previous review, several 

3 multicity studies (e.g., Cakmak et al., 2006b; Dales et al., 2006) and a multi-continent 

4 study (Katsouyanni et al., 2009) provide supporting evidence for an association between 

5 short-term O3 exposure and an increase in respiratory-related hospital admissions and ED 

6 visits. Collectively, in the studies evaluated, both single-city and multicity, there is 

7 continued evidence for increases in both hospital admissions and ED visits when 

8 examining all respiratory outcomes combined. Additionally, new studies support an 

9 association between short-term O3 exposure and asthma (Strickland et al., 2010; Stieb et 

10 al., 2009) and COPD (Stieb et al., 2009; Medina-Ramon et al., 2006) hospital admissions 

11 and ED visits, with more limited evidence for pneumonia hospital admissions and ED 

12 visits (Medina-Ramon et al., 2006; Zanobetti and Schwartz, 2006). In seasonal analyses, 

13 stronger associations were observed in the warm season or summer months compared to 

14 the cold season, particularly for asthma (Strickland et al., 2010; Ito et al., 2007b) and 

15 COPD (Medina-Ramon et al., 2006) (Figure 6-19; Table 6-27), which is consistent with 

16 the conclusions of the 2006 O3 AQCD. There is also continued evidence that children are 

17 particularly susceptible to O3-induced respiratory effects (Silverman and Ito, 2010; 

18 Strickland et al., 2010; Mar and Koenig, 2009; Villeneuve et al., 2007; Dales et al., 

19 2006). Although the collective evidence indicates a consistent positive association 

20 between O3 exposure and respiratory-related hospital admissions and ED visits, the 

21 magnitude of these associations may be underestimated due to behavioral modification in 

22 response to forecasted air quality (Neidell and Kinney, 2010; Neidell, 2009)

23 (Section 4.6.4).

24 Additional studies that focused on respiratory-related outpatient or physician visits found 

25 no evidence of an association with short-term O3 exposure, but this could be attributed to 

26 the severity of O3-induced respiratory effects requiring more immediate treatment or 

27 behavioral factors that result in delayed visits to a physician.

28 The studies that examined the potential confounding effects of copollutants found that O3

29 effect estimates remained relatively robust upon the inclusion of PM and gaseous 

30 pollutants in two-pollutant models (Figure 6-19; Table 6-27), including (Strickland et al., 

31 2010; Tolbert et al., 2007; Medina-Ramon et al., 2006), which did not present results 

32 quantitatively. These findings are consistent with the studies evaluated in the 2006 O3

33 AQCD (U.S. EPA, 2006b) (Figure 7-12, p. 7-80) which found O3 respiratory hospital 

34 admissions risk estimates remained robust to the inclusion of PM in copollutant models. 
Draft – Do Not Cite or Quote 6-133 September 2011

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.

Effect estimates are for a 20 ppb increase in 24 hours; 30 ppb increase in 8-h max; and 40 increase in 1-h max ozone 

concentrations. HA=hospital admission; ED=emergency department. Black=All-year analysis; Red=Summer only analysis; 

Blue=Winter only analysis. 

Figure 6-19 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; 196722)

Cakmak et al. (2006; 93272)

Dales et al. (2006; 90744)

Orazzo et al. (2009, 202800)a

Katsouyanni et al. (2009; 199899)

Katsouyanni et al. (2009; 199899)b

Darrow et al. (2009; 202800)

Tolbert et al. (2007, 090316)

Biggeri et al. (2005; 87395)c

Katsouyanni et al. (2009; 199899)

Katsouyanni et al. (2009; 199899)b

Stieb et al. (2009; 195858)

Villeneuve et al. (2007; 195859)

Strickland et al. (2010; 624878)

Silverman and Ito (2010; 386252)d

Ito et al. (2007; 156594)

Villeneuve et al. (2007; 195859)

Mar and Koenig (2009; 594410)

Strickland et al. (2010; 624878)

Silverman and Ito (2010; 386252)d

Mar and Koenig (2009; 594410)

Ito et al. (2007; 156594)

Villeneuve et al. (2007; 195859)

Strickland et al. (2010; 624878)

Stieb et al. (2009; 195858)

Medina-Ramon et al. (2006; 87721) Yang et al. (2006; 90184)

Stieb et al. (2009; 195858)e

Medina-Ramon et al. (2006; 87721) MedinaZanobetti and Schwartz (2006; 90195)

Medina-Ramon et al. (2006; 87721) Medina- MedinaLocation

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

7 Canadian Cities 36 U.S. cities

Vancouver 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

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) 1

0-2 0-3 0-1 0-1 DL (0-2) DL (0-2)

2

0-2 0-2 0-1 0-1 0-2

2

0-2 0-1

0

0-1 0-2 0-2

2

0-1 0-3

NR

0-1 0-1

0-1 0-1 0-1 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

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 6-134 September 2011

Table 6-27 Corresponding Effect Estimates for Figure 6-19

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. (2011b)

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. (2011b) 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)

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)
Draft – Do Not Cite or Quote 6-135 September 2011

Study

ED Visit or 

Hospital 

Admission 

Location Age Lag Avg Time

% Increase 

(95% CI)

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)

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.

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 ozone 

concentrations. An “a” represents studies that examined hospital admissions, “b” represents a study that examined ED visits, and “c”

represents risk estimates from APHENA -Canada standardized to an approximate IQR of 5.1 ppb for a 1-h max increase in ozone 

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 6-20 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; 199899)a

Yang et al. (2006; 90184)a

Ito et al. (2007; 156594)b

-10 -5 0 5 10 15 20 25 30

% Increase
Draft – Do Not Cite or Quote 6-136 September 2011

Table 6-28 Corresponding effect estimates for Figure 6-20

Studya Location Visit Type Age Lag Copollutant % Increase (95% CI)

All-year

Respiratory

Katsouyanni et al. (2009) APHENA-U.S. HA 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)

APHENA-Canada 5.54 (-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 HA 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)

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 Additionally, a preliminary examination of the C-R relationship found no evidence of a 

2 threshold between short-term O3 exposure and pediatric asthma ED visits (Silverman and 

3 Ito, 2010; Strickland et al., 2010). Overall, the new body of evidence supports an 

4 association between short-term O3 exposure and respiratory-related hospital admissions 

5 and ED visits, with additional evidence for stronger associations during the warm season 

6 for specific respiratory outcomes such as asthma and COPD. 

6.2.8 Respiratory Mortality

7 The epidemiologic, controlled human exposure, and toxicological studies discussed 

8 within this section (Section 6.2) provides evidence for multiple respiratory effects in 

9 response to short-term O3 exposure. Additionally, the evidence from experimental studies 

10 indicates multiple potential pathways of O3-induced respiratory effects, which support the 

11 continuum of respiratory effects that could potentially result in respiratory-related 

12 mortality. The 2006 O3 AQCD found inconsistent evidence for an association between 

13 short-term O3 exposure and respiratory mortality (U.S. EPA, 2006b). Although some 

14 studies reported a strong positive association between O3 exposure and respiratory 
Draft – Do Not Cite or Quote 6-137 September 2011

1 mortality, additional studies reported a small association or no association. Recent 

2 multicity studies found consistent positive associations between short-term O3 exposure 

3 and respiratory mortality, specifically during the summer months. 

4 The APHENA study, described earlier in Section 6.2.7.2, (Katsouyanni et al., 2009) also 

5 examined associations between short-term O3 exposure and mortality and found 

6 consistent positive associations for respiratory mortality in all-year analyses with stronger 

7 associations in analyses restricted to the summer season. Additional multicity studies 

8 from the U.S. (Zanobetti and Schwartz, 2008b), Europe (Samoli et al., 2009), Italy 

9 (Stafoggia et al., 2010), and Asia (Wong et al., 2010) that conducted summer season 

10 and/or all-year analyses provide additional support for an association between short-term 

11 O3 exposure and respiratory mortality (Figure 6-37). 

12 Of the studies evaluated, only the APHENA study (Katsouyanni et al., 2009) and the 

13 Italian multicity study (Stafoggia et al., 2010) conducted an analysis of the potential for 

14 copollutant confounding of the O3-respiratory mortality relationship. In the APHENA 

15 study, in the European dataset, when focusing on the natural spline model with 8 df/year 

16 (as discussed in Section 6.2.7.2) and lag 1 results (as discussed in Section 6.6.2.1), 

17 respiratory mortality risk estimates were robust to the inclusion of PM10 in copollutant 

18 models in all-year analyses with O3 respiratory mortality risk estimates increasing in the 

19 Canadian and U.S. datasets. In summer season analyses, respiratory O3 mortality risk 

20 estimates were robust in the U.S. dataset and attenuated in the European dataset. 

21 Similarly, in the Italian multicity study (Stafoggia et al., 2010), which was limited to the 

22 summer season, respiratory mortality risk estimates were attenuated in copollutant 

23 models with PM10. Based on the APHENA and Italian multicity results, O3 respiratory 

24 mortality risk estimates appear to be moderately to substantially sensitive (e.g., increased 

25 or attenuated) to inclusion of PM10. However, in the APHENA study, the mostly every26 6th-day sampling schedule for PM10 in the Canadian and U.S. datasets greatly reduced 

27 their sample size and limits the interpretation of these results. 

6.2.9 Summary and Causal Determination

28 The 2006 O3 AQCD concluded that there was clear, consistent evidence of a causal 

29 relationship between short-term O3 exposure and respiratory effects (U.S. EPA, 2006b). 

30 This conclusion was substantiated by evidence from controlled human exposure and 

31 toxicological studies indicating a range of respiratory effects in response to short-term O3

32 exposure, including pulmonary function decrements, respiratory symptoms, lung 

33 inflammation, increased lung permeability, and airway hyperresponsiveness. 

34 Toxicological studies provided additional evidence for O3-induced impairment of host 
Draft – Do Not Cite or Quote 6-138 September 2011

1 defenses. Combined, these findings from experimental studies provided support for 

2 epidemiologic evidence, in which short-term O3 exposure was consistently associated 

3 with decreases in lung function in populations with increased outdoor exposures, children 

4 with asthma, and healthy children; increases in respiratory symptoms and asthma 

5 medication use in children with asthma; and increases in respiratory-related hospital 

6 admissions and asthma-related ED visits. Short-term O3 exposure also was consistently 

7 associated with all-cause and cardiopulmonary mortality; however, the contribution of 

8 respiratory causes to these findings was uncertain.

9 Building on the large body of evidence presented in the 2006 O3 AQCD, recent studies 

10 support associations between short-term O3 exposure and respiratory effects. Controlled 

11 human exposure studies continue to provide the strongest evidence for lung function 

12 decrements in young healthy adults over a range of O3 concentrations. Studies previously 

13 reported mean O3-induced FEV1 decrements of 6-8% at 80 ppb O3 (Adams, 2006a, 

14 2003a; McDonnell et al., 1991; Horstman et al., 1990), and new evidence additionally 

15 indicates mean FEV1 decrements of 6% at 70 ppb O3 (Schelegle et al., 2009) and 2-3% at 

16 60 ppb O3 (Kim et al., 2011; Brown et al., 2008; Adams, 2006a) (Section 6.2.1.1). In 

17 healthy young adults, O3-induced decrements in FEV1 do not appear to depend on gender 

18 (Hazucha et al., 2003), body surface area or height (McDonnell et al., 1997), lung size or 

19 baseline FVC (Messineo and Adams, 1990). There is limited evidence that blacks may 

20 experience greater O3-induced decrements in FEV1 than do age-matched whites (Que et 

21 al.; Seal et al., 1993). Healthy children experience similar spirometric responses but 

22 lesser symptoms from O3 exposure relative to young adults (McDonnell et al., 1985b). 

23 On average, spirometric and symptom responses to O3 exposure appear to decline with 

24 increasing age beyond about 18 years of age (McDonnell et al., 1999; Seal et al., 1996). 

25 There is also a tendency for slightly increased spirometric responses in mild asthmatics 

26 and allergic rhinitics relative to healthy young adults (Jorres et al., 1996). Spirometric 

27 responses in asthmatics appear to be affected by baseline lung function, i.e., responses 

28 increase with disease severity (Horstman et al., 1995).

29 Available information from controlled human exposure studies on recovery from O3

30 exposure indicates that an initial phase of recovery in healthy individuals proceeds 

31 relatively rapidly, with acute spirometric and symptom responses resolving within about 

32 2 to 4 h (Folinsbee and Hazucha, 1989). Small residual lung function effects are almost 

33 completely resolved within 24 h. Effects of O3 on the small airways persisting a day 

34 following exposure, assessed by persistent decrement in FEF25-75 and altered ventilation 

35 distribution, may be due in part to inflammation (Frank et al., 2001; Foster et al., 1997). 

36 In more responsive individuals, this recovery in lung function takes longer (as much as 

37 48 hours) to return to baseline. Some cellular responses may not return to baseline levels 

38 in humans for more than 10-20 days following O3 exposure (Devlin et al., 1997). Airway 
Draft – Do Not Cite or Quote 6-139 September 2011

1 hyperresponsiveness and increased epithelial permeability are also observed as late as 24 

2 h postexposure (Que et al.). 

3 With repeated O3 exposures over several days, spirometric and symptom responses 

4 become attenuated in both healthy individuals and asthmatics, but this tolerance is lost 

5 after about a week without exposure (Gong et al., 1997a; Folinsbee et al., 1994; Kulle et 

6 al., 1982). Airway responsiveness also appears to be somewhat attenuated with repeated 

7 O3 exposures in healthy individuals, but becomes increased in individuals with 

8 preexisting allergic airway disease (Gong et al., 1997a; Folinsbee et al., 1994). Some

9 indicators of pulmonary inflammation are attenuated with repeated O3 exposures. 

10 However, other markers such as epithelial integrity and damage do not show attenuation, 

11 suggesting continued tissue damage during repeated O3 exposure (Devlin et al., 1997).

12 Collectively, epidemiologic evidence supports observations from controlled human 

13 exposure studies of O3-induced decrements in lung function (Section 6.2.1.2). A notable 

14 difference among newer studies was the relatively limited investigation of the effect of 

15 ambient O3 exposure on lung function in populations engaged in outdoor recreation, 

16 exercise, or work, which contributed to the weight of evidence in previous AQCDs. As in 

17 previous AQCDs, recent epidemiologic investigation focused on and most consistently 

18 demonstrated associations between increases in ambient O3 exposure and decreases in 

19 lung function in children with asthma. Across the diverse populations examined in 

20 epidemiologic studies, ambient O3 exposure was associated with 1-8% decreases in mean 

lung function per standardized increment in O3 concentration1 21 . Larger decreases (3-8%) 

22 were observed in children with asthma with increased outdoor exposures, CS use, or 

23 concurrent URI and older adults with airway hyperresponsiveness, elevated BMI, or 

24 GSTP1 Val/Val genotype, indicating the existence of groups within the population with 

25 potentially increased sensitivity to O3 exposure. Further, several epidemiologic studies 

26 found that O3-associated decreases in lung function were associated with concomitant 

27 increases in respiratory symptoms. Biological plausibility for O3-associated decrements 

28 in lung function in controlled human exposure, epidemiologic, and animal studies is 

29 provided by the well-documented effects of O3 activating bronchial C-fibers (Section 

30 5.3.2).

31 Across disciplines, studies have examined factors that may potentially increase an 

32 individual’s susceptibility to O3-induced decrements in lung function. In the controlled 

33 human exposure studies, there is a large degree of intersubject variability in lung function 

34 decrements, symptomatic responses, pulmonary inflammation, airway 

35 hyperresponsiveness, and altered epithelial permeability in healthy adults exposed to O3

 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 6-140 September 2011

1 (Que et al.; Holz et al., 2005; McDonnell, 1996). The magnitude of pulmonary 

2 inflammation, airway hyperresponsiveness, and increases in epithelial permeability do 

3 not appear to be correlated, nor are these responses to O3 correlated with changes in lung 

4 function, suggesting that different mechanisms may be responsible for these processes 

5 (Que et al.; Balmes et al., 1997; Balmes et al., 1996; Aris et al., 1995). However, these 

6 responses tend to be reproducible within a given individual over a period of several 

7 months indicating differences in the intrinsic responsiveness of individuals (Holz et al., 

8 2005; Hazucha et al., 2003; Holz et al., 1999; McDonnell et al., 1985a). Numerous 

9 reasons for differences in the susceptibility of individuals to O3 exposure have been 

10 reported in the literature. Dosimetric and mechanistic considerations are discussed in 

11 Section 5.4. Evidence in all three disciplines suggests a role for antioxidant defenses in 

12 modulating respiratory responses to O3. The biological plausibility of these findings is 

13 provided by the well-characterized evidence for O3 exposure leading to the formation of 

14 secondary oxidation products, which subsequently activate neural reflexes that mediate 

15 lung function decrements (Section 5.3.2). Secondary oxidation products also initiate 

16 pulmonary inflammation (Sections 5.3.3). Epidemiologic studies additionally have found 

17 that atopy (Khatri et al., 2009), concurrent respiratory infection (Lewis et al., 2005), 

18 AHR, and elevated BMI (Alexeeff et al., 2007) may modify respiratory responses to O3

19 exposure (Section 6.2.1.2). Retrospective analyses of controlled human exposure studies 

20 of data pooled across 15 controlled human exposure studies also show larger O3-induced 

21 FEV1 decrements in adults with higher BMI (McDonnell et al., 2010; Bennett et al., 

22 2007).

23 Additional respiratory effects induced by short-term O3 exposures in controlled human 

24 exposure studies of healthy, young adults include increases in respiratory symptoms with 

25 O3 concentrations <80 ppb (Schelegle et al., 2009; Adams, 2006a) (Section 6.2.1.1). 

26 Similarly, epidemiologic studies collectively demonstrate that increases in short-term 

27 ambient O3 exposure are associated with increases in respiratory symptoms and asthma 

28 medication use among subjects with asthma (Section 6.2.4.1). Among recent 

29 epidemiologic studies, the strongest evidence of O3-associated respiratory symptoms was 

30 found in populations with multiple potential susceptibility factors, specifically, 

31 individuals with asthma and atopy (Khatri et al., 2009; Escamilla-Nuñez et al., 2008; Feo 

32 Brito et al., 2007) and children with asthma with diminished antioxidant enzyme activity 

33 (Romieu et al., 2006).

34 Recent controlled human exposure studies (Section 6.2.3.1) and toxicological studies 

35 (Section 6.2.3.3) also continue to demonstrate lung injury and inflammatory responses 

36 upon O3 exposure. Evidence from more than a hundred toxicological studies clearly 

37 indicates that O3 induces damage and inflammation in the lung, and studies continue to 
Draft – Do Not Cite or Quote 6-141 September 2011

1 elucidate the mechanistic pathways involved (Section 5.3). Though inflammation may 

2 resolve, continued inflammation may alter theJanetrita2010

3 structure and function of pulmonary tissues. New controlled human studies support 

4 previous findings for pulmonary inflammation at 60 ppb O3, the lowest concentration 

5 evaluated . Building on the extensive experimental evidence, epidemiologic studies 

6 provide new evidence for ambient O3-associated increases in pulmonary inflammation in 

7 individuals with asthma. These associations were observed primarily for 8-h max or 8-h 

8 average O3 exposures but for both same-day and multiday average exposures. Multiple 

9 studies examined and found increases in eNO (Berhane et al., 2011; Khatri et al., 2009; 

10 Barraza-Villarreal et al., 2008). The clinical significance of these findings was supported 

11 by observations of concomitant O3-associated increases in respiratory symptoms (Khatri 

12 et al., 2009; Barraza-Villarreal et al., 2008). A smaller number of studies examined and 

13 found associations with cytokines such as IL-6 or IL-8 in nasal lavage samples (Barraza14 Villarreal et al., 2008; Sienra-Monge et al., 2004) inflammatory cells in blood (e.g., 

15 eosinophils) (Khatri et al., 2009), decreased levels of antioxidants (Sienra-Monge et al., 

16 2004), and increased levels of indicators of oxidative stress (Romieu et al., 2008)

17 (Section 6.2.3.2).

18 Modification of innate and adaptive immunity is emerging as a mechanistic pathway 

19 underlying the effects of ozone on asthma and allergic airways disease (Section 5.3.6). 

20 While the majority of evidence comes from animal studies, results from controlled 

21 human exposure studies suggest that these pathways may be relevant to humans and may 

22 lead to the induction and exacerbation of asthma (Alexis et al., 2010; Hernandez et al., 

23 2010; Alexis et al., 2009; Bosson et al., 2003). Further, differences between asthmatics 

24 and healthy controls in ozone-mediated innate and adaptive immune responses have been 

25 noted (Section 5.4.2.2). 

26 The subclinical and overt respiratory effects observed across disciplines collectively 

27 provide support for epidemiologic studies that demonstrate consistently positive 

28 associations of short-term O3 exposure with respiratory-related hospital admissions and 

29 ED visits (Section 6.2.7). Consistent with evidence presented in the 2006 O3 AQCD, new 

30 multicity studies and a multicontinent study (i.e., APHENA) (Katsouyanni et al., 2009)

31 found risk estimates ranging from an approximate 1.6 to 5.4% increase in all respiratory32 related hospital admissions and ED visits in all-year analyses for standardized increases 

in ambient O3 concentrations1 33 . Positive associations persisted in analyses restricted to the 

34 summer season, but the magnitude varied depending on the study location (Figure 6-19). 

35 Compared with studies reviewed in the 2006 O3 AQCD, a larger number of recent studies 

 1 Effect estimates were standardized to a 20-ppb increase for 24-h avg O3, a 30-ppb increase for 8-h max O3, and a 40-ppb 

increase for 1-h max O3.
Draft – Do Not Cite or Quote 6-142 September 2011

1 examined hospital admissions and ED visits for specific respiratory outcomes. Although 

2 still limited in number, both single- and multicity studies found consistent, positive 

3 associations between short-term O3 exposures and asthma and COPD hospital admissions 

4 and ED visits, with more limited evidence for pneumonia. Consistent with the 

5 conclusions of the 2006 O3 AQCD, in studies that conducted seasonal analyses, risk 

6 estimates were elevated in the warm season compared to cold season or all-season 

7 analyses, specifically for asthma and COPD. Although recent studies did not include 

8 detailed age-stratified results, the increased risk of asthma hospital admissions 

9 (Silverman and Ito, 2010; Strickland et al., 2010; Dales et al., 2006) observed for children 

10 strengthens the conclusion from the 2006 O3 AQCD that children are particularly 

11 susceptible to O3-induced respiratory effects (U.S. EPA, 2006b). Although the 

12 concentration-response relationship has not been extensively examined, preliminary 

13 examinations found no evidence of a threshold between short-term O3 exposure and 

14 asthma hospital admissions and pediatric asthma ED visits (Silverman and Ito, 2010; 

15 Strickland et al., 2010). 

16 New evidence extends the potential range of well-established O3-associated respiratory 

17 effects by demonstrating associations between short-term ambient O3 exposure and 

18 respiratory-related mortality. In all-year analyses, a multicontinent (APHENA) and 

19 multicity (PAPA) study found consistent, positive associations with respiratory mortality 

20 for all ages but less consistent evidence in analyses restricted to ages 75+. Further, 

21 multicity studies in the U.S. and Europe that conducted seasonal analyses found stronger 

22 associations during the summer season (Section 6.2.8). 

23 Several studies of respiratory morbidity and mortality evaluated the potential 

24 confounding effects of copollutants, in particular, PM10, PM2.5, or NO2. In most cases, 

25 effect estimates remained robust to the inclusion of copollutants; however, in several 

26 studies, changes were observed in the magnitude of the O3 association. In studies of lung 

27 function and respiratory symptoms, larger effects frequently were estimated for O3 when 

28 copollutants were added to models. Ozone effect estimates for respiratory-related hospital 

29 admissions and ED visits remained relatively robust upon the inclusion of PM and 

30 gaseous pollutants in two-pollutant models (Strickland et al., 2010; Tolbert et al., 2007; 

31 Medina-Ramon et al., 2006). Although copollutant confounding was not extensively 

32 examined in mortality studies, the O3-respiratory mortality relationship was moderately 

33 to substantially sensitive (e.g., increased or attenuated) to the inclusion of PM10 in 

34 copollutant models (Stafoggia et al., 2010; Katsouyanni et al., 2009). However, 

35 interpretation of these results requires caution due to the limited PM datasets used in 

36 these studies. Together, these findings across respiratory endpoints provide support for 

37 the independent effects of short-term ambient O3 exposures.
Draft – Do Not Cite or Quote 6-143 September 2011

1 In summary, new studies evaluated since the completion of the 2006 O3 AQCD support 

2 and expand upon the strong body of evidence that indicated a causal relationship between 

3 short-term O3 exposure and respiratory health effects. New controlled human exposure 

4 studies continue to demonstrate O3-induced decreases in FEV1 and pulmonary 

5 inflammation at concentrations as low as 60 ppb. New epidemiologic studies provide 

6 evidence for associations of ambient O3 exposure with biological markers of pulmonary 

7 inflammation and oxidative stress. Toxicological studies have continued to support the 

8 biological plausibility for the O3-induced respiratory effects observed in the controlled 

9 human exposure and epidemiologic studies. Additionally, recent epidemiologic studies 

10 further confirm that respiratory morbidity and mortality associations are stronger during 

11 the warm/summer months and remain relatively robust after adjustment for copollutants. 

