CHAPTER 2

AIR QUALITY AND HEALTH EFFECTS

Introduction

Ambient Air Quality Standards

Comparison to Other U.S. Areas

Current Air Quality Summary
Chapter 2 Air Quality and Health Effects

2 - 1

INTRODUCTION

In this chapter, 1995 air quality in the South Coast Air Basin (Basin), and in the portions 

of the Mojave Desert and Salton Sea Air Basins (MDAB/SSAB) monitored by the South 

Coast Air Quality Management District (District), is compared to state and federal 

ambient air quality standards. (The MDAB and SSAB were part of the Southeast Desert 

Air Basin or SEDAB until May 30, 1996, when the California Air Resources Board 

adopted the boundaries and names of the two new air basins.) For those pollutants which 

exceeded federal standards, maps which compare 1995 air quality in different areas of 

the Basin have been included.

Nationwide air quality for 1994 is also briefly summarized in this chapter. A comparison 

of air quality in the Basin to other U.S. and California urban areas is presented in the 

following pages.

AMBIENT AIR QUALITY STANDARDS

Ambient air quality standards for ozone, carbon monoxide, nitrogen dioxide, sulfur 

dioxide, particulate matter (PM10), and lead have been set by both the California state and 

federal governments. The state has also set standards for sulfate and visibility. The 

ambient air quality standards for each of these pollutants and their effects on health are 

summarized in Table 2-1.

In 1995 the Basin exceeded the federal standards for ozone, carbon monoxide, and PM10

on a total of 116 days. In recent years the Basin has recorded many more days exceeding 

the federal standards than any other area of the U.S.

COMPARISON TO OTHER U.S. AREAS

The Basin’s severe air pollution problem is a consequence of the combination of 

emissions from the nation’s second largest urban area and especially adverse 

meteorological conditions. The average wind speed for Los Angeles is the lowest of the 

nation’s ten largest urban areas. In addition, the summertime maximum mixing height 

(an index of how well pollutants can be dispersed vertically in the atmosphere) in 

Southern California averages the lowest in the U.S. The Southern California area is also 

an area with abundant sunshine, which drives the photochemical reactions which form 

pollutants such as ozone.
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TABLE 2-1

Ambient Air Quality Standards

STATE STANDARD FEDERAL PRIMARY 

STANDARD

MOST RELEVANT EFFECTS

AIR 

POLLUTANT

CONCENTRATION/

AVERAGING TIME

CONCENTRATION/

AVERAGING TIME

Ozone 0.09 ppm, 1-hr. avg. > 0.12 ppm, 1-hr avg.> (a) Short-term exposures: (1) Pulmonary 

function decrements and localized lung edema 

in humans and animals. (2) Risk to public 

health implied by alterations in pulmonary 

morphology and host defense in animals; (b) 

Long-term exposures: Risk to public health 

implied by altered connective tissue 

metabolism and altered pulmonary morphology 

in animals after long-term exposures and 

pulmonary function decrements in chronically 

exposed humans; (c) Vegetation damage; (d) 

Property damage 

Carbon 

Monoxide

9.0 ppm, 8-hr avg. >

20 ppm, 1-hr avg. >

9 ppm, 8-hr avg.>

35 ppm, 1-hr avg.>

(a) Aggravation of angina pectoris and other 

aspects of coronary heart disease; (b) 

Decreased exercise tolerance in persons with 

peripheral vascular disease and lung disease; 

(c) Impairment of central nervous system 

functions; (d) Possible increased risk to fetuses

Nitrogen 

Dioxide

0.25 ppm, 1-hr avg. > 0.053 ppm, ann. avg.> (a) Potential to aggravate chronic respiratory 

disease and respiratory symptoms in sensitive 

groups; (b) Risk to public health implied by 

pulmonary and extra-pulmonary biochemical 

and cellular changes and pulmonary structural 

changes; (c) Contribution to atmospheric 

discoloration

Sulfur Dioxide 0.04 ppm, 24-hr avg.> 

0.25 ppm, 1-hr. avg. >

0.03 ppm, ann. avg.>

0.14 ppm, 24-hr avg.>

(a) Bronchoconstriction accompanied by 

symptoms which may include wheezing, 

shortness of breath and chest tightness, during 

exercise or physical activity in persons with 

asthma

Suspended 

Particulate 

Matter (PM10)

30 μg/m3, ann. geometric mean >

50 μg/m3, 24-hr average>

50 μg/m3, annual

arithmetic mean >

150μg/m3, 24-hr avg.>

(a) Excess deaths from short-term exposures 

and exacerbation of symptoms in sensitive 

patients with respiratory disease; (b) Excess 

seasonal declines in pulmonary function, 

especially in children 

Sulfates 25 μg/m3, 24-hr avg. >= (a) Decrease in ventilatory function; (b) 

Aggravation of asthmatic symptoms; (c) 

