ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-13-4543-2013 Observations of total RONO<sub>2</sub> over the boreal forest: NO<sub>x</sub> sinks and HNO<sub>3</sub> sources Browne E. C. 1 Min K.-E. 2 10 Wooldridge P. J. 1 Apel E. 3 Blake D. R. 4 Brune W. H. https://orcid.org/0000-0002-1609-4051 5 Cantrell C. A. https://orcid.org/0000-0002-3844-1560 3 Cubison M. J. 6 11 Diskin G. S. 7 Jimenez J. L. https://orcid.org/0000-0001-6203-1847 6 Weinheimer A. J. 3 Wennberg P. O. https://orcid.org/0000-0002-6126-3854 8 Wisthaler A. https://orcid.org/0000-0001-5050-3018 9 Cohen R. C. https://orcid.org/0000-0001-6617-7691 1 2 Department of Chemistry, University of California Berkeley, Berkeley, CA, USA Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA, USA Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA Department of Chemistry, University of California Irvine, Irvine, CA, USA Department of Meteorology, Pennsylvania State University, University Park, PA, USA Cooperative Institute for Research in the Environmental Sciences (CIRES) and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA NASA Langley Research Center, Hampton, Virginia, USA Division of Geology and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA Institut für Ionenphysik & Angewandte Physik, University of Innsbruck, Innsbruck, Austria now at: NOAA Earth System Research Laboratory and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, USA now at: Tofwerk AG, Thun, Switzerland 02 05 2013 13 9 4543 4562 Copyright: © 2013 E. C. Browne et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/13/4543/2013/acp-13-4543-2013.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/13/4543/2013/acp-13-4543-2013.pdf

In contrast with the textbook view of remote chemistry where HNO<sub>3</sub> formation is the primary sink of nitrogen oxides, recent theoretical analyses show that formation of RONO<sub>2</sub> (&Sigma;ANs) from isoprene and other terpene precursors is the primary net chemical loss of nitrogen oxides over the remote continents where the concentration of nitrogen oxides is low. This then increases the prominence of questions concerning the chemical lifetime and ultimate fate of &Sigma;ANs. We present observations of nitrogen oxides and organic molecules collected over the Canadian boreal forest during the summer which show that &Sigma;ANs account for ~20% of total oxidized nitrogen and that their instantaneous production rate is larger than that of HNO<sub>3</sub>. This confirms the primary role of reactions producing &Sigma;ANs as a control over the lifetime of NO<sub>x</sub> (NO<sub>x</sub> = NO + NO<sub>2</sub>) in remote, continental environments. However, HNO<sub>3</sub> is generally present in larger concentrations than &Sigma;ANs indicating that the atmospheric lifetime of &Sigma;ANs is shorter than the HNO<sub>3</sub> lifetime. We investigate a range of proposed loss mechanisms that would explain the inferred lifetime of &Sigma;ANs finding that in combination with deposition, two processes are consistent with the observations: (1) rapid ozonolysis of isoprene nitrates where at least ~40% of the ozonolysis products release NO<sub>x</sub> from the carbon backbone and/or (2) hydrolysis of particulate organic nitrates with HNO<sub>3</sub> as a product. Implications of these ideas for our understanding of NO<sub>x</sub> and NO<sub>y</sub> budget in remote and rural locations are discussed.

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