12 However, despite the consistency of association between short-term O3 exposure and 

13 respiratory effects, new evidence suggests that the magnitude of association may be 

14 underestimated due to behavioral modification in response to forecasted air quality 

15 (Section 4.6.4). Collectively, the new evidence integrated across toxicological, controlled 

16 human exposure, and epidemiologic studies, in conjunction with that reviewed in 

17 previous AQCDs, is sufficient to conclude that there is a causal relationship between 

18 short-term O3 exposure and respiratory health effects.

6.3 Cardiovascular Effects

6.3.1 Controlled Human Exposure

19 O3 reacts rapidly on contact with respiratory system tissue and is not absorbed or 

20 transported to extrapulmonary sites to any significant degree as such. Controlled human 

21 exposure studies discussed in the previous AQCDs failed to demonstrate any consistent 

22 extrapulmonary effects. Some controlled human exposure studies have attempted to 

23 identify specific markers of exposure to O3 in blood. Foster et al. (1996) found a 

24 reduction in the serum levels of the free radical scavenger α-tocopherol after O3 exposure.

25 Liu et al. (1999; 1997) used a salicylate metabolite, 2,3, dehydroxybenzoic acid (DHBA), 

26 to indicate increased levels of hydroxyl radical which hydroxylates salicylate to DHBA. 

27 Increased DHBA levels after exposure to 120 and 400 ppb suggest that O3 increases 

28 production of hydroxyl radical. The levels of DHBA were correlated with changes in 

29 spirometry. 

30 Gong et al. (1998) observed a small, statistically significant O3-induced increase in the 

31 alveolar-to-arterial PO2 gradient in both healthy (n = 6) and hypertensive (n = 10) adult 

32 males (aged 41-78 years) exposed for 3 hours with exercise to 300 ppb O3. The 
Draft – Do Not Cite or Quote 6-144 September 2011

1 mechanism for the decrease in arterial oxygen tension in the Gong et al. (1998) study 

2 could be due to an O3-induced ventilation-perfusion mismatch. Gong et al. (1998)

3 suggested that by impairing alveolar-arterial oxygen transfer, the O3 exposure could 

4 potentially lead to adverse cardiac events by decreasing oxygen supply to the 

5 myocardium. The subjects in the Gong et al. (1998) study had sufficient functional 

6 reserve so as to not experience significant ECG changes or myocardial ischemia and/or 

7 injury. In studies evaluating the exercise performance of healthy adults, no significant 

8 effect of O3 on arterial O2 saturation has been observed (Schelegle and Adams, 1986).

9 More recently, Fakhri et al. (2009) evaluated changes in HRV among adult volunteers 

(n=50; 27 ± 7 years) during 2-h exposures to PM2.5 CAPs (127±62 μg/m3 10 ) and O3

11 (114±7 ppb), alone and in combination. High frequency HRV was increased following 

12 CAPs-only (p=0.046) and O3-only (p=0.051) exposures, but not in combination. The 

13 standard deviation of NN intervals and the square root of the mean squared differences of 

14 successive NN intervals also showed marginally significant (0.05<p<0.10) effect due to 

15 O3 but not CAPS. Diastolic blood pressure increased by 2 mmHg following the combined 

16 O3 + CAPs exposure, but was not altered by either O3 or CAPs alone. Ten of the subjects 

17 in this study were characterized as “mildly” asthmatic, however, asthmatic status was not 

18 found to modify these effects. For a subset of the subjects without asthma in the Fakhri et 

19 al. (2009) study, Urch et al. (2005) previously reported a 6 mmHg increase in diastolic 

20 blood pressure following a 2-h resting exposure to O3 (120 ppb) + PM2.5 CAPs (150 

μg/m3 21 ) in healthy adults (n=23; 32 ± 107 years), which was statistically different from the 

22 1 mmHg increase seen following FA exposure.

6.3.2 Epidemiology

23 The 2006 O3 AQCD concluded that the “generally limited body of evidence is highly 

24 suggestive that O3 directly and/or indirectly contributes to cardiovascular-related 

25 morbidity,” including physiologic effects (e.g., release of platelet activating factor 

26 [PAF]), HRV, arrhythmias, and myocardial infarctions, although the available body of 

27 evidence reviewed during the 2006 O3 AQCD does not “fully substantiate links between 

28 ambient O3 exposure and adverse cardiovascular outcomes” (U.S. EPA, 2006b). Since 

29 the completion of the 2006 O3 AQCD an increasing number of studies have examined the 

30 relationship between short-term O3 exposure and cardiovascular morbidity and mortality. 

31 These new studies, as well as evidence from the previous AQCDs, are presented within 

32 this section.
Draft – Do Not Cite or Quote 6-145 September 2011

6.3.2.1 Arrhythmia 

1 In the 2006 O3 AQCD, conflicting results were observed when examining the effect of O3

2 on arrhythmias (Dockery et al., 2005; Rich et al., 2005). A study by Dockery et al. (2005)

3 reported no association between O3 levels and ventricular arrhythmias among patients 

4 with implantable cardioverter defibrillators (ICD) living in Boston, MA, although when 

5 O3 was categorized into quintiles, there was weak evidence of an association with 

6 increasing O3 concentration (median O3 concentration: 22.9 ppb). Rich et al. (2005)

7 performed a re-analysis of this cohort using a case-crossover design and detected a 

8 positive association between O3 exposure and ventricular arrhythmias. Recent studies 

9 were conducted in various locations and each used a different cardiac episode to define 

10 an arrhythmic event and a different time period of exposure, which may help explain 

11 observed differences across studies. Ozone levels for each new study are reported in 

12 Table 6-29.

Table 6-29 Characterization of ozone concentrations (in ppb) from studies of 

arrhythmias 

`Reference Location Averaging Time Mean Concentration 

(Standard Deviation)

Upper Range 

of Concentration

Anderson et al. (2010) London, England 8-h max 8.08 75th: 11.5

Metzger et al. (2007) Atlanta, GA 8-h max

Summer only

53.9 (23) Max: 148

Rich et al. (2006a) St. Louis, MO 24-h 21* 75th: 31

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

Sarnat et al. (2006a) 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

*Median presented (information on mean not given).

13 Multiple studies examined O3-related effects on individuals with ICDs. One study of 518 

14 ICD patients who had at least 1 tachyarrythmia within a 10-year period (totaling 6287 

15 tachyarrhythmic event-days; 1993-2002) was conducted in Atlanta, Georgia (Metzger et 

16 al., 2007). Tachyarrhythmic events were defined as any ventricular tachyarrhythmic 

17 event, any ventricular tachyarrhythmic event that resulted in electrical therapy, and any 

18 ventricular tachyarrhythmic event that resulted in defibrillation. In the primary analysis, 

19 no evidence of an association was observed for a 30 ppb increase in 8-h max O3

20 concentrations and tachyarrhythmic events (OR: 1.00 [95% CI: 0.92, 1.08]; lag 0). 

21 Season-specific as well as several sensitivity analyses (including the use of an 
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1 unconstrained distributed lag model [lags 0-6]) were conducted resulting in similar null 

2 associations. A strength of this study is that it incorporated a large sample size over a 

3 long time period. 

4 In a case-crossover analysis, a population of ICD patients in Boston, previously examined 

5 by (Rich et al., 2005) was used to assess the association between air pollution and 

6 paroxysmal atrial fibrillation (PAF) episodes (Rich et al., 2006b). In addition to 

7 ventricular arrhythmias, ICD devices may also detect supraventricular arrhythmias, of 

8 which atrial fibrillation is the most common. Although atrial fibrillation is generally not 

9 considered lethal, it has been associated with increased premature mortality as well as 

10 hospitalization and stroke. Ninety-one electrophysiologist-confirmed episodes of PAF 

11 were ascertained among 29 patients. An association (OR: 3.86 [95% CI: 1.44, 10.28] per 

12 40 ppb increase in 1-h max O3 concentrations) was observed between increases in O3

13 during the concurrent hour and PAF episodes (lag 0-h). The estimated OR for the 24-h 

14 moving average concentration was elevated (OR: 1.81 [95% CI: 0.86, 3.83] per 20 ppb), 

15 but weaker than the estimate for the shorter exposure window. The association between 

16 PAF and O3 in the concurrent hour during the cold months was comparable to that during 

17 the warm months. In addition, no evidence of a deviation from linearity between O3

18 concentration and the log odds of PAF was observed. Authors report that the difference 

19 between O3 exposure and observed effect between this study (PAF and 1-h O3) and their 

20 previous study (ventricular arrhythmias and 24-h moving average O3) (Rich et al., 2005)

21 suggest a more rapid response to air pollution for PAF (Rich et al., 2006b).

22 In an additional study, Rich et al. (2006a) employed a case-crossover design to examine 

23 the association between air pollution and 139 confirmed ventricular arrhythmias among 

24 56 ICD patients in St Louis, Missouri. The authors observed a positive association with 

25 O3 (OR: 1.17 [95% CI: 0.58, 2.38] per 20 ppb increase in 24-h moving avg O3 

26 concentrations [lags 0-23 hours]). Although the authors concluded these results were 

27 similar to their results from Boston (Rich et al., 2005), they postulated that the pollutants 

28 responsible for the increased risk in ventricular arrhythmias are different (O3 and PM2.5 in 

29 Boston and sulfur dioxide in St Louis). 

30 Anderson et al. (2010) used a case-crossover framework to assess air pollution and 

31 activation of ICDs among patients from all 9 ICD clinics in the London National Health 

32 Service hospitals. “Activation” was defined as tachycardias for which the defibrillator 

33 delivered treatment. Investigators modeled associations using unconstrained distributed 

34 lags from 0 to 5 days. The sample consisted of 705 patients with 5,462 activation days 

(O3 35 information was for 543 patients and 4,092 activation days). Estimates for O3 were 

36 consistently positive, although weak (OR: 1.09 [95% CI: 0.76, 1.55] per 30 ppb for 0-
Draft – Do Not Cite or Quote 6-147 September 2011

1 1 day lag; OR: 1.04 [95% CI: 0.60, 1.81] per 30 ppb for 0-5 day lag) (Anderson et al., 

2 2010). 

3 In contrast to arrhythmia studies conducted among ICD patients, Sarnat et al. (2006a)

4 recruited non-smoking adults (age range: 54-90 years) to participate in a study of air 

5 pollution and arrhythmias conducted over two 12-week periods during summer and fall 

6 of 2000 in a region characterized by industrial pollution (Steubenville, Ohio). Continuous 

7 ECG data acquired on a weekly basis over a 30-minute sampling period were used to 

8 assess ectopy, defined as extra cardiac depolarizations within the atria (supraventricular 

9 ectopy, SVE) or the ventricles (ventricular ectopy, VE). Increases in the 5-day moving 

10 average (days 1-5) of O3 were associated with an increased odds of SVE (OR: 2.17 [95% 

11 CI: 0.93, 5.07] per 20 ppb increase in 24-h avg O3 concentrations). A weaker association 

12 was observed for VE (OR: 1.62 [95% CI: 0.54, 4.90] per 20 ppb increase in 24-h avg O3

13 concentrations). The results of the effect of 5-day O3 on SVE were robust to the inclusion 

of SO4

2- 14 in the model [OR: 1.62 (95% CI: 0.54, 4.90)]. The authors indicate that the 

15 strong associations observed at the 5-day moving averages, as compared to shorter time 

16 periods, suggests a relatively long-acting mechanistic pathways, such as inflammation, 

17 may have promoted the ectopic beats in this population (Sarnat et al., 2006a).

18 Although many studies report positive associations, collectively, studies of arrhythmias 

19 report inconsistent results. This may be due to variation in study populations, length and 

20 season of averaging time, and outcome under study. Future studies are expected to 

21 provide additional evidence for the various outcomes and exposure periods.

6.3.2.2 Heart Rate/Heart Rate Variability

22 In the 2006 O3 AQCD, two large population-based studies of air pollution and HRV were 

23 summarized (Park et al., 2005b; Liao et al., 2004a). In addition, the biological 

24 mechanisms and potential importance of HRV were discussed. Briefly, the study of acute 

25 adverse effects of air pollution on cardiac autonomic control is based on the hypothesis 

26 that increased air pollution levels may stimulate the autonomic nervous system and lead 

27 to an imbalance of cardiac autonomic control characterized by sympathetic activation 

28 unopposed by parasympathetic control (U.S. EPA, 2006b). Examples of HRV indices 

29 include the standard deviation of normal-to-normal intervals (SDNN), the square root of 

30 the mean of the sum of the squares of differences between adjacent NN intervals (r31 MSSD), high-frequency power (HF), low-frequency power (LF), and the LF/HF ratio. 

32 Liao et al. (2004a) examined the association between air pollution and cardiac autonomic 

33 control in the fourth cohort examination (1996-1998) of the U.S.-based Atherosclerosis 

34 Risk in Communities Study. A decrease in log-transformed HF was associated with an 
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1 increase in O3 concentration among white study participants. Park et al. (2005b)

2 examined the effects of air pollution on indices of HRV in a population-based study 

3 among men from the Normative Aging Study in Boston, Massachusetts. Several 

4 associations were observed with O3 and HRV outcomes; a reduction in LF was associated 

5 with increased O3 concentration, which was robust to inclusion of PM2.5. The associations 

6 with all HRV indices and O3 were stronger among those with ischemic heart disease and 

7 hypertension. In addition to these population-based studies included in the 2006 O3

8 AQCD was a study by Schwartz et al. (2005), who conducted a panel study to assess the 

9 relationship between exposure to summertime air pollution and HRV. A weak association 

10 of O3 during the hour immediately preceding the health measures was observed with r11 MSSD among a study population that consisted of mostly older female participants. In 

12 summary, these studies suggest that short-term exposures to O3 are predictors of 

13 decreased HRV and that the relationship may be stronger among certain subgroups. The 

14 generally consistent (although weak) associations between pollutants and reduced cardiac 

15 autonomic control were observed at relatively low pollution concentrations typically 

16 experienced by the U.S. general population on a daily basis (U.S. EPA, 2006b). More 

17 recent studies of O3 and HRV and are described below. The O3 concentrations for these 

18 studies are presented in Table 6-30.

Table 6-30 Characterization of ozone concentrations (in ppb) from studies of 

heart rate variability 

Reference Location Averaging Time Mean Concentration 

(Standard Deviation)

Upper Range of 

Concentration

Baja et al. (2010) Boston, MA 0 lag

10-h lag

23 (16)

21 (15)

Chan et al. (2005a) Taipei, Taiwan 1-h 21.9 (15.4) Max: 114.9

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

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)

Ruidavets et al. (2005a) Toulouse, France 8-h 38.3 (14.8) 75th: 46.9

Max: 80.3

Wheeler et al. (2006) Atlanta, GA 4-h

24-h

18.5

29.4

75th: 22.5

Wu et al. (2010) Taipei, Taiwan Working period 24.9 (14.0) Max: 59.2

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

*Median presented (information on mean not given).
Draft – Do Not Cite or Quote 6-149 September 2011

1 Several follow-up examinations of HRV were conducted among the participants of the 

2 Normative Aging Study in Boston. A trajectory cluster analysis was used to assess 

3 whether pollution originating from different locations had varying relationships with 

4 HRV (Park et al., 2007). Subjects who were examined on days when air parcels 

5 originated in the west had the strongest associations with O3; however, the O3

6 concentration in this cluster was low (24-h avg, 17.0 ppb) compared to the other clusters 

7 (24-h avg of 21.3-29.1 ppb). LF and SDNN decreased with increases in the 4-h moving 

8 average of O3 from the west (LF decreased by 51.2% [95% CI: 1.6, 75.9%] and SDNN 

9 decreased by 28.2% [95% CI: -0.5, 48.7%] per 30 ppb increase in 4-h avg O3

10 concentrations) (Park et al., 2007). The Boston air mass originating in the west traveled 

11 over Illinois, Indiana, and Ohio; states typically characterized by coal-burning power 

12 plants. Due to the low O3 concentrations observed in the west cluster, the authors 

13 hypothesize that O3 on those days could be capturing the effects of other, secondary 

14 and/or transported pollutants from the coal belt or that the relationship between ambient 

15 O3 and personal exposure to O3 is stronger during that period (supported by a 

16 comparatively low apparent temperature which could indicate a likelihood to keep 

17 windows open and reduced air conditioning use) (Park et al., 2007). An additional 

18 follow-up evaluation using the Normative Aging Study examined the potential for effect 

19 modification by chronic lead exposure on the relationship between air pollution and HRV 

20 (Park et al., 2008). Authors observed graded reductions in HF and LF of HRV in relation 

21 to O3 (and sulfate) across increasing quartiles of tibia and patella lead (HF: %change 32.3 

22 [95% CI: -32.5, 159.3] for the first quartile of tibia Pb and -59.1 [95% CI: -77.3, -26.1] 

23 for the fourth quartile of tibia Pb per 30 ppb increase in 4-h avg O3 concentrations; LF: 

24 %change 8.0 [95% CI: -36.9, 84.9] for the first quartile of tibia Pb and -59.3 [95% CI: -

25 74.6, -34.8] for the fourth quartile of tibia Pb per 30 ppb increase in 4-h avg O3

26 concentrations). In addition, O3 associations were similar when education and cumulative 

27 traffic-adjusted bone lead levels were used in analyses. Authors indicate the possibility 

28 that O3 (which has low indoor concentrations) was acting as a proxy for sulfate 

29 (correlation coefficient for O3 and sulfate = 0.57). Investigators of a more recent follow30 up to the Normative Aging Study hypothesized that the relationships between short-term 

31 air pollution exposures and ventricular repolarization, as measured by changes in the 

32 heart-rate corrected QT interval (QTc), would be modified by participant characteristics 

33 (e.g., obesity, diabetes, smoking history) and genetic susceptibility to oxidative stress 

34 (Baja et al., 2010). No evidence of an association between O3 (using a quadratic 

35 constrained distributed lag model and hourly exposure lag models over a 10-h time 

36 window preceding the visit) and QTc was reported (change in mean QTc -0.74 [95% CI: 

37 -3.73, 2.25]); therefore, potential effect modification of personal and genetic 

38 characteristics with O3 was not assessed (Baja et al., 2010). Collectively, the results from 

39 studies that examined the Normative Aging Study cohort found an association between 
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1 increases in short-term exposures to O3 and decreases in HRV (Park et al., 2008; Park et 

2 al., 2007; Park et al., 2005b) although not consistently in all of the studies (Baja et al., 

3 2010). Further, observed relationships appear to be stronger among those with ischemic 

4 heart disease, hypertension, and elevated bone lead levels, as well as when air masses 

5 arrive from the west (the coal belt). However, it is not clear if O3 is acting as a proxy for 

6 other, secondary particle pollutants (such as sulfate) (2008; 2007; Park et al., 2005b). In 

7 addition, since the Normative Aging Study participants were older, predominately white 

8 men, results may not be generalizable to women, younger individuals, or those of 

9 different racial/ethnic groups (Baja et al., 2010).

10 Additional studies of populations not limited to the Normative Aging Study have also 

11 examined associations between O3 exposure and HRV. A panel study among 18 

12 individuals with COPD and 12 individuals with recent myocardial infarction (MI) was 

13 conducted in Atlanta, Georgia (Wheeler et al., 2006). HRV was assessed for each 

14 participant on 7 days in fall 1999 and/or spring 2000. The mean 4-h O3 concentration 

15 (time period immediately preceding the HRV measures) was 18.5 ppb; however, O3

16 concentrations differed substantially within study sites (8.0 – 33.8 ppb). Ozone 

17 concentrations were not associated with HRV (SDNN) among all subjects (percent 

18 change of 2.36% [95% CI: -10.8%, 17.5%] per 30 ppb 4-h O3 increase) or when stratified 

19 by disease type (COPD, recent MI, and baseline FEV1) (Wheeler et al., 2006).

20 HRV and air pollution was assessed in a panel study among 46 predominately white male 

21 patients (study population: 80.4% male, 93.5% white) aged 43-75 years in Boston, 

22 Massachusetts, with coronary artery disease (Zanobetti et al., 2010). Up to four home 

23 visits were made to assess HRV over the year following the index event. Pollution lags 

24 used in analyses ranged between 30 minutes to a few hours and up to 5 days prior to the 

25 HRV assessments. Decreases in r-MSSD were reported for all averaging times of O3 

26 (percent change of -5.18% [95% CI: -7.89, -2.30] per 20 ppb of 5-day moving average of 

27 O3 concentration), but no evidence of an association between O3 and HF was observed 

28 (quantitative results not provided). In two-pollutant models with O3 and either PM2.5 or 

29 BC, O3 associations remained robust. 

30 A few studies were conducted outside of the U.S. to assess the relationship between air 

31 pollution concentrations and heart rate and HRV (Wu et al., 2010; Chuang et al., 2007b; 

32 Chuang et al., 2007a; Chan et al., 2005a; Ruidavets et al., 2005a). No associations were 

33 reported between O3 and HRV among CHD patients and patients with one or more major 

34 CHD risk factors residing in Taipei, Taiwan (Chan et al., 2005a). Another study in 

35 Taipei, Taiwan examined mail carriers and reported O3 levels measured using personal 

36 monitors. No association was observed between O3 and the measures of HRV (percent 

37 change for SDNN: 0.57 [95% CI: -21.27, 28.46], r-MSSD: -7.10 [95% CI: -24.24, 13.92], 
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1 HF: -1.92 [95% CI: -23.68, 26.02], LF: -4.82 [95% CI: -25.34, 21.35] per 40 ppb O3) 

2 (Wu et al., 2010). In addition, no consistent relationships were identified between O3 and 

3 resting heart rate among middle-aged (35-64 years) participants residing in Toulouse, 

4 France (Ruidavets et al., 2005a). A negative trend was reported for the 3-day cumulative 

5 (lag days 1-3) concentration of O3 with heart rate (p for trend = 0.02); however, the 

6 individual odds ratios comparing quintiles of exposure showed no association (OR for O3 

7 of 0.93 [95% CI: 0.86, 1.01] for the highest quintile of resting heart rate compared to the 

8 lowest). When stratified by current smoking status, non-smokers had a decreased trend 

9 with increased 3-day cumulative O3 concentrations but none of the quintiles for heart rate 

10 were statistically significant. A panel study was conducted in Taiwan to assess the 

11 relationship between air pollutants and inflammation, oxidative stress, blood coagulation, 

12 and autonomic dysfunction (Chuang et al., 2007b; Chuang et al., 2007a). Participants 

13 were apparently healthy college students (aged 18-25 year) who were living in a 

14 university dormitory in metropolitan Taipei. Health endpoints were measured three times 

15 from April to June in 2004 or 2005. Ozone was assessed in statistical models using the 

16 average of the 24, 48, and 72 hours before the hour of each blood sampling. Decreases in 

17 HRV (measured as SDNN, r-MSSD, LF, and HF) were associated with increases in O3

18 concentrations in single-pollutant models (percent change for SDNN: -13.45 [95% CI: -

19 16.26, -10.60], r-MSSD -13.76 [95% CI: -21.62, -5.44], LF -9.16 [95% CI: -13.29, -

20 4.95], HF -10.76 [95% CI: -18.88, -2.32] per 20 ppb 3-day avg O3 concentrations) and 

21 remained associated with 3-day O3 concentrations in two-pollutant models with sulfate. 

22 Another study in Taiwan recruited individuals with coronary heart disease or at risk for 

23 cardiovascular disease from outpatient clinics (Chuang et al., 2007b). Mean O3

24 concentrations were 35.1 ppb (SD 27.5 ppb) during the study period (two weeks in 

25 February). No association was observed between O3 concentration and HRV measures 

26 (SDNN, r-MSSD, LF, HF) (numerical results not provided in publication).

27 Overall, studies of O3 concentration and HRV report inconsistent results. Multiple studies 

28 in Boston observed positive associations but the authors of many of these studies 

29 postulated that O3 was possibly acting as a proxy for other pollutants. The majority of 

30 other studies, both in the U.S. and internationally, report null findings. The 

31 inconsistencies observed are further complicated by the different HRV measures and 

32 averaging times used by the studies.

6.3.2.3 Stroke

33 The 2006 O3 AQCD did not identify any studies that examined the association between 

34 short-term O3 exposure and stroke. However, recent studies have attempted to examine 

35 this relationship. Lisabeth et al. (2008) used a time-series approach to assess the 
Draft – Do Not Cite or Quote 6-152 September 2011

1 relationship between daily counts of ischemic stroke and transient ischemic attack (TIA) 

2 with O3 concentrations in a southeast Texas community among residents 45 years and 

3 older (2001-2005; median age of cases, 72 years). The median O3 (hourly average per 24-

4 h time-period) concentration was 25.6 ppb (IQR 18.1-33.8). The associations between 

5 same-day (RR: 1.03 [95% CI: 0.96, 1.10] per 20 ppb increase in 24-h avg O3 

6 concentrations) and previous-day (RR: 1.05 [95% CI: 0.99, 1.12] per 20 ppb increase in 

7 24-h avg O3 concentrations) O3 concentrations and stroke/TIA risk were positive. 

8 Associations were robust to adjustment for PM2.5. The effect of season on the relationship 

9 was not assessed. 

