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Published April 28, 2015 | Published + Supplemental Material
Journal Article Open

Hydroxy nitrate production in the OH-initiated oxidation of alkenes


Alkenes are oxidized rapidly in the atmosphere by addition of OH and subsequently O_2 leading to the formation of β-hydroxy peroxy radicals. These peroxy radicals react with NO to form β-hydroxy nitrates with a branching ratio α. We quantify α for C_2–C_8 alkenes at 295 K ± 3 and 993 hPa. The branching ratio can be expressed as α = (0.045 ± 0.016) × N − (0.11 ± 0.05) where N is the number of heavy atoms (excluding the peroxy moiety), and listed errors are 2σ. These branching ratios are larger than previously reported and are similar to those for peroxy radicals formed from H abstraction from alkanes. We find the isomer distributions of β-hydroxy nitrates formed under NO-dominated peroxy radical chemistry to be different than the isomer distribution of hydroxy hydroperoxides produced under HO2-dominated peroxy radical chemistry. Assuming unity yield for the hydroperoxides implies that the branching ratio to form β-hydroxy nitrates increases with substitution of RO_2. Deuterium substitution enhances the branching ratio to form hydroxy nitrates in both propene and isoprene by a factor of ~ 1.5. The role of alkene chemistry in the Houston region is re-evaluated using the RONO_2 branching ratios reported here. Small alkenes are found to play a significant role in present-day oxidant formation more than a decade (2013) after the 2000 Texas Air Quality Study identified these compounds as major contributors to photochemical smog in Houston.

Additional Information

© Author(s) 2015. CC Attribution 3.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 10 February 2014 – Published in Atmos. Chem. Phys. Discuss.: 13 March 2014 - Revised: 13 March 2015 – Accepted: 25 March 2015 – Published: 28 April 2015. The authors thank T. Ryerson, I. B. Pollack, and J. Peischl at NOAA ESRL for ozone observations and T. F. Hanisco and G. M. Wolfe at NASA for formaldehyde observations from the NASA SEAC4RS flight on 18 September 2013. We acknowledge grant funding from the National Science Foundation (NSF) under grant AGS-1240604 and funding from the National Aeronautics and Space Administration (NASA) under grant NNX12AC06G and NNX14AP46G-ACCDAM.

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Supplemental Material - acp-15-4297-2015-supplement.pdf

Published - acp-15-4297-2015.pdf


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August 22, 2023
August 22, 2023