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Summary
A primary objective of air quality management in the United States has
been to reduce human exposure to carbon monoxide (CO) and other pollut-
ants produced from incomplete combustion. Elevated ambient CO concen-
trations are due mainly to incomplete combustion of gasoline by light-duty
vehicles, such as passenger cars and pickup trucks.
CO controls are working. Problems with ambient CO were widespread
when automobile emissions regulations began in the 1960s. When the
health-based National Ambient Air Quality Standards (NAAQS) for CO
were promulgated in 1971, more than 90% of ambient monitors indicated
violations. Since then, motor-vehicle emissions controls have greatly
reduced ambient CO concentrations. Over the last 5 years, the number of
monitors showing CO violations has fallen to only a few, and the monitors
that continue to show violations do so much less frequently. For example,
Denver, Colorado, which had a persistent CO problem and registered as
many as 200 days with violations in the ~ 960s, has not had a violation since
995 . Fairbanks, Alaska, reduced the number of days with violations from
The standards for ambient air concentrations of CO were set at 9 parts per
million (ppm) for an 8-hour average and 35 ppm for a 1-hour average. These stan-
dards were set to protect public health with "an adequate margin of safety," as
specified in the Clean Air Act. A violation of an NAAQS occurs on the second
exceedance and all subsequent exceedances ofthe standard in a calender year. Only
the 8-hour standard of 9 ppm has been exceeded recently in a few locations in the
country.
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~ Managing CO in Meteorological and Topographical Problem Areas
well over 100 per year in the early 1970s to zero over the last 2 years.
Thus, CO regulation has been one of the greatest success stories in air
pollution control, reducing the problem, once widespread, to a few difficult
areas. As a result, the focus of U.S. air quality management has shifted to
characterizing and controlling other pollutants, such as tropospheric ozone,
fine particulate matter (PM2 5),2 and air tonics.
However, some locations, such as Anchorage, Alaska, and Lynwood
and Calexico, California, continue to be susceptible to occasional violations
of the NAAQS for CO. These areas are typically subject to problematic
meteorological and topographical conditions that produce severe atmo-
spheric inversions in winter.3 Although CO emissions from light-duty
vehicles are projectedto decrease in the future, atmospheric inversions and
Tow windspeeds prevalent in some locations during winter are extremely
effective in trapping the products of incomplete combustion, including CO,
emitted at ground level. For example, Fairbanks, Alaska, is subject to
extreme atmospheric inversions, at times experiencing inversion strengths
as much as 30°C per 100 meters of altitude. In addition, Fairbanks is situ-
ated in a three-sided bowl, surrounded by the Yukon-Tanana uplands,
which can inhibit air circulation. Although it is not heavily populated and
has no maj or air-pollution producing industries, Fairbanks ' s meteorological
and topographical characteristics make the city susceptible to high ambient
CO concentrations in winter.
The continuing vulnerability of a few locations to high CO concentra-
tions prompted Congress, in its fiscal 2001 appropriations report for the
U.S. Environmental Protection Agency (EPA), to ask the National Acad-
emy of Sciences to study CO episodes in meteorological and topographical
problem areas. The study was requested to address potential approaches to
predicting, assessing, and managing episodes of high CO concentrations in
such areas. In particular, the committee was to address:
2PM2 5 is a subset of particulate matter that includes particles with an aerody-
namic equivalent diameter less than or equal to a nominal 2.5 micrometers.
Inversions occur when the temperature of the atmosphere increases with alti-
tude. Combined with low windspeeds, this prevents air circulation, because colder
air is trapped near the ground by the warmer air above. A temperature increase of
several degrees celcius per 100 meters is considered a strong inversion. The stan-
dard lapse rate for the troposphere is a decrease of about 6.5°C per kilometer (or
about 3.6°F per 1,000 feet).
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Summary ~
.
Types of emission sources and operating conditions that contribute
most to episodes of high ambient CO.
· Scientific bases of current and potential additional approaches for
developing and implementing plans to manage CO air quality, including the
possibility of new catalyst technology, alternative fuels, and cold-start
technology, as well as traffic and other management programs for motor-
vehicle sources. Control of stationary-source contributions to CO air qual-
ity also was to be considered.
· The effectiveness of CO emissions control programs, including
comparisons among areas with and without unusual topographical or mete-
orological conditions.
· Relationships between monitored episodes of high ambient CO
concentrations and personal human exposure.
.
