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 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.
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.
TABLE 2-1
Ambient Air Quality Standards
STATE STANDARD FEDERAL PRIMARY most relevant effects
STANDARD
AIR CONCENTRATION/ CONCENTRATION/
POLLUTANT AVERAGING TIME AVERAGING TIME
Ozone 0.09 ppm, 1-hr. avg. 0.12 ppm, 1-hr (a) Short-term exposures:
> avg.> (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 9.0 ppm, 8-hr avg. > 9 ppm, 8-hr avg.> (a) Aggravation of angina
Monoxide 20 ppm, 1-hr avg. > 35 ppm, 1-hr avg.> 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 0.25 ppm, 1-hr avg. 0.053 ppm, ann. (a) Potential to aggravate
Dioxide > avg.> 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 0.04 ppm, 24-hr 0.03 ppm, ann. (a) Bronchoconstriction
Dioxide avg.> avg.> accompanied by symptoms
0.25 ppm, 1-hr. avg. 0.14 ppm, 24-hr which may include
> avg.> wheezing, shortness of
breath and chest
tightness, during exercise
or physical activity in
persons with asthma
Suspended 30 µg/m3, ann. 50 µg/m3, annual (a) Excess deaths from
Particulat geometric mean > arithmetic mean > short-term exposures and
e Matter 50 µg/m3, 24-hr 150µg/m3, 24-hr exacerbation of symptoms
(PM10) average> avg.> 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 1.5 µg/m3, calendar (a) Increased body burden;
avg. >= quarter> (b) Impairment of blood
formation and nerve
conduction
Visibility In sufficient amount Visibility impairment on
- such that the days when relative
Reducing extinction humidity is less than 70
Particles coefficient is percent
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)
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.
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.
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/m3 in the Metropolitan
Riverside County area) was 145 percent of the federal 24-hour
standard, and the maximum annual average PM10 (69 µg/m3 recorded
in Metropolitan Riverside County) was 138 percent of the federal
annual PM10 standard. The maximum sulfate concentration (26.3
µg/m3 in 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 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).
FIGURE 2-2
1995 Maximum Pollutant Concentrations as Percent of Federal and
State Standards
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 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 Percent of Area
1-Hr Avg. Federal
ppm Standard
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 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 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 Percent of Area
8-Hr Avg. Federal
ppm Standard
South Coast Air Basin
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 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.
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/m3 in 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/m3 in 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/m3 in 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/m3 in 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.
TABLE 2-4
1995 Maximum 24-hour Average PM10 Concentrations by Basin and
County
Basin/County Maximum Percent of Area
24-Hr Avg. Federal
g/m3 Standard
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 Percent of Area
Average Federal
g/m3 Standard
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
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.
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).
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 long-term 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
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 Percent of Area
Annual Avg. Federal
ppm Standard
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 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.
TABLE 2-7
1995 Maximum Sulfur Dioxide Concentrations by Basin and County
Basin/County Maximum Percent of Area
24-hr Avg. Federal
ppm Standard
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 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 Percent of Area
24-hr Avg. Federal
µg/m3 Standard
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.
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/m3
at 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/m3
in 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/m3 at 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 Percent of Area
Quarterly Federal
Average. Standard
g/m3
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
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 one-half times the federal
standards, and the maximum ozone concentration was twice the federal
standard.
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