Clean Air Status and Trends Network Annual Report: 2010 Page: 4 of 97
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The EPA Clean Air Status and Trends Network (CASTNET) provides measured atmospheric
pollution concentration data in order to evaluate the effectiveness of national and regional
air pollution control programs. This report presents maps of the geographic distribution of
sulfur and nitrogen pollutant concentrations, ozone levels, and deposition fluxes measured
in 2010 and examines trends in air quality since 1990. CASTNET measured rural, regionally
representative concentrations of sulfur and nitrogen species and ozone at 84 sites in the
United States and Canada during 2010.
Key Results through 2010
+ Mean annual sulfur dioxide and particulate sulfate concentrations declined
significantly over the 21-year period 1990 through 2010 and showed a substantive
decline since 2005. Three-year average sulfur dioxide (SO2) levels declined 65 percent
while sulfate concentrations declined 48 percent at eastern reference sites from
1990 through 2010. SO2 concentrations measured at western reference sites were
reduced by 49 percent over the 15-year period (1996-1999 through 2008-2010).
Western sulfate levels dropped by 40 percent over the same time period.
+ Total (dry + wet) sulfur deposition measured in the East declined by 55 percent from
1990 through 2010. Total sulfur deposition aggregated over western reference sites
fell by 28 percent over the 15 years 1996 through 2010. The 2010 total sulfur flux at
western sites was higher than the 2009 flux.
+ Three-year mean annual concentrations of total nitrate (nitric acid plus particulate
nitrate) declined 35 percent at eastern sites over the 21-year period. The 2010
concentration was about 8 percent higher than the 2009 level. Total nitrate levels
measured at western reference sites dropped by 35 percent over the 15 years.
+ Total nitrogen deposition fell by 26 percent from 1990 through 2010 at eastern
reference sites. Total nitrogen deposition estimated for western reference sites was
reduced by 20 percent over the 15 years. The 2010 total nitrogen flux at western sites
was higher than the 2009 flux.
+ The mean fourth highest daily maximum 8-hour average ozone concentration for
2010 (69 ppb) was higher than the 2009 value of 64 ppb, which was the lowest in the
history of the network. Only three eastern and five California sites recorded
exceedances of the 8-hour standard of 0.075 ppm during the most recent 3-year
+ Measurements taken during 2010 and historical data collected over the period
1990-2009 were analyzed relative to data quality objectives and their numerical
measures. These analyses demonstrate that CASTNET data can be used with
confidence and that CASTNET continues to produce information of the highest quality.
CASTNETAnnuaI Report -2010 ii Executive Summary
CAS TNE T Annual Report - 2010
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AMEC Environment & Infrastructure, Inc. Clean Air Status and Trends Network Annual Report: 2010, report, April 2012; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc949004/m1/4/: accessed February 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.