Aggravation of cardio-pulmonary disease; (d) 

Vegetation damage; (e) Degradation of 

visibility; (f) Property damage

Lead 1.5 μg/m3, 30-day avg. >= 1.5 μg/m3, calendar quarter> (a) Increased body burden; (b) Impairment of 

blood formation and nerve conduction

VisibilityReducing

Particles

In sufficient amount such that the 

extinction coefficient is greater than 

0.23 inverse kilometers (to reduce 

the visual range to less than 10 

miles) at relative humidity less than 

70 percent, 8-hour average (10am -

6pm)

Visibility impairment on days when relative 

humidity is less than 70 percent
Chapter 2 Air Quality and Health Effects

2 - 3

In the Basin, exceedances of the federal ozone standard are recorded largely during the 

spring to early fall months. By contrast, exceedances of the federal carbon monoxide 

standard occur in late fall and winter. Exceedances of the federal 24-hour PM10 standard 

can occur throughout the year, but occur most frequently in fall and winter. Although 

there are changes in emissions by season, the observed variations in pollutant 

concentrations are largely a result of seasonal differences in weather conditions.

In 1995, the federal standard for ozone was exceeded at one or more Basin locations on 

27 percent of days and the federal carbon monoxide standard was exceeded on 4 percent 

of days. The federal PM10 standard was exceeded on 10 percent of the days sampled.

1

Figure 2-1 shows maximum pollutant concentrations in 1994 for the South Coast Air 

Basin compared to other urban areas in the U.S. and California. Maximum 

concentrations in these other large U.S. urban areas exceeded the federal ozone and PM10

standards in some instances, and did not exceed the carbon monoxide standard. 

However several other areas in the country did report exceedances of the carbon 

monoxide standard. In California, some of the other large urban areas also exceeded the 

PM10 and ozone standards, but did not exceed the carbon monoxide standard.

The maximum second highest 1-hour average ozone concentration in the Basin was 

nearly twice the federal standard. New York and Houston exceeded by much less of a 

margin, and Philadelphia and Washington barely exceeded, while Chicago did not 

exceed the standard. Though New York is a much larger urban area than Houston, the 

maximum ozone concentration for Houston equaled that of New York. Houston, like 

Los Angeles, is an area with abundant sunshine which creates favorable conditions for 

the photochemical reactions that yield ozone and other photochemical pollutants. In 

California, San Francisco did not exceed the ozone standard, while the San Diego, 

Sacramento and Oxnard-Ventura metropolitan areas each exceeded the standard. Both 

the San Diego and Oxnard-Ventura metropolitan areas are subject to higher ozone levels 

due to transport from the South Coast Air Basin.

The maximum 8-hour average carbon monoxide concentration in the Basin was over one 

and a half times the federal standard. The standard was not exceeded in the other major 

urban areas depicted in Figure 2-1 in this comparison. 

Maximum annual average PM10 concentrations recorded in the Basin, New York, and 

Philadelphia exceeded the federal PM10 standard, and San Diego exceeded very narrowly. 

Only Philadelphia recorded a higher PM10 than the Basin, as a consequence of nearby 

stationary source emissions.

 

1

PM10 is sampled every sixth day, unlike the gaseous pollutants such as ozone and carbon monoxide which are sampled 

continuously.
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2 - 4

A) U.S. Metropolitan Areas Compared to the South Coast Air Basin

B) California Metropolitan Areas Compared to the South Coast Air Basin

FIGURE 2-1

1994 Air Quality 

Maximum Pollutant Concentrations as Percentages of the Federal Standard

In 1994, no location in the Basin or any other area of the U.S. exceeded the nitrogen 

dioxide standard. The Los Angeles County portion of the Basin was the last area of the 

U.S. to exceed the standard, but has remained in compliance since 1991. Sulfur dioxide 

concentrations in the Basin continued to remain well below federal standards, and were 

lower than those in the urban areas of the Eastern U.S. Concentrations of sulfur dioxide 

in urban areas in the Eastern U.S. have generally been higher than those in the Basin due 

to the use of fuels such as coal which have relatively high sulfur content.

CURRENT AIR QUALITY SUMMARY

Figure 2-2 shows the maximum pollutant concentrations for 1995 as percentages of the 

state and federal standards. The maximum ozone concentration exceeded the federal 

standard by the widest margin, with a maximum 1-hour average (0.26 ppm recorded in 

the Central San Bernardino Mountain area) that was 200 percent of the federal standard. 

The highest 8-hour average carbon monoxide concentration recorded (13.86 ppm in the 

South Central Los Angeles County area) was 146 percent of the federal carbon monoxide 

standard. The maximum 24-hour average PM10 (219 μg/m3in the Metropolitan Riverside 

County area) was 145 percent of the federal 24-hour standard, and the maximum annual 

average PM10 (69 μg/m3recorded in Metropolitan Riverside County) was 138 percent of 

the federal annual PM10 standard. The maximum sulfate concentration (26.3 μg/m3in

Metropolitan Riverside County) was 105 percent of the state sulfate standard.