10 A case-crossover design was used in a study conducted in Dijon, France between March 

11 1994 and December 2004, among those 40 years of age and older who presented with 

12 first-ever stroke (Henrotin et al., 2007). The mean O3 concentration, calculated over 8-h 

13 daytime periods, was 14.95 ppb (IQR: 6-22 ppb). No association was observed between 

14 O3 concentration at 0, 1, 2, or 3 days lag and hemorrhagic stroke. However, an 

15 association between ischemic stroke occurrence and O3 concentrations with a 1-day lag 

16 was observed (OR: 1.54 [95% CI: 1.14, 2.09] per 30 ppb increase in 8-h max O3 

17 concentrations). The effect of O3 persisted in two-pollutant models with PM10, SO2, NO2, 

18 or CO. This association was stronger among men (OR: 2.12 [95% CI: 1.36, 3.30] per 30 

19 ppb increase in 8-h max O3 concentrations) than among women (OR: 1.17 [95%CI: 0.77, 

20 1.78] per 30 ppb increase in 8-h max O3 concentrations) in single pollutant models. When 

21 stroke was examined by subtype among men, an association was observed for ischemic 

22 strokes of large arteries and for transient ischemic attacks but not for cardioembolic or 

23 lacunar ischemic strokes. The subtype analysis was not performed for women. 

24 Additionally, for men a linear exposure-response was observed when O3 was assessed 

25 based on quintiles (p for trend = 0.01) (Figure 6-21). A potential limitation of this study 

26 is that 67.4% of the participating men were smokers compared to 9.3% of the women. 

27 Another study, performed in Dijon, France, examined the association between O3

28 concentration and incidence of fatal and non-fatal ischemic cerebrovascular events 

29 (ICVE) (Henrotin et al., 2010). Mean 8-h O3 concentration was 19.1 ppb (SD 12.2 ppb). 

30 A positive association was observed between recurrent ICVE and O3 concentration with a 

31 3-day lag (OR: 1.92 [95% CI 1.17, 3.12]), but not for other lags (0, 1, 2, 4) or cumulative 

32 days (0-1, 0-2, 1-2, 1-3). Although some ORs for incident ICVEs were elevated, none 

33 were statistically significant. Results for associations using the maximum daily 1-h O3

34 concentrations were similar to the 8-h results but slightly attenuated. ORs were similar in 

35 two pollutant models (data not given). In stratified analyses, the association between 1-

36 day lagged O3 concentration and incident and recurrent ICVE was greater among those 

37 with multiple other preexisting vascular conditions. Increased associations with ICVE 

38 were also observed for individuals with diabetes or hypertension. 
Draft – Do Not Cite or Quote 6-153 September 2011

Source: Henrotin et al. (2007).

Figure 6-21 Odds ratio (95% confidence interval) for stroke by quintiles of 

ozone.

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. Table 6-

5 31 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 6-31 Characterization of ozone concentrations (in ppb) from studies of 

biomarkers

Reference Location Averaging 

Time

Mean Concentration

(Standard Deviation)

Upper Range of 

Concentration

Baccarelli et al. (2007) Lombardia, Italy 1-h 18.3* 75th: 35.1

Max: 202.3

Chen et al. (2007) Los Angeles and 

San Francisco, CA

8-h/2 wk 30.8* Max: 47.9

8-h/1 mo 28.3* Max: 43.1

Chuang et al. (2010) Taiwan 26.83 (9.7) Max: 62.1

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

Goldberg et al. (2008) Montreal, Quebec 24-h NS

Liao et al. (2005) 3 U.S. counties 8-h 40 (20)

Rudez et al. (2009) Rotterdam, the Netherlands 24-h 22* 75th: 31.5

Max: 90

Steinvil et al. (2008) Tel-Aviv, Israel 0.5-h 29.2 (9.7) 75th: 36

Thompson et al. (2010) Toronto, Ontario 1-h/1 yr 21.94 (15.78)

Wellenius et al. (2007) Boston, MA 1-h/24-h 25.1 (12.9)

*Median presented (information on mean not given).

Hemostasis and coagulation markers

1 Multiple studies used various markers to examine if associations were present between 

2 O3 concentrations and hemostatis and coagulation. Some of the markers included in these 

3 studies were as follows: fibrinogen, von Willebrand factor (vWF), plasminogen activator 

4 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 70 

13 ppb). The association between O3 and fibrinogen was more pronounced among those 

14 with a history of cardiovascular disease (CVD) and was statistically significant among 

15 only this subgroup of the population. The curvilinear relationship between exposure and 

16 outcome suggested stronger relationships at higher concentrations of O3 which could 

17 indicate threshold effects. The authors note that the most pronounced associations 

18 occurred when the pollutants were 2-3 standard deviations above the mean. The results 
Draft – Do Not Cite or Quote 6-155 September 2011

1 from this relatively large-scale cross-sectional study suggest weak associations with O3

2 and fibrinogen (among those with a history of CVD) and vWF. 

3 A retrospective repeated measures analysis was performed in Toronto, Canada among 

4 adults aged 18-40 years (n=45) between the years of 1999 and 2006 (Thompson et al., 

5 2010). Single pollutant models were used with moving averages up to 7 days. No 

6 evidence of an association was observed for O3 and fibrinogen. 

7 A repeated measures study was conducted in 40 healthy individuals living or working in 

8 the city center of Rotterdam, the Netherlands to assess the relationship between air 

9 pollution and markers of hemostatis and coagulation (platelet aggregation, thrombin 

10 generation, and fibrinogen) (Rudez et al., 2009). Each participant provided between 11 

11 and 13 blood samples throughout a 1-year period (498 samples on 197 days). Examined 

12 lags ranged from 6 hours to 3 days prior to blood sampling. No consistent evidence of an 

13 association was observed between O3 and any of the biomarkers (percent change of max 

14 platelet aggregation: -6.87 [95% CI: -21.46, 7.70] per 20 ppb 4-day average O3; percent 

15 change of endogenous thrombin potential: 0.95 [95% CI: -3.05, 4.95] per 20 ppb 4-day 

16 avg O3; percent change of fibrinogen: -0.57 [95% CI: -3.05, 2.00] per 20 ppb lag 1-day 

17 O3;). Some associations with O3 were in the opposite direction to that hypothesized which 

18 may be explained by the negative correlation between O3 and the other pollutants 

19 (correlation coefficients ranged from -0.4 to -0.6). The statistically significant inverse 

20 effects observed with O3 in single-pollutant models were no longer apparent when PM10

21 was included in the models (Rudez et al., 2009).

22 A panel study in Taiwan measured health endpoints using blood samples from healthy 

23 individuals (n=76) at three times from April to June in 2004 or 2005 (Chuang et al., 

24 2007a). Increases in fibrinogen and PAI-1 were associated with increases in O3

25 concentrations in single-pollutant models (percent change in fibrinogen: 11.76 [95% CI: 

26 4.03, 19.71] per 20 ppb 3-day avg O3; percent change in PAI-1: 6.08 [95% CI: 38.91, 

27 84.27] per 20 ppb 3-day avg O3). These associations were also observed at 1 and 2 day 

28 averaging times. Associations between PAI-1 and 3-day O3 concentrations remained 

29 robust in two-pollutant models with sulfate. No association was seen between O3 and 

30 tPA, a fibrinolytic factor (percent change 16.15 [95% CI: -4.62, 38.34] per 20 ppb 3-day 

31 avg O3). 

32 A study in Israel examined the association between pollutant concentrations and 

33 fibrinogen among 3659 apparently healthy individuals (Steinvil et al., 2008). In single 

34 pollutant models, O3 was associated with an increase in fibrinogen at a 4-day lag among 

35 men and a same-day O3 concentration among women but results for other lags (0 through 

36 7 days) were mixed (some positive, some negative; none statistically significant). 
Draft – Do Not Cite or Quote 6-156 September 2011

Inflammatory markers

1 Air pollution and inflammatory markers (C-reactive protein [CRP], white blood cell 

2 [WBC] count, albumin, and Interleukin-6 [IL-6]) were also examined in several studies.

3 The ARIC study cohort, which included men and women aged 45-64 years old at the start 

4 of the study, was utilized to assess the association between O3 concentrations and makers 

5 of inflammation (Liao et al., 2005). No association was observed between O3

6 concentrations and albumin or WBC count. 

7 Thompson et al. (2010) assessed ambient air pollution exposures and IL-6. This 

8 retrospective repeated measures analysis was conducted among 45 adults (18-40 years of 

9 age) in Toronto, Canada between the years of 1999 and 2006. Single pollutant models 

10 were used to analyze the repeated-measures data using moving averages up to 7 days. A 

11 positive association was observed between IL-6 and O3 with the strongest effects 

12 observed for the 4-day moving average of O3 (quantitative results not provided). No 

13 association was seen for shorter averaging times (<1 day). When examined by season 

14 using 2-day moving averages, the association between O3 and IL-6 was positive during 

15 only the spring and summer. 

16 In Rotterdam, the Netherlands, a repeated measures study of healthy individuals living or 

17 working in the city center reported no association between O3 concentration and CRP 

18 (Rudez et al., 2009). Each of the 40 participants provided between 11 and 13 blood 

19 samples throughout a 1-year period (498 samples on 197 days). No consistent evidence of 

20 an association was observed between O3 and CRP (percent change: -0.48 [95% CI: -

21 14.05, 13.10] per 20 ppb lag 1-day O3). Additionally, no association was observed with 2 

22 or 3 day lags. 

23 The relationship between pollutant concentrations and one-time measures of 

24 inflammatory biomarkers was assessed in sex-stratified analyses among 3659 apparently 

25 healthy individuals in Tel Aviv, Israel (Steinvil et al., 2008). No evidence of an 

26 association was observed between O3 and CRP or WBC for men and women. 

27 A panel study of healthy individuals (n=76) was conducted in Taiwan to assess the 

28 relationship between air pollutants and inflammation (Chuang et al., 2007a). Health 

29 endpoints were measured three times from April to June in 2004 or 2005. Ozone effects 

30 were assessed in statistical models using the average of the 24 hours (1 day), 48 hours 

31 (2 days), and 72 hours (3 days) before the hour of each blood sampling. Increases in CRP 

32 were associated with increases in O3 concentrations in single-pollutant models (percent 

33 change in CRP: 244.38 [95% CI: 4.54, 585.15] per 20 ppb 3-day avg O3). The association 

34 was also observed using a 2-day averaging time, but no association was present with a 1-

35 day averaging time.
Draft – Do Not Cite or Quote 6-157 September 2011

Oxidative stress markers

1 A few studies have reported on the relationships between O3 concentration and oxidative 

2 stress markers. The association between O3 exposure and markers of lipid peroxidation 

3 and antioxidant capacity was examined among 120 nonsmoking healthy college students, 

4 aged 18-22 years, from the University of California, Berkeley (February-June 2002) 

5 (Chen et al., 2007). By design, students were chosen that had experienced different 

6 geographic concentrations of O3 over their lifetimes and during recent summer vacation 

7 in either greater Los Angeles (LA) or the San Francisco Bay Area (SF). Long-term 

8 (based on lifetime residential history) and shorter-term (based on the moving averages of 

9 8-h max concentrations 1-30 days prior to the day of blood collection) O3 exposures were 

10 estimated (lifetime exposure results presented in the chronic exposure section). A marker 

11 of lipid peroxidation, 8-isoprostane (8-iso-PGF), was assessed. This marker is formed 

12 continuously under normal physiological conditions but has been found at elevated 

13 concentrations in response to environmental exposures. A marker of overall antioxidant 

14 capacity, ferric reducing ability of plasma (FRAP), was also measured. Substantial 

15 overlap in the more recent O3 exposure estimates (8-h moving averages) was observed 

16 between the two geographic areas sampled. Levels of 8-iso-PGF were associated with 

17 2-week (β = 0.035 [pg/mL]/8-h ppb O3, p = 0.007) and 1-month (β = 0.031 [pg/mL]/8-

18 h ppb O3, p = 0.006) estimated O3 exposure levels. No evidence of association was 

19 observed between O3 and FRAP. A chamber study performed among a subset of study 

20 participants supported the primary study results. The concentrations of 8-iso-PGF 

21 increased immediately after the 4-h controlled O3 exposure ended (p = 0.10). However, 

22 levels returned to near baseline by 18 hours without further exposure. The authors note 

23 that O3 was highly correlated with PM10-2.5 and NO2 in this study population; however, 

24 inclusion of these pollutants in the O3 models did not substantially change the magnitude 

25 of the associations with O3.

26 Using blood samples collected between April and June of 2004 or 2005 in Taiwan, the 

27 association between O3 concentrations and a marker of oxidative stress was studied 

28 among healthy individuals (n=76) (Chuang et al., 2007a). Increases in 8-hydroxy-2’-

29 deoxyguanosine (8-OHdG) were associated with increases in O3 concentrations in single30 pollutant models (percent change in 8-OHdG: 2.46 [95% CI: 1.01, 3.92] per 20 ppb 1-day 

31 avg O3). The association did not persist with 2- or 3-day averaging times.

Markers of overall cardiovascular health

32 Multiple studies used markers that assess overall cardiovascular well-being. Wellenius et 

33 al. (2007) examined Β-type natriuretic peptide (BNP), a marker of heart failure, in a 

34 repeated-measures study conducted in Boston among 28 patients with congestive heart 
Draft – Do Not Cite or Quote 6-158 September 2011

1 failure and impaired systolic function. The authors found no evidence of an association 

2 between BNP and short-term O3 exposures at lags 0-3 days (quantitative results not 

3 provided). BNP was chosen because it is directly associated with cardiac hemodynamics 

4 and symptom severity among those with heart failure and is, therefore, considered a 

5 marker of functional status. However, the authors conclude that the use of BNP may not 

6 be useful in studies of the health effects of ambient air pollutants due to the large amount 

7 of within-person variability in BNP levels observed in this population.

8 The relationship between air pollution and oxygen saturation and pulse rate, markers of 

9 physiological well-being, was examined in a 2-month panel study among 31 congestive 

10 heart failure patients (aged 50-85 years) in Montreal, Canada from July 2002 to October 

11 2003 (Goldberg et al., 2008). All participants had limited physical functioning 

12 (New York Heart Association Classification ≥ II) and an ejection fraction (the fraction of 

13 blood pumped out of the heart per beat) less than or equal to 35% (normal is above 55%). 

14 Daily mean O3 concentrations were calculated based on hourly measures at 10 monitoring 

15 stations. There was an inverse association between O3 (lag-0) and oxygen saturation 

16 when adjustment was made for temporal trends. In the models incorporating personal 

17 covariates and weather factors, the association remained but was not statistically 

18 significant. The associations of O3 with a lag of 1 day or a 3-day mean were not 

19 statistically significant. No evidence of association was observed between O3 exposure 

20 and pulse rate. 

21 Total homocysteine (tHcy) is an independent risk factor for vascular disease and 

22 measurement of this marker after oral methionine load is used to identify individuals with 

23 mild impairment of homocysteine metabolism. The effects of air pollution on fasting and 

24 postmethionine-load tHcy levels were assessed among 1,213 apparently healthy 

25 individuals from Lombardia, Italy from January 1995 to September 2005 (Baccarelli et 

26 al., 2007). An increase in the 24-h O3 concentrations was associated with an increase in 

27 fasting tHcy (percent change 6.25 [95% CI: 0.84, 11.91] per 20 ppb O3) but no 

28 association was observed with postmethionine-load tHcy (percent change 3.36 [95% CI: -

29 1.30, 8.39] per 20 ppb O3). In addition, no evidence of association was observed between 

30 7-day O3 concentrations and tHcy (percent change for fasting tHcy 4.16 [95% CI: -1.76, 

31 10.42] and percent change for postmethionine-load tHcy -0.65 [95% CI: -5.66, 4.71] per 

32 20 ppb O3). No evidence of effect modification by smoking was observed. 

Blood lipids and glucose metabolism markers

33 Chuang et al. (2010) conducted a population-based cross-sectional analysis of data 

34 collected on 7,778 participants during the Taiwanese Survey on Prevalence of 

35 Hyperglycemia, Hyperlipidemia, and Hypertension in 2001. Apolipoprotein B (ApoB), 
Draft – Do Not Cite or Quote 6-159 September 2011

1 the primary apolipoprotein among low-density lipoproteins, was associated with 3-day 

2 avg O3 at the p < 0.10 level. The 5-day mean O3 concentration was associated with an 

3 increase in triglycerides at p < 0.10. In addition, the 1-, 3-, and 5-day mean O3

4 concentrations were associated with increased HbA1c levels (a marker used to monitor 

5 the degree of control of glucose metabolism) at the p < 0.05 level. The 5-day mean O3

6 was associated with increased fasting glucose levels (p < 0.10). No association was 

7 observed between O3 concentration and ApoA1. Copollutant models were not assessed.

6.3.2.5 Myocardial Infarction (MI)

8 The 2006 O3 AQCD did not report consistent results indicating an association between 

9 short-term O3 exposure and MI. One study reported a positive association between 

10 current day O3 concentration and acute MI, especially among the oldest age group (55- to 

11 64-year olds) (Ruidavets et al., 2005b). No association was observed in a case-crossover 

12 study of O3 during the hours surrounding the event and MI (Peters et al., 2001). Since the 

13 2006 O3 AQCD, a few new epidemiologic studies have examined the association between 

14 O3 exposure and MI (Henrotin et al., 2010; Rich et al., 2010), as well as one study 

15 published on arterial stiffness (Wu et al., 2010) and one study published on ST-segment 

16 depression (Delfino et al., 2011). 

17 One of the studies conducted in the U.S. examined hospital admissions for first MI and 

18 reported no association with O3 concentrations (Rich et al., 2010). More details on this 

19 study are reported in the section on hospital admissions. Another study, performed in 

20 Dijon, France, examined the association between O3 concentration and incident and 

21 recurrent MI (Henrotin et al., 2010). The mean 8-h O3 concentration was 19.1 ppb (SD 

22 12.2 ppb). Odds ratios for the association between cumulative O3 concentrations and 

23 recurrent MIs were elevated but none of the results were statistically significant (OR: 

24 1.71 [95% CI: 0.91, 3.20] per 20 ppb for cumulative 1-3 day O3 exposure). No 

25 association was observed for incident MIs. In analyses stratified by vascular risk factors, 

26 positive associations were observed between 1-day lagged O3 concentrations and MIs 

27 (incident and recurrent combined) among those who reported having 

28 hypercholesterolaemia (OR: 1.52 [95% CI: 1.08, 2.15] per 20 ppb O3) and a slight inverse 

29 association was observed among those who reported not having hypercholesterolaemia 

30 (OR: 0.69 [95% CI: 0.50, 0.94] per 20 ppb O3). In other stratified analyses combining 

31 different vascular factors, only those containing individuals with hypercholesterolaemia 

32 demonstrated a positive association; none were inverse associations. 

33 Wu et al. (2010) examined mail carriers aged 25-46 years and measured exposure to O3 

34 through personal monitors [mean O3 24.9 (SD 14.0) ppb]. Ozone exposure was positively 
Draft – Do Not Cite or Quote 6-160 September 2011

1 associated with arterial stiffness (percent change 11.24% [95% CI: 3.67, 19.62] per 40 

2 ppb O3) and was robust to adjustment for ultrafine PM. 

3 A study performed in the Los Angeles basin reported on the association between O3 

4 exposure and ST-segment depression, a measure representing cardiac ischemia (Delfino 

5 et al., 2011). Study participants were nonsmokers, at least 65 years old, had a history of 

6 coronary artery disease, and were living in a retirement community. Study periods 

7 included five consecutive days in both July to mid-October and mid-October to February. 

8 Mean 24-h O3 concentrations were 27.1 ppb (SD 11.5 ppb). No association was observed 

9 between O3 concentrations and ST-segment depression of at least 1.0 mm during any of 

10 the exposure periods (i.e., 1-h, 8-h, 1-day, 2-day avg, 3-day avg, 4-day avg). 

6.3.2.6 Blood Pressure

11 In the 2006 O3 AQCD, no epidemiologic studies examined O3-related effects on blood 

12 pressure (BP). Recent studies have been conducted to evaluate this relationship and 

13 overall the findings are inconsistent. The O3 concentrations for these studies are listed in 

14 Table 6-32. 

Table 6-32 Characterization of ozone concentrations (in ppb) from studies of 

blood pressure

Reference Location Averaging Time Mean Concentration 

(Standard Deviation)

Upper Range of 

Concentration

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

Delfino et al. (2010b) Los Angeles, 

California

24-h 27.1 (11.5) Max: 60.7

Zanobetti et al. (2004) Boston, 

Massachusetts

1-h 20

5-days 24

Chuang et al. (2010) Taiwan 26.83 (9.7) Max: 62.1

15 Zanobetti et al. (2004) examined the relationship between air pollutants and BP from 

16 May 1999 to January 2001 for 631 repeat visits among 62 Boston residents with CVD. In 

17 single-pollutant models, higher resting diastolic blood pressure (DBP) was associated 

18 with the 5-day (0-4 days) averages of O3 (RR: 1.03 [95% CI: 1.00, 1.05] per 20 ppb 

19 increase in 24-h O3 concentrations). However, this effect was no longer apparent when 

20 PM2.5 was included in the model (data were not presented) (Zanobetti et al., 2004). 

21 Delfino et al. (2010b) examined 64 subjects 65 years and older with coronary artery 
Draft – Do Not Cite or Quote 6-161 September 2011

1 disease, no tobacco smoke exposure, and living in retirement communities in the 

2 Los Angeles air basin with hourly (up to 14-h/day) ambulatory BP monitoring for 5 days 

3 during a warm period (July-mid-October) and 5 days during a cool period (mid-October4 February). Investigators assessed lags of 1, 4, and 8 hours, 1 day, and up to 9 days before 

5 each BP measure; no evidence of association was observed for O3 exposures (change in 

6 BP associated with a 20 ppb change in 24-h O3 was 0.67 [95% CI: -1.16, 2.51 for systolic 

7 BP [SBP] and -0.25 [95% CI: -1.25, 0.75] for DBP) (Delfino et al., 2010b). Choi et al. 

8 (2007) conducted a cross-sectional study to investigate the relationship between air 

9 pollutants and BP among 10,459 participants of the Inha University Hospital health 

10 examination from 2001 to 2003. These individuals had no medical history of 

11 cardiovascular disease or hypertension. O3 exposure was associated with an increase in 

12 SBP for 1-day lag in the warm season and similar effect estimates were observed during 

13 the cold season but were not statistically significant (quantitative results not provided). 

14 Associations between O3 and DBP were present in the cold season but not the warm 

15 season (quantitative results not provided). The interaction term between O3 and season 

16 was statistically significant. Chuang et al. (2010) conducted a similar type of study 

17 among 7,578 participants of the Taiwanese Survey on Prevalence of Hyperglycemia, 

18 Hyperlipidemia, and Hypertension in 2001. Investigators examined 1-, 3-, and 5-day avg 

19 O3 concentrations. An increase in DBP was associated with the 3-day mean O3

20 concentration (change in BP for a 20 ppb increase in O3 was 0.61 [95% CI: 0.07, 1.14]) 

21 (Chuang et al., 2010). Associations were not observed for other days or with SBP.

6.3.2.7 Hospital Admissions and Emergency Department Visits

22 Upon evaluating the collective evidence for O3-related cardiovascular hospital admissions 

23 (HAs) and emergency department (ED) visits, the 2006 O3 AQCD concluded that “a few 

24 studies observed positive O3 associations, largely in the warm season. Overall, however, 

25 the currently available evidence is inconclusive regarding any association between 

26 ambient O3 exposure on cardiovascular hospitalizations” (U.S. EPA, 2006b). Table 6-33 

27 below provides information on the O3 concentrations reported in each of the recent HA 

28 and ED visit studies evaluated.

29 Multiple recent studies of O3 exposure and cardiovascular HAs and ED visits have been 

30 conducted in the U.S. and Canada. Peel et al. (2007) used a case-crossover framework 

31 (using a time-stratified approach matching on day of the week in the calendar month of 

32 the event) to assess the relationship between air pollutants and cardiovascular disease ED 

33 visits among those with and without secondary comorbid conditions (hypertension, 

34 diabetes, chronic obstructive pulmonary disease [COPD], congestive heart failure [CHF], 
Draft – Do Not Cite or Quote 6-162 September 2011

Table 6-33 Characterization of ozone concentrations (in ppb) from studies of 

HAs and ED visits

Study Location Averaging 

Time

Mean Concentration 

(Standard Deviation)

Upper Range of 

Concentration

Azevedo et al. (2011) Portugal 1-h NR

Ballester et al. (2006) Multicity, Spain 8-h

warm season

24.2 - 44.3

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

Cakmak et al. (2006a) Multicity, Canada 1-h max 17.4

Chan et al. (2006) Taipei, Taiwan 1-h max 50.9 (26.4) Max: 150.3

Halonen et al. (2009) Helsinki, Finland 8-h max

warm season

35.7* 75th: 42.1

Max: 79.6

Hosseinpoor et al. (2005) Tehran, Iran 8-h max 4.9 (4.8) 75th: 7.2

Max: 99.0

Lanki et al. (2006) Multicity, Europe 8-h max

warm season

31.7 - 57.2*

Larrieu et al. (2007) Multicity France 8-h max

warm season

34.2 - 53.1

Lee et al. (2003b) Seoul, Korea 1-h max 36.0 (18.6) 75th: 44.9

Lee et al. (2007) Kaohsiung, Taiwan 24-h 26.5 75th: 35.5

Max: 83.0

Middleton et al. (2008) Nicosia, Cyprus 8-h max 28.7 - 54.9

Peel et al. (2007) Atlanta, GA 8-h max

warm season

55.6 (23.8)

Rich et al. (2010) New Jersey 24-h NR

Stieb et al. (2009) Multicity, Canada 24-h 18.4

Symons et al. (2006) Baltimore, MD 8-h

warm season

31.0 (20.0) Max: 120.0

Tolbert et al. (2007) Atlanta, GA 8-h max

warm season

53.0 75th: 67.0

Max: 147.5

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

Von Klot et al. (2005) Multicity, Europe 8 h max

warm season

16.4 - 28.0

Wellenius et al. (2005) Allegheny County, PA 24-h 24.3 (12.2) 75th: 32.0

Yang (2008) Taipei, Taiwan 24-h 21.0 75th: 26.3

Max: 62.8

Zanobetti and Schwartz (2006) Boston, MA 24-h 22.4* 75th: 31.0

*Median presented (information on mean not given). NR: Not reported
Draft – Do Not Cite or Quote 6-163 September 2011

1 and dysrhythmia). Data on over 4 million ED visits from 31 hospitals were collected 

2 from January 1993 to August 2000. Ozone was monitored from March to October. This 

3 study was a re-analysis of a time series study conducted to assess the main effects of air 

4 pollutants on cardiovascular ED visits in Atlanta (Tolbert et al., 2007; Metzger et al., 

5 2004). In the initial study, no evidence of associations was observed between O3 and all 

6 CVD visits or visits for CVD subgroups, such as dysrhythmia, CHF, ischemic heart 

7 disease (IHD), and peripheral vascular and cerebrovascular disease. The relative risk for 

8 all CVD visits was 1.01 (95% CI: 0.99, 1.02) for a 20 ppb increase in the 3-day moving 

9 avg (lags 0-2 days) of 8-h O3 (Metzger et al., 2004). Similar to the initial investigation 

10 using a time-series analysis, no evidence of an association was observed for the O3 3-day 

11 moving average and CVD visits among the entire population using the case-crossover 

12 design (Peel et al., 2007). However, the relationship between O3 and peripheral and 

13 cerebrovascular disease visits was stronger among patients with comorbid COPD (OR: 

14 1.19 [95% CI: 1.03-1.36] per 20 ppb, lag 0-2 days) as compared to patients without 

15 COPD (OR: 1.01 [95% CI: 0.97-1.04] per 20 ppb, lag 0-2 days). The same research 

16 group expanded upon the number of Atlanta hospitals providing ED visit data (41 

17 hospitals) as well as the length of the study period (1993-2004) (Tolbert et al., 2007). 

