An estimated 152 million Americans live in areas that do not
meet national air-quality standards. In these locations, the ambient air contains
enough pollutants to affect residents’ health. Exposure to persistent
ground-level ozone (smog) and particle pollution has been tied to rising rates
of heart disease, lung cancer and childhood asthma. Recently, both the World
Health Organization and the American Academy of Pediatrics issued reports linking
these pollutants to children’s decreased lung functioning and increased
risk of respiratory infections.
In Maryland, 15 counties are not in attainment of Clean Air
Act standards. Baltimore ranks 11th of the 25 most-ozone polluted cities in
the American Lung Association’s 2005 National State of the Air Report.
Despite sustained corrective efforts by industry and regulators,
poor air quality is a fact of life in this region. Traditional air-quality
planning has focused on limiting pollution from emitting sources. Innovative
strategies may help improve air quality.
Clean Air Act Standards
Under the Clean Air Act, national ambient air-quality standards have been
set for certain common air pollutants. The U.S. Environmental Protection Agency
(EPA) uses health-based criteria for setting permissible levels of ground-level
ozone, particulate matter, carbon monoxide, nitrogen oxides, lead and sulfur
dioxide. A geographic area is in attainment of the Clean Air Act’s primary
standards when the level of each of these pollutants does not exceed the level
determined to negatively impact human health.
The Clean Air Act allows states flexibility in planning how
to meet and maintain national ambient air-quality standards. Each state or
district, with the legal authority to manage its air program, prepares air-quality
implementation plans (SIP) describing the measures that will be used to reduce
pollutant levels and/or maintain national standards. These plans must be approved
by the EPA. Once approved, SIPs are enforceable in court.
State Air-Quality Planning
In Maryland, controls placed on emitting sources, such as power plants,
gas stations, body shops and cars, have reduced ozone-forming pollutants by
approximately 40 percent from 1990 levels. However, this strategy has not reduced
smog enough to meet Clean Air Act standards. Pollutants transported from Ohio
and points south continue to degrade the air quality in much of the state.
New national ozone and particulate-matter standards will
become effective in June 2005. These standards must be attained by 2010 or
the state could face loss of federal funding.
The Maryland Department of the Environment is scheduled to
begin drafting its Ozone SIP early next year. Maryland’s Ozone SIP must
be submitted to the EPA by June 2007; the Particulate Matter SIP is due April
Emerging and Voluntary Measures
The EPA issued a new policy regarding incorporating emerging and voluntary
measures into SIPs in September 2004. This policy is designed to foster innovative
air-quality improvement strategies that have not typically been approved in
SIPs. It allows SIPs to include 1) emerging measures that foresee pollution
reductions that may not yet be fully quantifiable and 2) voluntary measures
that are not enforceable against an individual source.
The policy sets a presumptive limit on states’ use
of emerging and voluntary measures in SIPs. Emerging and voluntary measures
can only account for 6 percent of the emission reductions necessary to meet
Clean Air Act requirements. There are also practical challenges with demonstrating
progress towards improvement for longer term strategies. Nevertheless, since
many source controls have already been installed, scientists, policymakers
and the public are currently proposing new strategies as emerging or voluntary
measures in SIPs.
Innovative Strategies for Cleaner Air
Forest Service is exploring the feasibility of using urban forests to improve
air quality. Scientific research shows that increasing tree canopy cover can
reduce peak ozone concentration levels. The Forest Service is analyzing the
logistical issues associated with incorporating large-scale tree plantings
into state air-quality improvement planning.
environmental agencies in Georgia and Texas are considering strategies designed
to address the Heat Island Effect (the rise in temperature due to an increased
number of buildings and impermeable surface area). Because the emission of
many pollutants and ozone-forming chemicals is temperature-dependent, reducing
air temperature can improve air quality by reducing ozone formation. Studies
indicate that shade trees, permeable pavement and reflective rather than heat-absorbing
roofs work to offset air pollution in urban centers.
energy efficiency and maximizing energy conservation improves air quality by
decreasing reliance on power plants. Energy-efficient construction and long-term
commitments to alternative/zero-emission energies are being advanced as measures
to decrease regional air pollution.
In many parts of the United States, traditional emission-control
strategies have already been implemented to address the most acute air pollution
problems. While control technologies have limited source emissions, air quality
has not improved sufficiently to assure a healthy environment for almost half
of the population. Established source-control measures need to be supplemented
by more comprehensive strategies designed to create an environment that actively
Lisa Tilney is the Air Quality Program Manager for the National Tree Trust.