The public-health impact of such episodes.
· Statistically robust alternative methods to assist in tracking prog-
ress in reducing CO that bear a relation to the CO concentrations consid-
ered harmful to human health.
In response, the National Research Council convened the Committee
on Carbon Monoxide Episodes in Meteorological and Topographical Prob-
lem Areas, which prepared this report. Fairbanks, Alaska, was identified
as the subject for a case study in an interim report, which was completed
in 2002. The following report is the final report requested by Congress.
FINDINGS AND RECOMMENDATIONS
Vulnerability to Future Violations
Findings
Because of a number of factors including differences in topography
and temporal variability of local meteorology and emissions rates some
areas are especially vulnerable to violations of the 8-hour NAAQS for CO.
In geographical areas that have achieved attainment of the NAAQS, it
might still be possible for ambient concentrations of CO to sporadically
exceed the standard under unfavorable conditions, such as strong winter
inversions. This vulnerability, defined as the probability for violation in a
future year, depends on both the current CO levels and the variability of air
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4 Managing CO in Meteorological and Topographical Problem Areas
quality indicators. An area in attainment might still be substantially vuIner-
able if the variability of its air quality is high.
There is evidence that local meteorological conditions conducive to
high CO concentrations are sometimes associated with large-scare meteoro-
logical and cTimatological phenomena. For example, all recent exceed-
ances of the NAAQS for CO in Fairbanks have occurred with a low-pres-
sure system in the Gulf of Alaska with cyclonic flow extending over Fair-
banks. Although the role that this low-pressure system plays is unclear, it
might produce warm winds aloft that reinforce inversions near the ground.
In Denver, Colorado, the presence of Tong-term snow cover and light winds
can produce conditions conducive to CO buildup in the ambient air. Snow
cover diminishes ground-level solar heating, intensifying inversions, and
light winds reduce horizontal dispersion. However, over the past decade,
Denver has not experienced the combination of these meteorological fac-
tors, reducing the city's susceptibility to high CO concentrations. Changes
in the frequency of some large-scale meteorological and cTimatological
events, such as the frequency of low-pressure systems in the Gulf of
Alaska, will influence vulnerability to CO violations.
Recommendations
Air quality managers typically recognize whether their region is espe-
cially vulnerable to future CO violations as a result of increases in vehicle
activity, the spatial and temporal variability of meteorology, and problem-
atic topography. However, in some cases, air quality planning does not
encompass the worst-case combinations of emissions and meteorology.
Achieving sufficient emissions reductions to account for these conditions
is prudent, particularly in areas with high population growth and/or high
meteorological variability, to further reduce the risk of violations. In addi-
tion, given that the form of the CO standard defines a violation as the sec-
ond and all subsequent exceedances in a calendar year, regions are suscep-
tible to violating the standard due to extreme meteorological conditions,
which contributes to the difficulties that meteorological and topographical
problem areas have in reaching and maintaining attainment. It is also im-
portant to investigate how large-scare and local meteorological and climato-
logical phenomena can affect the susceptibility of a location to CO buildup
in ambient air.
Air quality managers should recognize that their regions might be espe-
cially vulnerable to future CO violations because of increases in vehicle
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Summary
activity, spatial and temporal variability of meteorology, and problematic
topography. The meteorological conditions assumed in current regulatory
air quality planning might not encompass the worst-case conditions.
Achieving additional emissions reductions is prudent to further reduce the
risk of violations, particularly in areas with high population growth and/or
high meteorological variability. It also might be important to investigate
how large-scale meteorological and climatological phenomena can affect
the susceptibility of a location to CO buildup in ambient air.
Health Effects
Findings
In patients diagnosed with coronary artery disease, CO alone has been
shown to exacerbate exercise-induced chest pain (angina) in controlled
laboratory experiments. Those studies serve as an important part of the
basis for the NAAQS. In addition, epidemiological studies have correlated
high CO concentrations with other adverse human health effects, such as
heart disease, childhood developmental abnormalities, and fetal loss. Some
of these effects have been correlated with ambient CO levels below the
NAAQS. However, CO is not produced alone, and epidemiological studies
have difficulty separating the effects of CO from those of other pollutants
that are often associated with CO (such as benzene, 1,3-butadiene, alde-
hydes, and various components of PM2.s). Though changes in ambient
levels of CO may sometimes correlate with health effects other than
exercise-induced angina, there is insufficient evidence that CO is the single
direct causative agent in the other effects. Thus, reducing CO alone may
or may not reduce the incidence of heart disease, childhood developmental
abnormalities, and fetal loss.
