United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/4-81-014
February 1981
Air
1980 Ambient Assessment
Air Portion
-------
EPA-450/4-81-014
February 1981
1980 Ambient Assessment-Air Portion
by
William F. Hunt, Jr.,
and
Edward J. Lillis
U.S. Environmental Protection Agency
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
February 1981
-------
This report is issued by the Environmental Protection Agency to report technical data of
interest to a limited number of readers. Copies are available - in limited quantities - from
the Library Services Office (MD-35), U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711; or, for a fee, from the National Technical Infor-
mation Service, 5285 Port Royal Road, Springfield, Virginia 22161.
Publication No. EPA-450/4-81-014
11
-------
CONTENTS
Figures JY
1. Executive Summary 1-1
1.1 Introduction 1-1
1.2 Major findings 1-1
2. Current Air Quality Status and Trends for Major
Pollutants 2-1
2.1 Total suspended particulates 2-1
2.2 Sulfur dioxide 2-2
2.3 Carbon monoxide 2-7
2.4 Nitrogen dioxide 2-10
3. Air Monitoring Strategy 3-1
3.1 Network description 3-1
3.2 Improving the criteria pollutant air monitoring
strategy 3-2
3.3 Non-criteria air pollutant monitoring strategy 3-4
3.4 References 3-5
4. An Examination of Ozone 4-1
4.1 Monitoring status and trends 4-1
4.2 Technical issues associated with the
development of ozone SIP's 4-6
4.3 References 4-12
-------
FIGURES
Number Page
2-1 National Trend in Average Particulate Levels,
1960-1979 2-3
2-2 National Trend in Particulate Emissions,
1970-1979 2-3
2-3 Comparison of 1979 Particulate Levels in
Urban Areas With Populations Greater Than
500,000 2-4
2-4 National Trend in Average Sulfur Dioxide
Levels, 1964-1979 2-6
2-5 National Trend in Emissions of Sulfur Oxides,
1970-1979 2-6
2-6 Comparison of 1979 Sulfur Dioxide Levels in
Urban Areas With Populations Greater Than
500,000 2-8
2-7 National Trend in Average Carbon Monoxide
Levels, 1972-1979 2-9
2-8 National Trend in Emissions of Carbon Monoxide,
1970-1979 2-9
2-9 Comparison of 1979 Carbon Monoxide Levels in
Urban Areas With Populations Greater Than
500,000 2-11
2-10 National Trend in Average Nitrogen Dioxide
Levels, 1974-1979 2-13
2-11 National Trend in Emissions of Nitrogen Oxides,
1970-1979 2-13
2-12 Comparison of 1979 Nitrogen Dioxide Levels in
Urban Areas With Populations Greater Than
500,000 2-14
-------
FIGURES (continued)
Number Page
4-1 Ozone Status by County, 1979 4-3
4-2 National Trends in Daily Maximum Ozone Levels
for May Through October, 1974-1979 4-5
4-3 National Trend in Emissions of Volatile
Organic Compounds, 1970-1979 4-5
-------
1. EXECUTIVE SUMMARY
1.1 INTRODUCTION
The Air Portion focuses on three principal categories—current air quali-
ty status and trends for the major pollutants, the new air monitoring strategy,
and a detailed analysis of the pollutant ozone. The current air quality status
and trends chapter (Chapter 2) deals with the major pollutants: total suspend-
ed particulates (TSP), sulfur dioxide (S02)» carbon monoxide (CO) and nitrogen
dioxide (N0?). Ozone is treated in greater depth in Chapter 4. The report is
limited to dealing with the criteria pollutants only and does not address acid
deposition, toxic chemicals, and other air pollutants of concern. The princi-
pal reason for this is the recommendation in last year's report that comprehen-
sive, multi-pollutant, environmental reports are not necessary more than once
every three years. Reports in intermediate years should focus on a comprehen-
sive analysis of particular pollutants or information problems of primary in-
terest to the Agency. Since last year's Administrator's Report was comprehen-
sive, covering many pollutants, this report falls within an intermediate year
and follows this recommendation.
The statistical analyses which have been undertaken in Chapter 2, Current
Air Quality Status and Trends, and Chapter 4, An Examination of Ozone, comply
with the recommendations of the Intra-Agency Task Force on Air Quality Indica-
tors. The Task Force was established in January 1980 to recommend standardized
air quality indicators and statistical methodologies for presenting air quali-
ty status and trends. Its members represent the EPA Offices of Air, Noise, and
Radiation; Planning and Management; and Research and Development; as well as EPA
Region 5. Also participating were representatives from the President's Council
on Environmental Quality, the Office of Water and Waste Management, and EPA Re-
gion 4. Statistical summaries of pollutant-specific analyses are presented in
Appendix A and in the text of Chapter 4.
1.2 MAJOR FINDINGS
The major findings of the Air Portion of the Report on Ambient Monitoring
are summarized by chapter as follows:
1-1
-------
o CURRENT AIR QUALITY. STATUS AND TRENDS FOR MAJOR POLLUTANTS
Total Suspended Particulate (TSP) - Ambient levels of TSP decreased 32
percent during the 20-year period from 1960 to 1979. From 1970 to 1979, parti-
cipate emissions decreased 50 percent due to the control of industrial emis-
sions. Actual measurements of air quality during this period did not show the
same rate of improvement, however. The difference is attributed to low-level
fugitive emissions from industry and to windblown dust.
Sulfur Dioxide (S02) - Levels in S02 in the Nation's urban areas de-
creased 67 percent between 1964 and 1979. Improvement was most rapid between
1966 and 1971 due to an increased use of cleaner burning fuels in the residen-
tial, commercial, and industrial sectors of most urban areas. Local and state
air pollution regulations led to a switch from coal and high sulfur oil to
natural gas and low sulfur oil. Between 1970 and 1979 national average ambient
S02 levels dropped 44 percent, with a corresponding 7 percent decrease in sul-
fur oxide emissions during this time. The greater improvement in ambient S02
levels reflects S02 trends in urban areas, where most of the emission reduc-
tions have taken place. Emission reductions in urban areas were offset with
new sources, such as large fossil fuel power stations, located in rural areas.
Carbon Monoxide (CO) - Nationally, ambient CO levels in center-city lo-
cations showed a steady decline of approximately 6 percent per year or an over-
all reduction of 36 percent between 1972 and 1979. In contrast, CO emissions
show only a 7 percent decrease since 1972. The smaller reduction in CO emis-
sions is largely due to a 35 percent increase in total vehicles miles travelled
since 1970. The improvement in average CO concentrations is greater than the
reduction in CO emissions because the trend reflects levels at traffic-saturat-
ed monitoring sites in the center-city.
Nitrogen Dioxide (N02) - Ambient N02 levels increased 15 percent between
1975 and 1979 at 180 sites, corresponding to a 12 percent increase in emissions.
The increase in emissions is due to an increase in emissions from motor vehi-
cles and electric utility generating plants. While this trend is cause for con-
cern, it is important to realize that only 3 percent of the nitrogen dioxide
measurements at 933 sites with acceptable data exceeded the health-related
standard in 1979.
o IMPROVING THE AIR MONITORING STRATEGY
The existing criteria pollutant air monitoring strategy will vastly
improve the quality and representativeness of ambient monitoring data being
collected by State and local air pollution control agencies. By January 1981,
over 95 percent of the National Air Monitoring Stations (NAMS) will be fully
adhering to the Part 58 monitoring regulations with respect to network design,
siting, and quality assurance. Additional efforts, however, are needed to im-
prove the way data are used by EPA and State officials in decision making.