18 Again, models assessing the health effects of O3 utilized data collected from March 

19 through October. Similar to the results presented by Metzger et al. (2004) and Peel et al. 

20 (2007) among the entire study population, no evidence of associations was observed for 

21 O3 and CVD visits (Tolbert et al., 2007). 

22 A study of HAs for MI was performed using a statewide registry from New Jersey 

23 between January 2004 and December 2006 (Rich et al., 2010). Using a case-crossover 

24 design, the association between the previous 24 hr O3 concentration and transmural 

25 infarction (n=1,003) was examined. No association was observed (OR: 0.94 [95% CI: 

0.79, 1.13] per 20 ppb) and this did not change with the inclusion of PM2.5 26 in the model. 

27 Cakmak et al, (2006b) investigated the relationship between gaseous air pollutants and 

28 cardiac hospitalizations in 10 large Canadian cities using a time-series approach. A total 

29 of 316,234 hospital discharge records for primary diagnosis of congestive heart failure, 

30 ischemic heart disease, or dysrhythmia were obtained from April 1993 through March 

31 2000. Correlations between pollutants varied substantially across cities, which could

32 partially explain discrepancies in effect estimates observed across the cities. In addition, 

33 pollutant lags differed across cities; the average lag for O3 was 2.9 days. The pooled 

34 effect estimate for a 20 ppb increase in the daily 1-h max O3 concentration and the 

35 percent change in hospitalizations among all 10 cities was 2.3 (95% CI: 0.11, 4.50) in an 

36 all-year analysis. The authors reported no evidence of effect modification by gender, 

37 neighborhood-level education, or neighborhood-level income. A similar multicity time38 series study was conducted using nearly 400,000 ED visits to 14 hospitals in seven 
Draft – Do Not Cite or Quote 6-164 September 2011

1 Canadian cities from 1992 to 2003 (Stieb et al., 2009). Primary analyses considered daily 

2 O3 single day lags of 0-2 days; in addition, sub-daily lags of 3-h avg concentrations up to 

3 12 hours before presentation to the ED were considered. Seasonal variation was assessed 

4 by stratifying analyses by warm and cold seasons. No evidence of effect of O3 on CVD 

5 ED visits was observed. One negative, statistically significant association was reported 

6 between a 1-day lag of O3 and visits for angina/myocardial infarction. Ozone was 

7 negatively correlated with many of the other pollutants, particularly during the cold 

8 season.

9 The effect of air pollution on daily ED visits for ischemic stroke (n=10,881 visits) in 

10 Edmonton, Canada was assessed from April 1992 through March 2002 (Szyszkowicz, 

11 2008). A 26.4% (95% CI: 3.16-54.5) increase in stroke ED visits was associated with a 

12 20 ppb increase in O3 at lag 1 among men aged 20-64 years in the warm season. No 

13 associations were present among women or among men age 65 and older. In addition, no 

14 associations were observed for the cold season or for other lags (lag 0 or lag 2). A similar 

15 investigation over the same time period in Edmonton, Canada, assessed the relationship 

16 between air pollutants and ED visits for stroke (ischemic stroke, hemorrhagic stroke, and

17 transient ischemic attack) among those 65 years of age and older using a case-crossover 

18 framework (Villeneuve et al., 2006a). Two-pollutant models were assessed. No evidence 

19 of association was reported for O3 and stroke hospitalization (Villeneuve et al., 2006a).

20 Additional studies reported no evidence of an association between O3 concentrations and 

21 ED visits, hospitalizations, or symptoms leading to hospitalization (Symons et al., 2006; 

22 Zanobetti and Schwartz, 2006; Wellenius et al., 2005). Symons et al. (2006) used a case23 crossover framework to assess the relationship between air pollutants and the onset of 

24 symptoms (dyspnea) severe enough to lead to hospitalization (through the ED) for 

25 congestive heart failure. The study was conducted from April to December of 2002 in 

26 Baltimore, Maryland. Exposures were assigned using 3 index times: 8-h and 24-h periods 

27 prior to symptom onset and date of hospital admission. No evidence of association was 

28 reported for O3 concentrations. Although seasonal variation was not assessed, the time 

29 frame for the study did not involve an entire year (April to December). Wellenius et al. 

30 (2005) investigated the association between air pollutants and congestive heart failure 

31 hospitalization among Medicare beneficiaries in Pittsburgh, Pennsylvania from 1987 to 

32 1999 utilizing a case-crossover framework. A total of 55,019 admissions from the 

33 emergency room with a primary discharge diagnosis of CHF were collected. No evidence 

34 of an association was reported for O3 and CHF hospitalization (Wellenius et al., 2005). 

35 Finally, Zanobetti and Schwartz (2006) assessed the relationship between air pollutants 

36 and hospital admissions through the ED for myocardial infarction and pneumonia among 

37 patients aged 65 and older residing in the greater Boston area (1995-1999) using a case38 crossover framework with control days in the same month matched on temperature. 
Draft – Do Not Cite or Quote 6-165 September 2011

1 Pollution exposures were assigned for the same day and for the mean of the exposure the 

2 day of and the day before the admission. Ozone was not associated with MI admissions in 

3 all-year and seasonal analyses. 

4 Several recent studies have examined the relationship between air pollution and CVD 

5 hospital admissions and/or emergency department visits in Asia. Of note, some areas of 

6 Asia have a more tropical climate than the U.S. and do not experience similar seasonal 

7 changes. In Taiwan, fairly consistent positive associations have been reported for O3 and 

8 congestive heart failure hospital admissions (for single- and copollutant models) in Taipei 

9 on warm days (Yang, 2008) and in Kaohsiung (Lee et al., 2007); cerebrovascular disease 

10 ED visits (for lag 0 single- and two-pollutant models but not other lags or 3-pollutant 

11 models) in Taipei (Chan et al., 2006); and arrhythmia ED visits in Taipei among those 

12 without comorbid conditions (Chiu et al., 2009; Lee et al., 2008a) and in Taipei on warm 

13 days among those with and without comorbid conditions (Lee et al., 2008a; Jansson et al., 

14 2001). However, one study in Taiwan did not shown an association. Bell et al. (2008)

15 reported no evidence of an O3 association with hospital admissions for ischemic heart 

16 disease or cerebrovascular disease. Three studies based in Asia but outside Taiwan were 

17 performed. First, a Hong Kong-based investigation (Wong et al., 2009) reported no 

18 consistent evidence of a modifying effect of influenza on the relationship between O3 and 

19 CVD admissions. Second, among elderly populations in Thailand, O3 was associated with 

20 CVD visits, but this association was not detected among younger age groups (15-64) 

21 (Buadong et al., 2009). Third, a study performed in Seoul, Korea reported a positive 

22 association between O3 levels and HAs for ischemic heart disease; the association was 

23 slightly greater among those over 64 years of age (Lee et al., 2003b). 

24 Positive effects of O3 on CVD hospital admissions and/or ED visits have been reported in 

25 other areas of the world as well (Azevedo et al., 2011; Linares and Diaz, 2010; Middleton 

26 et al., 2008; Turner et al., 2007; Yallop et al., 2007; Ballester et al., 2006; De Pablo et al., 

27 2006; Von Klot et al., 2005), although not consistently as some studies reported no 

28 association (Oudin et al., 2010; Halonen et al., 2009; Larrieu et al., 2007; Barnett et al., 

29 2006; Hinwood et al., 2006; Lanki et al., 2006; Hosseinpoor et al., 2005; Simpson et al., 

30 2005). 

31 A couple of studies (U.S. and Australia) have examined cardiac arrests where emergency 

32 services attempted treatment/resuscitation. No evidence of an association between O3 and 

33 out-of-hospital cardiac arrest was observed (Dennekamp et al., 2010; Silverman et al., 

34 2010).

35 An increasing number of air pollution studies have investigated the relationship between 

36 O3 concentrations and CVD hospital admissions and/or ED visits. As summarized in the 

37 2006 O3 AQCD, some, especially those reporting results stratified by season (or 
Draft – Do Not Cite or Quote 6-166 September 2011

1 temperature) or comorbid conditions have reported positive associations. However, even 

2 studies performing these stratified analyses are not consistent and the overall evidence 

3 remains inconclusive regarding the effects of O3 on CVD HAs and ED visits. These HA 

4 and ED visit studies are summarized in Figures 6-22 through 6-26, which depict the 

5 associations for studies in which numerical associations were presented for an overall 

6 study population. Tables 6-34 through 6-38 provide the numerical results displayed in the 

7 figures. 

Note: Increase 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. 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 Fung et al. (2005), Wong et al. (1999b), and Prescott et al. 

(1998), which included only individuals aged 65+.

Figure 6-22 Odds ratio (95% CI) per increment ppb increase in ozone for over 

all cardiovascular ED visits or HAs.

Reference

Buadong 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)

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

Nicosia, Cyprus

Windsor, Canada

Valencia, Spain

Brisbane, Australia

Los Angeles, CA

London, England

Hong Kong

Hong Kong

Edinburgh, Scotland

London, England

Helsinki, Finland

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

0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5
Draft – Do Not Cite or Quote 6-167 September 2011

Table 6-34 Odds ratio (95% CI) per increment ppb increase in ozone for overall 

cardiovascular ED visits or HAs in studies presented in Figure 6-22

Study Location Outcome Averaging Time Standardized Estimate (95% CI)

Atkinson et al. (2006a) London, England Cardiovascular disease 8-h 1.03 (1.00, 1.05)

Ballester et al. (2006) Multicity, Spain 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) Multicity, Canada 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. (2006a) 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)

Larrieu et al. (2007) Multicity France Cardiac disease 8-h max warm season 1.01 (0.98, 1.04)

Linn et al. (2006a) 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)

Morgan et al. (2008) 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 1.02 (0.98, 1.05)

Petroeschevsky et al. (2001) Brisbane, Australia Cardiovascular disease 8-h 0.96 (0.92, 1.01)

Poloniecki et al. (2006a) 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)

Von Klot et al. (2005) Multicity, Europe 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. (2005) Kaohsiung, Taiwan Cardiovascular disease 24-h warm season 1.33 (1.26 , 1.40)

24-h cold season 1.05 (0.96, 1.15)

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h averaging period. 

Ozone concentrations in ppb. Age groups of study populations were not specified or were adults with the exception of Fung et al. (2006a), Wong et 

al. (1999a), and Prescott et al. (1998), which included only individuals aged 65+.

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; Von Klot et al., 2005), ≥ 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 6-168 September 2011

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h 

averaging period. 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+. 

Figure 6-23 Odds Ratio (95% CI) per increment ppb increase in ozone for 

congestive heart failure ED visits or HAs.

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

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Draft – Do Not Cite or Quote 6-169 September 2011

Table 6-35 Odds Ratio (95% CI) per increment ppb increase in ozone for 

congestive heart failure ED visits or HAs for studies in Figure 6-23

Study Location Outcome Averaging Time Standardized 

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 0.96 (0.93, 1.00)

Poloniecki 

et al. (1997)

London, England congestive heart failure 8-h 0.99 (0.95, 1.03)

Stieb et al. (2009) Multicity, Canada 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)

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h averaging 

period. 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+.

Warm season defined as: March-October (Peel et al., 2007), April-November (Symons et al., 2006), May-October (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 6-170 September 2011

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h 

averaging period. 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. (2006a), which included only individuals aged 65+.

Figure 6-24 Odds Ratio (95% confidence interval) per increment ppb increase in 

ozone for ischemic heart disease, coronary heart disease, 

myocardial infarction, and angina pectoris ED visits or HAs.

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
Draft – Do Not Cite or Quote 6-171 September 2011

Table 6-36 Odds Ratio (95% CI) per increment ppb increase in ozone for 

ischemic heart disease, coronary heart disease, myocardial 

infarction, and angina pectoris ED visits or HAs for studies 

presented in Figure 6-24

Study Location Outcome Averaging Time Standardized 

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) Multicity, Europe Myocardial infarction 8-h max warm season 0.96 (0.92, 1.01)

Larrieu et al. (2007) Multicity France 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 (0.97, 1.03)

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. (Rich et al., 2010) New Jersey Myocardial infarction 24-h 0.94 (0.79, 1.13)

Stieb et al. (2009) Multicity, Canada Myocardial infarction 2-h 1.00 (0.96, 1.04)

Von Klot et al. (2005) Multicity, Europe 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. (2009) 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. (2008) 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)

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h averaging period. 

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. (2006a), which included only individuals aged 65+.

Warm season defined as: March-October (Peel et al., 2007), June-August (Lee et al., 2003b), May-September (Halonen et al., 2009), MayOctober (Buadong et al., 2009), and April-September (Larrieu et al., 2007; Lanki et al., 2006; Von Klot et al., 2005). Cold season defined as: 

November-April (Buadong et al., 2009)
Draft – Do Not Cite or Quote 6-172 September 2011

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h 

averaging period. 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+.

Figure 6-25 Odds Ratio (95% confidence interval) per increment ppb increase in 

ozone for stroke ED visits or HAs.

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
Draft – Do Not Cite or Quote 6-173 September 2011

Table 6-37 Odds Ratio (95% CI) per increment ppb increase in ozone for stroke 

ED visits or HAs for studies presented in Figure 6-25

Study Location Outcome Averaging Time Standardized 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) Multicity, France 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)

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h averaging period. 

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+.

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).

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h 

averaging period. 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+.

Figure 6-26 Odds Ratio (95% confidence interval) per increment ppb* increase 

in ozone for arrhythmia and dysrhythmia ED visits or HAs.

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

0.7 0.8 0.9 1 1.1 1.2 1.3 1.4
Draft – Do Not Cite or Quote 6-174 September 2011

Table 6-38 Odds Ratio (95% CI) per increment ppb* increase in ozone for 

arrhythmia and dysrhythmia ED visits or HAs for studies presented 

in Figure 6-26

Study Location Outcome Averaging Time Standardized

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 (0.98, 1.04)

Poloniecki et al. (2009) London, England Arrhythmia 8-h 1.02 (0.96, 1.07)

Stieb et al. (2009) Multicity, Canada Dysrhythmia 24-h 1.02 (0.95, 1.09)

Wong et al. (2009) 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)

Note: Increase in O3 standardized to 20 ppb for 24-h averaging period, 30 ppb for 8-h averaging period, and 40 ppb for 1-h averaging period. 

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+. Warm season defined as: March-October (Peel et al., 2007), May-October (Wong et al., 1999a) and MaySeptember (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 

6 provided evidence, primarily from single-city studies, of consistent positive associations 

7 between short-term O3 exposure and cardiovascular mortality. Recent multicity studies 

8 conducted in the U.S., Canada, and Europe further confirm the association between short9 term O3 exposure and cardiovascular mortality. 

10 As discussed in Section 6.2.7.2, the APHENA study (Katsouyanni et al., 2009) also 

11 examined associations between short-term O3 exposure and mortality and found 

12 consistent positive associations for cardiovascular mortality in all-year analyses with 

13 associations persisting in analyses restricted to the summer season. Additional multicity 

14 studies from the U.S. (Zanobetti and Schwartz, 2008b), Europe (Samoli et al., 2009), 

15 Italy (Stafoggia et al., 2010), and Asia (Wong et al., 2010) that conducted summer season 

16 and/or all-year analyses provide additional support for an association between short-term 

17 O3 exposure and cardiovascular mortality (Figure 6-37). 

18 Of the studies evaluated, only the APHENA study (Katsouyanni et al., 2009) and the 

19 Italian multicity study (Stafoggia et al., 2010) conducted an analysis of the potential for 

20 copollutant confounding of the O3-cardiovascular mortality relationship. In the European 
Draft – Do Not Cite or Quote 6-175 September 2011

1 dataset, when focusing on the natural spline model with 8 df/year (Section 6.2.7.2) and 

2 lag 1 results in order to compare results across study locations (Section 6.6.2.1), 

3 cardiovascular mortality risk estimates were robust to the inclusion of PM10 in 

4 copollutant models in all-year analyses with more variability in the Canadian and U.S. 

5 datasets (i.e., cardiovascular O3 mortality risk estimates were reduced or increased in 

6 copollutant models). In summer season analyses, cardiovascular O3 mortality risk 

7 estimates were robust in the European dataset and attenuated but remained positive in the 

8 U.S. dataset. Similarly, in the Italian multicity study (Stafoggia et al., 2010), which was 

9 limited to the summer season, cardiovascular mortality risk estimates were robust to the 

10 inclusion of PM10 in copollutant models. Based on the APHENA and Italian multicity 

11 results, O3 cardiovascular mortality risk estimates appear to be robust to inclusion of 

12 PM10 in copollutant models. However, in the U.S. and Canadian datasets there was 

13 evidence that O3 cardiovascular mortality risk estimates are moderately to substantially 

14 sensitive (e.g., increased or attenuated) to PM10. The mostly every-6th-day sampling 

15 schedule for PM10 in the Canadian and U.S. datasets greatly reduced their sample size 

16 and limits the interpretation of these results. 

6.3.2.9 Summary of Epidemiologic Studies

17 Overall, the available body of evidence examining the relationship between short-term 

18 exposures to O3 and cardiovascular morbidity is inconsistent. Differences in exposure 

19 metrics and windows of exposure, a wide variety of biomarkers considered, and a lack of 

20 consistency among definitions used for specific cardiovascular disease endpoints (e.g. 

21 arrhythmias, HRV) make comparisons across studies difficult. In addition, several 

22 investigators reporting associations between O3 and cardiovascular morbidity postulate 

23 that O3 may be acting as a proxy for sulfate; differences reported across multicity studies 

24 and across studies conducted in specific cities/regions point to the importance of 

25 considering multipollutant relationships that vary across geographic regions. Additionally 

26 mortality studies indicate a consistent positive association between O3 and cardiovascular 

27 mortality. 

6.3.3 Toxicology

6.3.3.1 Summary of Findings from Previous Ozone AQCDs

28 In the previous O3 AQCDs (U.S. EPA, 2006b, 1996a) experimental animal studies have 

29 reported relatively few cardiovascular system alterations after exposure to O3 and other 
Draft – Do Not Cite or Quote 6-176 September 2011

1 photochemical oxidants. The limited amount of research directed at examining O3-

2 induced cardiovascular effects has primarily found alterations in heart rate (HR) and BP 

3 after O3 exposure. A group of studies (Arito et al., 1992; Arito et al., 1990; Uchiyama and 

4 Yokoyama, 1989; Yokoyama et al., 1989; Uchiyama et al., 1986) report O3 (0.1-1.0 ppm) 

5 exposure in rats decreased core temperature (TCO), HR, and mean arterial pressure 

6 (MAP). However, these cardiovascular responses to O3 could be attenuated by increased 

7 ambient temperatures, exhibited adaptation, and were the result of the rodent 

8 hypothermic response (Watkinson et al., 2003; Watkinson et al., 1993). This hypothermic 

9 response could be an attempt to minimize the irritant effects of O3 inhalation, serving as a 

10 physiological and behavioral defense mechanism (Iwasaki et al., 1998; Arito et al., 1997). 

11 As humans do not appear to exhibit decreased HR, MAP, and TCO with routine 

12 environmental exposures to O3, caution must be used in extrapolating the results of these 

13 animal studies to humans (Section 6.3.1). 

14 Other studies have shown that O3 can increase BP in animal models. Rats exposed to 

15 0.6 ppm O3 for 33 days had increased systolic pressure and HR (Revis et al., 1981). 

16 Increased BP triggers the release of atrial natriuretic factor (ANF), which has been found 

17 in increased levels in the heart, lungs, and circulation of O3 exposed (0.5 ppm) rats 

18 (Vesely et al., 1994a, b, c). High concentration O3 exposure (1.0 ppm) has also been 

19 found to lead to heart and lung edema (Friedman et al., 1983), which could be the result 

20 of increased ANF levels. Thus, O3 may increase blood pressure and HR, leading to 

21 increased ANF and tissue edema. 

22 The toxicological studies that have examined the effect of O3 on the cardiovascular 

23 system demonstrate O3-induced responses, but it remains unclear if the mechanism is 

24 through a reflex response or due to O3 reaction products, which have been sparsely 

25 studied. Oxysterols derived from cholesterol ozonation, such as β-epoxide and 5β,6β26 epoxycholesterol (and its metabolite cholestan-6-oxo-3,5-diol), have been implicated in 

27 inflammation associated with cardiovascular disease (Pulfer et al., 2005; Pulfer and 

28 Murphy, 2004). Two other cholesterol ozonolysis products, atheronal-A and -B (e.g. 

29 cholesterol secoaldehyde), have been found in human atherosclerotic plaques and shown 

30 in vitro to induce foam cell formation and induce cardiomyocyte apoptosis and necrosis 

31 (Sathishkumar et al., 2005; Wentworth et al., 2003); however, these products have not 

32 been found in the lung compartment or systemically after O3 exposure. The ability to 

33 form these cholesterol ozonation products in the circulation in the absence of O3 exposure 

34 complicates their implication in O3 induced cardiovascular disease. 

35 Although it has been proposed that O3 reaction products released after the interaction of 

36 O3 with ELF constituents (See Section 5.1.2 on O3 interaction with ELF) are responsible 

37 for systemic effects, it is not known whether they gain access to the vascular space. 
Draft – Do Not Cite or Quote 6-177 September 2011

1 Alternatively, extrapulmonary release of diffusible mediators, such as cytokines or 

2 endothelins, may initiate or propagate inflammatory responses in the vascular or systemic 

3 compartments (Cole and Freeman, 2009) (Section 5.1.9.1). Ozone reacts within the lung 

4 to amplify ROS production, induce pulmonary inflammation, and activate inflammatory 

5 cells, resulting in a cascading proinflammatory state and extrapulmonary release of 

6 diffusible mediators that could lead to cardiovascular injury. 

6.3.3.2 Recent Cardiovascular Toxicology Studies

7 According to recent short-term O3 exposure animal toxicology studies, O3 plays a role in 

8 inducing vascular oxidative stress and proinflammatory mediators, altering HR and HRV, 

9 and regulating the pulmonary endothelin system (study details are provided in Table 6-

10 39). A number of these effects were variable between strains examined, suggesting a 

11 genetic component to development of O3 induced cardiovascular effects. Further, new 

12 studies provide evidence that extended O3 exposure enhances susceptibility to ischemia13 reperfusion (I/R) injury and atherosclerotic lesion development. Still, few studies have 

14 investigated the role of O3 reaction products in these processes, but more evidence is 

15 provided for elevated inflammatory and reduction-oxidation (redox) cascades known to 

16 initiate these cardiovascular pathologies. 

17 A recent study in young mice and rhesus monkeys examined the effects of short-term O3

18 exposure on a number of cardiovascular endpoints (Chuang et al., 2009). Mice exposed to 

19 O3 for 5 days had increased HR as well as mean and diastolic blood pressure. Increased 

20 blood pressure could be explained by the inhibition in endothelial-dependent 

21 (acetylcholine) vasorelaxation from decreased bioavailability of aortic nitric oxide (·NO). 