A significant collateral benefit from reducing CO vehicle emissions
standards has been the substantial reduction in accidental deaths due to
acute CO poisoning. CO is unique among criteria pollutants4 because it is
relevant to both ambient air quality management and public safety. Expo-
Criteria pollutants are air pollutants emitted from numerous or diverse station-
ary or mobile sources for which NAAQS have been set to protect human health and
public welfare. The other criteria pollutants are ozone, particulate matter, sulfur
dioxide, nitrogen dioxide, and lead.
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6 Managing CO in Meteorological and Topographical Problem Areas
sures to mobile-source emissions cross these two areas of public-health
management. Using computerized death-certificate data, a recent study by
researchers at the Centers for Disease Control and Prevention estimated
that over 11,000 deaths from accidental CO poisoning have been avoided
over the 1 968- ~ 99 ~ time period because of the more stringent vehicle-emis-
sions standards. This collateral benefit is not accounted for in EPA's recent
report to Congress on the benefits and costs of the Clean Air Act.
Recommendations
To reduce the potential adverse health effects of CO, the few remaining
areas not in attainment need to continue making progress towards meeting
and maintaining the CO standard. Public-health issues associated with
ambient CO should be emphasized through enhanced public-awareness
campaigns. Further study to reveal the effects of CO on the fetus and to
separate the effects of CO from its copollutants is encouraged. Also, there
should be more toxicology studies of the automobile exhaust mixture.
Management and Control of CO
Management of CO
Fin dings
To reach attainment, communities vulnerable to exceeding the health-
based NAAQS for CO can implement various local measures to comple-
ment federal vehicle emissions standards. These include but are not limited
to vehicle emissions inspection and maintenance (~/M) programs, the use
of cold weather engine-block heaters in vehicles, and the use of low-sulfur
gasoline and oxygenated fuels. These measures reduce CO emissions by
reducing the number of malfunctioning vehicles (~/M programs), reducing
the length of time before a vehicle's emissions control catalyst is fully
functional (cold weather engine-block heaters), and improving the eff~-
ciency of the vehicle's emissions control catalyst (Iow-sulfur gasoline).
Other measures include mass transit initiatives, traffic management, and
bans on wood burning.
Air quality issues have tended to be assessed and regulated independ-
ently. As such, CO management frequently occurs in isolation, even
OCR for page 7
Summary
though other pollutants have similar emissions sources. The committee
recognizes that few areas in the country continue to violate CO standards
and that the focus of air quality management in the near future will not be
on CO but on attaining new PM2 s and tropospheric ozone air quality stan-
dards and reducing air tonics.
Recommendations
.
Communities with special CO problems should be encouraged to de-
sign locally effective programs. Federal and state assistance should be
provided to these communities for characterization and implementation of
management options. This should include assistance to improve non-road
and stationary-source emissions characterizations. Because the CO stan-
dards are health-based, all communities need to be diligent in working
toward attaining and maintaining the CO standards. In addition, the pro-
grams implemented to reduce CO emissions should be reassessed periodi-
cally. This reassessment should include evaluation of their impact on CO,
as well as other pollutants, and their impact at low temperatures.
CO management should be better integrated into air quality manage-
ment. Although the focus of air quality management in the near future will
be on other air pollution issues, winter inversion conditions not only affect
CO buildup but can also be related to higher concentrations of PM2 5 and
some air tonics. In addition, the primary source of CO, fuel-rich operations
of light-duty vehicles, is a major source of other pollutants of concern. The
committee therefore recommends that EPA assess the relationship of CO
to these other pollutants when the CO criteria are updated.
Federal Tier 2 and Cold-Start Emissions Standards
Findings
Federal new-vehicle emissions standards have been effective in reduc-
ing CO emissions, including emissions from vehicles operated in cold
climates. Emissions from passenger vehicles have been reduced from their
pre-contro] levels of over 80 grams per mile (g/mi) in the late 1 960s to the
3.4 g/mi standard implemented in 1981. Also, progressively Tower stan-
dards for hydrocarbon emissions, as well as other requirements, have
tended to decrease CO emissions levels. Since 1994, new cars have been
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8 Managing CO in Meteorological arid Topographical Problem Areas
required to meet a winter cold-start CO limit, which reduces emissions
from vehicles started at cold temperatures (20°F).