1-2
-------
The technical basis for establishing attain/nonattainment boundaries needs to
be strengthened to minimize inconsistencies which result among States and Re-
gions. More refined data analysis techniques must be developed and used in de-
termining air quality trends and progress in attaining NAAQS. The following
specific actions are being pursued:
Expand Data Base in One to Three Urban Areas - The purpose is to esta-
blish an enhanced long-term data base (air quality, emissions, and meteorology)
to be used in pinpointing the effects of source control and for refining and
validating diffusion models. EPA would provide funds to participating state or
local agencies to purchase and operate monitors necessary to supplement the
established NAMS/SLAMS network and to periodically update the emission invento-
ry. State or local agencies would be direct participants with EPA in the de-
sign of the studies and share in the analysis and interpretation of monitoring
information. The anticipated benefits of the cooperative effort would be a
more sound technical basis for using and interpreting air quality and modeling
information and improved NAAQS reviews.
Expand Program to Improve Models
- Continue a program of formal review of air quality simulation models
by the scientific and air quality management communities. The objectives of
the review are to insure that the models are founded on sound scientific bases
and function in an efficient, cost-effective manner to insure that appropriate
new arid superior models are promptly incorporated into the analytical system.
As models are developed which adhere to accepted theoretical and objective mea-
sures of performance, they will be incorporated into guidelines for models and
in regulations.
- Develop performance standards and performance measures for dispersion
models to provide an objective method of determining model reliability for
specific applications.
Expand Guidance for Interpreting and Using Monitoring/Modeling Data -
To reduce inconsistency in the uses of monitoring and modeling data and to im-
prove the technical bases for decision-making, additional guidance will be de-
veloped. The guidance will focus on when and how to use monitoring and model-
ing data to arrive at conclusions on attainment/nonattainment, on establishing
emission control targets to achieve NAAQS and in reviewing the impact of
sources. Additional emphasis will be given to developing and improving data
analysis and the use of probability concepts in decision-making.
Improve Monitoring Modeling Coordination
- SAMWG has been reestablished as a vehicle for identifying and resolv-
ing technical and administrative problems involving the use of monitoring data.
SAMWG will assume an important role in developing and reviewing workable moni-
toring and data interpretation guidelines for air program managers at the Fed-
eral, state, and local levels.
1-3
-------
-EPA Regions will be asked to participate more fully in developing and
implementing monitoring policies.
Develop a Non-Criteria Air Pollutant Air Monitoring Strategy - The
strategy will summarize the state of knowledge about monitoring methods and
quality assurance practices and outline a plan for monitoring specific pollu-
tants, sources, and geographic areas. A draft strategy report will be avail-
able by February 1981.
o AN EXAMINATION OF OZONE
Monitoring Status
- In 1979, ozone monitors at 475 sites in 282 counties across the na-
tion collected at least 50 percent of the possible days in the ozone season.
The majority of these counties are in major metropolitan areas. Approximately
111 million people live in the 282 counties or 54 percent of the 1970 total
U.S. population. Of these people, 81 million (73%) live in counties where
ozone levels were above the standard in 1979.
- Seventy-seven of the 282 counties did not violate the ozone standard
over the 4-year period 1976-1979.
- A comparison of counties east and west of the Mississippi River in
1979 shows 110 of 188 counties (59%) exceeding the standard in the East and 45
of 94 counties (48%) exceeding the standard in the West.
Air Quality and Emission Trends
- While no long-term nationwide ozone trend is revealed in the 6-year
period, 1974-1979, a short-term decrease o,f 5 percent is observed between 1978
and 1979.
- Most of the decrease took place in the Midwest, principally the EPA
Region 5 states (Ohio, Indiana, Illinois, Wisconsin, Minnesota and Michigan).
The median percent change in the EPA Region 5 states was 11.1 percent. The
large improvement in ozone levels in Regions 5 appears to be due to a combina-
tion of factors: more conducive meteorological conditions for ozone formation
in 1978, calibration changes, changes in quality assurance procedures, and re-
ductions in emissions.
- Outside Region 5 there appears to be no difference between the groups
of sites where calibration was or was not a factor. The overall median percent
change for the non-Region 5 sites is 3.1 percent, a value consistent with the
2.5 percent decrease in estimated nationwide VOC emissions.
Technical Issues Associated with Ozone SIP's
- In July 1982, 37 nonattainment areas that sought an extension to 1987
to attain the ozone standard will be required to submit revised SIP's. States
are currently in the process of collecting a good data base to develop SIP's.
1-4
-------
- Because of the complex nature of ozone, it has been difficult to de-
velop the technical tools needed to fully implement the air resource management
approach, which is prescribed by the Clean Air Act for SIP development.
- For various reasons, ozone models are limited and not widely accept-
ed. High priority Agency efforts have resulted in an improved model (e.g., the
Empirical Kinetic Modeling Approach (EKMA) having been recently proposed by EPA
for use in 1982 ozone SIP development.
- Validated photochemical dispersion models are generally believed to
be theoretically superior to other ozone models. However, photochemical disper-
sion models are data intensive and their results are affected by errors inher-
ent in the data input required by the model.
- The Northeast Regional Modeling Project (NERMP) is a multi-year,
multi-million dollar effort designed to better define the ozone transport prob-
lem in the North East Corridor, and to develop control strategies to provide
for attainment. The data collection phase of the project is currently underway.
Modeling results are projected to be available by 1986.
1-5
-------
2. CURRENT AIR QUALITY STATUS AND TRENDS FOR MAJOR POLLUTANTS
This chapter focuses on the current air quality status and trends of the
major pollutants: total suspended particulate (TSP), sulfur dioxide (S02),
carbon monoxide (CO) and nitrogen dioxide (N02). Ozone is treated in greater
depth in Chapter 4. The report deals with these criteria pollutants only and
does not address acid rain, toxic chemicals, carcinogens, and other air pollu-
tants which are now of mounting environmental concern.
The following sections discuss the current air quality and emission
trends by pollutant, their significance in terms of health, and the effective-
ness of various pollution abatement programs.
2.1 TOTAL SUSPENDED PARTICULATES
Total suspended particulate matter is the general term for particles
found in the atmosphere. In addition to soot and dust, particulates are com-
posed of organic matter and compounds containing sulfur, nitrogen, and metals.
Since particles are formed in the air as a result of various chemical and
physical processes, the chemical composition of particulates varies widely ac-
cording to location and time of year.
Ambient levels of total suspended particles decreased 32 percent during
the 20-year period from 1960 to 1979, an improvement of about 2 percent per
year. From 1970 to 1979, particulate emissions decreased 50 percent due to
the control of industrial emissions. Actual measurements of air quality dur-
ing this period did not show the same rate of improvement, however. The dif-
ference is attributed to low-level fugitive emissions from industry and to
windblown dust, factors which are difficult to quantify and do not usually ap-
pear in emission inventories. Dust levels remain fairly stable over time.
Some sections of the country show more improvement than others. The
Northeast, Great Lakes, and Southern states show high rates of improvement,
while Western states show little change. In the West, agricultural and nat-
ural sources continue to be major contributors of windblown particulates.
Despite the improvements, total suspended particulates remain a problem.
Approximately 21 percent of the Nation's population live in areas where the
annual standard is exceeded. Although there has been a nationwide decrease in
levels of total suspended particulate matter, there is evidence that atmospher-
ic levels of particulates in some size ranges are increasing. This is indicat-
2-1
-------
ed by the increasing levels of small participates such as sulfates, and the de-
terioration of visibility in the Southwest and non-urban areas of the East.
These patterns are consistent with the growth of emission sources outside large
metropolitan areas.