Concentrations of other pollutants remained below the standards. The maximum annual 

average nitrogen dioxide concentration (0.0464 ppm in the East San Gabriel Valley and 
Chapter 2 Air Quality and Health Effects

2 - 5

Northwest San Bernardino Valley areas) was 87 percent of the federal standard, while 

the maximum annual average sulfur dioxide concentration (0.0030 ppm in South Central 

Los Angeles County) was 10 percent of the federal standard. The maximum quarterly 

average lead concentration recorded at any District air monitoring station was 4 percent 

of the federal standard. However, higher concentrations of lead (40 percent of the 

standard) were recorded at special monitoring locations immediately adjacent to 

stationary sources.

Figure 2-3 shows the percent of days on which the federal and state standards were 

exceeded in 1995 at the Basin locations which exceeded most frequently. The federal 

ozone standard was exceeded on a maximum of 20 percent of days (in the East San 

Gabriel Valley area of Los Angeles County), and the federal carbon monoxide standard 

was exceeded on a maximum of 4 percent of days (in South Central Los Angeles 

County). Exceedances of the federal 24-hour PM10 standard were recorded on a 

maximum of 7 percent of days sampled (Metropolitan Riverside County), while the state 

sulfate standard was exceeded on a maximum of 2 percent of days sampled 

(Metropolitan Riverside County).

0

50

100

150

200

250

300

Ozone

(1-Hour)

Carbon

Monoxide

(8-Hour)

Nitrogen

Dioxide

 (1-Hour/

Annual)

Sulfur

Dioxide

 (1-Hour/

Annual)

PM10

(Annual)

Sulfate*

 (24-Hour)

Lead**

(Month/

Quarter)

State Standard

Federal Standard

Percent of Standard

Standard

* There is no federal standard for sulfate.

** Higher lead concentrations w ere recorded at special monitoring sites immediately adjacent to sources. 

 The Maximum onthly average concentration w as .62 μg/m3, and the maximum quarterly average w as .60 μg/m3, 

 both recorded at Southeast Los Angeles County.

FIGURE 2-2

1995 Maximum Pollutant Concentrations as Percent of Federal and State Standards
FINAL 1997 AQMP

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0

10

20

30

40

50

60

70

Ozone

(1-Hour)

Carbon

Monoxide

(8-Hour)

Nitrogen

Dioxide

(1-Hour)

Sulfur

Dioxide

(Annual/

1-Hour)

PM10

(Annual)

Sulfate*

 (24-Hour)

Lead**

(Month/

Quarter)

State Standard

Federal Standard

Percent of Days Exceeding

* There is no federal standard for sulfate, and no short-term federal standard for nitrogen dioxide.

** Percent of months for state lead standard and percent of quarters for federal lead standard.

State 

Standard 

Met

Standards 

Met

Standards 

Met

FIGURE 2-3

1995 Percent of Days/Months/Quarters Exceeding Federal and 

State Standards at Most Affected Locations

Detailed analyses of current air quality and statistics for all monitoring areas are 

contained in Appendix II. The following sections present summary information on 

health effects and how frequently, and by how much of a margin, different areas of the 

Basin and MDAB/SSAB exceeded the federal and state ambient air quality standards in 

1995.

Ozone (O3) Specific Information

Health Effects

Individuals exercising outdoors, children and people with preexisting lung disease such 

as asthma and chronic pulmonary lung disease are considered to be the most susceptible 

sub-groups for ozone effects. Short-term exposures (lasting for a few hours) to ozone at 

levels typically observed in Southern California can result in breathing pattern changes, 

reduction of breathing capacity, increased susceptibility to infections, inflammation of 

the lung tissue, and some immunological changes. In recent years, a correlation between 

elevated ambient ozone levels and increases in daily hospital admission rates, as well as 

mortality, has also been reported.

Ozone exposure under exercising conditions is known to increase the severity of the 

above mentioned observed responses. Similarly, animal studies suggest that exposures to 

a combination of pollutants which include ozone is more toxic than exposure to ozone 
Chapter 2 Air Quality and Health Effects

2 - 7

alone. Although lung volume and resistance changes observed after a single exposure 

diminish with repeated exposures, biochemical and cellular changes appear to persist, 

which can lead to subsequent lung structural changes. The cancer causing potential of 

ozone exposure identified in some studies needs further evaluation to draw any definitive 

conclusions.

Air Quality

In 1995, the South Coast Air Quality Management District monitored ozone 

concentrations at 33 locations in the Basin and MDAB/SSAB. In the Basin, the 

maximum ozone concentration (0.26 ppm recorded in the central San Bernardino 

Mountain area) was 200 percent of the federal standard and 260 percent of the state 

standard. Los Angeles, Riverside and San Bernardino Counties had maxima above the 

stage I episode level (0.20 ppm). Ozone concentrations at Orange County locations 

remained below the episode level, but the maximum exceeded the health advisory level 

(0.15 ppm). Table 2-2 shows maximum ozone concentrations by Basin and County.

