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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 4 | Copyright
Atmos. Chem. Phys., 16, 2575-2596, 2016
https://doi.org/10.5194/acp-16-2575-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 02 Mar 2016

Research article | 02 Mar 2016

On the effectiveness of nitrogen oxide reductions as a control over ammonium nitrate aerosol

S. E. Pusede1,a, K. C. Duffey1, A. A. Shusterman1, A. Saleh1, J. L. Laughner1, P. J. Wooldridge1, Q. Zhang2, C. L. Parworth2, H. Kim3, S. L. Capps4, L. C. Valin5, C. D. Cappa6, A. Fried7, J. Walega7, J. B. Nowak8, A. J. Weinheimer9, R. M. Hoff10, T. A. Berkoff11, A. J. Beyersdorf11, J. Olson11, J. H. Crawford11, and R. C. Cohen1,12 S. E. Pusede et al.
  • 1Department of Chemistry, University of California Berkeley, Berkeley, CA 94720, USA
  • 2Department of Environmental Toxicology, University of California at Davis, Davis, CA 95616, USA
  • 3Center for Environment, Health and Welfare Research, Korea Institute of Science and Technology, Seoul, Korea
  • 4Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
  • 5Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
  • 6Department of Civil and Environmental Engineering, University of California at Davis, Davis, CA 95616, USA
  • 7Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309, USA
  • 8Aerodyne Research, Inc., Billerica, Billerica, MA 01821, USA
  • 9Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO 80307, USA
  • 10Department of Physics, University of Maryland Baltimore County, Baltimore, MD 21250, USA
  • 11NASA Langley Research Center, Hampton, VA 23681, USA
  • 12Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA 94720, USA
  • anow at: Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA

Abstract. Nitrogen oxides (NOx) have fallen steadily across the US over the last 15 years. At the same time, NOx concentrations decrease on weekends relative to weekdays, largely without co-occurring changes in other gas-phase emissions, due to patterns of diesel truck activities. These trends taken together provide two independent constraints on the role of NOx in the nonlinear chemistry of atmospheric oxidation. In this context, we interpret interannual trends in wintertime ammonium nitrate (NH4NO3) in the San Joaquin Valley of California, a location with the worst aerosol pollution in the US and where a large portion of aerosol mass is NH4NO3. Here, we show that NOx reductions have simultaneously decreased nighttime and increased daytime NH4NO3 production over the last decade. We find a substantial decrease in NH4NO3 since 2000 and conclude that this decrease is due to reduced nitrate radical-initiated production at night in residual layers that are decoupled from fresh emissions at the surface. Further reductions in NOx are imminent in California, and nationwide, and we make a quantitative prediction of the response of NH4NO3. We show that the combination of rapid chemical production and efficient NH4NO3 loss via deposition of gas-phase nitric acid implies that high aerosol days in cities in the San Joaquin Valley air basin are responsive to local changes in NOx within those individual cities. Our calculations indicate that large decreases in NOx in the future will not only lower wintertime NH4NO3 concentrations but also cause a transition in the dominant NH4NO3 source from nighttime to daytime chemistry.

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