2.1.1 NATIONAL TREND IN AVERAGE PARTICULATE LEVELS. 1960-1979
Figure 2-1 shows year-by-year changes in average ambient paniculate lev-
els based on measurements taken throughout the country. Nationally, ambient
particulate levels measured in 95 urban areas with a long history of data
dropped dramatically between 1960 and 1971. This was followed by a more grad-
ual decline from 1972 to 1979, as measured at more than 3000 monitoring sites.
The rapid improvement in the late 1960's was largely due to the emission con-
trol programs of state and local air pollution control agencies. The improve-
ment in air quality during the 1970's is due mainly to control of traditional
particulate sources such as fuel combustion, solid waste disposal operations,
and industrial process emissions. The slight reversal in the downward trend
in 1976 is believed to be due to an increase in windblown dust caused by abnor-
mally dry weather.
2.1.2 NATIONAL TREND IN PARTICULATE EMISSIONS. 1970-1979
The dramatic 50 percent reduction in particulate emissions from 1970 to
1979 (Figure 2-2) results largely from installation of control equipment on in-
dustrial processes, reduced coal burning by non-utility users, installation of
control equipment by electric utilities that burn coal, and a decrease in the
burning of solid waste.
2.1.3 COMPARISON OF PARTICULATE LEVELS
Currently, 395 counties (or county equivalents) are classified as nonat-
tainment for TSP. Of the 45 urbanized areas with populations above 500,000
that monitored TSP, 33 (73%) exceeded the NAAQS for TSP in 1979 (Figure 2-3).
Five of these urbanized areas had annual average TSP concentrations exceeding
150 ug/m3 (double the NAAQS level of 75 ug/m3).
2.2 SULFUR DIOXIDE
Sulfur dioxide (S02) is one of a number of sulfur-containing compounds
found in the atmosphere. Although S02 enters the air primarily from the burn-
ing of coal and oil, it is also produced by various other industrial processes.
2-2
-------
90
80
70
>0
E
5 60
2 50
i—
£ 40
•z.
UJ
30
20
10
o
o
95 SITES
>3000 SITES
60
Figure 2-1.
65
70
YEAR
75
National trend in average participate
levels, 1960-1979.
70 71 72 73 74 75 76 77 78 79
Transportation
Fuel combustion
Q Industrial processes
HI Solid waste and misc
Figure 2-2. National trend in particulate emissions,
1970-1979.
2-3
-------
ro
O>
O,
O
O
O
o"
o
< o:
ii 2
y *
h- <
Qi UJ
< cc
Q- <
O o
LU LU
Q N
Z z
LU <
Q_ CD
co o:
ID =5
CO U_
_. °
< CO
<
Z<
O
CO
s
in
O
0>
O
d
I/)
(O
0}
03
(O
o
CO O
r— O
^) *>
> O
d) O
i— in
(O
O S-
•!- -M
S- to
(O QJ
0. S-
-------
Levels of S02 in the air over the Nation's urban areas decreased by 67
percent from 1964 to 1979. Improvement was most rapid from 1966 to 1971 be-
cause of an increased use of cleaner burning fuels in the residential, com-
mercial, and industrial sectors of most urban areas. Local and state air
pollution regulations led to a switch from coal and high sulfur oil to natural
gas and low sulfur oil. Between 1970 and 1979 the improvement continued with
the national average SC^ levels dropping 44 percent. A corresponding 7 percent
decrease in sulfur oxides emissions was observed between 1970 and 1979. The
greater improvement in ambient levels reflects SOo trends in urban areas, where
most of the emission reductions have taken place. Partially offsetting the
emission reductions in the urban areas was the location of new sources, such as
fossil fuel power stations, in rural areas.
Nationally, the urban S02 problem has diminished to the point that only a
small number of urban areas now exceed the air quality standard. Some regions
outside major urban areas continue to have high S02 because of single sources,
such as non-ferrous smelters. Today, these individual sources pose the great-
est obstacle to the attainment of air quality standards for $$2-
2.2.1 NATIONAL TREND IN AVERAGE SULFUR DIOXIDE LEVELS. 1965-1979
Nationally, annual average S02 levels measured at 32 urban locations de-
clined significantly from 1966 to 1971. This was followed by a more gradual de-
cline from 1972 to 1979 as measured at more than 1000 monitoring sites (Figure
2-4). The improvement in air quality during the first half of this period is
due mainly to (1) the change from coal with a high sulfur content to natural
gas, electricity, and low sulfur oils for residential and commercial space
heating; (2) strict local emission regulations, which caused the reduction in
sulfur content of coal and fuel oil or required the installation of control
equipment to remove sulfur; and (3) the location of major new sources, such as
fossil-fuel burning power plants, away from urban areas. In recent years,
most urban areas have attained the S02 standards and are now working to main-
tain these lower levels rather than reduce sulfur oxide emissions further.
2.2.2 NATIONAL TREND IN EMISSION OF SULFUR OXIDES, 1970-1979
Sulfur oxides emissions declined 7 percent from 1970 to 1979 (Figure 2-5).
The moderate decline in emissions corresponds to a considerable reduction in
S02 levels in urban areas. This difference between emission and air quality
2-5
-------
70
60
CO
E
"5 50
£ 40
UJ
o
o
o
^— J
(J-)
30
20
10
I I
_ 32 SITES
._ >1000 SITES
... 188 SITES
I I I I
I I 1 I
I 1 I I
I I I
I I I
65
Figure 2-4.
70
75
YEAR
National trend in average sulfur dioxide
levels, 1964-1979.
40
oo
o 30
o
20
tS)
z
o
Z
(S)
X
o
oo
10
70 71 72 73 74 75 76 77 78 79
YEAR
I Transportation H Fuel combustion
Q Industrial processes
Figure 2-5. National trend in emissions of
sulfur oxides, 1970-1979.
2-6
-------
trends arises because the use of high sulfur fuels has shifted from urban areas
to a growing number of sources outside of densely populated areas where there
are few other sources.
2.2.3 COMPARISON OF SULFUR DIOXIDE LEVELS
There are 97 counties (or county equivalents) which are currently classi-
fied as nonattainment for SC^. Of the 45 urbanized areas with populations
above 500,000 that monitored S02, only 6 (13%) exceeded the 24-hr NAAQS of
365 yg/m3 in 1979 (Figure 2-6). Peak 24-hour average values of 182 yg/m3 or
less were recorded in 20 (44%) of the urbanized areas.
2.3 CARBON MONOXIDE
Carbon monoxide (CO) is a byproduct of the incomplete burning of fuels-
mostly by cars and trucks. CO is also released by some industrial processes.
In some urban areas, automobiles and other modes of transportation are re-
sponsible for over 99 percent of these emissions, although any city with heavy
traffic may have a potential problem from CO. In some cases, the problem is
highly localized with only a few street corners experiencing high CO levels.
In other cases, the problem is spread throughout the center-city area and
along major commuter corridors.
Nationally, ambient CO levels in center-city locations have shown a steady
decline. From 1972 to 19,79 CO levels dropped at a rate of 6 percent per year
with an overall reduction of about 36 percent. The greatest improvements oc-
curred at sites traditionally having the worst CO problem. Estimates of na-
tionwide CO emissions from highway vehicles, in contrast, show only a 7 percent
decrease since 1972. The smaller reduction in CO emissions is largely due to a
35 percent increase in total vehicle miles travelled since 1970. The improve-
ment in average concentrations is greater than the reduction in CO emissions,
because the trend reflects levels at traffic-saturated monitoring sites in the
center city. These sites have recorded little or no change in vehicle miles
travelled. Therefore, the ambient CO trend reflects the reduction in emissions
from new cars brought about by federal standards on vehicle emissions.