Maximum ozone concentrations in the MDAB/SSAB areas monitored by the District 

were lower than in the Basin. However, the maximum concentration in the Riverside 

County SSAB (0.16 ppm in the Coachella Valley area) still exceeded the health advisory 

level.

TABLE 2-2

1995 Maximum Ozone Concentrations by Basin and County

Basin/County Maximum

1-Hr Avg. 

ppm

Percent of 

Federal 

Standard

Area

South Coast Air Basin

Los Angeles Co. 0.22 169 East San Gabriel Valley

Orange Co. 0.16 123 North Orange County

Riverside Co. 0.21 162 Metropolitan Riverside Co.

San Bernardino Co. 0.26 200 Cent San Bernardino Mtn

Mojave Desert/Salton Sea Area Basins

Los Angeles Co. 0.14 108 Antelope Valley

Riverside Co. 0.16 123 Coachella Valley

The number of days exceeding the federal standard varied widely by area (Figure 2-4). 

Areas along the immediate coast did not exceed the federal standard, due in large part to 

the prevailing sea breeze which transports polluted air inland before high ozone 

concentrations can be reached. In addition, some inland areas which are remote from 
FINAL 1997 AQMP

2 - 8

urban areas of the Basin did not exceed the standard. The standard was exceeded most 

frequently in the inland valleys extending from East San Fernando Valley through the 

San Gabriel Valley into the Riverside-San Bernardino area, and in the adjacent 

mountains. The East San Gabriel Valley recorded the greatest number of exceedances of 

the federal standard (73 days), health advisory level (48 days) and Stage I episode level 

(9 days). The greatest number of state standard exceedances (123 days) was recorded in 

the East San Bernardino Valley area.

FIGURE 2-4

Ozone -1995

Number of Days Exceeding the Federal Standard

(1-hour average ozone > 0.12 ppm)

Carbon Monoxide (CO) Specific Information

Health Effects

A consistent association between increasing ambient CO levels and excess admissions 

for heart diseases, such as congestive heart failure, is observed in many cities across the 

United States. Individuals with a deficient blood supply to the heart are more susceptible 

to the adverse effects of CO exposure. The effects observed include earlier onset of 

M IL ES

0

2 5

SOUTH COAST

AIR BASIN (SCAB)

COUNTY LINES

JUNE1996 VERSION

Interval of 10

Interval of 20

0

20

60 70

40

40 20

0

Anaheim

San Bernardino

Riverside

Long Beach

Los Angeles

SCAQMD

AIR MONITORING NETWORK

AIR MONITORING

STATION
Chapter 2 Air Quality and Health Effects

2 - 9

chest pain with exercise, and electrocardiograph changes indicative of worsening oxygen 

supply to the heart.

Inhaled CO has no direct toxic effect on the lungs, but exerts its effect on tissues by 

interfering with oxygen transport by competing with oxygen to combine with

hemoglobin present in the blood to form carboxyhemoglobin (COHb). Hence, 

conditions with an increased demand for oxygen supply can be adversely affected by 

exposure to CO. Examples include fetal development, chronic hypoxemia (oxygen 

deficiency) as seen in high altitudes, anemia, and diseases involving heart and blood 

vessels.

Reduction in birth weight and impaired neurobehavioral development have been 

observed in animals chronically exposed to CO resulting in COHb levels similar to those 

observed in smokers.

Air Quality

Carbon monoxide concentrations were measured at 22 locations in the Basin and 

neighboring MDAB/SSAB areas in 1995. Table 2-3 shows the 1995 maximum 8-hour 

average concentrations of carbon monoxide by air basin and county. The highest 

concentration recorded in the Basin (13.86 ppm in South Central Los Angeles County) 

was 146 percent of the federal standard and 152 percent of the state standard. Maximum 

carbon monoxide concentrations in Orange, Riverside, and San Bernardino County areas 

of the Basin did not exceed the standards.

Maxima for the MDAB/SSAB were much lower. Carbon monoxide levels in both Los 

Angeles and Riverside County MDAB/SSAB areas remained well below the federal 

standard.

Figure 2-5 shows the number of days exceeding the federal standard in 1995. 

Exceedances were limited to the areas of Los Angeles County where vehicular traffic is 

most dense, with the maximum number of exceedances (13 days exceeding the federal 

standard and 15 days exceeding the state standard) recorded in the South Central Los 

Angeles County area.

TABLE 2-3

1995 Maximum Carbon Monoxide Concentrations by Basin and County

Basin/County Maximum

8-Hr Avg.

ppm

Percent of 

Federal 

Standard

Area

South Coast Air Basin
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Los Angeles 13.86 146 South Central L.A. Co.