22 Ozone caused a decrease in aortic NOX (nitrite and nitrate levels) and a decrease in total, 

23 but not phosphorylated, endothelial nitric oxide synthase (eNOS). Ozone also increased 

24 vascular oxidative stress in the form of increased aortic and lung lipid peroxidation (F2-

25 isoprostane), increased aortic protein nitration (3-nitrotyrosine), decreased aortic 

26 superoxide dismutase (SOD2) protein and activity, and decreased aortic aconitase 

activity, indicating specific inactivation by O2

- and ONOO- 27 . Mitochondrial DNA 

28 (mtDNA) damage was also used as a measure of oxidative and nitrative stress in mice 

29 and infant rhesus monkeys exposed to O3. Chuang et al. (2009) observed that MtDNA 

30 damage accumulated in the lung and aorta of mice after 1 and 5 days of O3 exposure and 

31 in the proximal and distal aorta of O3 treated nonhuman primates. Additionally, 

32 genetically hyperlipidemic mice exposed to O3 for 8 weeks had increased aortic 

33 atherosclerotic lesion area (Section 7.3.1), which may be associated with the short-term 

34 exposure changes discussed. Overall, this study suggests that O3 initiates an oxidative 

environment by increasing O2

- 35 production, which leads to mtDNA damage and ·NO 
Draft – Do Not Cite or Quote 6-178 September 2011

1 consumption, known to perturb endothelial function (Chuang et al., 2009). Endothelial 

2 dysfunction is characteristic of early and advanced atherosclerosis and coincides with 

3 impaired vasodilation and blood pressure regulation.

4 Vascular occlusion resulting from atherosclerosis can block blood flow causing ischemia. 

5 The restoration of blood flow in the vessel or reperfusion can cause injury to the tissue 

6 from subsequent inflammation and oxidative damage. Perepu et al. (2010) observed that 

7 O3 exposure enhanced the sensitivity to myocardial I/R injury in rats while increasing 

8 oxidative stress levels and pro-inflammatory mediators and decreasing production of anti9 inflammatory proteins. Ozone was also found to decrease the left ventricular developed 

10 pressure, rate of change of pressure development, and rate of change of pressure decay 

11 while increasing left ventricular end diastolic pressure in isolated perfused hearts. In this 

12 ex vivo heart model, O3 induced oxidative stress by decreasing SOD enzyme activity and 

13 increasing malondialdehyde levels. Ozone also elicited a proinflammatory state which 

14 was evident by an increase in TNF-α and a decrease in the anti-inflammatory cytokine 

15 IL-10. Perepu et al. (2010) concluded that O3 exposure may result in a greater I/R injury.

Heart Rate and Heart Rate Variability

16 Strain differences in HR and HRV have been observed in response to a 2-h O3

17 pretreatment followed by exposure to carbon black (CB) in mice (C3H/HeJ [HeJ], 

18 C57BL/6J [B6], and C3H/HeOuJ [OuJ]) (Hamade and Tankersley, 2009; Hamade et al., 

19 2008). These mice strains were chosen from prior studies on lung inflammatory and 

20 hyperpermeability responses to be susceptible (B6 and OuJ) and resistant (HeJ) to O3-

21 induced health effects (Kleeberger et al., 2000). HR decreased during O3 pre-exposure for 

22 all strains, but recovered during the CB exposure (Hamade et al., 2008). This is contrary 

23 to the tachycardia that was reported in 6-week-old B6 mice treated on 1 or 5 days with 

24 O3, as described above (Chuang et al., 2009). Percent change in HRV parameters, SDNN 

25 (indicating total HRV) and rMSSD (indicating beat-to-beat HRV), were increased in both 

26 C3H mice strains, but not B6 mice, during O3 pre-exposure and recovered during CB 

27 exposure when compared to the filtered air group. The two C3H strains differ by a 

28 mutation in the Toll-like receptor 4 (TLR4) gene, but these effects did not seem to be 

29 related to this mutation since similar responses were observed. Hamade et al. (2008)

30 speculate that the B6 and C3H strains differ in mechanisms of HR response after O3

31 exposure between withdrawal of sympathetic tone and increase of parasympathetic tone; 

32 however, no direct evidence for this conclusion was reported. The strain differences 

33 observed in HR and HRV suggest that genetic variability affects cardiac responses after 

34 acute air pollutant exposures. 
Draft – Do Not Cite or Quote 6-179 September 2011

1 Hamade and Tankersley (2009) continued this investigation of gene-environment 

2 interactions on cardiopulmonary adaptation of O3 and CB induced changes in HR and 

3 HRV using the previously described (Hamade et al., 2008) daily exposure scheme for 3 

4 consecutive days. By comparing day-1 interim values it is possible to observe that O3

5 exposure increased SDNN and rMSSD, but decreased HR in all strains. Measures of HR 

6 and HRV in B6 and HeJ mice recovered to levels consistent with filtered air treated mice 

7 by day 3; however, these responses in OuJ mice remained suppressed. B6 mice had no 

8 change in respiratory rate (RR) after O3 treatment, whereas HeJ mice on days 1 and 2 had 

9 increased RR and OuJ mice on days 2 and 3 exhibited increased RR. VT did not change 

10 with treatment among the strains. Overall, B6 mice were mildly responsive with rapid 

11 adaptation, whereas C3 mice were highly responsive with adaptation only in HeJ mice 

12 with regards to changes in cardiac and respiratory responses. HR and HRV parameters 

13 were not equally correlated with VT and RR between the three mice strains, which 

14 suggest that strains vary in the integration of the cardiac and respiratory systems. These 

15 complex interactions could help explain variability in interindividual susceptibility to 

16 adverse health effects of air pollution.

17 Hamade et al. (2010) expanded their investigation to explore the variation of these strain 

18 dependent cardiopulmonary responses with age. As was observed previously, all 

19 experimental mouse strains (B6, HeJ, and OuJ) exhibited decreased HR and increased 

20 HRV after O3 exposure. Younger O3-exposed mice had a significantly lower HR 

21 compared to older exposed mice, indicating an attenuation of the bradycardic effect of O3

22 with age. Younger mice also had a greater increase in rMSSD in HeJ and OuJ strains and 

23 SDNN in HeJ mice. Conversely, B6 mice had a slightly greater increase in SDNN in 

24 aged mice compared to the young mice. No change was observed in the magnitude of the 

25 O3 induced increase of SDNN in OuJ mice or rMSSD in B6 mice. The B6 and HeJ mice 

26 genetically vary in respect to the nuclear factor erythroid 2-related factor 2 (Nrf-2). The 

27 authors propose that the genetic differences between the mice strains could be altering the 

28 formation of ROS, which tends to increase with age, thus modulating the changes in 

29 cardiopulmonary physiology after O3 exposure. 

30 Strain and age differences in HR and heart function were further investigated in B6 and 

31 129S1/SvlmJ (129) mice in response to a sequential O3 and filtered air or CB exposure 

32 (Tankersley et al., 2010). Young 129 mice showed a decrease in HR after O3 or O3 and 

33 CB exposure. This bradycardia was not observed in B6 or older animals in this study, 

34 suggesting a possible alteration or adaptation of the autonomic nervous system activity 

35 with age. However, these authors did previously report bradycardia in similarly aged 

36 young B6 mice (Hamade et al., 2010; Hamade and Tankersley, 2009; Hamade et al., 

37 2008). Ozone exposure in 129 mice also resulted in an increase in left ventricular 

38 chamber dimensions at end diastole (LVEDD) in young and old mice and a decrease in 
Draft – Do Not Cite or Quote 6-180 September 2011

1 left ventricular posterior wall thickness at end systole (PWTES) in older mice. The 

2 increase in LVEDD caused a decrease in fractional shortening, which can be used as a 

3 rough indicator of left ventricular function. Regression analysis revealed a significant 

4 interaction between age and strain on HR and PWTES, which implies that aging affects 

5 the HR and function in response to O3 differently between mouse strains.

Effects on Cardiovascular-Related Proteins

6 Increased BP, changes in HRV, and increased atherosclerosis may be related to increases 

7 in the vasoconstrictor peptide, endothelin-1 (amino acids 1-21, ET-1[1-21]). Regulation of 

8 the pulmonary endothelin system can be affected in rats by inhalation of PM (0, 5, 

50 mg/m3 9 , 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] 10 , and the ET-1 precursor 

11 peptide, bigET-1. Increases in circulating ET-1[1-21] could be a result of a transient 

12 increase in the gene expression of lung preproET-1 and endothelin converting enzyme-1 

13 (ECE-1) immediately following inhalation of O3 or PM. These latter gene expression 

14 changes (e.g. preproET-1 and ECE-1) were additive with co-exposure to O3 and PM. 

15 Conversely, preproET-3 decreased immediately after O3 exposure, suggesting the 

16 increase in ET-3[1-21] was not through de novo production. A recent study also found 

17 increased ET-1 gene expression in the aorta of O3 exposed rats (Kodavanti et al., 2011). 

18 These rats also exhibited an increase in ETBR after O3 exposure; however, they did not 

19 demonstrate increased biomarkers for vascular inflammation, thrombosis, or oxidation.

20 O3 can oxidize protein functional groups and disturb the affected protein. For example, 

21 the soluble plasma protein fibrinogen is oxidized by O3 (0.01-0.03 ppm) in vitro, creating 

22 fibrinogen and fibrin aggregates, characteristically similar to defective fibrinogen 

23 (Rosenfeld et al., 2009; Rozenfeld et al., 2008). In these studies, oxidized fibrinogen 

24 retained the ability to form fibrin gels that are involved in coagulation, however the 

25 aggregation time increased and the gels were rougher than normal with thicker fibers. 

26 Oxidized fibrinogen also developed the ability to self assemble creating fibrinogen 

27 aggregates that may play a role in thrombosis. Since O3 does not readily translocate past 

28 the ELF and pulmonary epithelium and fibrinogen is primarily a plasma protein, it is 

29 uncertain if O3 would have the opportunity to react with plasma fibrinogen. However, 

30 fibrinogen can be released from the basolateral face of pulmonary epithelial cells during 

31 inflammation, where the deposition of fibrinogen could lead to lung injury (Lawrence 

32 and Simpson-Haidaris, 2004).
Draft – Do Not Cite or Quote 6-181 September 2011

Studies on Ozone Reaction Products

1 Although recent toxicological studies have demonstrated O3-induced effects on the 

2 cardiovascular system, as concluded in previous O3 AQCDs, it remains unclear if the 

3 mechanism is through a reflex response or the result of effects from O3 reaction products 

4 (U.S. EPA, 2006b, 1996a). A new study that examined O3 reaction byproducts has shown 

5 that cholesterol secoaldehyde (e.g., atheronal A) induces apoptosis in vitro in mouse 

6 macrophages (Gao et al., 2009b) and cardiomyocytes (Sathishkumar et al., 2009). 

7 Additionally, atheronal-A and -B has been found to induce in vitro macrophage and 

8 endothelial cell proinflammatory events involved in the initiation of atherosclerosis 

9 (Takeuchi et al., 2006). These O3 reaction products when complexed with low density 

10 lipoprotein upregulate scavenger receptor class A and induce dose-dependent 

11 macrophage chemotaxis. Atheronal-A increases expression of the adhesion molecule, E12 selectin, in endothelial cells, while atheronal-B induces monocyte differentiation. These 

13 events contribute to both monocyte recruitment and foam cell formation in 

14 atherosclerotic vessels. It is unknown whether these O3 reaction products gain access to 

15 the vascular space from the lungs. Alternative explanations include the extrapulmonary 

16 release of diffusible mediators that may initiate or propagate inflammatory responses in 

17 the vascular or systemic compartments.
Draft – Do Not Cite or Quote 6-182 September 2011

Table 6-39 Characterization of study details for Section 6.3.3.2a

Study 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 

Monkey; rhesus Macaca endothelial function.

mulatta; M; Infant (180 

days old)

0.5 5 days, 8-h/day

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 g0.4 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 g0.8 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.

Summary of Toxicological Studies

1 Overall, animal studies suggest that O3 exposure may disrupt both the ·NO and 

2 endothelin systems, which can result in an increase in HR, HRV, and ANF, as is 

3 observed after O3 exposure. Conversely, studies in rodents also exhibit O3 induced 

4 bradycardia, but it is uncertain if this decrease in HR is also observed in humans. 

5 Additionally, O3 may increase oxidative stress and vascular inflammation promoting the 

6 progression of atherosclerosis and leading to increased susceptibility to I/R injury. As O3

7 reacts quickly with the ELF and does not translocate to the heart and large vessels, 

8 studies suggest that the cardiovascular effects exhibited could be caused by reaction 
Draft – Do Not Cite or Quote 6-183 September 2011

1 byproducts of O3 exposure. However, direct evidence of translocation of O3 reaction 

2 products to the cardiovascular system has not been demonstrated in vivo. Alternatively, 

3 extrapulmonary release of diffusible mediators, such as cytokines or endothelins, may 

4 initiate or propagate inflammatory responses in the vascular or systemic compartments 

5 leading to the reported cardiovascular pathologies. Further discussion of the modes of 

6 action that may lead to cardiovascular effects can be found in Section 5.3.8.

6.3.4 Summary and Causal Determination

7 In past O3 AQCDs the effects of O3 to the cardiovascular system did not receive much 

8 attention due to the paucity of information available. However, in recent years, 

9 investigation of O3-induced cardiovascular events has advanced. In general, compared 

10 with the epidemiologic evidence, the toxicological evidence is more supportive of O3-

11 induced cardiovascular effects. Epidemiologic evidence does not consistently 

12 demonstrate a positive relationship between short-term O3 exposure and cardiovascular13 related morbidity. However, most epidemiologic studies have not extensively 

14 investigated the cardiovascular effects of O3 exposure in susceptible populations, which 

15 may further support the toxicological findings. Although the epidemiologic evidence of 

16 cardiovascular morbidity is limited, single-city studies reviewed in the 2006 O3 AQCD, 

17 recent multicity studies, and the multicontinent APHENA study provide evidence of 

18 consistently positive associations between short-term O3 exposure and cardiovascular 

19 mortality. However, in contrast with respiratory effects, there is weak coherence between 

20 associations for cardiovascular morbidity and mortality. Further, there is no apparent 

21 biological mechanism to explain the association observed for short-term O3 exposure 

22 with cardiovascular mortality.

23 Animal toxicological studies provide evidence for O3-induced cardiovascular effects, 

24 specifically enhanced I/R injury, disrupted NO-induced vascular reactivity, decreased 

25 cardiac function, and increased HRV. The observed increase in HRV is supported by a 

26 recent controlled human exposure study that also finds increased high frequency HRV, 

27 but not altered blood pressure, following O3 exposure. Toxicological studies investigating 

28 the role of O3 in heart rate regulation are mixed with both bradycardic and tachycardic 

29 responses observed. These changes in cardiac function provide evidence for O3-induced 

30 alterations in the autonomic nervous system leading to cardiovascular complications. 

31 Epidemiologic studies showing positive association between O3 and arrhythmias confirm 

32 the development of autonomic dysfunction following O3 exposure. It is still uncertain 

33 how O3 inhalation may cause systemic toxicity; however the cardiovascular effects of O3

34 found in animals correspond to the development and maintenance of an extrapulmonary 

35 oxidative, proinflammatory environment. 
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1 In conclusion, animal toxicological studies provide stronger evidence for O3 exposure 

2 leading to cardiovascular morbidity than do epidemiologic studies, among which there is 

3 a lack of coherence among endpoints. Based on the relatively strong body of 

4 toxicological evidence, and the consistent evidence of an association between O3 and 

5 cardiovascular mortality, but weak coherence and biological plausibility for O3-induced 

6 cardiovascular morbidity, the generally limited body of evidence is suggestive of a 

7 causal relationship between relevant short-term exposures to O3 and 

8 cardiovascular effects.

6.4 Central Nervous System Effects 

9 The 2006 O3 AQCD included toxicological evidence that acute exposures to O3 are 

10 associated with alterations in neurotransmitters, motor activity, short and long term 

11 memory, and sleep patterns. Additionally, histological signs of neurodegeneration have 

12 been observed. Reports of headache, dizziness, and irritation of the nose with O3

13 exposure are common complaints in humans, and some behavioral changes in animals 

14 may be related to these symptoms rather than indicative of neurotoxicity. Peterson and 

15 Andrews (1963) and Tepper et al. (1983) showed that mice would alter their behavior to 

16 avoid O3 exposure. Murphy et al. (1964) and Tepper et al. (1982) showed that running17 wheel behavior was suppressed, and Tepper et al. (1985) subsequently demonstrated the 

18 effects of a 6-h exposure to O3 on the suppression of running-wheel behavior in rats and 

19 mice, with the lowest effective concentration being about 0.12 ppm O3 in the rat and 

20 about 0.2 ppm in the mouse. The suppression of active behavior by 6 h of exposure to 

21 0.12 ppm O3 has recently been confirmed by Martrette et al. (2011) in juvenile female 

22 rats, and the suppression of three different active behavior parameters was found to 

23 become more pronounced after 15 days of exposure. A table of studies examining the 

24 effects of O3 on behavior can be found on p 6-128 of the 1996 O3 AQCD. Generally 

25 speaking, transient changes in behavior in rodent models appear to be dependent on a 

26 complex interaction of factors such as (1) the type of behavior being measured, with 

27 some behaviors increased and others suppressed; (2) the factors motivating that behavior 

28 (differences in reinforcement); and (3) the sensitivity of the particular behavior (e.g., 

29 active behaviors are more affected than more sedentary behaviors). Many behavioral 

30 changes are likely to result from avoidance of irritation, but more recent studies indicate 

31 that O3 also directly affects the CNS.

32 Research in the area of O3-induced neurotoxicity has notably increased over the past few 

33 years, with the majority of the evidence coming from toxicological studies that examined 

34 the association between O3 exposure, neuropathology, and neurobehavioral effects, and 

35 more limited evidence from epidemiologic studies. In an epidemiologic study conducted 
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1 by Chen and Schwartz (2009), data from the NHANES III cohort was utilized to study 

2 the relationship between long-term O3 exposure (mean annual O3 concentration of 

3 26.5 ppb) and neurobehavioral effects among adults aged 20-59 years. The authors 

4 observed an association between annual exposure to O3 and tests measuring coding 

5 ability and attention/short-term memory. Each 10-ppb increase in annual O3 levels 

6 corresponded to an aging-related cognitive performance decline of 3.5 years for coding 

7 ability and 5.3 years for attention/short-term memory. These associations persisted in 

8 both crude and adjusted models. There was no association between annual O3

9 concentrations and reaction time tests. The authors conclude that overall there is a 

10 positive association between O3 exposure and reduced performance on neurobehavioral 

11 tests. Although Chen and Schwartz (2009) is a long-term exposure study, it is included in 

12 this section because it is the first epidemiologic study to demonstrate that exposure to 

13 ambient O3 is associated with decrements in neurocognitive tests related to memory and 

14 attention in humans. This epidemiologic evidence of an effect on the CNS due to 

15 exposure to ambient concentrations of O3 is coherent with animal studies demonstrating 

16 that exposure to O3 can produce a variety of CNS effects including behavioral deficits, 

17 morphological changes, and oxidative stress in the brains of rodents. In these rodent 

18 studies, interestingly, CNS effects were reported at O3 concentrations that were generally 

19 lower than those concentrations commonly observed to produce pulmonary or cardiac 

20 effects in rats. 

21 A number of new studies demonstrate various perturbations in neurologic function or 

22 histology, including changes similar to those observed with Parkinson’s and Alzheimer’s 

23 disease pathologies occurring in similar regions of the brain (Table 6-40). Many of these 

24 include exposure durations ranging from short-term to long-term, and as such are 

25 discussed here and in Chapter 7 with emphasis on the effects resulting from exposure 

26 durations relevant to the respective chapter. Several studies assess short- and long-term 

27 memory acquisition via passive avoidance behavioral testing and find decrements in test 

28 performance after O3 exposure, consistent with the aforementioned observation made in 

29 humans by Chen and Schwartz (2009). Impairment of long-term memory has been 

30 previously described in rats exposed to 0.2 ppm O3 for 4 h (Rivas-Arancibia et al., 1998)

31 and in other studies of 4-hour exposures at concentrations of 0.7 to 1 ppm (Dorado32 Martinez et al., 2001; Rivas-Arancibia et al., 2000; Avila-Costa et al., 1999). More 

33 recently, statistically significant decreases in both short and long-term memory were 

34 observed in rats after 15 days of exposure to 0.25 ppm O3 (Rivas-Arancibia et al., 2010).

35 The central nervous system is very sensitive to oxidative stress, due in part to its high 

36 content of polyunsaturated fatty acids, high rate of oxygen consumption, and low 

37 antioxidant enzyme capacity. Oxidative stress has been identified as one of the 

38 pathophysiological mechanisms underlying neurodegenerative disorders such as 
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1 Parkinson’s and Alzheimer’s disease, among others (Simonian and Coyle, 1996). It is 

2 also believed to play a role in altering hippocampal function, which causes cognitive 

3 deficits with aging (Vanguilder and Freeman, 2011). A particularly common finding in 

4 studies of O3-exposed rats is lipid peroxidation in the brain, especially in the 

5 hippocampus, which is important for higher cognitive function including contextual 

6 memory acquisition. Performance in passive avoidance learning tests is impaired when 

7 the hippocampus is injured, and the observed behavioral effects are well correlated with 

8 histological and biochemical changes in the hippocampus, including reduction in spine 

9 density in the pyramidal neurons (Avila-Costa et al., 1999), lipoperoxidation (Rivas10 Arancibia et al., 2010; Dorado-Martinez et al., 2001), progressive neurodegeneration, and 

11 activated and phagocytic microglia (Rivas-Arancibia et al., 2010). The hippocampus is 

12 also one of the main regions affected by age-related neurodegenerative diseases, 

13 including Alzheimer’s disease, and it may be more sensitive to oxidative damage in aged 

14 rats. In a study of young (47 days) and aged (900 days) rats exposed to 1 ppm O3 for 4 h, 

15 O3-induced lipid peroxidation occurred to a greater extent in the striatum of young rats, 

16 whereas it was highest in the hippocampus in aged rats (Rivas-Arancibia et al., 2000). 

17 Martínez-Canabal et al. (2008) showed exposure of rats to 0.25 ppm, 4h/day, for 7, 15, or 

18 30 days increased lipoperoxides in the hippocampus. This effect was observed at day 7 

19 and continued to increase with time, indicating cumulative oxidative damage. O3-induced 

20 changes in lipid peroxidation, neuronal death, and COX-2 positive cells in the 

21 hippocampus could be significantly inhibited by daily treatment with growth hormone 

22 (GH), which declines with age in most species. The protective effect of GH on -induced 

23 oxidative stress was greatest at 15 days of exposure and was non-significant at day 30. 

24 Consistent with these findings, lipid peroxidation in the hippocampus of rats was 

25 observed to increase significantly after a 30-day exposure to 0.25 ppm , but not after a 

26 single 4-h exposure to the same concentration (Mokoena et al., 2010). However, 4 hours 

27 of exposure was sufficient to cause significant increases in lipid peroxidation when the 

28 concentration was increased to 0.7 ppm, and another study observed lipid peroxidation 

29 after a 4-h exposure to 0.4 ppm (Dorado-Martinez et al., 2001). 

30 Other commonly affected areas of the brain include the striatum, substantia nigra, 

31 cerebellum, olfactory bulb, and frontal/prefrontal cortex. The striatum and substantia 

32 nigra are particularly sensitive to oxidative stress because the metabolism of dopamine, 

33 central to their function, is an oxidative process perturbed by redox imbalance. Oxidative 

34 stress has been implicated in the premature death of substantia nigra dopamine neurons in 

35 Parkinson’s disease. Angoa-Pérez et al. (2006) have shown progressive lipoperoxidation 

36 in the substantia nigra and a decrease in nigral dopamine neurons in ovariectomized 

37 female rats exposed to 0.25 ppm O3, 4h/day, for 7, 15, or 30 days. Estradiol, an 

38 antioxidant, attenuated O3-induced oxidative stress and nigral neuronal death, and the 

39 authors note that in humans, estrogen therapy can ameliorate symptoms of Parkinson’s 
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1 disease, which is more prevalent in men. Progressive oxidative stress has also been 

2 observed in the striatum and substantia nigra of rats after 15 and 30 days of exposure to 

3 0.25 ppm O3 for 4 h/day, along with a loss of dopaminergic neurons from the substantia 

4 nigra (Pereyra-Muñoz et al., 2006). Decreases in motor activity were also observed at 15 

5 and 30 days of exposure, consistent with other reports (Martrette et al., 2011; Dorado6 Martinez et al., 2001). Using a similar O3 exposure protocol, Santiago-López and 

7 colleagues (2010) also observed a progressive loss of dopaminergic neurons within the 

8 substantia nigra, accompanied by alterations in the morphology of remaining cells and an 

9 increase in p53 levels and nuclear translocation. 

10 The olfactory bulb also undergoes oxidative damage in O3 exposed animals, in some 

11 cases altering olfactory-dependent behavior. Lipid peroxidation was observed in the 

12 olfactory bulbs of ovariectomized female rats exposed to 0.25 ppm O3 (4 h/day) for 30 or 

13 60 days (Guevara-Guzmán et al., 2009). O3 also induced decrements in a selective 

14 olfactory recognition memory test, and the authors note that early deficits in odor 

15 perception and memory are components of human neurodegenerative diseases. The 

16 decrements in olfactory memory were not due to damaged olfactory perception based on 

17 other tests. However, deficits in olfactory perception emerged with longer exposures 

18 (discussed in Chapter 7). As with the study by Angoa-Pérez et al. (2006) described 

19 above, a protective effect for estradiol was demonstrated for both lipid peroxidation and 

20 olfactory memory defects. The role of oxidative stress in memory deficits and associated 

21 morphological changes has also been demonstrated via attenuation by other antioxidants 

22 as well, such as α-tocopherol (Guerrero et al., 1999) and taurine (Rivas-Arancibia et al., 

23 2000).

24 It is unclear how persistent these effects might be. One study of acute exposure, using 

25 1 ppm O3 for 4 hours, observed morphological changes in the olfactory bulb of rats at 

26 2 hours, and 1 and 10 days, but not 15 days, after exposure (Colín-Barenque et al., 2005). 

