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Understanding and Predicting Ozone Pollution
Atmospheric chemists delve into the processes that control ozone
formation.
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Ground-level ozone pollution, which stems in part from vehicle emissions, can cause
lung dysfunction in humans and significant losses in agricultural productivity. So it is
important for scientists to understand the processes that control ozone in the
atmosphere and the processes that foster ozone pollution in urban and rural
environments.
photo
by Stanley Leary
Atlanta traffic jams
at the interstate connector in downtown.(300-dpi JPEG version - 243k)
Click here to see film of average
ground-level ozone levels in Atlanta.
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Dr. William Chameides, Regents' Professor and Smithgall Chair of
Georgia Tech's School of
Earth and Atmospheric Sciences, focuses his
research on these processes. He and his colleagues are also identifying
effective methods for prediction and control of ozone pollution.
Ozone is a secondary pollutant, meaning it is not directly
emitted into the atmosphere, but is instead generated in the atmosphere
by chemical reactions. The pollutants that react to produce a secondary
pollutant are called "precursor compounds." In the case of ozone, there
are two key precursors: volatile organic compounds (VOCs) and nitrogen
oxides (NOx). Automobiles emit both of these pollutants. But there are
many other sources, including natural ones, of both chemicals. So,
Chameides explains, while eliminating vehicle emissions would
undoubtedly improve air quality, it would not totally solve the ozone
pollution problem and other air quality issues.
"The problem is further confounded by the non-proportional way in
which ozone responds to changes in precursor emissions," Chameides says.
"So, while vehicle emissions account for about half of Atlanta's ozone
precursor compounds, eliminating all vehicle emissions would probably
cut ozone concentrations in Atlanta by less than 50 percent."
In the past 20 years, automobile emission controls —
catalytic converters, for example — have led to major reductions
in vehicle emissions. Without emission controls, the ozone pollution
problem in Atlanta and other U.S. cities would probably be much worse.
But further progress will require even greater emission reductions
because of substantial increases over the past two decades in the number
of automobiles on the road and the number of vehicle miles driven
annually, Chameides says.
"Unfortunately, further reductions in automobile emissions
involve some difficult choices," Chameides says. "Traditionally,
automobile emissions have been lowered technologically with emission
control devices. These innovations do not come free of charge. They are
paid for by consumers when they purchase their cars. More recently,
programs have been implemented to lower emissions through the use of
gasolines specifically formulated for this purpose. These also have a
cost. Every spring when the specially formulated gasolines arrive at the
gas pumps, consumers pay about 5 to 10 cents per gallon more.
"There are other, perhaps less costly options, like mass
transport, telecommuting and having people closer to their place of
work," Chameides says. "But these require significant lifestyle changes
that many people are probably not prepared to make. Finally, there's one
other option: Don't do anything and live with deteriorating and
unhealthful air quality. This also has a cost, although it is often
difficult to quantify."
The need for greater reductions in ozone precursor emissions
controls will become more apparent, Chameides says, when the U.S.
Environmental Protection Agency's new ambient air quality standard for
ozone — 0.08 parts per million (ppm) over an 8-hour period —
is implemented (after cities achieve three consecutive years of meeting
the old standard). His data show that Atlanta will exceed the new
standard more often than the current one, which is 0.12 ppm over a
1-hour period.
Also, Chameides' research indicates that EPA's proposed new air
quality standard for fine particles will put Atlanta close to, if not
in, non-compliance on an annual basis. Vehicle exhausts contribute to
the particulate load in Atlanta's air, according to preliminary studies,
but how those particulates are produced is unclear, Chameides says.
Much of Chameides' air quality research falls under the umbrella
of the
Southern Oxidants Study (SOS), which was initiated in 1989 under
the leadership of Chameides and his Georgia Tech colleagues, Drs. C.S.
Kiang and Michael Rodgers. SOS is funded by EPA and other federal
agencies, as well as the private sector. "This study has made
significant contributions to our fundamental understanding of
atmospheric chemistry," Chameides says. "And it has provided tools
directly relevant to policy makers in the South and elsewhere."
Forecasting Ozone
Pollution
But predicting the ozone level for a given day is an inexact
science to say the least. Current forecasting approaches only yield a 50
percent accuracy rate. School of Earth and Atmospheric Science
researchers, including Dr. Michael Chang, believe they can improve that
statistic.
Chang and his colleagues are analyzing data and developing new
models for the
Georgia Department of Natural Resources to improve the
ozone forecasting capabilities of the agency's Atlanta Ozone Forecasting
Team. They are analyzing meteorological data to
uncover key physical and/or chemical elements
to better describe ozone events, times when the pollution exceeds EPA
standards.
To forecast ozone events, the researchers are applying models
developed to study the efficacy of potential ozone control strategies
for Atlanta. This forecast modeling may lead to improved understanding
of day-to-day variation in ozone concentrations. The new model accounts
for the relationship between chemical and physical meteorology, as well
as the spatial and temporal aspects of natural and human
activity-related emissions.
Meanwhile, a Georgia State University study seems to indicate
that some residents of the 13-county Atlanta region are responding to
the Atlanta Ozone Forecasting Team's calls for telecommuting, carpooling
and filling their gas tanks after dark on Smog Alert Days. These are
the days between May 1 and Sept. 30 when the team predicts that
Atlanta's air quality may exceed the EPA ozone pollution standard. But a
key question remains as to whether the Smog Alert Days are actually
effective in reducing ozone pollution levels, Chang says. Despite the
public's response, Atlanta still exceeded the EPA standard 22 times in
1998.
Chameides echoes Chang's concern. He believes a major missing
link in solving air quality problems is the government's frequent lack
of monitoring systems to determine the effectiveness of various
strategies.
"It would not be technically or scientifically difficult to give
the public this feedback," Chameides says. "Billions are spent on air
pollution control. If 1 or 2 percent of this was spent on monitoring
programs, there would be an enormous benefit to the public, as well as
the research community."
— Jane M. Sanders
With lung dysfunction and agricultural production decline
at stake, people need to know when ground-level ozone concentrations are
unhealthful. Perhaps their response can abate these problems.
For more information, contact Dr. William Chameides, School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332-0340. (Telephone: 404/894-1749) (E-mail: william.chameides@eas.gatech.edu)
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