Orange 8.00 84 Central Orange Co.

Riverside 6.50 68 Metropolitan Riverside Co.

San Bernardino 6.25 66 Cent San Bernardino V.

Mojave Desert/Salton Sea Area Basins

Los Angeles 4.87 51 Antelope Valley

Riverside 1.50 16 Coachella Valley

FIGURE 2-5

Carbon Monoxide - 1995

Number of Days Exceeding the Federal Standard

(8-hour average CO  9.5 ppm)

Particulate Matter (PM10) Specific Information

Health Effects

A consistent correlation between elevated ambient PM10 levels and an increase in 

mortality rates, respiratory infections, number and severity of asthma attacks and the 

number of hospital admissions has been observed in different parts of the United States 

and various areas around the world. Although the concentrations and/or combinations of 

M IL ES

0 25

SOUTH COAST

AIR BASIN (SCAB)

COUNTY LINES

AIR MONITORING

STATION

JUNE 1996VERSION

Interval of 5

Interval of10

0

5

10

Anaheim

San Bernardino

Riverside

Long Beach

Los Angeles

SCAQMD

AIR MONITORINGNETWORK
Chapter 2 Air Quality and Health Effects

2 - 11

pollutants are significantly different in these studies, most of the PM10 levels recorded in 

these studies are lower than those observed in the South Coast Air Basin.

In recent years, some studies have reported an association between long-term exposure to 

air pollution dominated by fine particles and increased mortality, reduction in life-span, 

and the possibility of an increased incidence of cancer.
FINAL 1997 AQMP

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Daily fluctuations in PM10 levels have also been related to hospital admissions for acute 

respiratory conditions in children, to school and kindergarten absences, to a decrease in 

respiratory lung volumes in normal children and to increased medication use in children 

and adults with asthma.

The elderly, people with pre-existing respiratory and/or cardiovascular disease and 

children appear to be susceptible to the effects of PM10. There is a growing consensus 

among the scientific community that the fine fraction of PM10 is relatively more toxic 

than the coarse fraction and is responsible for the majority of effects observed.

Air Quality

PM10 concentrations were monitored at 21 locations by the South Coast Air Quality 

Management District in 1995. Maximum 24-hour and annual average concentrations are 

shown in Tables 2-4 and 2-5. The maximum 24-hour PM10 concentration recorded in the 

Basin (219 μg/m3in the Metropolitan Riverside County area) was 145 percent of the 

federal standard and 429 percent of the state standard. The maximum was associated 

with high winds, but other exceedances of the federal standard not associated with high 

winds were recorded. Maximum concentrations in all four of the Basin counties 

exceeded the federal 24-hour standard. The maximum annual average PM10 (69 μg/m3in 

Metropolitan Riverside County) was 138 percent of the federal annual standard. The 

federal annual standard was exceeded in Riverside and San Bernardino Counties but not 

in Los Angeles or Orange Counties. The much more stringent state annual standard was 

exceeded in all areas of the Basin.

In 1995, both annual and 24-hour maximum concentrations of PM10 in the Los Angeles 

County portion of the MDAB were below the federal standards. However in the 

Riverside County area of the SSAB, both standards were exceeded. The maximum 24-

hour PM10 concentration (199 μg/m3in the Coachella Valley) was 132 percent of the 

federal 24-hour standard, and was associated with high winds in the desert areas. The 

maximum annual average PM10 concentration (52.0 μg/m3in the Coachella Valley) was 

104 percent of the federal annual standard. It should be noted that the exclusion of the 

high wind event day reduces the annual average to 49.5 μg/m3, or 99 percent of the 

standard.
Chapter 2 Air Quality and Health Effects

2 - 13

TABLE 2-4

1995 Maximum 24-hour Average PM10 Concentrations by Basin and County

Basin/County Maximum

24-Hr Avg.

g/m3

Percent of 

Federal 

Standard

Area

South Coast Air Basin

Los Angeles 177 104 Pomona/Walnut Valley

Orange 172 114 Central Orange Co.

Riverside 219 145 Metropolitan Riverside Co.

San Bernardino 178 118 Cent San Bernardino V.

Mojave Desert/Salton Sea Area Basins

Los Angeles 61 40 Antelope Valley

Riverside 199 132 Coachella Valley

Riverside, corrected* 133* 88* Coachella Valley

*Adjusted for one high-wind natural event day.

TABLE 2-5

1995 Maximum Annual Average PM10 Concentrations by Basin and County

Basin/County Annual

Average

g/m3

Percent of 

Federal 

Standard

Area

South Coast Air Basin

Los Angeles 49.1 98 East San Gabriel Valley

Orange 43.5 86 Central Orange Co.

Riverside 69.0 138 Metropolitan Riverside Co.

San Bernardino 61.0 122 Cent. San Bernardino V.

