Decadal Changes in Summertime Reactive Oxidized Nitrogen and Surface Ozone over the Southeast United States

• Published in: Atmospheric chemistry and physics Vol. 18; no. 3; pp. 2341 - 2361
• Main Authors: Li, Jingyi, Mao, Jingqiu, Fiore, Arlene M., Cohen, Ronald C., Crounse, John D., Teng, Alex P., Wennberg, Paul O., Lee, Ben H., Lopez-Hilfiker, Felipe D., Thornton, Joel A., Peischl, Jeff, Pollack, Ilana B., Ryerson, Thomas B., Veres, Patrick, Roberts, James M., Neuman, J. Andrew, Nowak, John B., Wolfe, Glenn M., Hanisco, Thomas F., Fried, Alan, Singh, Hanwant B., Dibb, Jack, Paulot, Fabien, Horowitz, Larry W.
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center Coopernicus Publications 16.02.2018; Copernicus GmbH; Copernicus Publications
• Subjects: Aerosols; Air pollution; Aircraft; Anthropogenic factors; Atmospheric chemistry; Atmospheric gases; Atmospheric research; Biogenic emissions; Climate change; Climate models; Datasets; Emissions; Emissions (Pollution); Emissions control; Environment Pollution; Estimates; Human influences; Laboratories; Model testing; Nitrates; Nitric acid; Nitric acids; Nitrogen; Nitrogen compounds; Nitrogen oxides; Nitrogen oxides emissions; Oxides; Ozone; Photochemicals; Pollution abatement; Profiles; Ron protein; Smog; Speciation; Species; Summer; Vertical profiles; VOCs; Volatile organic compounds; Southern United States; United States > US
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-18-2341-2018

Widespread efforts to abate ozone (O3) smog have significantly reduced emissions of nitrogen oxides (NOx) over the past 2 decades in the Southeast US, a place heavily influenced by both anthropogenic and biogenic emissions. How reactive nitrogen speciation responds to the reduction in NOx emissions in this region remains to be elucidated. Here we exploit aircraft measurements from ICARTT (International Consortium for Atmospheric Research on Transport and Transformation - July-August 2004), SENEX (Southeast Nexus - June-July 2013), and SEAC4RS (Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys - August-September 2013) and long-term ground measurement networks alongside a global chemistry-climate model to examine decadal changes in summertime reactive oxidized nitrogen (RON) and ozone over the Southeast US. We show that our model can reproduce the mean vertical profiles of major RON species and the total (NO (sub y)) in both 2004 and 2013. Among the major RON species, nitric acid (HNO3) is dominant (approximately 42-45 percent), followed by NOx (31 percent), total peroxy nitrates (Sigma PNs; 14 percent), and total alkyl nitrates (Sigma ANs; 9-12 percent) on a regional scale. We find that most RON species, including NOx, Sigma PNs, and HNO3, decline proportionally with decreasing NOx emissions in this region, leading to a similar decline in NO (sub y). This linear response might be in part due to the nearly constant summertime supply of biogenic VOC (Volatile Organic Compounds) emissions in this region. Our model captures the observed relative change in RON and surface ozone from 2004 to 2013. Model sensitivity tests indicate that further reductions of NOx emissions will lead to a continued decline in surface ozone and less frequent high-ozone events.