27 Other acute studies also report changes in the CNS. Lipid peroxidation was observed in 

28 multiple regions of the brain after a 1- to 9-h exposure to 1 ppm O3 (Escalante-Membrillo 

29 et al., 2005). Ozone has also been shown to alter gene expression of endothelin-1 

30 (pituitary) and inducible nitric oxide synthase (cerebral hemisphere) after a single 4-h 

31 exposure to 0.8 ppm O3, indicating potential cerebrovascular effects. This concentration32 dependent effect was not observed at 0.4 ppm O3 (Thomson et al., 2007). Vascular 

33 endothelial growth factor was upregulated in astroglial cells in the central respiratory 

34 areas of the brain of rats exposed to 0.5 ppm O3 for 3 hours (Araneda et al., 2008). The 

35 persistence of CNS changes after a single exposure was also examined and the increase in 

36 vascular endothelial growth factor was present after a short (3 hours) recovery period. 

37 Thus, there is evidence that O3-induced CNS effects are both concentration- and time38 dependent. 
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1 Because O3 can produce a disruption of the sleep-wake cycle (U.S. EPA, 2006b), Alfaro2 Rodriguez et al. (2005) examined whether acetylcholine in a region of the brain involved 

3 in sleep regulation was altered by O3. After a 24-h exposure to 0.5 ppm O3, the 

4 acetylcholine concentration in the medial preoptic area was decreased by 58% and 

5 strongly correlated with a disruption in paradoxical sleep. Such behavioral-biochemical 

6 effects of O3 are confirmed by a number of studies which have demonstrated 

7 morphological and biochemical changes in rats.

8 CNS effects have also been demonstrated in newborn and adult rats whose only exposure 

9 to O3 occurred in utero. Several neurotransmitters were assessed in male offspring of 

10 dams exposed to 1 ppm O3 during the entire pregnancy (Gonzalez-Pina et al., 2008). The 

11 data showed that catecholamine neurotransmitters were affected to a greater degree than 

12 indole-amine neurotransmitters in the cerebellum. CNS changes, including behavioral, 

13 cellular, and biochemical effects, have also been observed after in utero exposure to 

14 0.5 ppm O3 for 12 h/day from gestational days 5-20 (Boussouar et al., 2009). Tyrosine 

15 hydroxylase labeling in the nucleus tractus solatarius was increased after in utero 

16 exposure to O3 whereas Fos protein labeling did not change. When these offspring were 

17 challenged by immobilization stress, neuroplasticity pathways, which were activated in 

18 air-exposed offspring, were inhibited in O3-exposed offspring. Although an O3 exposure 

19 concentration-response was not studied in these two in utero studies, it has been 

20 examined in one study. Santucci et al. (2006) investigated behavioral effects and gene 

21 expression after in utero exposure of mice to as little as 0.3 ppm O3. Increased 

22 defensive/submissive behavior and reduced social investigation were observed in both the 

23 0.3 and 0.6 ppm O3 groups. Changes in gene expression of brain-derived neurotrophic 

24 factor (BDNF, increased in striatum) and nerve growth factor (NGF, decreased in 

25 hippocampus) accompanied these behavioral changes. Thus, these three studies 

26 demonstrate that CNS effects can occur as a result of in utero exposure to O3, and 

27 although the mode of action of these effects is not known, it has been suggested that 

28 circulating lipid peroxidation products may play a role (Boussouar et al., 2009). 

29 Importantly, these CNS effects occurred in rodent models after in utero only exposure to 

30 relevant concentrations of O3. 
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Table 6-40 Central Nervous System and Behavioral Effects of Short-term O3

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/wk

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 et al. (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 DARPP-32, 

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 memory-retention 

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 post exposure

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 

concentration-dependent increase in preproendothelin-1 mRNA levels in the cerebral 

hemisphere and pituitary, whereas TNFa and 

iNOS mRNA levels were decreased at 0 hrs and 

unchanged or increased, respectively, at 24 h.

Alfaro-Rodríguez and GonzálezPina (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; 280-320g0.5 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. 

Boussouar et al. (2009) Rat; Sprague-Dawley; 

M; adult offspring of 

prenatally exposed 

dams; 403-414g

0.5 From embryonic day 

E5 to E20 for 12-

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; Sprague-Dawley; 

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. 
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Study Model O3

(ppm)

Exposure 

Duration Effects

Guzmán et al. (2006; 2005) Rat; Wistar; M; 21 

days old; wellnourished 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 ozone in certain brain 

areas and the ozone-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 d. 5-hydroxy-indoleacetic 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, 

11 and motor control, effects that may be responsible for some of the behavioral effects seen 

12 with O3 exposure. A more recent study exposing immature female rats to 0.12 ppm O3

13 demonstrated significantly increased serum levels of the thyroid hormone free T3 after 15 

14 days of exposure, whereas free T4 was unchanged (Martrette et al., 2011). These results 

15 are in contrast to those previously presented whereby 1 ppm O3 for 1 day significantly 

16 decreased T3 and T4 (Clemons and Garcia, 1980), although comparisons are made 

17 difficult by highly disparate exposure regimens along with sex differences. Martrette et 

18 al.(2011) also demonstrated significantly increased corticosterone levels after 15 days of 

19 exposure, suggesting a stress related response.
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6.4.2 Summary and Causal Determination 

1 In rodents, O3 exposure has been shown to cause physicochemical changes in the brain 

2 indicative of oxidative stress and inflammation. Newer toxicological studies add to earlier 

3 evidence that acute exposures to O3 can produce a range of effects on the central nervous 

4 system and behavior. Previously observed effects, including neurodegeneration, 

5 alterations in neurotransmitters, short and long term memory, and sleep patterns, have 

6 been further supported by recent studies. In instances where pathology and behavior are 

7 both examined, animals exhibit decrements in behaviors tied to the brain regions or

8 chemicals found to be affected or damaged. For example, damage in the hippocampus, 

9 which is important for memory acquisition, was correlated with impaired performance in 

10 tests designed to assess memory. Thus the brain is functionally affected by O3 exposure. 

11 The single epidemiologic study conducted showed an association between O3 exposure 

12 and memory deficits in humans as well, albeit on a long-term exposure basis. Notably, 

13 exposure to O3 levels as low as 0.25 ppm for 7 days has resulted in progressive 

14 neurodegeneration and deficits in both short and long-term memory in rodents. 

15 Examination of changes in the brain at lower exposure concentrations or at 0.25 ppm for 

16 shorter durations has not been reported, but 0.12 ppm O3 has been shown to alter 

17 behavior. It is possible that some behavioral changes may reflect avoidance of irritation 

18 as opposed to functional changes in brain morphology or chemistry, but in many cases 

19 functional changes are related to oxidative stress and damage. In some instances, changes 

20 were dependent on the nutritional status of the rats (high versus low protein diet). For 

21 example, O3 produced an increase in glutathione in the brains of rats fed the high protein 

22 diet but decreases in glutathione in rats fed low protein chow (Calderon Guzman et al., 

23 2006). The hippocampus, one of the main regions affected by age-related 

24 neurodegenerative diseases, appears to be more sensitive to oxidative damage in aged rats 

25 (Rivas-Arancibia et al., 2000), and growth hormone, which declines with age in most 

26 species, may be protective (Martínez-Canabal and Angora-Perez, 2008). Developing 

27 animals may also be sensitive, as changes in the CNS, including biochemical, cellular, 

28 and behavioral effects, have been observed in juvenile and adult animals whose sole 

29 exposure occurred in utero, at levels as a low as 0.3 ppm. A number of studies 

30 demonstrate ozone-induced changes that are also observed in human neurodegenerative 

31 disorders such as Alzheimer’s and Parkinson’s disease, including signs of oxidative 

32 stress, loss of neurons/neuronal death, reductions in dopamine levels, increased COX-2 

33 expression, and increases in activated microglia in important regions of the brain 

34 (hippocampus, substantia nigra). 

35 Although evidence from epidemiologic and controlled human exposure studies is lacking, 

36 the toxicological evidence for ozone’s impact on the brain and behavior is strong, and at 
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1 least is suggestive of a causal relationship between O3 exposure and effects on the 

2 central nervous system.

6.5 Effects on Other Organ Systems

6.5.1 Effects on the Liver and Xenobiotic Metabolism

3 Early investigations of the effects of O3 on the liver centered on xenobiotic metabolism, 

4 and the prolongation of drug-induced sleeping time, which was observed at 0.1 ppm O3

5 (Graham et al., 1981). In some species, only adults and especially females were affected. 

6 In rats, high (1.0-2.0 ppm for 3 hours) acute O3 exposures caused increased production of 

7 NO by hepatocytes and enhanced protein synthesis (Laskin et al., 1996; Laskin et al., 

8 1994). Except for the earlier work on xenobiotic metabolism, the responses occurred only 

9 after very high acute O3 exposures. One study, conducted at 1 ppm O3 exposure, has been 

10 identified (Last et al., 2005) in which alterations in gene expression underlying O3-

11 induced cachexia and downregulation of xenobiotic metabolism were examined. A 

12 number of the down-regulated genes are known to be interferon (IFN) dependent, 

13 suggesting a role for circulating IFN. A more recent study by Aibo et al. (2010)

14 demonstrates exacerbation of acetaminophen-induced liver injury in mice after a single 

15 6-h exposure to 0.25 or 0.5 ppm O3. Data indicate that O3 may worsen drug-induced liver 

16 injury by inhibiting hepatic repair. The O3-associated effects shown in the liver are 

17 thought to be mediated by inflammatory cytokines or other cytotoxic mediators released 

18 by activated macrophages or other cells in the lungs (Laskin and Laskin, 2001; Laskin et 

19 al., 1998; Vincent et al., 1996b). Recently, increased peroxidated lipids were detected in 

20 the plasma of O3 exposed animals (Santiago-López et al., 2010).

21 In summary, mediators generated by O3 exposure may cause effects on the liver in 

22 laboratory rodents. Ozone exposures as low as 0.1 ppm have been shown to affect drug23 induced sleeping time, and exposure to 0.25 ppm can exacerbate liver injury induced by a 

24 common analgesic. However, very few studies at relevant concentrations have been 

25 conducted, and no data from controlled human exposure or epidemiologic studies are 

26 currently available. Therefore the collective evidence is inadequate to determine if a

27 causal relationship exists between short-term O3 exposure and effects on the liver 

28 and metabolism.
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6.5.2 Effects on Cutaneous and Ocular Tissues

1 In addition to the lungs, the skin is highly exposed to O3 and contains O3 reactive targets 

2 (polyunsaturated fatty acids) that can produce lipid peroxides. The 2006 O3 AQCD 

3 reported that although there is evidence of oxidative stress at near ambient O3

4 concentrations, skin and eyes are only affected at high concentrations (greater than 

5 1-5 ppm). Ozone exposure (0.8 ppm for 7 days) induces oxidative stress in the skin of 

6 hairless mice, along with proinflammatory cytokines (Valacchi et al., 2009). A recent 

7 study demonstrated that 0.25 ppm O3 differentially alters expression of 

8 metalloproteinases in the skin of young and aged mice, indicating age-related 

9 susceptibility to oxidative stress (Fortino et al., 2007). In young mice, healing of skin 

10 wounds is not significantly affected by O3 exposure (Lim et al., 2006). However, 

11 exposure to 0.5 ppm O3 for 6 h/day significantly delays wound closure in aged mice. As 

12 with effects on the liver described above, the effects of O3 on the skin and eyes have not 

13 been widely studied, and information from controlled human exposure or epidemiologic 

14 studies is not currently available. Therefore the collective evidence is inadequate to 

15 determine if a causal relationship exists between short-term O3 exposure and 

16 effects on cutaneous and ocular tissues.

6.6 Mortality 

6.6.1 Summary of Findings from 2006 Ozone AQCD 

17 The 2006 O3 AQCD reviewed a large number of time-series studies consisting of single18 and multicity studies, and meta-analyses. In the large U.S. multicity studies that 

19 examined all-year data, summary effect estimates corresponding to single-day lags 

20 ranged from a 0.5-1% increase in all-cause (nonaccidental) mortality per the standardized 

unit increase1 21 in O3. The association between short-term O3 exposure and mortality was 

22 substantiated by a collection of meta-analyses and international multicity studies. The 

23 studies evaluated found some evidence for heterogeneity in O3 mortality risk estimates 

24 across cities and studies. Studies that conducted seasonal analyses, although more limited 

25 in number, reported larger O3 mortality risk estimates during the warm or summer 

26 season. Overall, the 2006 O3 AQCD identified robust associations between various 

27 measures of daily ambient O3 concentrations and all-cause mortality, with additional 

28 evidence for associations with cardiovascular mortality, which could not be readily 

29 explained by confounding due to time, weather, or copollutants. However, it was noted 

 1 In the 2006 O3 AQCD and throughout this document to compare across studies that used the same exposure metric, effect 

estimates were standardized to 40 ppb for 1-h maximum, 30 ppb for 8-h maximum, and 20 ppb for 24-h average O3 concentrations.
Draft – Do Not Cite or Quote 6-194 September 2011

1 that multiple uncertainties remain regarding the O3-mortality relationship including: the 

2 extent of residual confounding by copollutants; factors that modify the O3-mortality 

3 association; the appropriate lag structure for identifying O3-mortality effects (e.g., single4 day lags versus distributed lag model); the shape of the O3-mortality C-R function and 

5 whether a threshold exists; and the identification of susceptible populations. Collectively, 

6 the 2006 O3 AQCD concluded that “the overall body of evidence is highly suggestive that 

7 O3 directly or indirectly contributes to non-accidental and cardiopulmonary-related 

8 mortality.”

6.6.2 Associations of Mortality and Short-Term Ozone Exposure 

9 The recent literature that examined the association between short-term O3 exposure and 

10 mortality further confirmed the associations reported in the 2006 O3 AQCD. New 

11 multicontinent and multicity studies reported consistent positive associations between 

12 short-term O3 exposure and all-cause mortality in all-year analyses, with additional 

13 evidence for larger mortality risk estimates during the warm or summer months (Figure 

14 6-27; Table 6-41). These associations were reported across a range of ambient O3

15 concentrations that were in some cases quite low (Table 6-42).
Draft – Do Not Cite or Quote 6-195 September 2011

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 ozone 

concentrations. An “a” represent multicity studies and meta-analyses from the 2006 ozone 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 ozone concentrations (see explanation in Section 6.2.7.2). 

Figure 6-27 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; 57276)

Bell et al. (2007; 93256)

Schwartz (2005; 57333)

Bell and Dominici (2008; 193828)

Bell et al. (2004; 94417)a

Levy et al. (2005; 74347)a

Katsouyanni et al. (2009; 199899)

Bell et al. (2005; 74345)a

Ito et al. (2005; 74346)a

Wong et al. (2010; 732535)

Katsouyanni et al. (2009; 199899)

Cakmak et al. (2011, 699135)

Katsouyanni et al. (2009; 199899)

Katsouyanni et al. (2009; 199899)b

Samoli et al. (2009; 195855)

Bell et al. (2004; 94417)a

Schwartz (2005; 57333)

Zanobetti and Schwartz (2008; 195755)

Zanobetti and Schwartz (2008; 101596)

Franklin and Schwartz (2008; 156448)

Gryparis et al. (2004; 57276)

Medina-Ramon and Schwartz (2008)

Katsouyanni et al. (2009; 199899)

Bell et al. (2005; 74345)a

Katsouyanni et al. (2009; 199899)

Katsouyanni et al. (2009; 199899)b

Levy et al. (2005; 74347)a

Ito et al. (2005; 74346)a

Katsouyanni et al. (2009; 199899)

Stafoggia et al. (2010; 625034)

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 6-196 September 2011

Table 6-41 Corresponding effect estimates for Figure 6-27

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-Ramon 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)

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 6-197 September 2011

Table 6-42 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

Zanobetti and 

Schwartz (2008a)

48 U.S. citiesc 1989-2000

(Winter: December-February)

(Spring: March-May)

(Summer: June-August)

(Autumn: SeptemberNovember)

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.

CV=coefficient of variation

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 
Draft – Do Not Cite or Quote 6-198 September 2011

1 short-term O3 exposure and mortality presented across studies in the 2006 O3 AQCD and 

2 supported in the new multicity studies, the following sections primarily focus on the 

3 examination of previously identified uncertainties in the O3-mortality relationship, 

4 specifically: O3 associations with cause-specific mortality, confounding, lag structure 

5 (e.g., multiday effects and mortality displacement), effect modification (i.e., sources of 

6 heterogeneity in risk estimates across cities); and the O3-mortality C-R relationship. 

7 Focusing specifically on these uncertainties allows for a more detailed characterization of 

8 the relationship between short-term O3 exposure and mortality.

6.6.2.1 Confounding

9 Recent epidemiologic studies examined potential confounders of the O3-mortality 

10 relationship. These studies specifically focused on whether PM and its constituents or 

11 seasonal trends confounded the association between short-term O3 exposure and 

12 mortality. 

Confounding by PM and PM Constituents

13 An important question in the evaluation of the association between short-term O3

14 exposure and mortality is whether the relationship is confounded by particulate matter, 

15 particularly the PM chemical components that are found in the “summer haze” mixture 

16 which also contains O3. However, because of the temporal correlation among these PM

17 components and O3, and their possible interactions, the interpretation of results from 

18 multipollutant models that attempt to disentangle the health effects associated with each 

19 pollutant is challenging.

20 The potential confounding effects of PM10 and PM2.5 on the O3-mortality relationship 

21 were examined by Bell et al. (2007) using data on 98 U.S. urban communities for the 

22 years 1987-2000 from the National Morbidity, Mortality, and Air Pollution Study 

23 (NMMAPS). In this analysis the authors included PM as a covariate in time-series 

24 models, and also examined O3-mortality associations on days when O3 concentrations were 

25 below a specified value. This analysis was limited by the small fraction of days when 

26 both PM and O3 data were available, due to the every-3rd- or 6th-day sampling schedule 

27 for the PM indices, and the limited amount of city-specific data for PM2.5 because it was 

28 only collected in most cities since 1999. As a result, of the 91 communities with PM2.5

29 data, only 9.2% of days in the study period had data for both O3 and PM2.5, resulting in 

30 the use of only 62 communities in the PM2.5 analysis. An examination of the correlation 

31 between PM (PM10 and PM2.5) and O3 across various strata of daily PM10 and PM2.5

32 concentrations found that neither PM size fraction was highly correlated with O3 across 
Draft – Do Not Cite or Quote 6-199 September 2011

1 any of the strata examined. These results were also observed when using 8-h max and 1-h 

2 max O3 exposure metrics. National and community-specific effect estimates of the 

3 association between short-term O3 exposure and mortality were robust to inclusion of 

4 PM10 or PM2.5 in time-series models through the range of O3 concentrations (i.e., 

5 <10 ppb, 10-20, 20-40, 40-60, 60-80, and >80 ppb). For example, the percent increases in 

6 nonaccidental deaths per 10 ppb increase 24-h avg O3 concentrations at lag 0-1 day were 

7 0.22% (95% CI: -0.22, 0.65) without PM2.5 and 0.21% (95% CI: -0.22, 0.64) with PM2.5

8 in 62 communities.

9 Although no strong correlations between PM and O3 were reported by Bell et al. (2007)

10 the patterns observed suggest regional differences in their correlation. (Table 6-43). Both 

11 PM10 and PM2.5 show positive correlations with O3 in the Industrial Midwest, Northeast, 

12 Urban Midwest, and Southeast, especially in the summer months, presumably, because of 

13 the summer peaking sulfate. However, the mostly negative or weak correlations between 

14 PM and O3 in the summer in the Southwest, Northwest, and southern California could be 

15 due to winter-peaking nitrate. Thus, the potential confounding effect of PM on the 

16 O3-mortality relationship could be influenced by the relative contribution of sulfate and 

17 nitrate, which varies regionally and seasonally. 

Table 6-43 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 6-200 September 2011

Source: Reprinted with permission of Informa UK Ltd (Smith et al., 2009b). 

The diagonal line indicates 1:1 ratio.

Figure 6-28 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. The authors conducted a number of analyses using 

4 constrained distributed lag models and the average of 0- and 1-day lags. In addition, 

5 Smith et al. (2009b) examined the effect of different averaging times (24-h, 8-h, and 1-h 

6 max) on O3-mortality regression coefficients, and whether PM10 confounded the 

7 O3-mortality relationship. The authors reported that, in most cases, O3 mortality risk 

8 estimates were reduced by between 22% and 33% in copollutant models with PM10. This 

9 is further highlighted in Figure 6-28, which shows scatter plots of O3-mortality risk 

10 estimates with adjustment for PM10 versus without adjustment for PM10. Smith et al. 

11 (2009b) point out that a larger fraction (89 out of 93) of the posterior estimates lie below 

12 the diagonal line (i.e., estimates are smaller with PM10 adjustment) compared to the raw 

13 estimates (56 out of 93). This observation could be attributed to both sets of posterior 

14 estimates being calculated by “shrinking towards the mean.” However, the most 
Draft – Do Not Cite or Quote 6-201 September 2011

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-h summertime O3 concentrations across 

13 the 18 U.S. communities. Adjustment for PM2.5 mass, which was available for 84% of the 

14 days, decreased the O3-mortality risk estimate only slightly (from 0.88% to 0.79%), but the 

15 inclusion of sulfate in the model reduced the risk estimate by 31% (from 0.85% to 

16 0.58%). However, sulfate data were only available for 18% of the days. Therefore, a 

17 limitation of this study is the limited amount of data for PM2.5 chemical components due 

18 to the every-3rd-day or every-6th-day sampling schedule. For example, when using a 

19 subset of days when organic carbon measurements were available (i.e., 17% of the 

20 available days), O3 mortality risk estimates were reduced to 0.51% (95% CI: -0.36 to 

21 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 presented in Figure 

25 6-29, the regional and city-to-city variations in O3 mortality risk estimates appear greater 

26 than the impact of adjusting for copollutants. In addition, in some cases, a negative O3

27 mortality risk estimate becomes even more negative with the inclusion of sulfate (e.g., 

28 Seattle) in a copollutant model, or a null O3 mortality risk estimate becomes negative 

29 when sulfate is included (e.g., Dallas and Detroit). Thus, the reduction in the overall O3

30 mortality risk estimate (i.e., across cities) needs to be assessed in the context of the 

31 heterogeneity in the single-city estimates. 
Draft – Do Not Cite or Quote 6-202 September 2011

Source: Reprinted from Franklin and Schwartz (2008).

Figure 6-29 Community-specific ozone-mortality risk estimates for 

nonaccidental mortality per 10 ppb increase in same-day 24-h avg 

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 

11 results are presented in figures because alternative spline models have previously been 

12 shown to result in similar effect estimates (HEI, 2003). Additionally, for the Canadian 

13 results, figures contain risk estimates standardized to both a 40 ppb increment for 1-h 
Draft – Do Not Cite or Quote 6-203 September 2011

1 max O3 concentrations, consistent with the rest of the ISA, but also the approximate IQR 

2 across the Canadian cities as discussed previously (Section 6.2.7.2). 

3 In the three datasets, the authors found generally positive associations between short-term 

4 O3 exposure and all-cause, cardiovascular, and respiratory mortality. The estimated 

5 excess risks for O3 were larger for the Canadian cities than for the U.S. and European 

6 cities. When examining the potential confounding effects of PM10 on O3 mortality risk 

7 estimates, the sensitivity of the estimates varied across the data sets and age groups. In 

8 the Canadian dataset, adjusting for PM10 modestly reduced O3 risk estimates for all-cause 

9 mortality for all ages in the PS (4.5% [95% CI: 2.2, 6.7%]) and NS (4.2% [95% CI: 1.9, 

10 6.5%]) models to 3.8% (95% CI: -1.4, 9.8%) and 3.2% (95% CI: -2.2, 9.0%), 

11 respectively, at lag 1 for a 40 ppb increase in 1-h max O3 concentrations (Figure 6-30; 

12 Table 6-44). However, adjusting for PM10 reduced O3 mortality risk estimates in the ≥ 

13 75-year age group, but increased the risk estimates in the <75-year age group. For 

14 cardiovascular and respiratory mortality more variable results were observed with O3 risk 

15 estimates being reduced and increased, respectively, in copollutant models with PM10

16 (Figure 6-30; Table 6-44). Unlike the European and U.S. datasets, the Canadian dataset 

17 only conducted copollutant analyses at lag 1; as a result, to provide a comparison across 

18 study locations only the lag 1 results are presented for the European and U.S. datasets in 

19 this section. 

20 In the European data, O3 risk estimates were robust when adjusting for PM10 in the year21 round data for all-cause, cardiovascular and respiratory mortality. When restricting the 

22 analysis to the summer months moderate reductions were observed in O3 risk estimates 

23 for all-cause mortality with more pronounced reductions in respiratory mortality. In the 

24 U.S. data, adjusting for PM10 moderately reduced O3 risk estimates for all-cause mortality 

25 in a year-round analysis at lag 1 (e.g., both the PS and NS models were reduced from 

26 0.18% to 0.13%) (Figure 6-30; Table 6-44). Similar to the European data, when 

27 restricting the analysis to the summer months, adjusting for PM10 moderately reduced O3

28 mortality risk estimates in the U.S. However, when examining cause-specific mortality 

29 risk estimates, consistent with the results from the Canadian dataset, which employed a 

30 similar PM sampling strategy (i.e., every-6th-day sampling), O3 risk estimates for 

31 cardiovascular and respiratory mortality were more variable; reduced or increased in 

32 all-year and summer analyses. Overall, the estimated O3 risks appeared to be moderately 

33 to substantially sensitive to inclusion of PM10 in copollutant models. Despite the multicity 

34 approach, the mostly every-6th-day sampling schedule for PM10 in the Canadian and U.S. 