2.3.1 NATIONAL TREND IN AVERAGE CARBON MONOXIDE LEVELS, 1972-1979
Figure 2-7 shows year-by-year changes in annual average CO levels at
221 urban sites over the 8 year period, 1972-1979. Carbon monoxide levels
2-7
-------
-I
o>
CO
o
o
o
•k
o
o
A
O
Q.
*-^
LU tO
O ^
x Q:
O <
o S
C£ N
=3 2
u. <
Z> <£
U.
0
H
h-
co
/^N
fi.
O)
*^
o
CO
1^
0
CO
r*^
\
uo
c
<
<
O
*O
*o
<)
*o
1 =
cf
:CM
*•••"•
i
1
1
J
j
|
i
i
i/)
%o
CO
i
CO
OO
O>4
OO
• —
1
O
—
-
-
o
CO
o
CN
tn
0)
V-
<
*0
6
O
to
"3
O)
(O
-Q
S-
>— O
cu o
> o
r- O
o
oj un
T3
•r- C
X (O
O -C
•I- +->
-a
s_
S- Q)
3 •»->
3 S-
LO Dl
(Ti to
r^ c
cr> o
4- «o
O r—
3
c n.
o o
to Q.
03
Q.
VO
I
c\j
a>
S-
Z3
cn
co •—
(£UJ/STI)
2-8
-------
en
£
LU
O
O
O
O
O
72 73 74 75 76 77 78 79
YEAR
Figure 2-7. National trend in average carbon
monoxide levels, 1972-1979.
74 75
YEAR
76
Transportation
i! Solid waste and misc
77 78 79
Industrial processes
Figure 2-8. National trend in emissions of carbon
monoxide, 1970-1979.
2-9
-------
improved at a rate of 6 percent per year with an overall reduction of about 36
percent. The improvement reflects levels at traffic-saturated monitoring sites
in the center-city. Since these sites have experienced little or no change in
the number of vehicles in their vicinity, the improvement in CO levels reflects
the reductions in emissions from new cars brought about by federal standards on
vehicle emissions.
2.3.2 NATIONAL TREND IN EMISSIONS OF CARBON MONOXIDE, 1970-1979
Carbon monoxide emissions in 1979 were 7 percent lower than in 1972
(Figure 2-8). Highway vehicles are the main source of this pollutant, and
there was an increase of 35 percent in total vehicle miles travelled during
this period. The increase in traffic offset the decrease in emissions per car
achieved by recent pollution control measures. Outside transportation, rela-
tively small reductions in CO emissions were observed in the solid waste dis-
posal and agricultural burning categories.
2.3.3 COMPARISON OF CARBON MONOXIDE LEVELS
Currently, 161 counties (or county equivalents) are classified as nonat-
tainment for CO. In 1979, 45 urbanized areas with populations above 500,000
monitored CO; of these, 28 (61%) exceeded the 8-hour NAAQS (Figure 2-9). Five
urbanized areas recorded peak 8-hour average values exceeding 18 ppm (double
the NAAQS level of 9 ppm).
2.4 NITROGEN DIOXIDE
Nitrogen dioxide (N02) is one of a family of nitrogen oxides. The oxides
important to air pollution control usually come from high-temperature combus-
tion. Nitrogen dioxide plays a major role in the atmospheric reactions which
produce photochemical oxidants (smog) and is primarily responsible for smog's
yellow-brown color.
From 1975 to 1979, N02 levels increased about 15 percent at 180 trend
sites while emissions for the same period were up 12 percent. In 1979, only
3 percent of the N02 measurements at 933 sites with acceptable data exceeded
the health-related ambient air quality standard.
Most of the increase in N02 emissions came from motor vehicles and elec-
tric utility generating plants. Although the emission rates for motor vehicles
and generating plants have been steadily reduced, increased demands for trans-
2-10
-------
E
a
a
to
cb
£
a*
a
a
o
o
lO
A
uj o:
Q £
T li-
X ~
O £
Z^
m
0 c
^— » -J
^ <
^ •»
Q
Z iu
o N
\^ «
CO Z
c* <
^
h-
<
en
v>
i^-
22
q
06
A
" -. '
*
Q
CO
*~~
>&
<
Z
IO
CO
cr
''OO
j
•1
0
o'
i
O
—
™
—
1 — 1
1 I
to
xf
t
0
I/)
O
«
0 "§
rxi ^ ^
CN -o
•i- C
(/) X <0
O o .c
i. c -P
o> §*"
y= E s-
<
CO
CTi C
o £.2
r~~ 1— 1 +->
(0
M— r—
O 3
Q.
C O
O Q.
CO
£_
fO
Q.
r—
0
o
001
i
C\J
0)
S-
3
en
CO
(ujdd)
-JH-8
2-11
-------
portation and power have more than offset the reductions. During the 1975-1979
period the number of miles travelled by all types of motor vehicles increased
substantially and higher electricity demands caused utilities to burn more fuel.
2.4.1 NATIONAL TREND IN AVERAGE NITROGEN DIOXIDE LEVELS. 1974-1979
Figure 2-10 shows year-by-year changes in average N02 levels based on
measurements obtained at 180 sites. There is an increasing trend from 1975 to
1979 with N02 levels rising 15 percent. The increase in N02 levels corresponds
to increases in nitrogen oxides emissions from transportation and from fuel com-
bustion in stationary sources.
2.4.2 NATIONAL TREND IN EMISSIONS OF NITROGEN OXIDES. 1970-1979
Nitrogen oxides emissions increased 18 percent from 1970 to 1979 (Fig-
ure 2-11). The increase in nitrogen oxides emissions resulted primarily from
increased fuel use by stationary sources and increased highway motor vehicle
travel. Vehicle miles driven increased 35 percent over the decade. During
this same period industrial process emissions remained relatively constant,
while solid waste and miscellaneous emissions decreased.
2.4.3 COMPARISON OF NITROGEN DIOXIDE LEVELS
In 1979, N02 was monitored in 45 urban areas which had populations greater
than 500,000. As Figure 2-12 indicates, 6 (13%) of these urbanized areas re-
corded annual average values which exceed the NAAQS level of 0.050 ppm. The
majority of the urbanized areas recorded annual average values between 0.026
ppm and 0.050 ppm. Only 7 counties (or county equivalents) are currently
classified as nonattainment for N02-
2-12
-------
n
o
40
30
o 20
OsJ
o
10
74
75
76 77
YEAR
78
79
Figure 2-10. National trend in average nitrogen
dioxide levels, 1974-1979.
70 71 72
S| Transportation @ Fuel combustion
^Industrial processes and solid waste
Figure 2-11. National trend in emissions of nitrogen
oxides, 1970-1979.
2-13
-------
CO to
O ^
I
CL
<. c O
Z -' -^f V 1%
••:'•'.:.•• :- •'••• .-•" .. :'••• .-••: '-.:•:•.. -l-'-J
••:.;..'•.;." . ... ._..::. ;,:',;, -p: r^ J j
":.-;::; .,;. ,.;..;• . ..j-'r^.i -1^. ?1
-.'''"• ' " "'"•/' : :-::':-"---; '^.= >:'S|
o o 10
o o r^
--. — . o
006
A ^ J_
O
»O
q
0
W^>
-
:
«0
CM
O
o
I
o
0
CO
CM
0
o
to
ea
0)
(O
c
10
(ft
o
0>
o
d
O) O
> o
S-
•r- CD
c
I/)
<7i C
r^ o
M- •—
O 3
Q.
C O
O Q-
(/>
fO
Q.
CM
t—l
C\J
s-
3
CD
q
o
q
o
q
6
•&AV
2-14
-------
3. AIR MONITORING STRATEGY
In October 1975, a Standard Air Monitoring Work Group (SAMWG) composed of
Federal, State and local air pollution control officials was established.