New Tier 2 and California certification standards5 are expected to
further reduce hydrocarbon and nitrogen oxides (NOX) emissions. Average
CO emissions from vehicles certified to Tier 2 standards are expected to
decrease due to the technological improvements in emissions control sys-
tems needed to meet the standards, especially the Tower hydrocarbon stan-
dards and lower CO standards on some light-duty trucks.
In CO problem areas, the decrease in emissions resulting from Federal
Tier 2 standards will depend on the mix of vehicles sold and used in these
areas. As such, the following uncertainties arise in predicting the continued
motor-vehicle emissions reductions in CO problem areas:
· The sales strategy used by manufacturers to comply with average
NOX limits. [f manufacturers tend to sell higher-emitting vehicles in CO
problem areas, the improvements in CO emissions will not be as large as
those predicted based on national averages.6
· The impact of the emissions averaging and trading provisions
(which allow vehicle manufacturers to generate, trade, and bank emissions
credits) on the fleet of vehicles operating in CO problem areas.7
· The effects of Tier 2 requirements on CO emissions at temperatures
below 20°F.
5Federal Tier 2 emissions standards will be introduced for passenger cars in
model-year 2004 and fully implemented by model-year 2007. The standards will
require that vehicle manufacturers meet a fleet average NOX limit of 0.07 grams per
mile (g/mi) along with lower standards for hydrocarbons. California, which is
allowed under the Clean Air Act to adopt its own vehicle emissions standards, has
already implemented a similar set of emissions limits. Both the Tier 2 and Califor-
nia standards are for vehicles certified at 68-86°F. Since 1994, new cars also have
been subject to a cold-start CO standard, which requires cars and most light-duty
trucks to meet a CO limit of 10 g/mi on a certification test run at 20°F. The Clean
Air Act Amendments of 1990 include a provision for more stringent cold-start
standards to be set if needed.
6The Tier 2 standard is a sales-weighted fleet-averaged standard. Thus, some
vehicles that are sold will have emissions greater than the standard, some less than
the standard.
7The Tier 2 standard has provisions that allow manufacturers bettering the fleet-
averaged standard to generate tradable emissions credits that can be sold to manu-
facturers who have not met the fleet-averaged standard. Manufacturers can also
bank credits for use in later years.
OCR for page 9
Summa7y 9
· The ability of EPA's MOBILE emissions rate model to adequately
account for the effects of Tier 2 standards on CO emissions rates.8
Recommendations
In the absence of compelling evidence, the committee does not recom-
mend tightening the national cold-start standard below 10.0 g/mi or requir-
ing that the 10.0 g/mi standard be met at a lower temperature. However,
supplemental emissions testing should be undertaken at temperatures below
20°F to determine to what extent CO emissions systematically increase as
ambient temperature decreases. Testing data should be obtained and ana-
Tyzed at 0°F and ~ 0°F, and should include CO as well as other pollutants
(air toxics and PM).
The extent of the anticipated reduction in CO emissions from Tier 2
vehicles needs to be confirmed through analysis of data, including those
from cold starts at 0°F and 10°F. Again, testing should include CO as well
as other pollutants. Tfthe analysis of Tier 2 end prior controls indicates that
all locations will attain the 8-hour CO standard, more stringent federal CO
vehicle emissions standards will be unnecessary. The results of all emis-
sions testing must be incorporated into EPA's MOBILE model to accu-
rately estimate future CO emissions. The effects on CO problem areas of
the sales strategy used by manufacturers to meet the NOX limits and of the
trading and banking provisions also need to be assessed and incorporated
into emissions modeling.
High-Emitting Vehicles
Findings
A relatively small number of high-emitting vehicles contribute dispro-
portionately to CO and other motor-vehicle emissions. The vehicle fleets
operating in and around places with high local concentrations of CO (hot
spots) often include a higher proportion of high-emitting vehicles compared
with the surrounding region. Elimination or repair of high emitters would
The MOBILE model is used to estimate current and future on-road motor-
vehicle emissions. MOBILE6 is the current version of that model.
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10 Managing CO in Meteorological and Topographical Problem Areas
likely reduce the severity of CO hot spots and reduce motor-vehicle emis-
sions overall.