Mojave Desert/Salton Sea Area Basins

Los Angeles 25.6 52 Antelope Valley

Riverside 52.0 104 Coachella Valley

Riverside, corrected* 49.5* 99* Coachella Valley

*Adjusted for one high-wind natural event day.

Figure 2-6 shows the percent of days exceeding the federal 24-hour average PM10

standard in 1995. (PM10 is normally sampled every sixth day, and for this reason is 

reported in terms of the percent of days sampled which exceeded the standard.) The 

federal standard was exceeded in parts of all four Basin counties, with the greatest 
FINAL 1997 AQMP

2 - 14

percent of days exceeding recorded in the vicinity of the Metropolitan Riverside County 

area. No exceedances were recorded in the coastal Los Angeles and Orange County 

areas, or in the inland areas of the Basin most removed from urban areas. However, still 

further inland (east of the area on the map) the SSAB’s Coachella Valley area did record 

an exceedance of the standard, which was associated with high winds. The more 

stringent state 24-hour PM10 standard was exceeded at all District monitoring locations in 

the Basin and MDAB/SSAB.

Anaheim

San Bernardino

M IL ES

0 25

JU N E 19 96 V ER SIO N

Long Beach

Riverside

Los Angeles

5

2

0

IN TER VAL S O F 2

I N TER VA LS OF 5

SCAQMD

AIR MONITORING NETWORK

AIR MONITORING

STATION

COUNTY LINES

SOUTH COAST

AIR BASIN (SCAB)

FIGURE 2-6

PM10 - 1995

Percent of Days Exceeding the Federal Standard 

(24-hour average PM10 > 150 μg/m3)

Figure 2-7 shows the 1995 annual average PM10 concentration. The federal standard was 

exceeded in the areas of Riverside and San Bernardino Counties in and around the 

Metropolitan Riverside County area. Most areas of the Basin did not exceed the federal 

annual PM10 standard. However the more stringent state annual PM10 standard was 

exceeded throughout most of the Basin and in part of the SSAB (Riverside County’s 

Coachella Valley area).
Chapter 2 Air Quality and Health Effects

2 - 15

M IL ES

0

2 5

SOUTH COAST

AIR BASIN (SCAB)

COUNTY LINES

AIR MONITORING

STATION

J UNE 1996 VE RSION

20

Feder al Standard

30

30

20

40

50

60

Los Angeles

Riverside

Anaheim

San Bernardino

Long Beach

SC A QM D

AI R M ON ITOR IN G NE TWO R K

FIGURE 2-7

PM10 - 1995

Annual Average Concentration Compared to Federal Standard

(Federal standard = 50 μg/m3, annual arithmetic mean)

Nitrogen Dioxide (NO2) Specific Information

Health Effects

Population-based studies suggest that an increase in acute respiratory illness, including 

infections and respiratory symptoms in children (not infants), is associated with longterm exposures to NO2 at levels found in homes with gas stoves, which are higher than 

ambient levels found in Southern California. Increase in resistance to air flow and 

airway contraction without any effect on lung volumes (breathing capacity) is observed 

after short-term exposure to NO2 in healthy subjects. Larger decreases in lung volumes 

are observed in individuals with asthma and/or chronic obstructive pulmonary disease 

(e.g., chronic bronchitis, emphysema) than in healthy individuals, following exposure to 

lower levels of NO2, indicating the greater susceptibility of these sub-groups.

In animals, exposure to levels of NO2 considerably higher than ambient concentrations 

results in increased susceptibility to infections, possibly due to the observed changes in 

cells involved in maintaining immune functions. The severity of lung tissue damage 
FINAL 1997 AQMP

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associated with high levels of ozone exposure increases when animals are exposed to a 

combination of ozone and NO2.

Air Quality

In 1995, nitrogen dioxide concentrations were monitored at 24 locations. No area of the 

Basin, MDAB or SSAB exceeded the federal or state standards for nitrogen dioxide. 

Maximum annual average concentrations for 1995 are shown in Table 2-6. The highest 

annual average concentrations recorded in the Basin (0.0464 ppm in the East San Gabriel 

Valley and Northwest San Bernardino Valley areas) were 87 percent of the federal 

standard, while the highest concentration recorded in the MDAB/SSAB was 42 percent 

of the standard. The Basin has not exceeded the federal standard for nitrogen dioxide 

since 1991, when the Los Angeles County portion of the Basin recorded the last 

exceedance of the standard in any U.S. county.

The state standard was not exceeded at any District monitoring location in 1995. The 

highest 1-hour average concentration recorded (0.24 ppm in Central Los Angeles) was 

92 percent of the state standard.

TABLE 2-6

1995 Maximum Nitrogen Dioxide Concentrations by Basin and County

Basin/County Maximum

Annual Avg.

ppm

Percent of 

Federal 

Standard

Area

South Coast Air Basin

Los Angeles 0.0464 87 East San Gabriel Valley

Orange 0.0391 73 North Orange Co.

