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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 20 | Copyright
Atmos. Chem. Phys., 18, 15419-15436, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Oct 2018

Research article | 26 Oct 2018

A comprehensive organic nitrate chemistry: insights into the lifetime of atmospheric organic nitrates

Azimeh Zare1, Paul S. Romer1, Tran Nguyen2, Frank N. Keutsch3,a, Kate Skog3,b, and Ronald C. Cohen1,4 Azimeh Zare et al.
  • 1Department of Chemistry, University of California Berkeley, Berkeley, CA, USA
  • 2College of Agricultural and Environmental Sciences, University of California, Davis, CA, USA
  • 3Department of Chemistry, University of Wisconsin-Madison, Madison, WI, USA
  • 4Department of Earth and Planetary Sciences, University of California Berkeley, Berkeley, CA, USA
  • anow at: School of Engineering and Applied Sciences and Department of Chemistry & Chemical Biology, Harvard University, Cambridge, MA, USA
  • bnow at: Department of Chemical & Environmental Engineering, Yale University, New Haven, CT, USA

Abstract. Organic nitrate chemistry is the primary control over the lifetime of nitrogen oxides (NOx) in rural and remote continental locations. As NOx emissions decrease, organic nitrate chemistry becomes increasingly important to urban air quality. However, the lifetime of individual organic nitrates and the reactions that lead to their production and removal remain relatively poorly constrained, causing organic nitrates to be poorly represented by models. Guided by recent laboratory and field studies, we developed a detailed gas-phase chemical mechanism representing most of the important individual organic nitrates. We use this mechanism within the Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem) to describe the role of organic nitrates in nitrogen oxide chemistry and in comparisons to observations. We find the daytime lifetime of total organic nitrates with respect to all loss mechanisms to be 2.6h in the model. This is consistent with analyses of observations at a rural site in central Alabama during the Southern Oxidant and Aerosol Study (SOAS) in summer 2013. The lifetime of the first-generation organic nitrates is  ∼ 2h versus the 3.2h lifetime of secondary nitrates produced by oxidation of the first-generation nitrates. The different generations are subject to different losses, with dry deposition to the surface being the dominant loss process for the second-generation organic nitrates and chemical loss being dominant for the first-generation organic nitrates. Removal by hydrolysis is found to be responsible for the loss of  ∼ 30% of the total organic nitrate pool.

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Short summary
Organic nitrates play an important role in concentrations and distribution of NOx, ozone and aerosol as the most important air pollutants. We develop a state-of-the-science detailed chemical mechanism representing individual organic nitrates, which is appropriate to use in air quality models and results in a more accurate simulation of atmospheric chemistry. Using this mechanism we explore production and removal processes of organic nitrates in a rural environment that are poorly constrained.
Organic nitrates play an important role in concentrations and distribution of NOx, ozone and...