Recommendations
Air quality management agencies should identify high-emitting vehi-
cles and target them for repair or removal from the fleet. Enhanced
onboard diagnostic testing programs, tailpipe testing, motor-vehicle emis-
sions profiling, and/or remote sensing can identify these vehicles. How-
ever, programs designed to mandate repair or removal of high-emitting
vehicles might raise issues of fairness, because high emitters are often
ownedby people with limited economic means. The cost-effectiveness and
equity impacts of policies that provide incentives for owners of high-emit-
ting vehicles to seek repairs or vehicle replacement, such as repair assis-
tance programs, should be explored. There should also be additional Tow-
temperature testing to evaluate the effectiveness of programs aimed at
controlling high-emitting vehicles. This evaluation should include the
impacts on CO as well as other emissions.
Oxygenated Fuels
Findings
An oxygenated fuel is a gasoline containing an oxygenate (typically
methyl tertia~y-buty] ether ~MTBE] or ethanol) intended to reduce produc-
tion of CO. Oxygenated fuels program benefits are declining in effective-
ness as more modern vehicles enter the fleet. EPA's MOBILE model pre-
dicts CO emissions reductions from oxygenated fuels of 3-7% for the 2010-
2015 fleet because of reduced emissions from pre-1994 vehicles, cold
starts, and malfunctioning vehicles. There is still uncertainty about the
overall effectiveness of oxygenated fuels, especially at temperatures below
20°F.
Recommendations
EPA should undertake a science and policy review of the current oxy-
genated fuels programs to determine the conditions under which these
OCR for page 11
Summa7y 1 1
programs are cost-ettective. The review should also determine when
changes in fleet technologies will render these programs ineffective. Low-
temperature testing, especially below 20°F, is recommended. Oxygenated
fuels programs should be implemented only when they provide cost-effec-
tive reductions in CO that help areas come into compliance or prevent areas
that have attained the NAAQS from falling back into nonattainment.
Public Education
Findings
On the basis of its review of programs in Fairbanks, Alaska, the com-
mittee is concerned that public education campaigns have not sufficiently
emphasized the adverse health effects associated with exposure to high
ambient concentrations of CO. Also, the public is not fully aware of the
link between transportation choices and overall air quality. As a result,
public acceptance of and participation in locally proposed programs to
achieve and maintain attainment of the NAAQS for CO is often poor.
Recommendations
Public-health education to improve public acceptance and compliance
should tee a component ofall local emissions-reduction programs. Commu-
nities should use surveys and focus groups to regularly evaluate the effec-
tiveness of public education programs and the impact they have on the
success of CO emissions control.
CO Assessment
CO As an Indicator of Motor-Vehicle Pollutants
Findings
In urban environments, ambient CO concentrations are a strong indica-
tor of motor-vehicle emissions. EPA estimates that as much as 95°/O of all
CO emissions in some cities can be from automobile exhaust. Spatial and
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12 Managing CO in Meteorological and Topographical Problem Areas
temporal variability in motor-vehicle activity and atmospheric dispersion
characteristics can lead to CO hot spots.
CO is useful as a gauge of human exposure to other directly emitted
mobile-source pollutants, such as air tonics and PM2 s. However, CO is not
a perfect indicator of all mobile-source pollutant emissions, because CO
reacts more slowly than many other pollutants, and the ratio of CO to
copollutants varies by emissions source. The atmospheric conditions that
produce high CO concentrations are different from those that produce high
concentrations of photochemical pollutants. Despite these caveats, mea-
surements in the Los Angeles area and elsewhere have shown strong corre-
lations between ambient CO and benzene concentrations. A strong correla-
tion between CO and concentrations of the relatively short-lived 1 ,3-buta-
diene also was observed.
Recommendations
The committee has several recommendations in regard to the use of CO
to represent the distribution of other pollutants. CO can be used to demon-
strate the spatial distribution of some mobile-source pollutants, to identify
hot spots, and to improve model representation of relationships between
transportation activity and emissions. CO can also be used to approximate
the concentrations of some air tonics arising from motor-vehicle exhaust
emissions, such as benzene, I,3-butadiene, and perhaps directly emitted
PM2 s CO is most useful as an indicator in the microscale setting where
concentrations of pollutants vary dramatically over short distances (e.g.,
with distance from a roadway). it is less reliable in representing regional
distributions of these pollutants and is probably a poor indicator of motor-
vehicle air tonics, such as formaldehyde and acetaldehyde, that react rap-
idly and have substantial sources in the atmosphere.
Spatial Distribution of CO
Findings
Although ambient CO concentrations have dropped considerably
throughout the country, the number of monitors is inadequate to character-
ize CO distribution and identify all locations of high CO concentrations.
