A predominantly rural ozone monitoring network was
operated under the auspices of the Clean Air Status and
Trends Network (CASTNet) from 1988 until 1995. Ozone
data from sites in the eastern United States are presented
and several indices are used to describe the spatial and
temporal distribution of ozone concentration and expo-sure.
These indices are SUM06, W126, the 8-hour rolling
average (MAX 8hr >80), and the current National Ambient
Air Quality Standards (NAAQS) for ozone. Ozone indices
were selected to illustrate the spatial and temporal distri-bution
of ozone, and the sensitivity of this distribution
to different representations of concentration or exposure.
CASTNet is unique in that a uniform set of site selec-tion
criteria and uniform procedures, including traceabil-ity
to a single primary standard, provide a high degree of
comparability across sites. Sites were selected to avoid
undue influence from point sources, area sources, or local
activities. The sites reflect a wide range of land use and
terrain types including agricultural and forested, in flat,
rolling, and complex terrain from the eastern seaboard
across the Appalachian Mountains to the Midwest.
Results indicate that ozone concentrations varied
greatly in time and space across the eastern United States.
Sites in the upper northeast, upper midwest, and southern
periphery subregions experienced relatively low ozone
during the years of record compared to sites in the north-east,
midwest, and south central subregions. Ozone ex-posures
at an individual rural site are dependent on many
factors, including terrain, meteorology, and distance from
sources of precursors. Relative to the current (as of 1996)
NAAQS, only a handful of CASTNet sites near major ur-ban
areas report exceedances. In contrast, the majority of
CASTNet sites might exceed the proposed new primary
standard for ozone.
Sites at high elevation (>900m) in the east exhibit
relatively high exposure statistics (e.g., SUM06 and W126),
but no exceedance of the current ozone standard from
1988 through 1995. Terrain effects explain some of the
variability within subregions and are an important con-sideration
in the design of monitoring networks for ozone
and possibly other pollutants.
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Publication Type:
Journal
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Publication Date:
August 1998
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