SAMWG developed an ambient air monitoring strategy that was approved in June
1977. This strategy is now being implemented through air monitoring regula-
2
tions promulgated on May 10, 1979. These regulations require the states to:
o Establish requirements for a refined national monitoring network in
areas with high population and pollutant concentrations to provide a sound
data base for assessing national trends.
o Give the States flexibility to use resources freed from unnecessary
monitoring work to meet their own needs.
o Establish uniform criteria for siting, quality assurance, equivalent
analytical methodology, sampling intervals, and instrument selection to assure
consistent data reporting among the States.
o Establish a standard national pollutant reporting index and require
its use for major metropolitan areas.
o Require the submission of precision and accuracy estimates with air
quality data to enable better interpretation of data quality.
These changes should result in a streamlined, high-quality, more cost-effec-
tive, national air monitoring program.
The States are required to establish a network of stations to monitor pol-
lutants for which National Ambient Air Quality Standards (NAAQS) have been es-
tablished. Each network is to be designed so that stations are located in all
areas where the State and the EPA Regional Office decide that monitoring is
necessary. The stations in the network are termed State and Local Air Monitor-
ing Stations (SLAMS).
Data from the network will be condensed and reported annually to EPA.
Data from a subset of SLAMS to be designated as National Air Monitoring Sta-
tions (NAMS) will be reported quarterly to EPA.
3.1 NETWORK DESCRIPTION
3.1.1 THE SLAMS NETWORK
The SLAMS network will be designed to meet a minimum of four objectives:
o To determine the highest concentrations expected in each area cover-
ed by the network;
3-1
-------
o To determine representative concentrations in areas of high popula-
tion density;
o To determine the impact on ambient pollution levels from significant
sources or source categories; and
o To determine- background concentrations.
Each monitoring site is required to be identified by location and type of
surroundings as well as by monitoring objective and spatial scale of represent-
ativeness. The spatial scale of representativeness is described in terms of the
physical dimensions of the air parcel sampled by the monitoring station through-
out which actual pollutant concentrations are reasonably similar; the scale ad-
jectives are micro, middle, neighborhood, urban, and regional.
3.1.2 THE NAMS NETWORK
The NAMS stations are selected from the SLAMS network to emphasize urban
and multisource areas. The primary objective for NAMS is to monitor areas
where pollutant levels and population exposure are expected to be highest, con-
sistent with the averaging time of the NAAQS. Accordingly, NAMS fall into two
categories:
o Stations in area(s) of expected maximum concentrations; and
o Stations with poor air quality and high population density but not
necessarily in area(s) of expected maximum concentrations.
3.2 IMPROVING THE CRITERIA POLLUTANT AIR MONITORING STRATEGY
The February 8, 1980 memorandum from the Administrator to the Assistant
Administrators of EPA requested that they prepare a monitoring strategy for
their respective programs. In April 1980, the air program and SAMWG began a
review of the existing monitoring strategy to determine if any deficiencies
remained to be resolved. Four principal issues were identified:
3.2.1 EXPAND THE DATA BASE IN SELECTED URBAN AREAS
EPA will investigate the feasibility of establishing a continuing inten-
sive monitoring program in one or more cities representing different emission
patterns to provide a comprehensive data base for dealing with new issues and
issues unresolved because of inadequate data. Establishing data intensive ef-
forts in these representative cities would provide a long-term data base for
3-2
-------
studying a variety of pollutant-specific issues, such as the extent of nonat-
tainment, determining the impact of specific source categories and causes of
air quality trends.
Over several years, a history of pollutant concentration levels and gra-
dients, meteorological characteristics, and emission patterns could be develop-
ed within each special study area. The result would be a comprehensive and co-
operatively-used data base that could replace the continuing need for special
short-term monitoring programs and would be responsive to a variety of nation-
al as well as state and local data needs. Although the program would be cost-
ly in the beginning, significant resources might be saved in the long run,
since resource-intensive special studies could be minimized. Once established,
the data base would serve as a reference for future special studies, and it
could replace the need for continually establishing special monitoring programs
with limited applications.
3.2.2 IMPROVE THE TECHNICAL BASIS FOR POLICY AND REGULATORY DECISIONS
The relationship of the technical and nontechnical aspects of monitoring
and modeling to the decision-making process must be better understood before
improved guidance can be issued. Specific items to be accomplished are list-
ed below:
o Develop performance standards and performance measures for air quali-
ty monitoring. Such standards and measures are needed to provide an objective
method of assessing the representativeness of monitoring.
o Develop performance standards and performance measures for dispersion
models. These standards and measures will provide an objective method of de-
termining model reliability for specific applications.
o Continue the program of formal review of air quality simulation mod-
els by the scientific and air quality management communities. The objectives
of the review are to ensure that the models are founded on sound scientific
bases and function in an efficient, cost-effective manner and to ensure that
appropriate new and superior models are promptly incorporated into the analy-
tical system.
3.2.3 EXPAND AND STRENGTHEN DATA ANALYSIS CAPABILITIES
Data analysts are exploring ways to use statistical and probability analy-
sis to improve the rationale for using monitoring data and model outputs in de-
cision-making. Such analysis will receive greater administrative attention as
3-3
-------
a priority item in the budgeting process. Specific actions for expanding and
strengthening data analysis include the following:
o Continue to explore the feasibility of using a probability approach
as the basis for reviewing the impact of new sources.
o Maintain the Intra-Agency Task Force for Air Quality Indicators as
the vehicle for establishing statistically sound and consistent approaches for
analyzing air quality data and trends.
o Establish priorities for exploratory data analysis that would include:
(a) Representativeness of monitoring and model estimates - extent
of nonattainment.
(b) Technique development - time series analysis, factor analysis,
probability models and Markov process applications.
(c) Trends analysis - Areawide indicators, statistical significance
of observed air quality changes.
(d) Data validation and consistency - detection of data anomolies.
3.2.4 IMPROVE THE COORDINATION AND MANAGEMENT OF MONITORING AND MODELING ACTI-
VITIES
SAMWG has identified critical problems in managing EPA's air monitoring
program. It has provided the perspective of air program managers at the Feder-
al, state, and local levels. This is a key element in planning, because the
strategy must address the real problems that will occur at any of those levels
to be successful. Accordingly, SAMWG is being maintained to provide continual
review of the overall air monitoring strategy and to insure that data users'
viewpoints are properly addressed. SAMWG will be asked to develop and review
issues related to how monitoring/modeling data should be used to make control-
related decisions.
Mid-level managers within the Regional Offices are being asked to play a
greater role in implementation of the NAMS network through RO/HQ NAMS workshops
and troubleshooting work groups.
3.3 NON-CRITERIA AIR POLLUTANT MONITORING STRATEGY
A forthcoming report, will include a description of current monitoring
programs for measurement of non-criteria air pollutants, the status of monitor-
ing techniques as well as quality assurance procedures. In addition, data
3-4
-------
needs will be identified and a proposed future monitoring program will be dis-
cussed. A draft of this report should be available in 1981.
3.4 REFERENCES
1. "Air Monitoring Strategy for State Implementation Plans," prepared by
Standing Air Monitoring Work Group, June 1977.
2. Federal Register, Vol. 44, May 10, 1979, pp 17558-27604.
3-5
-------
4. AN EXAMINATION OF OZONE
Unlike the other criteria pollutants, ozone is not emitted directly by
specific sources. Instead, it is formed in the air by chemical reactions
between nitrogen oxides and volatile organic compounds, such as the vapors of
gasoline, chemical solvents, and the combustion products of various fuels.
Since these reactions are stimulated by sunlight, ozone reaches peak levels
in most parts of the country during the summer. This type of pollution first
gained attention in the 1940's as Los Angeles "smog." Since then, photochemi-
cal smog has been observed frequently in many other cities.
