Articles | Volume 16, issue 12
Research article
23 Jun 2016
Research article |  | 23 Jun 2016

The lifetime of nitrogen oxides in an isoprene-dominated forest

Paul S. Romer, Kaitlin C. Duffey, Paul J. Wooldridge, Hannah M. Allen, Benjamin R. Ayres, Steven S. Brown, William H. Brune, John D. Crounse, Joost de Gouw, Danielle C. Draper, Philip A. Feiner, Juliane L. Fry, Allen H. Goldstein, Abigail Koss, Pawel K. Misztal, Tran B. Nguyen, Kevin Olson, Alex P. Teng, Paul O. Wennberg, Robert J. Wild, Li Zhang, and Ronald C. Cohen

Abstract. The lifetime of nitrogen oxides (NOx) affects the concentration and distribution of NOx and the spatial patterns of nitrogen deposition. Despite its importance, the lifetime of NOx is poorly constrained in rural and remote continental regions. We use measurements from a site in central Alabama during the Southern Oxidant and Aerosol Study (SOAS) in summer 2013 to provide new insights into the chemistry of NOx and NOx reservoirs. We find that the lifetime of NOx during the daytime is controlled primarily by the production and loss of alkyl and multifunctional nitrates (ΣANs). During SOAS, ΣAN production was rapid, averaging 90 ppt h−1 during the day, and occurred predominantly during isoprene oxidation. Analysis of the ΣAN and HNO3 budgets indicate that ΣANs have an average lifetime of under 2 h, and that approximately 45 % of the ΣANs produced at this site are rapidly hydrolyzed to produce nitric acid. We find that ΣAN hydrolysis is the largest source of HNO3 and the primary pathway to permanent removal of NOx from the boundary layer in this location. Using these new constraints on the fate of ΣANs, we find that the NOx lifetime is 11 ± 5 h under typical midday conditions. The lifetime is extended by storage of NOx in temporary reservoirs, including acyl peroxy nitrates and ΣANs.

Short summary
The lifetime of nitrogen oxides (NOx) is evaluated by analysis of field measurements from the southeastern United States. At warm temperatures in the daytime boundary layer, NOx interconverts rapidly with both PAN and alkyl and multifunctional nitrates (RONO2), and the relevant lifetime is the combined lifetime of these three classes. We find that the production of RONO2, followed by hydrolysis to produce nitric acid, is the dominant pathway for NOx removal in an isoprene dominated forest.
Final-revised paper