Constraints on Aerosol Nitrate Photolysis as a Potential Source of HONO and NOₓ
2018
Romer, Paul S. | Wooldridge, Paul J. | Crounse, John D. | Kim, Michelle J. | Wennberg, Paul O. | Dibb, Jack E. | Scheuer, Eric | Blake, Donald R. | Meinardi, Simone | Brosius, Alexandra L. | Thames, Alexander B. | Miller, David O. | Brune, William H. | Hall, Samuel R. | Ryerson, Thomas B. | Cohen, Ronald C.
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. Gas-phase 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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