This chapter examines the current status of ozone monitoring and recent
trends in ozone levels based on data available on EPA's National Aerometric
Data Bank (NADB). VOC emission trends are also presented based on data in the
National Emission Data System (NEDS).
The second part of the chapter is concerned with the development of the
1982 State Implementation Plan (SIP) data base, particularly the effort to col-
lect emissions, air quality, and meteorological data within the Northeast Cor-
ridor (Washington, D.C. to Boston, Massachusetts) and other urban areas.
The chapter ends with a discussion on efforts to standardize and improve
ozone air quality models. Results from the preliminary application of the air-
shed model are discussed.
4.1 MONITORING STATUS AND TRENDS
During the 1970's the number of ozone/oxidant monitors increased consid-
1 2
erably. ' In 1970, there were one ozone monitor and 56 oxidant monitors in
use; by 1979, there were 475 ozone monitors reporting at least 50 percent of
the possible days in the ozone season, May through October.
An examination of the ozone levels recorded at these sites shows that many
areas across the country are not violating the new ozone standard of 0.12 parts
per million (ppm). In fact, 77 of 282 counties did not report violations of
the ozone standard over the 4-year period 1976-79. A comparison of counties
east and west of the Mississippi River in 1979 shows 110 of 188 counties (59%)
exceeding the standard in the East and 45 of 94 counties (48%) exceeding the
standard in the West. Therefore, while the ozone problem is widespread, it is
not universal.
Nationwide, ozone air quality levels decreased approximately 5 percent
between 1978 and 1979. Most of the decrease took place in the Midwest,
4-1
-------
principally the EPA Region 5 states—Ohio, Indiana, Illinois, Wisconsin,
Minnesota, and Michigan. The decrease appears to be due to a combination of
factors. Meteorology was more conducive to ozone formation in 1978 than 1979.
3 4
In addition, there were changes in the way ozone monitors were calibrated,
and there were regionwide changes in quality assurance procedures. Most moni-
tors outside Region 5 showed a small decline in ozone levels.
4.1.1 MONITORING STATUS
In February 1979, the EPA adopted a new ozone standard requiring that
the expected number of days per calendar year with daily maximum hourly ozone
concentrations exceeding 0.12 parts per million (ppm) be less than or equal to
1. The expected number of exceedances (the statistical indicator used in mon-
itoring summaries) is further discussed in an EPA guideline on interpretation
of ozone standards and in a paper by Curran and Cox.
Only sites reporting sufficient data for at least 50 percent of the possi-
ble 184 days in the ozone season were considered in this analysis. The crite-
rion for a valid day was either 75 percent of the hours between 9:01 a.m. and
9 p.m. (9 of the 12 hours) or one recorded hour in exceedance of the standard;
this completeness criterion is reasonable for determining whether sites and/or
counties are exceeding the new ozone standard.
Nationwide Summary
In 1979, ozone monitors at 475 sites in 282 counties across the Nation
collected at least 50 percent of the possible days in the ozone season (Fig-
ure 4-1). Exceedances of the standard were reported at 155 (55%) of the
counties. The majority of these counties are in major metropolitan centers.
The approximately 110 million people living in the 282 counties account for
about 54 percent of the total 1970 U.S. population; of these, 81 million peo-
ple or 73 percent were exposed to ozone levels above the standard in 1979.
4.1.2 OZONE TRENDS
4.1.2.1 Long-Term Trend, 1974-1979
Measurements of ozone taken over a 6-year period, 1974-1979, show no sig-
nificant change in ambient levels. This is consistent with the trend in ozone
precursor emissions (volatile organic compounds). Emissions from transporta-
tion have decreased despite an 18 percent increase in vehicle miles driven
4-2
-------
CTl
C
3
O
o
3
.(->
ns
C
O
N
O
*±
<1J
4-3
-------
between 1974 and 1979, because of the increasing effectiveness of emissions
controls. Emissions from industrial sources have increased because of growth
or increased industrial production.
Figure 4-2 shows year-by-year changes in the composite May through Octo-
ber average of daily maximum hour ozone values of 230 urban sites over the 6-
year period, 1974-1979. The data reveal no long-term trend, which is consist-
ent with a similar lack of change in volatile organic compound emissions (Fig-
ure 4-3).
4.1.2.2 Short-Term Trend. 1978-1979
The long-term nationwide analysis has been supplemented with a short-term
2-year (1978-79) analysis to examine the short-term decline in ozone levels be-
tween 1978 and 1979. The completeness criterion for trend analysis was more re-
strictive than that used for the monitoring summaries (Section 4.1.1)—75 per-
cent of the possible days of data had to be available during the May through
October period. One hundred and fifty seven sites met this criterion for 1978
and 1979.
Ozone sites meeting the 75 percent completeness criterion showed a 5 per-
cent decrease in the May through October average of the daily maxima from 1978
to 1979. A partial factor in the overall decrease in ozone levels may have
been the 2.5 percent decrease in estimated VOC emissions from 27.8 million me-
tric tons in 1978 to 27.1 million metric tons in 1979. Between 1978 and 1979,
VOC emissions from industrial processes remained relatively unchanged, while
VOC emissions from motor vehicles dropped, largely due to increased emission
control and decreased motor vehicle miles travelled.
Other possible causes for the decline in ozone levels between 1978 and
1979 are the effects of meteorology, calibration change and regional differ-
ences. Most of the decreasing trends are in the Midwest, principally EPA Re-
gion 5 states - Ohio, Indiana, Illinois, Wisconsin, Minnesota and Michigan.
These decreases appear to be due to a combination of three factors. First, me-
teorology was more conducive to ozone formation in 1978 than 1979 in the Mid-
western states (see Appendix B). Secondly, as in other regions there were
changes in the way ozone monitors are being calibrated. Third, estimated na-
tionwide volatile organic compound emissions decreased between 1978 and 1979.
Finally, the Region 5 office applied uniform auditing procedures to all ozone
4-4
-------
C£.
OO
z:
o
(S)
z
o
GO
GO
O
o
E
_c
Q.
Q.
D. C
J
2 *
et
S3
UJ
O
z 9
O ^
)
1
0
ro
O
74
75
76 77
YEAR
78
79
Figure 4-2. National trends in daily maximum ozone
levels for May through October, 1974-1979.
10
70
Transportation
Industrial processes
79
[D Solid waste and misc
3 Nonindustrial organic
solvent
Figure 4-3. National trend in emissions of volatile
organic compounds, 1970-1979.
4-5
-------
monitors in the Region 5 states for the first time. A paper by Hunt, et. al.
o
examines these factors in depth.
4.1.2.3 Trend Conclusion
While no statistically significant long-term trend is apparent, a statis-
tically significant short-term decreasing trend (1978-1979) has been found.
Most of the decrease occurs in the EPA Region 5 states, although a statistical-
ly significant decrease of 3 percent is observed for the non-Region 5 sites.
Several general conclusions also emerge:
o Since VOC emission decreases are gradual, ozone trends are difficult
to determine and probably will not emerge until 10 or 15 years of data are
available.
o Analytical techniques are steadily improving but will not lead to a
significantly improved capability for detecting ozone trends in the near fu-
ture.
4.2 TECHNICAL ISSUES ASSOCIATED WITH THE DEVELOPMENT OF OZONE SIP'S
Revised State Implementation Plans (SIP's) are to be submitted by July
1982 for each of the 37 ozone nonattainment areas that sought an extension to
attain the standard. These SIP's are to contain the regulatory and legisla-
tive measures that are needed to attain the ozone standard. Currently, the
States are collecting the environmental data base needed to develop the SIP's.
