Changes in United States deposition of nitrogen and sulfur compounds over five decades from 1970 to 2020. (15th July 2019)

• Record Type: Journal Article
• Authors: Nopmongcol, Uarporn; Beardsley, Ross; Kumar, Naresh; Knipping, Eladio; Yarwood, Greg
• Is Part Of: Atmospheric environment. Volume 209(2019)
• Page Start: 144
• Page End: 151
• Publication Date: 2019-07-15
• Subjects: Nitrogen -- Sulfur -- Air quality trends -- Photochemical modeling -- CAMx -- Deposition trends; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2019.04.018
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Evaluating long-term air quality and deposition trends can demonstrate effectiveness of control strategies and guide future air quality management planning. Observations show a reduction of atmospheric concentrations of NOx and SOx species and their wet and dry deposition since monitoring began in 1978 and 1987, respectively, although deposition observations are sparse. This study used a regional model (CAMx) nested within a global model (GEOS-Chem) to characterize regional changes in sulfur and nitrogen deposition due to intercontinental transport and local/regional anthropogenic emissions representing six modeling years spanning five decades (1970–2020). The meteorological year and the natural emissions were fixed at 2005 to isolate the effects of changing anthropogenic emissions. The downward trend from 1970 to 2020 of mean atmospheric SO2 concentration is 1.5–1.8%; of total S deposition is 1.0–1.7%; and of SO2 emissions is 1.4–1.8% per year. The rate of decline in NOy deposition of 0.6–1.4% per year is similar to the 0.5–1.6% per year reduction in NOx emissions, thus showing that the changes in deposition have tracked changes in emissions of SO2 and NOx emissions quite well. Further reducing N deposition could face some challenges due to increasing NHx contribution from NH3 emissions and the expectation of these to increase globally. Our study also examined the transference ratios of NOy and SOx in the context of the secondary NAAQS for NOx and SOx and found them to be sensitive to emission reductions over the study period. Highlights: U.S. emissions contributions to sulfur and oxidized nitrogen deposition have reduced since 1970. The relative contribution of NHx to total N deposition has increased during this period. Transference ratios in the context of the secondary NAAQS for NOx and SOx are sensitive to emission reductions.