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Atmospheric Chemistry and Physics









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 (July-August 2004), SENEX (June-July 2013), and SEAC4RS (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 (NOy) in both 2004 and 2013. Among the major RON species, nitric acid (HNO3) is dominant (∼ 42-45 %), followed by NOx (31 %), total peroxy nitrates (ΣPNs; 14 %), and total alkyl nitrates (ΣANs; 9-12 %) on a regional scale. We find that most RON species, including NOx, ΣPNs, and HNO3, decline proportionally with decreasing NOx emissions in this region, leading to a similar decline in NOy. This linear response might be in part due to the nearly constant summertime supply of biogenic VOC 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.


Jingyi Li1, Jingqiu Mao2, Arlene M. Fiore3, Ronald C. Cohen4,5, John D. Crounse6, Alex P. Teng6,Paul O. Wennberg6,7, Ben H. Lee8, Felipe D. Lopez-Hilfiker8, Joel A. Thornton8, Jeff Peischl9,10,Ilana B. Pollack11, Thomas B. Ryerson9, Patrick Veres9,10, James M. Roberts9, J. Andrew Neuman9,10,John B. Nowak12,a, Glenn M. Wolfe13,14, Thomas F. Hanisco14, Alan Fried15, Hanwant B. Singh16,Jack Dibb17, Fabien Paulot18,19, and Larry W. Horowitz19

1Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Science and Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China
2Department of Chemistry and Biochemistry & Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775, USA
3Department of Earth and Environmental Sciences & Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA
4Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
5Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720, USA
6Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
7Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA
8Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA
9Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO 80305, USA
10Cooperative Institute for Research in Environmental Science, University of Colorado Boulder, Boulder, CO 80309, USA
11Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523, USA
12Aerodyne Research, Inc., Billerica, MA 01821, USA
13Joint Center for Earth System Technology, University of Maryland Baltimore County, Baltimore, MD 21250, USA
14Atmospheric Chemistry and Dynamics Lab, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
15Institute of Arctic & Alpine Research, University of Colorado Boulder, Boulder, CO 80309, USA
16NASA Ames Research Center, Moffett Field, CA 94035, USA
17Department of Earth Sciences and Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824, USA
18Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ 08544, USA
19Geophysical Fluid Dynamics Laboratory/National Oceanic and Atmospheric Administration, Princeton, NJ 08540, USA
anow at: NASA Langley Research Center, Hampton, VA 23681, USA

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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.