Riverside 0.0306 57 Metropolitan Riverside Co.

San Bernardino 0.0464 87 Northwest San Bernardino V.

Mojave Desert/Salton Sea Area Basins

Los Angeles 0.0193 36 Antelope Valley

Riverside 0.0223 42 Coachella Valley

Sulfur Dioxide (SO2) Specific Information

Health Effects

Even an exposure of a few minutes to low levels of SO2 can result in airway constriction 

in some asthmatics. All asthmatics are sensitive to the effects of SO2. In asthmatics, 

increase in resistance to air flow, as well as reduction in breathing capacity leading to 
Chapter 2 Air Quality and Health Effects

2 - 17

severe breathing difficulties, are observed after acute exposure to SO2. In contrast, 

healthy individuals do not exhibit similar acute responses even after exposure to higher 

concentrations of SO2.

Animal studies suggest that despite SO2 being a respiratory irritant, it does not cause 

substantial acute or chronic toxicity at ambient concentrations. However, very high 

levels of exposure can cause lung edema (fluid accumulation), lung tissue damage, and 

sloughing off of cells lining the respiratory tract.

Some population-based studies indicate that the mortality and morbidity effects 

associated with fine particles show a similar association with ambient SO2 levels. In 

these studies, efforts to separate the effects of SO2 from fine particles have not been 

successful. It is not clear whether the two pollutants act synergistically or whether one 

pollutant alone is the predominant factor.

Air Quality

No exceedances of federal or state standards for sulfur dioxide occurred in 1995 at any of 

the nine District locations monitored. Though sulfur dioxide concentrations remain well 

below the standards, sulfur dioxide is a precursor to sulfate, which is a component of 

PM10. Standards for both sulfate and PM10 were exceeded in 1995.

Maximum concentrations of sulfur dioxide for 1995 are shown in Table 2-7. The 

maximum 24-hour average sulfur dioxide (0.018 ppm, recorded in South Coastal Los 

Angeles County) was 13 percent of the federal 24-hour standard. The maximum annual 

average concentration (0.0030 ppm in the South Central Los Angeles County area) was 

10 percent of the federal annual standard.

Sulfur dioxide was not measured at MDAB/SSAB sites in 1995. Historical 

measurements showed concentrations to be well below standards and monitoring has 

been discontinued.

The more stringent state 1-hour standard was last exceeded in 1990, due to a breakdown 

at a Basin refinery (the first such exceedance since 1984). In 1995, the maximum 1-hour 

average sulfur dioxide concentration (0.14 ppm in the South Coastal Los Angeles County 

area) recorded was 54 percent of the state standard.
FINAL 1997 AQMP

2 - 18

TABLE 2-7

1995 Maximum Sulfur Dioxide Concentrations by Basin and County

Basin/County Maximum

24-hr Avg.

ppm

Percent of 

Federal 

Standard

Area

South Coast Air Basin

Los Angeles 0.018 13 South Coastal L.A. Co.

Orange 0.010 7 North Orange Co.

Riverside 0.006 4 Metropolitan Riverside Co.

San Bernardino 0.010 7 Central San Bernardino V.

Mojave Desert/Salton Sea Area Basins

Los Angeles N.D.

Riverside N.D.

N.D. = No Data. Historical measurements indicate concentrations are below standard

Sulfates (SO4

=

) Specific Information

Health Effects

Most of the health effects associated with fine particles and sulfur dioxide at ambient 

levels are also attributable to sulfates. Thus, both mortality and morbidity effects are 

observable with an increase in ambient sulfate concentrations. However, efforts to 

separate the effects of sulfates from the effects of other pollutants, including ozone, have 

not been successful.

Clinical studies of asthmatics exposed to sulfuric acid suggest that adolescent asthmatics 

are probably a subgroup susceptible to acid aerosol exposure. Animal studies suggest 

that acidic particles such as sulfuric acid aerosol and ammonium bisulfate are probably 

more toxic than non-acidic particles like ammonium sulfate. Whether the effects are 

attributable to acidity or to particles remains unresolved. However, the severity of 

effects observed appears to be greater in population studies from the eastern United 

States and Canada, where sulfate concentrations are higher, than in the western United 

States.

Air Quality

In 1995, the state sulfate standard was exceeded in one area of the Basin (the 

Metropolitan Riverside County area) on 2 percent of days sampled. The maximum 

concentration recorded (26.3 μg/m3) was 105 percent of the state standard. Maximum 
Chapter 2 Air Quality and Health Effects

2 - 19

concentrations by air basin and county are shown in Table 2-8. No exceedances were 

recorded in Los Angeles, Orange, or San Bernardino Counties in 1995.

No sulfate data were obtained at MDAB/SSAB stations in 1995. Historical sulfate data 

showed concentrations in the MDAB/SSAB areas to be well below the standard, and 

measurements have been discontinued.

