1Department of Chemistry, Reed College, Portland, OR, USA
2Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO, USA
3Cooperative Institute for Research in Environmental Sciences (CIRES), Boulder, CO, USA
4Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
5Department of Chemistry, University of California at Berkeley, Berkeley, CA, USA
6Institute for Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
7IASMA Research and Innovation Centre, Fondazione Edmund Mach, Food Quality and Nutrition Area, S. Michele a/A, Italy
8Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
9Department of Earth and Atmospheric Science, University of Houston, Houston, TX, USA
Received: 23 Oct 2012 – Discussion started: 21 Jan 2013
Abstract. At the Rocky Mountain Biogenic Aerosol Study (BEACHON-RoMBAS) field campaign in the Colorado front range, July–August 2011, measurements of gas- and aerosol-phase organic nitrates enabled a study of the role of NOx (NOx = NO + NO2) in oxidation of forest-emitted volatile organic compounds (VOCs) and subsequent aerosol formation. Substantial formation of peroxy- and alkyl-nitrates is observed every morning, with an apparent 2.9% yield of alkyl nitrates from daytime RO2 + NO reactions. Aerosol-phase organic nitrates, however, peak in concentration during the night, with concentrations up to 140 ppt as measured by both optical spectroscopic and mass spectrometric instruments. The diurnal cycle in aerosol fraction of organic nitrates shows an equilibrium-like response to the diurnal temperature cycle, suggesting some reversible absorptive partitioning, but the full dynamic range cannot be reproduced by thermodynamic repartitioning alone. Nighttime aerosol organic nitrate is observed to be positively correlated with [NO2] × [O3] but not with [O3]. These observations support the role of nighttime NO3-initiated oxidation of monoterpenes as a significant source of nighttime aerosol. Nighttime production of organic nitrates is comparable in magnitude to daytime photochemical production at this site, which we postulate to be representative of the Colorado front range forests.
Revised: 25 May 2013 – Accepted: 23 Jul 2013 – Published: 02 Sep 2013
Fry, J. L., Draper, D. C., Zarzana, K. J., Campuzano-Jost, P., Day, D. A., Jimenez, J. L., Brown, S. S., Cohen, R. C., Kaser, L., Hansel, A., Cappellin, L., Karl, T., Hodzic Roux, A., