Clean Air Status and Trends Network Annual Report: 2011 Page: 4 of 101
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CASTNET 2011 Annual Report
The EPA Clean Air Status and Trends Network (CASTNET) measures atmospheric pollution
concentrations in order to evaluate the effectiveness of national and regional air pollution control
programs. This report presents 2011 maps of the geographic distribution of sulfur and nitrogen
pollutant concentrations, ozone (03) levels, and deposition fluxes and examines trends in air
quality since 1990. CASTNET measured rural, regionally representative concentrations of sulfur
and nitrogen species and 03 at 83 sites in the United States and Canada during 2011.
" Mean annual sulfur dioxide (SO2) and particulate sulfate (SO4) concentrations declined
significantly over the 22-year period 1990 through 2011 and showed a substantive decline
since 2005. Three-year mean annual SO2 levels declined 72 percent while SO0
concentrations declined 52 percent at eastern reference sites from 1990 through 2011. SO2
concentrations measured at western reference sites were reduced by 54 percent, and SO4
levels dropped by 21 percent over the 16-year period (1996 through 2011).
" Total (dry + wet) sulfur deposition estimated in the eastern United States declined by
59 percent from 1990 through 2011. Total sulfur deposition aggregated over western
reference sites fell by 35 percent over the 16 years 1996 through 2011.
" Three-year mean annual concentrations of total nitrate (NO), which is comprised of
nitric acid (HNO3) plus particulate NO3 declined 37 percent at eastern sites over the 22-year
period. Total NOQ levels measured at western reference sites dropped by 29 percent over
the 16 years.
" Total nitrogen deposition [particulate NOQ (dry + wet) and HNO3] fell by 26 percent from
1990 through 2011 at eastern reference sites. Total nitrogen deposition estimated for
western reference sites was reduced by 22 percent over the 16 years. However, total
nitrogen deposition increased significantly at eastern reference sites from 2010 to 2011
because of increased nitrogen concentration in precipitation. The network recorded the
highest annual average precipitation over the 22 years.
" The mean fourth highest daily maximum 8-hour average 03 concentration for 2011 was
68 parts per billion (ppb), which was lower than the 2010 value of 69 ppb and higher than
the 2009 concentration of 64 ppb, the lowest in the history of the network. Four eastern and
three California sites recorded exceedances of the 8-hour standard of 0.075 parts per
million during the most recent 3-year period (2009 through 2011).
" Measurements taken during 2011 and historical data collected over the period 1990
through 2010 were analyzed relative to data quality indicators 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.
" In 2011, EPA-sponsored CASTNET sites became compliant with the requirements of
40 CFR Part 58, and 03 data from EPA sites were delivered to the EPA Air Quality System.
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AMEC Environement & Infrastucture, Inc. Clean Air Status and Trends Network Annual Report: 2011, report, February 2013; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc949427/m1/4/: accessed April 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.