TABLE 2-8

1995 Maximum Sulfate Concentrations by Basin and County

Basin/County Maximum

24-hr Avg.

μg/m3

Percent of 

Federal 

Standard

Area

South Coast Air Basin

Los Angeles 20.4 82 South Coastal L.A. Co.

Orange 12.8 51 Central Orange Co.

Riverside 26.3 105 Metropolitan Riverside Co.

San Bernardino 13.4 54 Central San Bernardino V.

Mojave Desert/Salton Sea Area Basins

Los Angeles N.D.

Riverside N.D.

N.D. = No Data. Historical measurements indicate concentrations are below standard

Lead (Pb) Specific Information

Health Effects

Fetuses, infants, and children are more sensitive than others to the adverse effects of lead 

exposure. Exposure to low levels of lead can adversely affect the development and 

function of the central nervous system, leading to learning disorders, distractibility, 

inability to follow simple commands, and lower intelligence quotient. In adults, 

increased lead levels are associated with increased blood pressure. 

Lead poisoning can cause anemia, lethargy, seizures and death. It appears that there are 

no direct effects of lead on the respiratory system. Lead can be stored in the bone from 

early-age environmental exposure, and elevated blood lead levels can occur due to 

breakdown of bone tissue during pregnancy, hyperthyroidism (increased secretion of 

hormones from the thyroid gland) and osteoporosis (breakdown of bony tissue). Fetuses 

and breast-fed babies can be exposed to higher levels of lead because of previous 

environmental lead exposure of their mothers.
FINAL 1997 AQMP

2 - 20

Air Quality

The federal and state standards for lead were not exceeded in any area of the District in 

1995. There have been no violations of the standards at the District’s regular air 

monitoring stations since 1982 as a result of removal of lead from gasolines. However, 

special monitoring stations immediately adjacent to stationary sources of lead have 

recorded exceedances of the standards in very localized areas of the Basin as recently as 

1991 for the federal standard and 1994 for the state standard. Table 2-9 shows the 

maximum concentrations recorded in 1995.

The maximum quarterly average lead concentration (0.06 μg/m3at several Los Angeles 

County sites) recorded at District air monitoring stations was 4 percent of the federal 

standard. The highest quarterly average lead concentration (0.60 μg/m3in Southeast Los 

Angeles County) measured at special monitoring locations immediately adjacent to 

stationary sources of lead was 40 percent of the federal standard. 

The maximum monthly average lead concentration at the regular monitoring stations (.07 

μg/m3at several Los Angeles County locations) was 5 percent of the state standard, and 

the maximum at the special monitoring sites immediately adjacent to sources (0.62 μg/m3

in Southeast Los Angeles County) was 41 percent of the standard.

TABLE 2-9

1995 Maximum Lead Concentrations*by Basin and County

Basin/County Maximum

Quarterly 

Average.

g/m3

Percent of 

Federal 

Standard

Area

South Coast Air Basin

Los Angeles 0.06 4 Multiple Sites

Orange 0.04 3 Central Orange Co.

Riverside 0.04 3 Metropolitan Riverside Co.

San Bernardino 0.04 3 Central San Bernardino V.

Mojave Desert/Salton Sea Area Basins

Los Angeles N.D.

Riverside N.D.

N.D. = No Data. Historical measurements indicate concentrations are below standard

 

*

Higher concentrations of lead were recorded at special monitoring stations in the immediate vicinity of 

stationary sources of lead. The maximum concentration (quarterly average lead concentration 0.60 μg/m3in 

the Southeast Los Angeles County area) at the special monitoring sites was 40 percent of the federal 

standard.
Chapter 2 Air Quality and Health Effects

2 - 21

Visibility Specific Information

Air pollution induced visibility degradation in the Basin is due primarily to particulate 

matter. On some days, the presence of water droplets may contribute significantly to 

visibility reduction. Days for which this is true are removed by excluding days on which 

the relative humidity was greater than 70 percent from consideration when determining 

compliance with the standard

In 1995, visual range data were collected at two locations in the Basin. Both sites 

exceeded the state standard by a significant margin. The standard was exceeded on a 

maximum of 35 percent of days in the only area (East San Gabriel Valley area of Los 

Angeles County) for which complete data were available.

Summary

In 1995, the Basin continued to exceed federal and state standards for ozone, PM10, and 

carbon monoxide, and the state standards for sulfate and visibility. The MDAB/SSAB 

areas continued to exceed standards for ozone and PM10. However for PM10, the removal 

of one high wind natural event in the Coachella Valley results in MDAB/SSAB meeting 

the federal PM10 standards, but not the state PM10 standards.

The Basin exceeded one or more federal standards on nearly one third of the days of the 

year. Maximum concentrations of PM10 and carbon monoxide were nearly one and onehalf times the federal standards, and the maximum ozone concentration was twice the 

federal standard.