35 datasets greatly reduced the sample size and limits the interpretation of these results. 
Draft – Do Not Cite or Quote 6-204 September 2011

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. An “a” 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 6-30 Percent increase in all-cause (nonaccidental) and cause-specific 

mortality 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 6-205 September 2011

Table 6-44 Corresponding Effect Estimates for Figure 6-30

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 -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 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 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 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 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

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 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 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)

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 
Draft – Do Not Cite or Quote 6-206 September 2011

1 2001 to 2005. In a time-stratified case-crossover analysis, using data for the summer 

2 months (i.e., April-September), the authors examined O3-mortality associations across 

3 each city, and then obtained a pooled estimate through a random-effects meta-analysis. 

4 Stafoggia et al. (2010) found a strong association with nonaccidental mortality (9.2% 

5 [95% CI: 5.4, 13.0%] for a 30 ppb increase in 8-h max O3 concentrations) in an 

6 unconstrained distributed lag model (lag 0-5) that persisted in copollutant models with 

7 PM10 (9.2% [95% CI: 5.4, 13.7%]). Additionally, when examining cause-specific 

8 mortality, the authors found positive associations between short-term O3 exposure and 

9 cardiovascular (14.3% [95% CI: 6.7, 22.4%]), cerebrovascular (8.5% [95% CI: 0.1, 

10 16.3%]), and respiratory (17.6% [95% CI: 1.8, 35.6%]) mortality in single-pollutant 

11 models. In copollutant models, O3-mortality effect estimates for cardiovascular and 

12 cerebrovascular mortality were robust to the inclusion of PM10 (9.2% [95% CI: 5.4, 

13 13.7%]) and 7.3% [95% CI: -1.2, 16.3%], respectively), and attenuated, but remained 

14 positive, for respiratory mortality (9.2% [95% CI: -6.9, 28.8%]). Of note, the correlations 

15 between O3 and PM10 across cities were found to be generally low, ranging from (-0.03 to 

16 0.49). The authors do not specify the sampling strategy used for PM10 in this analysis.

Confounding by Seasonal Trend

17 The APHENA study (Katsouyanni et al., 2009), mentioned above, also conducted 

18 extensive sensitivity analyses to identify the appropriate: smoothing method and basis 

19 functions to estimate smooth functions of time in city-specific models; and degrees of 

20 freedom to be used in smooth functions of time, to adjust for seasonal trends. Because O3

21 peaks in the summer and mortality peaks in the winter, not adjusting or not sufficiently 

22 adjusting for the seasonal trend would result in an apparent negative association between 

23 the O3 and mortality time-series. Katsouyanni et al. (2009) examined the effect of the 

24 extent of smoothing for seasonal trends by using models with 3 df/year, 8 df/year (the 

25 choice for their main model), 12 df/year, and df/year selected using the sum of absolute 

26 values of partial autocorrelation function of the model residuals (PACF) (i.e., choosing 

27 the degrees of freedom that minimizes positive and negative autocorrelations in the 

28 residuals). Table 6-45 presents the results of the degrees of freedom analysis using 

29 alternative methods to calculate a combined estimate: the Berkey et al. (1998) meta30 regression and the two-level normal independent sampling estimation (TLNISE) 

31 hierarchical method. The results show that the methods used to combine single-city 

32 estimates did not influence the overall results, and that neither 3 df/year nor choosing the 

33 df/year by minimizing the sum of absolute values of PACF of regression residuals was 

34 sufficient to adjust for the seasonal negative relationship between O3 and mortality. 

35 However, it should be noted, the majority of studies in the literature that examined the 

36 mortality effects of short-term O3 exposure, particularly the multicity studies, used 7 or 
Draft – Do Not Cite or Quote 6-207 September 2011

1 8 df/year to adjust for seasonal trends, and in both methods a positive association was 

2 observed between O3 exposure and mortality. 

Table 6-45 Sensitivity of ozone risk estimates per 10 μg/m3 increase in 

24-h avg ozone concentrations at lag 0-1 to alternative methods for 

adjustment of seasonal trend, for all-cause mortality using Berkey 

MLE and TLNSE 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 (2009).

6.6.2.2 Effect Modification

3 There have been several multicity studies that examined potential effect modifiers, or 

4 time-invariant factors, that may modify O3 mortality risk estimates. These effect 

5 modifiers can be categorized into either individual-level or community-level

6 characteristics, which are traditionally, examined in second stage regression models. The 

7 results from these analyses also inform upon whether certain populations are susceptible 

8 to O3-related health effects (Chapter 8). In addition to potentially modifying the 

9 association between short-term O3 exposure and mortality, both individual-level and 

10 community-level characteristics may also contribute to the apparent geographic pattern of 

11 spatial heterogeneity in O3 mortality risk estimates. As a result, the geographic pattern of 

12 O3 mortality risk estimates is also evaluated in this section.

Individual-Level Characteristics

13 Medina-Ramón and Schwartz (2008) conducted a case-only study in 48 U.S. cities to 

14 identify populations potentially susceptible to O3-related mortality for the period 

15 1989-2000 (May through September of each year [i.e., warm season]). A case-only 

16 design predicts the occurrence of time-invariant characteristics among cases as a function 

17 of the exposure level (Armstrong, 2003). For each potential effect modifier (time18 invariant individual-level characteristics), city-specific logistic regression models were 

19 fitted, and the estimates were pooled across all cities. Furthermore, the authors examined 

20 potential differences in individual effect modifiers according to several city 

21 characteristics (e.g., mean O3 level, mean temperature, households with central air
Draft – Do Not Cite or Quote 6-208 September 2011

1 conditioning, and population density) in a meta-regression. Across cities the authors 

2 found a 1.96% (95% CI: 1.14-2.82%) increase in mortality at lag 0-2 for a 30 ppb 

3 increase in 8-h max O3 concentrations. Additionally, Medina-Ramón and Schwartz 

4 (2008) examined a number of individual-level characteristics (e.g., age, race) and chronic 

5 conditions (e.g., secondary causes of death) as effect modifiers of the association between 

6 short-term O3 exposure and mortality. The authors found that older adults (i.e., ≥ 65), 

7 women >60 years of age, black race, and secondary atrial fibrillation showed the greatest 

8 additional percent change in O3-related mortality (Table 6-46). In addition, when 

9 examining city-level characteristics, the authors found that older adults, black race, and 

10 secondary atrial fibrillation had a larger effect on O3 mortality risk estimates in cities with 

11 lower O3 levels. Of note, a similar case-only study (Schwartz, 2005b) examined potential 

12 effect modifiers of the association between temperature and mortality, which would be 

13 expected to find results consistent with the Medina-Ramón and Schwartz (2008) study 

14 due to the high correlation between temperature and O3. However, when stratifying days 

15 by temperature Schwartz (2005b) found strong evidence that diabetes modified the 

16 temperature-mortality association on hot days, which was not as evident when examining 

17 the O3-mortality association in Medina-Ramón and Schwartz (2008). This difference 

18 could be due to the study design and populations included in both studies, a multicity 

19 study including all ages (Medina-Ramón and Schwartz, 2008) compared to a single-city 

20 study of individuals ≥ 65 years of age (Schwartz, 2005b). However, when examining 

21 results stratified by race, nonwhites were found to have higher mortality risks on both hot 

22 and cold days, which provide some support for the additional risk found for black race in 

23 Medina-Ramón and Schwartz (2008).

24 Individual-level factors that may result in susceptibility to O3-related mortality were also 

25 examined by Stafoggia et al. (2010). As discussed above, using a time-stratified case26 crossover analysis, the authors found an association between short-term O3 exposure and 

27 nonaccidental mortality in an unconstrained distributed lag model in 10 Italian cities 

28 (9.2% [95% CI: 5.4, 13.0%; lag 0-5 for a 30 ppb increase in 8-h max O3 concentrations). 

29 Stafoggia et al. (2010) conducted additional analyses to examine whether age, sex, 

30 income level, location of death, and underlying chronic conditions increased the risk of 

31 O3-related mortality, but data were only available for nine of the cities for these analyses. 

32 Of the individual-level factors examined, the authors found the strongest evidence for 

33 increased risk of O3-related mortality in individuals ≥ 85 years of age (22.4% [95% CI: 

34 15.0, 30.2%]), women (13.7% [95% CI: 8.5, 19.7%]), and out-of-hospital deaths (13.0% 

35 [95% CI: 6.0, 20.4%]). When focusing specifically on out-of hospital deaths and the 

36 subset of individuals with chronic conditions, Stafoggia et al. (2010) found the strongest 

37 association for individuals with diabetes, which is consistent with the potentially 

38 increased susceptibility of diabetics on hot days observed in Schwartz (2005b). 
Draft – Do Not Cite or Quote 6-209 September 2011

Table 6-46 Additional percent change in ozone-related mortality for individuallevel susceptibility factors 

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 from 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 

10 examination of the influence of SES indicators (i.e., educational attainment, income level, 

11 and employment status) on the O3-mortality relationship. The authors found the largest 

12 risk estimates in the lowest SES categories for each of the indicators examined this 

13 includes: primary school not completed when examining educational attainment; the 

14 lowest quartile of income level; and unemployed individuals when comparing 

15 employment status. 

16 Overall, uncertainties exist in the interpretation of the potential effect modifiers, 

17 identified in Medina-Ramón and Schwartz (2008), Stafoggia et al. (2010), and Cakmak et 
Draft – Do Not Cite or Quote 6-210 September 2011

1 al. (2011) of the O3-mortality relationship due to the expected heterogeneity in O3 mortal2 ity risk estimates across cities as highlighted in Smith et al. (2009b) (Figure 6-28) and 

3 Franklin and Schwartz (2008) (Figure 6-29). For example, it is difficult to determine the 

4 relative importance of a susceptibility factor that results in an additional percent increase 

5 in mortality in a multicity analysis when analyses of the individual cities within the study 

6 did not indicate associations between O3 and mortality. In addition, it is likely that 

7 individual-level susceptibility factors identified in Medina-Ramón and Schwartz (2008), 

8 Stafoggia et al. (2010), and Cakmak et al. (2011) only modify the O3-mortality relation9 ship. The factors identified span pollutants as is evident by older adults (i.e., ≥ 65) often 

10 being identified as an effect modifier of PM mortality risk estimates (U.S. EPA, 2009d). 

Community-level Characteristics

11 Several studies also examined city-level (i.e., ecological) variables to explain city-to-city 

12 variation in estimated O3 mortality risk estimates. Bell and Dominici (2008) investigated 

13 whether community-level characteristics, such as race, income, education, urbanization, 

14 transportation use, PM and O3 levels, number of O3 monitors, weather, and air 

15 conditioning use could explain the heterogeneity in O3-mortality risk estimates across 

16 cities. The authors analyzed 98 U.S. urban communities from NMMAPS for the period 

17 1987-2000. In the all-year regression model that included no community-level variables, 

18 a 20 ppb increase in 24-h avg O3 concentrations during the previous week was associated 

19 with a 1.04% (95% CI: 0.56, 1.55) increase in mortality. Bell and Dominci (2008) found 

20 that higher O3-mortality effect estimates were associated with higher: percent 

21 unemployment, fraction of the population Black/African-American, percent of the 

22 population that take public transportation to work; and with lower: temperatures and 

23 percent of households with central air conditioning (Figure 6-31). The modification of 

24 O3-mortality risk estimates reported for city-specific temperature and prevalence of 

25 central air conditioning in this analysis confirm the result from the meta-analyses 

26 reviewed in the 2006 O3 AQCD. 

27 The APHENA project (Katsouyanni et al., 2009) examined potential effect modification 

28 of O3 risk estimates in the Canadian, European, and U.S. data sets using a consistent set 

29 of city-specific variables. Table 6-47 presents the results from all age analyses for all30 cause mortality using all-year O3 data for the average of lag 0-1 day. While there are 

31 several significant effect modifiers in the U.S. data, the results are mostly inconsistent 

32 with the results from the Canadian and European data sets. The positive effect 

33 modification by percentage unemployed and the negative effect modification by mean 

34 temperature (i.e., a surrogate for air conditioning rate) are consistent with the results 

35 reported by Bell and Dominici (2008) discussed above. However, the lack of consistency 

36 across the data sets, even between the Canadian and U.S. data, makes it difficult to 
Draft – Do Not Cite or Quote 6-211 September 2011

1 interpret the results. Some of these associations may be due to coincidental correlations 

2 with other unmeasured factors that vary regionally (e.g., mean SO2 tend to be higher in 

3 the eastern U.S.).

Source: Reprinted with permission of Johns Hopkins Bloomberg School of Public Health, Bell and Dominici (2008).

Figure 6-31 Ozone mortality risk estimates and community-specific 

characteristics, U.S., 1987-2000. 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. 
Draft – Do Not Cite or Quote 6-212 September 2011

Table 6-47 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

Age 

standardized

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 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 6-48). 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 (Figure 6-

9 32). It is worth noting that in the analysis of PM10 using the same data set, Peng et al. 

10 (2005) also found that both the Northeast and Industrial Midwest showed particularly 
Draft – Do Not Cite or Quote 6-213 September 2011

1 elevated effects, especially during the summer months. As mentioned above, although no 

2 evidence for confounding of O3 mortality risk estimates by PM10 was observed, Bell et al. 

3 (2007) did find regional differences in the correlation between O3 and PM10. Thus, the 

4 heterogeneity in O3 mortality risk estimates may need to be examined as a function of the 

5 correlation between PM and O3. 

6 Smith et al. (2009b), as discussed earlier, also examined the regional difference in O3

7 mortality risk estimates across the same seven regions and similarly found evidence for 

8 regional heterogeneity. In addition, Smith et al. (2009b) constructed spatial maps of the 

9 risk estimates by an extension of a hierarchical model that allows for spatial auto10 correlation among the city-specific random effects. Figure 6-31 presents the spatial map 

11 of O3 mortality coefficients from the Smith et al. (2009b) analysis that used 8-h max O3

12 concentrations during the summer. The results from the Bell and Dominici (2008)

13 analysis (Figure 6-32) shows much stronger apparent heterogeneity in O3-mortality risk 

14 estimates across cities than the smoothed map from Smith et al. (2009b) (Figure 6-33), 

15 but both maps generally show larger risk estimates in the eastern region of the U.S. 

Table 6-48 Percentage increase in daily mortality for a 10 ppb increase in 24-h 

avg 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: Used with permission from Johns Hopkins Bloomberg School of Public Health, Bell and Dominici (2008).
Draft – Do Not Cite or Quote 6-214 September 2011

Source: Reprinted with permission of Johns Hopkins Bloomberg School of Public Health (Bell and Dominici, 2008). 

Figure 6-32 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 6-33 Map of spatially dependent ozone-mortality coefficients for 8-h max 

ozone concentrations using summer data. 
Draft – Do Not Cite or Quote 6-215 September 2011

6.6.2.3 Interaction 

1 The terms effect modification and interaction are often used interchangeably, but 

2 theoretically they represent different concepts. Although interactions can lead to either 

3 antagonistic or synergistic effects, most studies attempt to identify potential factors that 

4 interact synergistically with O3 to increase the risk of mortality. Within this section, 

5 interactive effects are defined as time-varying covariates, such as temperature and 

6 copollutants that are included in 1st stage time-series regression models. To date, only a 

7 few time-series studies have investigated the potential interaction between O3 exposure 

8 and copollutants or weather variables. This can be attributed to the moderate to high 

9 correlation between O3 and these covariates, which makes such investigations 

10 methodologically challenging. 

11 Ren et al. (2008) examined the possible synergistic effect between O3 and temperature on 

12 mortality in the 60 largest eastern U.S. communities from the NMMAPS data during the 

13 warm months (i.e., April to October) from 1987-2000. This analysis was restricted to the 

14 eastern areas of the U.S. (i.e., Northeast, Industrial Midwest and Southeast) because a 

15 previous study which focused specifically on the eastern U.S. found that 

16 temperature-mortality patterns differ between the northeast and southeast regions 

17 possibly due to climatic differences (Curriero et al., 2002). To examine possible 

18 geographic differences in the interaction between temperature and O3, Ren et al. (2008)

19 further divided the NMMAPS regions into the Northeast, which included the Northeast 

20 and Industrial Midwest regions (34 cities), and the Southeast, which included the 

21 Southeast region (26 cities). The potential synergistic effects between O3 and temperature 

22 were examined using two different models. Model 1 included an interaction term in a 

23 Generalized Additive Model (GAM) for O3 and maximum temperature (3-day avg values 

24 were used for both terms) to examine the bivariate response surface and the pattern of 

25 interaction between the two variables in each community. Model 2 consisted of a 

26 Generalized Linear Model (GLM) that used interaction terms to stratify by “low,”

27 “moderate,” and “high” temperature days using the first and third quartiles of temperature 

28 as cut-offs to examine the percent increase in mortality in each community. Furthermore, 

29 a two-stage Bayesian hierarchical model was used to estimate the overall percent increase 

30 in all-cause mortality associated with short-term O3 exposure across temperature levels 

31 and each region using model 2. The same covariates were used in both model 1 and 2. 

32 The bivariate response surfaces from model 1 suggest possible interactive effects 

33 between O3 and temperature although the interpretation of these results is not 

34 straightforward due to the high correlation between these terms. The apparent interaction 

35 between temperature and O3 as evaluated in model 2 varied across geographic regions. In 

36 the northeast region, a 20 ppb increase in 24-h avg O3 concentrations at lag 0-2 was 

37 associated with an increase of 4.49% (95% posterior interval [PI]: 2.39, 6.36%), 6.21% 
Draft – Do Not Cite or Quote 6-216 September 2011

1 (95% PI: 4.47, 7.66%) and 12.8% (95% PI: 9.77, 15.7%) in mortality at low, moderate 

2 and high temperature levels, respectively. The corresponding percent increases in 

3 mortality in the southeast region were 2.27% (95% PI: -2.23, 6.46%) for low temperature, 

4 3.02% (95% PI: 0.44, 5.70%) for moderate temperature, and 2.60% (95% PI: -0.66, 

5 6.01%) for high temperature.

6 When examining the relationship between temperature and O3-related mortality, the 

7 results reported by Ren et al. (2008) (i.e., higher O3-mortality risks on days with higher 

8 temperatures) may appear to contradict the results of Bell and Dominici (2008) described 

9 earlier (i.e., communities with higher temperature have lower O3-mortality risk 

10 estimates). However, the observed difference in results can be attributed to the 

11 interpretation of effect modification in a second-stage regression which uses long-term 

12 average temperatures, as was performed by Bell and Dominici (2008), compared to a 

13 first-stage regression that examines the interaction between daily temperature and O3-

14 related mortality. In this case, the second-stage regression results from Bell and Dominici 

15 (2008) indicate that a city with lower temperatures, on average, tend to show a stronger 

16 O3 mortality effect, whereas, in the first-stage regression performed by Ren et al. (2008), 

17 the days with higher temperature tend to show a larger O3-mortality effect. This observed 

18 difference may in part reflect the higher air conditioning use in communities with higher 

19 long-term average temperatures. Therefore, the findings from Ren et al. (2008) indicating 

20 generally lower O3 risk estimates in the southeast region where the average temperature is 

21 higher than in the northeast region is consistent with the regional results reported by Bell 

22 and Dominici (2008). As demonstrated by the results from both Ren et al. (2008) and 

23 Bell and Dominici (2008) caution is required when interpreting results from studies that 

24 examined interactive effects using two different approaches because potential effect 

25 modification as suggested in a second-stage regression generally does not provide 

26 evidence for a short-term interaction examined in a first-stage regression. Overall, further 

27 examination of the potential interactive (synergistic) effects of O3 and covariates in time28 series regression models is required to more clearly understand the factors that may 

29 influence O3 mortality risk estimates.

6.6.2.4 Evaluation of the Ozone-Mortality C-R Relationship and 

Related Issues

30 Evaluation of the O3-mortality concentration-response relationship is not straightforward 

31 because the evidence from multicity studies (using log-linear models) suggests that 

32 O3-mortality associations are highly heterogeneous across regions. In addition, there are 

33 numerous issues that may influence the shape of the O3-mortality concentration-response 

34 relationship that warrant examination including: multi-day effects (distributed lags), 
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1 potential adaptation, mortality displacement (i.e., hastening of death by a short period), 

2 and the exposure metric used to compute risks (e.g., 1-h daily max versus 24-h avg). The 

3 following section presents the recent studies identified that conducted an initial 

4 examination of these issues.

Multiday Effects, Mortality Displacement, and Adaptation

5 The pattern of positive lagged associations followed by negative associations in a 

6 distributed lag model may be considered an indication of “mortality displacement” (i.e., 

7 deaths are occurring in frail individuals and exposure is only moving the day of death to a 

8 day slightly earlier). Zanobetti and Schwartz (2008b) examined this issue in 48 U.S. cities 

9 during the warm season (i.e., June-August) for the years 1989-2000. In an initial analysis, 

10 the authors applied a GLM to examine same-day O3-mortality effects, and in the model 

11 included an unconstrained distributed lag for apparent temperature to take into account 

12 the effect of temperature on the day death occurred and the previous 7 days. To examine 

13 mortality displacement Zanobetti and Schwartz (2008b) refit models using two 

14 approaches: an unconstrained and a smooth distributed lag each with 21-day lags for O3. 

15 In this study, all-cause mortality as well as cause-specific mortality (i.e., cardiovascular, 

16 respiratory, and stroke) were examined for evidence of mortality displacement. The 

17 authors found a 0.96% (95% CI: 0.60, 1.30%) increase in all-cause mortality across all 48 

18 cities for a 30 ppb increase in 8-h max O3 concentrations at lag 0 whereas the combined 

19 estimate of the unconstrained distributed lag model (lag 0-20) was 1.54% (95% CI: 0.15, 

20 2.91%). Similarly, when examining the cause-specific mortality results (Table 6-49), 

21 larger risk estimates were observed for the distributed lag model compared to the lag 

22 0 day estimates. However, for stroke a slightly larger effect was observed at lags 4-20 

23 compared to lags 0-3 suggesting a larger window for O3-induced stroke mortality. This is 

24 further supported by the sum of lags 0 through 20 days showing the greatest effect. 

25 Overall, these results suggest that estimating the mortality risk using a single day of O3

26 exposure may underestimate the public health impact, but the extent of multi-day effects 

27 appear to be limited to a few days. This is further supported by the shape of the combined 

28 smooth distributed lag (Figure 6-34). It should be noted that the proportion of total 

29 variation in the effect estimates due to the between-cities heterogeneity, as measured by 

I

2 30 statistic, was relatively low (4% for the lag 0 estimates and 21% for the distributed 

31 lag), but 21 out of the 48 cities exhibited null or negative estimates. As a result, the 

32 estimated shape of the distributed lag cannot be interpreted as a general form of lag 

33 structure of associations applicable to all the cities included in this analysis. 
Draft – Do Not Cite or Quote 6-218 September 2011

Table 6-49 Estimated effect of a 10 ppb increase in 8-h max ozone 

concentrations on mortality during the summer months for singleday 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 from American Thoracic Society, Zanobetti and Schwartz (2008b). 

1 Samoli et al. (2009) also investigated the temporal pattern of mortality 

2 effects in response to short-term exposure to O3 in 21 European cities that were included 

3 in the APHEA2 project. Using a method similar to Zanobetti and Schwartz (2008b), the 

4 authors applied unconstrained distributed lag models with lags up to 21 days in each city 

5 during the summer months (i.e., June through August) to examine the effect of O3 on all6 cause, 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 

14 effects on respiratory mortality were extended for a period of two weeks. However, for

15 all-cause and cardiovascular mortality, the 21-day distributed lag models yielded null or 

16 (non-significant) negative estimates (Table 6-50). Figure 6-35 shows the distributed lag 

17 coefficients for all-cause mortality, which exhibit a declining trend and negative 
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1 coefficients beyond 5-day lags. The authors’ interpretation of these results was that 

2 “using single-day exposures may have overestimated the effects on all-cause and 

3 cardiovascular mortality, but underestimated the effects on respiratory mortality.” Thus, 

4 the results in part suggest evidence of mortality displacement for all-cause and 

5 cardiovascular mortality. 

Source: Reprinted with permission of American Thoracic Society (Zanobetti and Schwartz, 2008b). 

The triangles represent the percent increase in all-cause mortality for a 10 ppb increase in 8-h max ozone concentrations at each 

lag while the shaded areas are the 95% point-wise confidence intervals. 

Figure 6-34 Estimated combined smooth distributed lag for 48 U.S. cities 

during the summer months.
Draft – Do Not Cite or Quote 6-220 September 2011

Table 6-50 Estimated percent increase in cause-specific mortality (and 95% 

CIs) for a 10-μg/m3 increase in maximum 8-h ozone during 

June-August, 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)

Fixed effects Random effects

% (95% CI) % (95% CI)

Total mortality

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 mortality

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 mortality

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)

Source: Used with permission from 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, a reported 

9 percent excess risk for mortality for a 40 ppb increase in 1-h max O3 concentrations for 

10 lag 0-1, lag 1, and the distributed lag model (lag 0-2) was 2.70% (95% CI: 1.02, 4.40%), 

11 1.42% (95% CI: 0.08, 2.78%), and 3.02% (95% CI: 1.10, 4.89%), respectively. Thus, the 

12 observed associations appear to occur over a short time period, (i.e., a few days). 