There may be hot spots within cities that have already attained the NAAQS
OCR for page 13
Summary 13
for CO or have not previously registered high ambient CO concentrations.
The locations of these hot spots may raise social equity issues regarding
exposure to mobile-source-related pollutants.
The monitors that have registered CO concentrations in excess of the
NAAQS since 1995 are predominantly located in Tower-income areas with
greater minority populations. However, unidentified hot spots might exist
in any location. Current data are insufficient to adequately characterize the
relationships between hot spot locations, population characteristics, and
health impacts.
Recommendations
EPA should employ air quality modeling and saturation studies9 in CO
problem areas to better characterize the spatial distribution of CO and the
populations affected. The information garnered can be used to improve site
selection for permanent monitoring, to improve model performance, and to
address possible environmental equity issues. Programs targeted to local
conditions can be developed using this information. These results should
also be linked to health impact studies in these locations. In particular,
EPA should try to better understand the upper end (higher CO levels) ofthe
distribution of ambient exposures to motor-vehicle emissions that occur in
most CO hot spots.
Permanent Monitoring
Findings
Although fewer and fewer locations are experiencing CO concentra-
tions above or near the NAAQS, the continued operation of most current
Saturation studies typically rely on portable monitors that "saturate" a geo-
graphical area with samplers to assess the air quality in places where high concen-
trations of pollutants are possible. Monitors can be deployed at temporary fixed-
site locations or in mobile sampling vehicles. These studies are helpful to air pollu-
tion control agencies for evaluating their ambient air monitoring networks, charac-
terizing pollutant concentrations over the entire saturation study area, and locating
hot spots or high pollutant impact points. Personal monitoring could be incorpo-
rated into such studies to relate ambient concentrations to personal exposure.
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14 Managing CO in Meteorological and Topographical Problem Areas
ambient monitors remains essential for Tong-term assessments of air quality
and health impacts.
Recommendations
Because of the value of CO monitoring information for air quality
management in general, agencies should resist removing CO monitors in
locations not expected to show violations. Instead, they should consider
continuing operations at existing CO monitoring sites, noting that when
monitors are co-Iocated the incremental costs of continued operation may
be relatively small compared with the data's usefulness for purposes be-
yond demonstrating attainment. The number and placement of permanent
monitors also need to reflect changes in growth and development patterns
to accurately assess the local air pollution situation. However, communi-
ties that have attained the CO standard with an adequate level of protection
of safety might not be willing to pay to obtain data from these monitors.
Support from federal and other sources might be needed to continue moni-
toring operations.
Ambient CO Modeling
Findlings
Emissions and air quality models are important tools for air quality
planning. Models help forecast changes in the mass of pollutants emitted
resulting from controls and severe air pollution events. Models are also
used to demonstrate attainment of the CO NAAQS, evaluate the effects of
new construction projects that greatly increase emissions, and research the
causes of pollution episodes and how to predict them. However, the spatial
and temporal resolution of models typically used in CO management at this
time is too coarse to capture the variability in pollutant concentrations,
which is necessary to identify local hot spots and accurately represent
unusual meteorological conditions.
Statistical forecasting models have been used to assess the probability
of future high-CO episodes. The approach was used in Denver, Colorado,
to assess the probability of having CO concentrations in excess of the
NAAQS after the alteration of the oxygenated fuels program. This model
OCR for page 15
Summary 15
takes into account the historical variability in CO concentrations resulting
from meteorology and unusual traffic events.
Recommendations
More sophisticated, physically comprehensive models that can simulate
how CO concentrations vary in time and space should be developed, ap-
plied, and evaluated. Ongoing research should be continued. Such models
would be used for air quality planning and forecasting and for assessing
human exposure to high concentrations of CO and related pollutants. Be-
cause CO is a relatively unreactive pollutant, the ability to better represent
CO's temporal and spatial distribution provides an effective diagnosis of
atmospheric dispersionpatterns. Mode! improvements would have applica-
tions for other air quality management issues and would offer the potential
to better understand the dispersion of chemical, biological, and radiological
materials. Most important, improved models will permit more effective
and realistic planning, leading to better-informed decisions by administra-
tors. Mode] development should occur in concert with improved monitor-
ing to enable mode] evaluation. In addition, the statistical forecasting mod-
els should be improved.
Representative terms from entire chapter:
hot spots
