Changes in air quality and atmospheric deposition in the eastern United States: 1990–2004

Abstract

Data collected in the eastern United States (U.S.) between 1990 and 2004 at 34 dry and paired wet monitoring sites are examined. A goal is to evaluate the air quality impacts occurring between 1990 and 2004 resulting from legislatively mandated changes in emissions. Three 5‐year periods, 1990–1994 (P1), 1995–1999 (P2), and 2000–2004 (P3) are considered. Period‐to‐period changes in selected pollutant metrics are examined, focusing on P1‐to‐P3 changes. Data are composed from reported weekly measurements into estimates of means for year, site, and season. The mean squared error derived from analysis of variance applied to these means for atmospheric concentration, dry deposition velocity, precipitation rate, and dry, wet and total deposition is used to examine differences between periods for seasons and predefined regional groupings of sites. Results suggest that relationships exist at the current scale between changes in both concentration and deposition of relevant atmospheric pollutants and changes in SO2 emissions that are generally less than 1:1 and that these disparities are more pronounced for SO42− (a reaction product) than SO2 (the primary pollutant). Coincident timing and location suggest that legislatively mandated summertime reductions in estimated NOx emissions contributed strongly to observed reductions of atmospheric HNO3 concentration and dry deposition in the eastern U.S. Less than 1:1 relationships are also indicated at the current scale between changes in both concentration and deposition of the relevant measured secondary atmospheric pollutants, HNO3 and NO3−, and changes in NOx emissions. In the face of P1‐to‐P3 reductions in estimated emissions of both SO2 and NOx, wintertime changes in the sum of atmospheric SO42−, NO3−, and NH4+ concentrations, relative to those for corresponding SO42− concentrations, range from reductions that are less than 1:1 to actual increases.

Retention of surface nitrate additions in a temperate old field: implications for atmospheric nitrogen deposition over winter and plant nitrogen availability

“…These results were surprising, given that the addition rate of 2 g m −2 of N more than doubles current background deposition rates in the region of the site (Sickles and Shadwick 2007), and is consistent with projected increases in atmospheric nitrogen deposition over the next 50 years in the region (Galloway et al 2004). This lack of a significant plant growth response could reflect a proportionately low retention of the added N across all treatments or, as suggested above, the sequestration of the 15 N label in recalcitrant fractions of the soil organic matter.…”

“…In eastern North America, nitrate is the dominant component in atmospheric nitrogen deposition, and the proportion of nitrate further increases over winter as a result of decreased ammonium emissions from agricultural sources (Sickles and Shadwick 2007). Nitrate is highly mobile in soil and thus vulnerable to leaching losses, and the extent to which it is retained in temperate systems from late fall through early spring may have important implications for plant nitrogen availability during the following growing season.…”

Comparisons of watershed sulfur budgets in southeast Canada and northeast US: new approaches and implications

“…Similarly, implementation of the Eastern Canada Acid Rain Program reduced Canadian emissions such that total Canada-US SO 2 emissions were 14 million tonnes in 2006-a 50% reduction relative to 1980 levels (Canada-US 1992. These historical emission trends are matched by changes in the atmospheric concentration and deposition of S (Lynch et al 1996;Sickles and Shadwick 2007;Weathers et al 2006a). Spatially extensive and quantitatively constrained results showing these changes have been documented for wet deposition, but decreases have also been noted for components of dry deposition (composed mostly of SO 2 and SO 4 2-aerosols; Baumgardner et al 2002).…”

Spatial and temporal variation of stream chemistry associated with contrasting geology and land-use patterns in the Chesapeake Bay watershed—Summary of results from Smith Creek, Virginia; Upper Chester River, Maryland; Conewago Creek, Pennsylvania; and Difficult Run, Virginia, 2010–2013

“…Atmospheric wet deposition (nitrate plus ammonium) to the study watersheds was computed by using the methods described in Ruddy and others (2006) and data from the National Atmospheric Deposition Program. Although this approach uses only wet deposition data, the wet fraction is the majority fraction in this region (Sickles II and Shadwick, 2007). Wastewater inputs were computed by using the approach of Lindsey and others (2009), with population data obtained from the United States Census Bureau.…”