13 Similarly, the Public Health and Air Pollution in Asia (PAPA) study (Wong et al., 2010)

14 also examined multiple lag days (i.e., lag 0, lag 0-1, and lag 0-4), and although it did not 

15 specifically examine mortality displacement it does provide additional evidence 

16 regarding the timing of mortality effects proceeding O3 exposure. In a combined analysis 

17 using data from all four cities examined (Bangkok, Hong Kong, Shanghai, and Wuhan), 

18 excess risk estimates at lag 0-4 were larger than those at lag 0 or lag 0-1 in both fixed and 
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1 random effect models (results not presented quantitatively). The larger risk estimates at 

2 lag 0-4 can primarily be attributed to the strong associations observed in Bangkok and 

3 Shanghai. However, it is worth noting that Bangkok differs from the three Chinese cities 

4 included in this analysis in that it has a tropical climate and does not exhibit seasonal 

5 patterns of mortality. As a result, Wong et al. (2010) examined the O3-mortality 

6 associations at lag 0-1 in only the three Chinese cities and found that risk estimates were 

7 slightly reduced from 2.26% (95% CI: 1.36, 3.16) in the 4 city analysis to 1.84% (0.77, 

8 2.86) in the 3 city analysis for a 30 ppb increase in 8-h max O3 concentrations. Overall, 

9 the PAPA study further supports the observation of the APHENA study that associations 

10 between O3 and mortality occur over a relatively short-time period, but also indicates that 

11 it may be difficult to interpret O3-mortality associations across cities with different 

12 climates and mortality patterns.

13 When comparing the studies that explicitly examined the potential for mortality 

14 displacement in the O3-mortality relationship, the results from Samoli et al. (2009), which 

15 provide evidence that suggests mortality displacement, are not consistent with those 

16 reported by Zanobetti and Schwartz (2008b). However, the shapes of the estimated 

17 smooth distributed lag associations are similar (Figure 6-34 and Figure 6-35). A closer 

18 examination of these figures shows that in the European data beyond a lag of 5 days the 

19 estimates remain negative whereas in the U.S. data the results remain near zero for the 

20 corresponding lags. These observed difference could be due the differences in the model 

21 specification between the 2 studies, specifically the use of: an unconstrained distributed 

22 lag model for apparent temperature up to 7 previous days (Zanobetti and Schwartz, 

23 2008b) versus a linear term for humidity and an unconstrained distributed lag model of 

24 temperature up to 3 previous days (Samoli et al., 2009); and natural cubic splines with 

25 2 df per season (Zanobetti and Schwartz, 2008b) versus dummy variables per month per 

26 year to adjust for season (Samoli et al., 2009). It is important to note, that these 

27 differences in model specification may have also influenced the city-to-city variation in 

28 risk estimates observed in these two studies (i.e., homogenous estimates across cities in 

29 Zanobetti and Schwartz (2008b) and heterogeneous estimates across cities in Samoli et 

30 al. (2009). Overall, the evidence of mortality displacement remains unclear, but Samoli et 

31 al. (2009), Zanobetti and Schwartz (2008b), and Katsouyanni et al. (2009) all suggest that 

32 the positive associations between O3 and mortality are observed mainly in the first 

33 few days after exposure. 
Draft – Do Not Cite or Quote 6-222 September 2011

Source: Reprinted with permission of BMJ Group (Samoli et al., 2009). 

The triangles represent the percent increase in all-cause mortality for a 10 μg/m3 increase in 8-h max ozone concentrations at 

each lag; the shaded area represents the 95% CIs. 

Figure 6-35 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 (Table 6-

11 51). The estimated O3 mortality risk estimate at lag 0 was found to be highest in the 

12 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% 
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[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 6-51 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: Reprinted with permission from BioMed Central Ltd. (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%) 

10 compared to July (1.96%) appears to support the existence of an adaptive response. 

11 However, unlike an individual’s adaptive response to decrements in lung function from 

12 short-term O3 exposure, an examination of mortality prevents a direct observation of 

13 adaptation. Rather, for mortality the adaptation hypothesis is tested with a tacit 

14 assumption that, whatever the mechanism for O3-induced mortality, the risk of death 

 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 6-47 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 6-224 September 2011

1 from short-term O3 exposure is reduced over the course of the summer months through 

2 repeated exposures. This idea would translate to a smaller population that would die from 

3 O3 exposure towards the end of summer. This may complicate the interpretation of the 

4 distributed lag coefficients with long lag periods because the decreased coefficients may 

5 reflect diminished effects of the late summer, rather than diminished effects that are 

6 constant across the summer. These inter-twined issues need to be investigated together in 

7 future research. 

Ozone-Mortality Concentration-Response Relationship and Threshold 

Analyses

8 Several of the recent studies evaluated have applied a variety of statistical approaches to 

9 examine the shape of the O3-mortality C-R relationship and whether a threshold exists. 

10 The approach used by Bell et al. (2006) consisted of applying four statistical models to 

11 the NMMAPS data, which included 98 U.S. communities for the period 1987-2000. 

12 These models included: a linear analysis (i.e., any change in O3 concentration can be 

13 associated with mortality) (Model 1); a subset analysis (i.e., examining O3-mortality 

14 relationship below a specific concentration, ranging from 5 to 60 ppb) (Model 2); a 

15 threshold analysis (i.e., assuming that an association between O3 and mortality is 

16 observed above a specific concentration and not below it, using the threshold values set at 

17 an increment of 5 ppb between 0 to 60 ppb and evaluating a presence of a local minima in 

18 AICs computed at each increment) (Model 3); and nonlinear models using natural cubic 

19 splines with boundary knots placed at 0 and 80 ppb, and interior knots placed at 20 and 

20 40 ppb (Model 4). A two-stage Bayesian hierarchical model was used to examine these 

21 models and O3-mortality risk estimates at the city-level in the first stage analysis and 

22 aggregate estimates across cities in the 2nd stage analysis using the average of 0- and 

23 1-day lagged 24-h avg O3 concentrations. The results from all of these models suggest 

24 that if a threshold exists it does so well below the current O3 NAAQS. When restricting 

25 the analysis to all days when the current 8-h standard (i.e., 84 ppb daily 8-h max) is met 

26 in each community, Bell et al. (2006) found there was still a 0.60% (95% PI: 0.30, 

27 0.90%) increase in mortality per 20 ppb increase in 24-h avg O3 concentrations at lag 0-1. 

28 Figure 6-36 shows the combined C-R curve obtained using the nonlinear model (Model 

29 4). Although these results suggest the lack of threshold in the O3-mortality relationship, it 

30 is difficult to interpret such a curve because it does not take into consideration the 

31 heterogeneity in O3-mortality risk estimates across cities. 
Draft – Do Not Cite or Quote 6-225 September 2011

Source: Bell et al. (2006). 

Figure 6-36 Estimated combined C-R curve for ozone and nonaccidental 

mortality 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 O3 concentrations above a value are so 

8 limited that the variability around the central estimate is increased. In the Smith et al. 

9 (2009b) analysis this observation was initially observed at 45 ppb, with the largest 

10 variability at 60 ppb; however, unlike Bell et al. (2006) where 73% of days are excluded 

11 when subsetting the data to less than 20 ppb, the authors do not detail the number of days 

12 of data included in the subset analyses at higher concentrations. In addition to the subset 

13 analysis, Smith et al. (2009b) examined the shape of the C-R curve using a piecewise 

14 linear approach with cutpoints at 40 ppb, 60 ppb, and 80 ppb. Smith et al. (2009b) found 

15 that the shape of the C-R curve is similar to that reported by Bell et al. (2006) (Figure 

16 6-36), but argue that slopes of the β for each piece of the curve are highly variable with 
Draft – Do Not Cite or Quote 6-226 September 2011

1 the largest variation in the 60-80 ppb range. However, the larger variability around the β 

2 between 60-80 would be expected due to the small number of days with O3

3 concentrations within that range in an all-year analysis. This result is consistent with that 

4 observed by Bell et al. (2006), which is presented in Figure 6-36.

5 The APHENA project (Katsouyanni et al., 2009) also analyzed the Canadian and 

6 European datasets (the U.S. data were analyzed for PM10 only) for evidence of a 

7 threshold, using the threshold analysis method (Model 3) applied in Bell et al.’s (2006)

8 study described above. There was no evidence of a threshold in the Canadian data (i.e., 

9 the pattern of AIC values for each increment of a potential threshold value varied across 

10 cities, most of which showed no local minima). Likewise, the threshold analysis 

11 conducted using the European data also showed no evidence of a threshold. 

12 The PAPA study, did not examine whether a threshold exists in the O3-mortality C-R 

13 relationship, but instead the shape of the C-R curve individually for each city (Bangkok, 

14 Hong Kong, Shanghai, and Wuhan) (Wong et al., 2010). Using a natural spline smoother 

15 with 3df for the O3 term, Wong et al. (2010) examined whether non-linearity was present 

16 by testing the change in deviance between this smoothed, non-linear, model and an 

17 unsmoothed, linear, model with 1 df. For each of the cities, both across the full range of 

18 the O3 distribution and specifically within the range of the 25th to 75th percentile of each 

19 city’s O3 concentrations (i.e., a range of 9.7 ppb to 60.4 ppb across the cities) there was 

20 no evidence of a non-linear relationship in the O3-mortality C-R curve. It should be noted 

that the range of the 25th to 75th 21 percentiles in all of the cities, except Wuhan, was lower 

than that observed in the U.S. using all-year data where the range from the 25th to 75th 22

23 percentiles is 30 ppb to 50 ppb (Table 3-6). 

24 Additional threshold analyses were conducted using NMMAPS data, by Xia and Tong 

25 (2006) and Stylianou and Nicolich (2009). Both studies used a new statistical approach 

26 developed by Xia and Tong (2006) to examine thresholds in the O3 mortality C-R 

27 relationship. The approach consisted of an extended GAM model, which accounted for 

28 the cumulative and nonlinear effects of air pollution using a weighted cumulative sum for 

29 each pollutant, with the weights (non-increasing further into the past) derived by a 

30 restricted minimization method. The authors did not use the term distributed lag model, 

31 but their model has the form of distributed lag model, except that it allows for nonlinear 

32 functional forms. Using NMMAPS data for 1987-1994 for 3 U.S. cities (Chicago, 

33 Pittsburgh, and El Paso), Xia and Tong (2006) found that the extent of cumulative effects 

34 of O3 on mortality were relatively short. While the authors also note that there was 

35 evidence of a threshold effect around 24-h avg concentrations of 25 ppb, the threshold 

36 values estimated in the analysis were sometimes in the range where data density was low. 

37 Thus, this threshold analysis needs to be replicated in a larger number of cities to confirm 
Draft – Do Not Cite or Quote 6-227 September 2011

1 this observation. It should be noted that the model used in this analysis did not include a 

2 smooth function of days to adjust for unmeasured temporal confounders, and instead 

3 adjusted for season using a temperature term. As a result, these results need to be viewed 

4 with caution because some potential temporal confounders (e.g., influenza) do not always 

5 follow seasonal patterns of temperature. 

6 Stylianou and Nicolich (2009) examined the existence of thresholds following an 

7 approach similar to Xia and Tong (2006) for all-cause, cardiovascular, and respiratory 

8 mortality using data from NMMAPS for nine major U.S. cities (i.e., Baltimore, Chicago, 

9 Dallas/Fort Worth, Los Angeles, Miami, New York, Philadelphia, Pittsburgh, and 

10 Seattle) for the years 1987-2000. The authors found that PM10 and O3 were the two 

11 important predictors of mortality. Stylianou and Nicolich (2009) found that the estimated 

12 O3-mortality risks varied across the nine cities with the models exhibiting apparent 

13 thresholds, in the 10-45 ppb range for O3. However, given the city-to-city variation in 

14 risk estimates, combining the city-specific estimates into an overall estimate complicates 

15 the interpretation of a threshold. Unlike the Xia and Tong (2006) analysis, Stylianou and 

16 Nicolich (2009) included a smooth function of time to adjust for seasonal/temporal 

17 confounding, which could explain the difference in results between the two studies. 

18 In conclusion, the evaluation of the O3-mortality C-R relationship did not find any 

19 evidence that supports a threshold in the relationship between short-term exposure to O3

20 and mortality within the range of O3 concentrations observed in the U.S. Additionally, 

21 recent evidence suggests that the shape of the O3-mortality C-R curve remains linear 

22 across the full range of O3 concentrations. However, the studies evaluated demonstrated 

23 that the heterogeneity in the O3-mortality relationship across cities (or regions) 

24 complicates the interpretation of a combined C-R curve and threshold analysis. Given the 

25 effect modifiers identified in the mortality analyses that are also expected to vary 

26 regionally (e.g., temperature, air conditioning prevalence), a national or combined 

27 analysis may not be appropriate to identify whether a threshold exists in the O3-mortality 

28 C-R relationship. Overall, the studies evaluated support a linear O3-mortality C-R 

29 relationship and continue to support the conclusions from the 2006 O3 AQCD, which 

30 stated that “if a population threshold level exists in O3 health effects, it is likely near the 

31 lower limit of ambient O3 concentrations in the United States” (U.S. EPA, 2006b).

6.6.2.5 Associations of Cause-Specific Mortality and Short-term 

Ozone Exposure

32 In the 2006 O3 AQCD, an evaluation of studies that examined cause-specific mortality 

33 found consistent positive associations between short-term O3 exposure and 
Draft – Do Not Cite or Quote 6-228 September 2011

1 cardiovascular mortality, with less consistent evidence for associations with respiratory 

2 mortality. The majority of the evidence for associations between O3 exposure and cause3 specific mortality were from single-city studies, which had small daily mortality counts 

4 and subsequently limited statistical power to detect associations. 

5 New multicity studies evaluated in this review build upon and confirm the associations 

6 between short-term O3 exposure and cause-specific mortality identified in the 2006 O3

7 AQCD (U.S. EPA, 2006b) (Figure 6-37; Table 6-52). In APHENA, a multicontinent 

8 study that consisted of the NMMAPS, APHEA2 and Canadian multicity datasets, 

9 consistent positive associations were reported for both cardiovascular and respiratory 

10 mortality in all-year analyses when focusing on the natural spline model with 8 df/year 

11 (Section 6.6.2.1). The associations between O3 exposure and cardiovascular and 

12 respiratory mortality in all-year analyses were further supported by the multicity PAPA 

13 study (Wong et al., 2010). Cardiovascular mortality associations persisted in analyses 

14 restricted to the summer season with evidence for stronger respiratory mortality 

15 associations compared to those observed in all-year analyses (Figure 6-37; Table 6-52). 

16 Additional multicity studies from the U.S. (Zanobetti and Schwartz, 2008b) and Europe 

17 (Stafoggia et al., 2010; Samoli et al., 2009) that conducted summer season analyses also 

18 found strong associations between O3 exposure and cardiovascular and respiratory 

19 mortality. 

20 Of the studies evaluated, only the APHENA study (Katsouyanni et al., 2009) and an 

21 Italian multicity study (Stafoggia et al., 2010) conducted an analysis of the potential for

22 copollutant confounding of the O3 cause-specific mortality relationship. When focusing 

23 on the natural spline model with 8 df/year and lag 1 results (as discussed in Section 

24 6.6.2.1), the APHENA study found that O3 cause-specific mortality risk estimates were 

25 fairly robust to the inclusion of PM10 in copollutant models in the European dataset with 

26 more variability in the U.S. and Canadian datasets (i.e., copollutant risk estimates 

27 increased and decreased for respiratory and cardiovascular mortality). In summer season 

28 analyses cardiovascular O3 mortality risk estimates were robust in the European dataset 

29 and attenuated but remained positive in the U.S. datasets; whereas, respiratory O3

30 mortality risk estimates were attenuated in the European dataset and robust in the U.S. 

31 dataset. The authors did not examine copollutant models during the summer season in the 

32 Canadian dataset (Figure 6-30; Table 6-49). Interpretation of these results requires 

33 caution; however, due to the different PM sampling schedules employed in each of these 

34 study locations (i.e., primarily every-6th day in the U.S. and Canadian datasets and every35 day in the European dataset). The results of the summer season analyses from the 

36 APHENA study (Katsouyanni et al., 2009) are consistent with those from a study of 10 

37 Italian cities during the summer months (Stafoggia et al., 2010). Stafoggia et al. (2010)

38 found that cardiovascular (14.3% [95% CI: 6.7, 22.4%]) and cerebrovascular (8.5% [95% 
Draft – Do Not Cite or Quote 6-229 September 2011

1 CI: 0.06, 16.3%]) mortality O3 effect estimates were robust to the inclusion of PM10 in 

2 copollutant models (14.3% [95% CI: 6.7, 23.1%] and 7.3% [95% CI: -1.2, 16.3], 

3 respectively), while respiratory mortality O3 effects estimates (17.6% [95% CI: 1.8, 

4 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 ozone concentrations. Red 

= cardiovascular; blue = respiratory; closed circles = all-year analysis; and open circles = summer-only analysis. An “a” represents 

studies from the 2006 ozone 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 ozone concentrations (Section 6.2.7.2).

Figure 6-37 Percent increase in cause-specific mortality. 

Study

Bell et al. (2005; 74345)a

Wong et al. (2010; 732535)

Katsouyanni et al. (2009; 199899)

Gryparis et al. (2004; 57276)a

Samoli et al. (2009; 195855)

Zanobetti and Schwartz (2008; 101596)

Stafoggia et al. (2010; 625034)

Katsouyanni et al. (2009; 199899)

Bell et al. (2005; 74345)a

Wong et al. (2010; 732535)

Katsouyanni et al. (2009; 199899)

Gryparis et al. (2004; 57276)a

Zanobetti and Schwartz (2008; 101596)

Katsouyanni et al. (2009; 199899)

Samoli et al. (2009; 195855)

Stafoggia et al. (2010; 625034)

Katsouyanni et al. (2009; 199899)

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 6-230 September 2011

Table 6-52 Corresponding effect estimates for Figure 6-37

Study Location Ages Lag Avg Time %Increase (95% CI)

Cardiovascular

All-year

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

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

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)

Summer

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) 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 the case of respiratory 

4 mortality are strengthened, in the summer season. Although copollutant analyses of 

5 cause-specific mortality are limited, the APHENA study found that O3 cause-specific 
Draft – Do Not Cite or Quote 6-231 September 2011

1 mortality risk estimates were fairly robust to the inclusion of PM10 in copollutant models 

2 in the European dataset, which is supported by the results from Stafoggia et al. (2010). 

3 Additionally, APHENA found that O3 cause-specific mortality risk estimates were 

4 moderately to substantially sensitive (e.g., increased or attenuated) to inclusion of PM10

5 in the U.S. and Canadian datasets. However, the mostly every-6th-day sampling schedule 

6 for PM10 in the U.S. and Canadian datasets greatly reduced their sample size and limits 

7 the interpretation of these results. 

6.6.3 Summary and Causal Determination

8 The evaluation of new multicity studies that examined the association between short-term 

9 O3 exposure and mortality found evidence which supports the conclusions of the 2006 O3

10 AQCD. These new studies reported consistent positive associations between short-term 

11 O3 exposure and all-cause (nonaccidental) mortality, with associations being stronger 

12 during the warm season, as well as additional support for associations between O3

13 exposure and cardiovascular and respiratory mortality. 

14 New studies further examined potential confounders (e.g., copollutants and seasonality) 

15 of the O3-mortality relationship. Because the PM-O3 correlation varies across regions, 

16 due to the difference in PM chemical constituents, interpretation of the combined effect 

17 of PM on the relationship between O3 and mortality is not straightforward. Unlike 

18 previous studies that were limited to primarily examining the confounding effects of 

19 PM10, the new studies expanded their analyses to include multiple PM indices (e.g., PM10, 

20 PM2.5, and PM components). An examination of copollutant models found evidence that 

21 associations between O3 and all-cause mortality were robust to the inclusion of PM10 or 

22 PM2.5 (Stafoggia et al., 2010; Katsouyanni et al., 2009; Bell et al., 2007), while other 

23 studies found evidence for a modest reduction (~20-30%) when examining PM10 (Smith 

24 et al., 2009b). Additional evidence suggests potential sensitivity (e.g., increases and 

25 attenuation) of O3 mortality risk estimates to copollutants by age group or cause-specific 

26 mortality (e.g., respiratory and cardiovascular) (Stafoggia et al., 2010; Katsouyanni et al., 

27 2009). An examination of PM components, specifically sulfate, found evidence for 

28 reductions in O3-mortality risk estimates in copollutant models (Franklin and Schwartz, 

29 2008). Overall, across studies, the potential impact of PM indices on O3-mortality risk 

30 estimates tended to be much smaller than the variation in O3-mortality risk estimates 

31 across cities suggesting that O3 effects are independent of the relationship between PM 

32 and mortality. Although some studies suggest that O3-mortality risk estimates may be 

33 confounded by PM or its chemical components the interpretation of these results requires 

34 caution due to the limited PM datasets used as a result of the every-3rd- and 6th-day PM 

35 sampling schedule. When examining the potential for seasonal confounding of the 
Draft – Do Not Cite or Quote 6-232 September 2011

1 O3-mortality relationship it was observed that the extent of smoothing or the methods 

2 used for adjustment can influence O3 risk estimates because of the opposing seasonal 

3 trends of O3 and mortality when not instituting enough degrees of freedom to control for 

4 temporal/seasonal trends (Katsouyanni et al., 2009).

5 The multicity studies evaluated in this review also examined the regional heterogeneity 

6 observed in O3-mortality risk estimates. These studies provide evidence which suggests 

7 generally higher O3-mortality risk estimates in northeastern U.S. cities with some regions 

8 showing no associations between O3 exposure and mortality (e.g., Southwest, Urban 

9 Midwest) (Smith et al., 2009b; Bell and Dominici, 2008). Multicity studies that examined 

10 individual- and community-level characteristics identified characteristics that may 

11 explain the observed regional heterogeneity in O3-mortality risk estimates as well as 

12 characteristics of populations potentially susceptible to O3-related health effects. An 

13 examination of community-level characteristics found an increase in the O3-mortality risk 

14 estimates in cities with higher unemployment, percentage of the population 

15 Black/African-American, percentage of the working population that uses public 

16 transportation, lower temperatures, and lower prevalence of central air conditioning 

17 (Medina-Ramón and Schwartz, 2008). Additionally, a potential interactive, or synergistic, 

18 effect on the O3-mortality relationship was observed when examining differences in the 

19 O3-mortality association across temperature levels (Ren et al., 2008). An examination of 

20 individual-level characteristics found evidence that older age, female sex, Black race, 

21 having atrial fibrillation, SES indicators (i.e., educational attainment, income level, and 

22 employment status), and out-of hospital deaths, specifically in those individuals with 

23 diabetes, are modify O3-mortality associations (Cakmak et al., 2011; Stafoggia et al., 

24 2010; Medina-Ramón and Schwartz, 2008), and may increase susceptibility to O3-related 

25 mortality. Overall, additional research is warranted to further confirm whether these 

26 characteristics, individually or in combination, can explain the observed regional 

27 heterogeneity. 

28 Additional studies were evaluated that examined factors, such as multi-day effects, 

29 mortality displacement, adaptation, and whether a threshold exists in the O3-mortality 

30 relationship, which may influence the shape of the O3-mortality C-R curve. An 

31 examination of multiday effects in a U.S. and European multicity study found conflicting 

32 evidence for mortality displacement, but both studies suggest that the positive 

33 associations between O3 and mortality are observed mainly in the first few days after 

34 exposure (Samoli et al., 2009; Zanobetti and Schwartz, 2008b). A U.S. multicity study 

35 found evidence of an adaptive response to O3 exposure, with the highest risk estimates 

36 earlier in the O3 season (i.e., July) and diminished effects later (i.e., August) (Zanobetti 

37 and Schwartz, 2008a). However, the evidence of adaptive effects has an implication for 

38 the interpretation of multi-day effects, and requires further analysis. Analyses that 
Draft – Do Not Cite or Quote 6-233 September 2011

1 specifically focused on the O3-mortality C-R relationship supported a linear O3-mortality 

2 relationship and found no evidence of a threshold within the range of O3 concentrations 

3 in the U.S., but did observe evidence for potential differences in the C-R relationship 

4 across cities (Katsouyanni et al., 2009; Stylianou and Nicolich, 2009; Bell et al., 2006). 

5 Collectively, these studies support the conclusions of the 2006 O3 AQCD that “if a 

6 population threshold level exists in O3 health effects, it is likely near the lower limit of 

7 ambient O3 concentrations in the U.S.”

8 In conclusion, the new epidemiologic studies build upon and confirm the associations 

9 reported in the 2006 O3 AQCD. Additionally, these new studies have provided additional 

10 information regarding key uncertainties previously identified including the potential 

11 confounding effects of copollutants and seasonal trend, individual- and community-level 

12 factors that may lead to increased risk of O3-induced mortality and the heterogeneity in 

13 O3-mortality risk estimates, and continued evidence of a linear no-threshold C-R 

14 relationship. Although some uncertainties still remain, the collective body of evidence is 

15 sufficient to conclude that there is likely to be a causal relationship between short16 term O3 exposure and mortality.

6.7 Overall Summary

17 The evidence reviewed in this chapter describes the recent findings regarding the health 

18 effects of short-term exposure to ambient O3 concentrations. Table 6-53 provides an 

19 overview of the causal determinations for each of the health categories evaluated.

Table 6-53 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

Mortality Likely to be a causal relationship
Draft – Do Not Cite or Quote 6-234 September 2011

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