Atmos. Chem. Phys., 13, 4543-4562, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Observations of total RONO2 over the boreal forest: NOx sinks and HNO3 sources
E. C. Browne1, K.-E. Min2,*, P. J. Wooldridge1, E. Apel3, D. R. Blake4, W. H. Brune5, C. A. Cantrell3, M. J. Cubison6,**, G. S. Diskin7, J. L. Jimenez6, A. J. Weinheimer3, P. O. Wennberg8, A. Wisthaler9, and R. C. Cohen1,2
1Department of Chemistry, University of California Berkeley, Berkeley, CA, USA
2Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA, USA
3Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
4Department of Chemistry, University of California Irvine, Irvine, CA, USA
5Department of Meteorology, Pennsylvania State University, University Park, PA, USA
6Cooperative Institute for Research in the Environmental Sciences (CIRES) and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA
7NASA Langley Research Center, Hampton, Virginia, USA
8Division of Geology and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
9Institut 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

Abstract. In contrast with the textbook view of remote chemistry where HNO3 formation is the primary sink of nitrogen oxides, recent theoretical analyses show that formation of RONO2 (ΣANs) 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 ΣANs. We present observations of nitrogen oxides and organic molecules collected over the Canadian boreal forest during the summer which show that ΣANs account for ~20% of total oxidized nitrogen and that their instantaneous production rate is larger than that of HNO3. This confirms the primary role of reactions producing ΣANs as a control over the lifetime of NOx (NOx = NO + NO2) in remote, continental environments. However, HNO3 is generally present in larger concentrations than ΣANs indicating that the atmospheric lifetime of ΣANs is shorter than the HNO3 lifetime. We investigate a range of proposed loss mechanisms that would explain the inferred lifetime of ΣANs 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 NOx from the carbon backbone and/or (2) hydrolysis of particulate organic nitrates with HNO3 as a product. Implications of these ideas for our understanding of NOx and NOy budget in remote and rural locations are discussed.

Citation: Browne, E. C., Min, K.-E., Wooldridge, P. J., Apel, E., Blake, D. R., Brune, W. H., Cantrell, C. A., Cubison, M. J., Diskin, G. S., Jimenez, J. L., Weinheimer, A. J., Wennberg, P. O., Wisthaler, A., and Cohen, R. C.: Observations of total RONO2 over the boreal forest: NOx sinks and HNO3 sources, Atmos. Chem. Phys., 13, 4543-4562, doi:10.5194/acp-13-4543-2013, 2013.
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