Measurements of Rural Sulfur Dioxide and Particle Sulfate: Analysis of CASTNet Data, 1987 through 1996

Abstract

The Clean Air Status and Trends Network (CASTNet) was implemented by the U.S. Environmental Protection Agency (EPA) in 1991 in response to Title IX of the Clean Air Amendments of 1990, which mandated the deployment of a national ambient air monitoring network to track progress of the implementation of emission reduction programs in terms of deposition, air quality, and changes to affected ecosystems. CASTNet evolved from the National Dry Deposition Network (NDDN).CASTNet currently consists of 45 sites in the eastern United States and 28 sites in the West. Each site measures sulfur dioxide (SO 2 ), nitric acid (HNO 3 ), particle sulfate (SO 4 = ), particle nitrate (NO 3 -), and ozone. Nineteen sites collect precipitation samples. NDDN/CASTNet uses a uniform set of site-selection criteria which provides the data user with consistent measures to compare each site. These criteria also ensure that, to the extent possible, CASTNet sites are located away from local emission sources.This paper presents an analysis of SO 2 and SO 4 = concentration data collected from 1987 through 1996 at rural NDDN/CASTNet sites. Annual and seasonal variability IMPLICATIONS Atmospheric concentrations of SO 2 and SO -play major roles in the processes of acidic deposition and visibility degradation. Understanding spatial patterns of these atmospheric constituents provides key information to determine whether the emission reduction program for sulfur will mitigate the environmental effects of acid deposition.is examined. Gradients of SO 2 and SO 4 = are discussed. The variability of the atmospheric mix of SO 2 and SO 4 = is explored spatially and seasonally. Data from CASTNet are also compared to SO 2 and SO 4 = data from concurrent monitoring studies in rural areas.The Midwest and the Northeast have the highest annual averages of SO 2 , greater than 10 µg/m 3 . SO 2 concentrations vary by a factor of 6 across the six eastern subregions. The annual SO 2 concentrations for western sites average less than 1 µg/m 3 . A gradient in SO 2 concentrations in the Ohio River Valley was observed, decreasing in northeasterly, easterly, and southeasterly directions. Also, a decreasing concentration gradient was observed for SO 4 = from the Midwest to the East and Southeast, although the gradient was not as pronounced as for SO 2 . Both SO 2 and SO 4 = exhibited strong seasonal cycles.

Multi-source SO<sub>2</sub> emission retrievals and consistency of satellite and surface measurements with reported emissions

“…In situ SO 2 ground-level measurements from the US Clean Air Status and Trend Network (CASTNet; Baumgardner et al, 1999;Park et al, 2004;Schwede et al, 2011), operated by the US EPA (http://www.epa.gov/ castnet), and the Canadian Air and Precipitation Monitoring Network (CAPMoN: http://www.ec.gc.ca/rs-mn/default. asp?lang=En&n=752CE271-1; Schwede et al, 2011), operated by Environment and Climate Change Canada (ECCC), were used in this study.…”

“…Ground-based networks such as the US Clean Air Status and Trends Network (CASTNet) and Canadian Air and Precipitation Monitoring Network (CAPMoN) are specifically designed to monitor long-term trends of gaseous pollutants in rural areas away from major pollution emission sources (Baumgardner et al, 1999;Park et al, 2004;Schwede et al, 2011). Their measurements show that over the eastern US, reductions in regional SO 2 emissions have led to significant reductions in monitored SO 2 concentrations (Sickles II and Shadwick, 2015;Xing et al, 2013).…”

Spatial sampling design for prediction with estimated parameters

“…The data we used to fit the spatial model are the 2002 annual mean of the SO 2 level in the unit of parts per billion, downloaded from http://www.epa.gov/air/data/index.html. Baumgardner, Isil, Bowser, and Fitzgerald (1999) and Baumgardner et al (2002) provided descriptions of the measurement methods used and some summary statistics. Recent research on SO 2 data focused on the estimation of the temporal trend (Malm et al 2002;Mueller 2003;Holland, Caragea, and Smith where (s) is a stationary Gaussian random field with isotropic Gaussian covariance function.…”

Seasonal Aerosol Sulfate Trends for Selected Regions of the United States

“…CASTNet, along with its predecessor NDDN, uses an open-face filter pack sampler to collect weekly-integrated samples of particulate SO 4 2Ϫ (PS) and SO 2 as well as other species. 5,6 This system does not attempt to distinguish particles by size (e.g., no size-selective inlet is used).…”