4.2.1 FACTORS AFFECTING THE FORMATION OF OZONE
Ozone is a pollutant formed in the atmosphere when ambient concentrations
of nonmethane organic compounds (NMOC) and oxides of nitrogen (NOX) react in
the presence of sunlight during meteorological conditions typical of summertime
(i.e., high temperature and strong sunlight intensity). Of critical importance
in ozone formation is the ambient ratio of nonmethane organic compounds to ox-
ides of nitrogen (NMOC/NO ). NMOC reductions are most effective in reducing
A
ozone levels when the ambient ratio of NMOC/NOV is less than about 10:1, as it
A
is in most urban areas. In remote areas, where NMOC/NO ratios are about 30:1
A
or above increases or decreases in ambient NMOC concentrations may have an in-
significant impact on ozone concentrations.
Ozone is unlike most of the other criteria pollutants in many respects.
For example:
4-6
-------
a. Peak ozone concentrations occur a number of hours after precur-
sor emissions are emitted. Higher levels of ozone are frequently measured in
rural areas downwind from urban areas than in the urban areas themselves. This
is due to transport from the urban area rather than from sources located in the
rural area.
b. The formation of ozone is dependent upon the emissions of two
pollutants—volatile organic compounds and oxides of nitrogen (NO ). It is
widely believed that control of (VOC) sources of volatile organic compounds
is more effective, especially when the cost and technology limitations asso-
ciated with NO control are considered.
/\
c. Volatile organic compounds from stationary sources are emitted
from a wide range of industrial and commercial sources as well as from consum-
er products. Stationary sources of VOC emissions are so diffuse that no one
stationary source category is likely to emit more than a small fraction of the
total emissions. The ubiquitous nature of stationary sources of VOC makes the
development and enforcement of VOC control regulations more difficult than for
most other criteria pollutants.
While there is general agreement with respect to the technical issues dis-
cussed above, there are other issues which are more controversial and which
can be misleading unless the available information is presented in proper
perspective. For example:
a. While upwind sources may contribute to ozone concentrations mea-
sured in a downwind city, in most cases the city itself is primarily responsi-
ble for the peak ozone concentrations measured further downwind. All too
often attention is focused on the contribution from upwind sources, while the
city's own contribution to peak ozone concentrations is deemphasized.
b. It is frequently stated that the magnitude of VOC emissions from
vegetative sources is greater than those from man-made sources. Although
there is uncertainty in such estimates, various studies have indicated that
natural sources of VOC emit 3 to 5 times the amount of emissions from man-made
sources. However, in raising this issue, many fail to mention the more impor-
tant fact that the contribution of natural emissions to ambient ozone concen-
trations has been estimated to be small. Emissions from vegetation tend to
be widely dispersed geographically, whereas emissions from man-made sources
tend to be concentrated in urban areas. In addition, scientific evidence
suggests that the major vegetative emissions, terpenes, are a major sink for
ozone.
4.2.2 THE TECHNICAL DATA BASE NEEDED FOR OZONE SIP'S
The Clean Air Act prescribes the use of the air resource management ap-
proach in developing SIP's. The air resource management approach essentially
requires: (a) that emission sources be identified and quantified; (b) that
ambient air quality concentrations be determined; and (c) that a model, which
4-7
-------
simulates the relationship between emissions and air quality, be available.
The purpose of the model is to estimate the impact of control strategies on
future ambient ozone concentrations.
4.2.3 AIR MONITORING DATA AND SIP DEVELOPMENT
More specialized air quality data are needed for the development of the
ozone SIP's than for other pollutants. Ambient measurements of three pollu-
tants—ozone, oxides of nitrogen, and nonmethane organic compounds are needed.
Monitoring networks must be designed to account for the transport phenomenon
associated with ozone. For example, additional monitors must be located up-
wind of the city (to measure incoming transport) and downwind (to measure peak
ozone concentrations produced by the city). Because there is no continuous,
reliable method to measure ambient nonmethane organic compounds, particularly
at concentrations below 0.5 parts per million carbon (ppmc), specialized re-
search procedures must be used. These procedures are more reliable, but are
also more resource intensive, and more technically complicated. To minimize
these and other problems the Agency has undertaken an active program to pro-
vide financial and other assistance to the States so that a good data base can
be collected for the 1982 ozone SIP's. A major effort is underway in the
Northeast Corridor to collect a good data base for SIP development.
Two recent developments will improve the overall quality of the ozone air
quality data base. These developments are (1) the recent change in the Agency's
recommended ozone calibration technique and (2) the implementation of the
national air monitoring strategy.
The national monitoring strategy has been discussed in earlier chapters
of this report. The quality assurance program required by the strategy should
eliminate the use of faulty air quality data in regulatory decisions. Also,
adherence to monitor siting guidance should provide a national network of
similarly-sited ambient monitors located where one would expect maximum ozone
impact. Analysis of data from these sites should result in more meaningful
intercity comparisons of data than previously possible.
The national monitoring strategy will result in an increase in the number
of ozone monitors currently operated in some cities. In other cities, some ex-
isting monitors may be relocated to areas where peak ozone concentrations are
more likely to occur. Consequently, ozone levels higher than those currently
4-8
-------
being recorded are likely to be measured, particularly in medium and smaller
sized cities where the monitoring networks are likely to be more deficient than
in larger cities (e.g., New York and Los Angeles).
The modification to the ozone calibration technique will eliminate the 5
to 20 percent positive bias that has existed in the Agency's recommended ozone
calibration procedure. As a result, peak ozone concentrations should be con-
sistently 5 to 20 percent lower than previously reported. There continues to
be a +15 percent error associated with the ozone monitoring procedure that
will not be affected by the change in the calibration procedure. At the cur-
rent level of the ozone standard (0.12 ppm, 1-hour standard), this results in
a probable +0.02 ppm error. This generally recognized error is typically ig-
nored when making regulatory decisions since the measured value is the best
estimate of the true value available.
4.2.4 EMISSION INVENTORY DATA
Another requirement for the effective implementation of the air resource
management approach is an inventory of emission sources. Emission data are
needed for two pollutants (VOC and NOX). Unlike air quality data, which are
direct measurements, an emission inventory is a compilation of a series of
estimates. Consequently, there are inherent errors associated with any inven-
tory. The magnitude of the error is greatest when emission estimates are at-
tempted for a single source. More confidence is attached to estimates of total
emissions for an urban area as random errors associated with individual esti-
mates cancel each other to some degree producing a more reasonable estimate of
total emissions.
It is generally believed that inventories for VOC emissions are less re-
liable than those for other criteria pollutants. Emission inventory procedures
for stationary sources were originally developed to estimate emissions from
particulate matter and sulfur dioxide sources. As new pollutants were inven-
toried, existing inventory procedures were applied to these pollutants without
much change. In some cases, this was appropriate (e.g. oxides of nitrogen).
However, due to the nature of VOC sources, the historical procedures have been
found to be generally insufficient. Improved procedures have recently been de-
veloped to more completely account for emission from the ubiquitous sources of
VOC emissions.
4-9
-------
4.2.5 AVAILABLE MODELING PROCEDURES FOR OZONE
The development of a technically sound and widely accepted model has been
a difficult task. For the 1979 ozone SIP's, the Agency allowed States to use
any one of a number of modeling techniques to relate source emissions to air
quality since it was not possible to determine which of the available ozone mod-
eling procedures was best.
Since that time, considerable progress has been made to develop and vali-
date the Empirical Kinetic Modeling Approach (EKMA). As a result of preliminary
validation efforts, the Agency recently proposed that the States use EKMA for
the development of 1982 ozone SIP's. However, because of the inherent errors
in the data base and with model estimates, it is anticipated that the estimates
of control provided by EKMA may be used as a guide to determine the general
level of control needed to attain the standard. Despite recent efforts, there
continues to be uncertainty associated with ozone model results. The best we
can do today is to implement a control strategy, measure the effect on the am-
bient ozone and later make appropriate adjustments to the control strategy as
required.
