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Cite This: Environ. Sci. Technol. 2018, 52, 13738−13746 pubs.acs.org/est...

Romer, P., P. J. Wooldridge, J. D. Crounse, M. Kim, P. Wennberg, J. Dibb, E. Scheuer, D. R. Blake, S. Meinardi, A. Brosius, A. Thames, D. Miller, W. H. Brune, S. R. Hall, T. B. Ryerson, and R. C. Cohen (2018), Cite This: Environ. Sci. Technol. 2018, 52, 13738−13746 pubs.acs.org/est Constraints on Aerosol Nitrate Photolysis as a Potential Source of HONO and NOx, Environ. Sci. Technol., doi:10.1021/acs.est.8b03861.

The concentration of nitrogen oxides (NOx) plays a central role in controlling air quality. On a global scale, the primary sink of NOx is oxidation to form HNO3. Gasphase HNO3 photolyses slowly with a lifetime in the troposphere of 10 days or more. However, several recent studies examining HONO chemistry have proposed that particle-phase HNO3 undergoes photolysis 10−300 times more rapidly than gas-phase HNO3. We present here constraints on the rate of particle-phase HNO3 photolysis based on observations of NOx and HNO3 collected over the Yellow Sea during the KORUS-AQ study in summer 2016. The fastest proposed photolysis rates are inconsistent with the observed NOx to HNO3 ratios. Negligible to moderate enhancements of the HNO3 photolysis rate in particles, 1−30 times faster than in the gas phase, are most consistent with the observations. Small or moderate enhancement of particle-phase HNO3 photolysis would not significantly affect the HNO3 budget but could help explain observations of HONO and NOx in highly aged air.

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Atmospheric Composition
Tropospheric Composition Program (TCP)