4.2.6 THE POTENTIAL OF PHOTOCHEMICAL DISPERSION MODELS
Unlike EKMA, which is a relatively simplified model, urban photochemical
dispersion models are sophisticated, detailed mathematical representations of
the chemical and meteorological phenomena associated with the photochemical pro-
cess. Since such models represent the state-of-the-science, the development of
a validated photochemical dispersion model is viewed as a valuable tool for im-
proving the Agency's credibility with respect to its ozone control program.
Advantages of a validated photochemical dispersion model include:
1. the ability to demonstrate the appropriateness of the Agency's cur-
rent strategy for ozone control;
2. the ability to determine the potential effectiveness of new strate-
gies, and to determine the most cost-effective strategy to attain standards;
3. the capability to provide decision-makers with pertinent information
to allow them to make reasonable and supportable decisions.
On the other hand, model results may be limited for the following reasons:
a. Photochemical dispersion models are data and resource intensive.
The cost to obtain the emission, air quality, and meteorological data for one
4-10
-------
city often exceeds $1 million and may take 2 to 4 years to complete the data
collection-model application process.
b. A photochemical dispersion model cannot be expected to produce
accurate and unquestioned results if the input data contain significant errors.
Consequently, the results from photochemical dispersion models will be limited
in credibility due to the inherent errors in the data bases needed to operate
the model and the implicit assumptions in model formulation.
Efforts are currently underway to validate a photochemical dispersion
model. Detailed data bases have been assembled for St. Louis, MO and Tulsa,
OK and data collection efforts are underway in Philadelphia. A comprehensive
testing protocol has been formulated for St. Louis, which requires the evalua-
tion of model performance of 50 separate days of varying air quality and mete-
orological conditions. Less rigorous, but nevertheless comprehensive testing
is underway on the Tulsa data base. These validation efforts are scheduled to
be completed by the end of FY 81.
While limited results are available concerning the performance of photo-
chemical dispersion models, a sensitivity study was recently conducted to eval-
uate the impact of various input parameters on model predictions. Noteworthy
results, which should be considered preliminary at this time (since the model
has not yet been validated) include the following:
a. Errors in peak ozone predictions from photochemical dispersion
models appear to be directly related to errors in emission input data. In
other words, an error of 10 percent in emission estimates could have as much
as a 10 percent error in ozone prediction.
b. Sensitivity tests indicate that peak ozone concentrations are
not very sensitive to the spatial distribution of emissions. These results
suggest that either the model or ambient ozone formation itself is not sensitive
to the spatial distribution of emissions. If ozone formation is not particular-
ly sensitive to such changes, this would question the air quality benefits to be
gained from implementing various transportation and land use strategies that are
designed primarily to relocate rather than reduce emissions.
In summary, while photochemical dispersion models are believed to have the
capability of providing more theoretically sound results, the extent of the data
bases required by the model and their inherent errors may limit the usefulness
of the results from such models. Efforts are continuing to validate these mod-
els in a number of cities. Only limited use of sophisticated photochemical
dispersion models for the development of 1982 ozone SIP's is anticipated.
4-11
-------
Summary: Technical Issues Associated with Ozone SIP's
- In July 1982, 37 nonattainment areas that sought an extension to attain
the ozone standard will be required to submit revised SIP's. States are cur-
rently in the process of collecting a good data base to develop SIP's.
- Because of the complex nature of ozone, it has been difficult to de-
velop the technical tools needed to fully implement the air resource manage-
ment approach, which is prescribed by the Clean Air Act for SIP development.
- Available ozone models are limited and not widely accepted. High priori-
ty Agency efforts have resulted in an improved model i.e., the Empirical Kinetic
Modeling Approach (EKMA) having been recently proposed by EPA for use in 1982
ozone SIP development.
- Photochemical dispersion models are generally believed to be superior
to other ozone models and efforts are underway to validate such models. How-
ever, the results from photochemical dispersion models will be limited in
credibility due to the inherent errors in the data bases needed to operate the
model and the implicit assumptions in model formation.
4.3 REFERENCES
1. Monitoring and Air Quality Trends Report. 1974, U.S. Environmental Pro-
tection Agency, Office of Air Quality Planning and Standards, Research
Triangle Park, North Carolina 27711. Publication No. EPA-450/1-76-001.
February 1976.
2. National Air Quality Monitoring and Emission Trends Report, 1977, U.S. En-
vironmental Protection Agency, Office of Air Quality Planning and Stand-
ards, Research Triangle Park, North Carolina 27711. Publication No. EPA-
450/2-78-052. December 1978.
3. Federal Register, Vol. 44, February 8, 1979, pp. 8202-8237.
4. "Collaborative Study of Reference Method for Measurement of Photochemical
Oxidants in the Atmosphere (Ozone-Ethylene Chemiluminescent Method)." U.S.
Environmental Protection Agency, Office of Research and Development, Wash-
ington, D.C. Publication No. EPA-650/4-75-016. February 1975.
5. "Guideline for the Interpretation of Ozone Air Quality Standards." U.S.
Environmental Protection Agency, Office of Air Quality Planning and Stand-
ards, Research Triangle Park, North Carolina 27711. Publication No. EPA-
450/2-78-003. January 1979.
6. T.C. Curran and W.M. Cox, "Data Analysis Procedures for the Ozone NAAQS
Statistical Format." J. Air Pollution Control Association 29:532 (1979).
7. Personal Communication, Charles Mann, U.S. Environmental Protection Agen-
cy, Office of Air Quality Planning and Standards, to William F. Hunt, Jr.,
U.S. Environmental Protection Agency, Office of Air Quality Planning and
Standards, June 10, 1980.
4-12
-------
8. W.F. Hunt, Jr., T.C. Curran, R.B. Faoro, N.H. Frank and V.M. Henderson,
"National Ozone Monitoring Status and Trends, 1979," to be presented at
the 74th Annual Meeting of the Air Pollution Control Association, June
1981.
4-13
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO. 2.
EPA-450-4/81-014
4, TITLE AND SUBTITLE
1980 Ambient Assessment-Air Portion
7. AUTHOR(S)
William F. Hunt, Jr. and Edward 0. Lillis
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air, Noise and Radiation
Office of Air Quality and Planning
Research Triangle Park, N.C. 27711
12. SPONSORING AGENCY NAME AND ADDRESS
15. SUPPLEMENTARY NOTES
3. RECIPIENT'S ACCESSIOf*NO.
February 1981
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
13. TYPE OF REPORT AND PERIOD COVERED
Annual 1 QflCI
14. SPONSORING AGENCY CODE
16. ABSTRACT
This report presents national ambient air quality and emission trends through
1979 for total suspended particulate, sulfur dioxide, carbon monoxide, nitroqen
dioxide and ozone. Ozone is treated in greater depth focussing on monitoring states
as well .
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS b.lDENTIFI
Air Pollution Trends — Air Pollution
[mission Trends Air Monitoring
-arbon Monoxide
Nitrogen Dioxide
)zone
Sulfur Dioxide
Total Suspended Parti culates
TS. DISTRIBUTION STATEMENT 19. SECURI
Q i i Hi- • j. .1 Hncla«
Heltdse Unlimited 20. SECURI
Unclas
ERS/OPEN ENDED TERMS C. COSATI Field/GlOUp
TY CLASS (This Report) 21. NO. OF PAGES
isified ^
TY CLASS (This page) 22. PRICE
;sified
EPA Form 2220-1 (S-73)
------- |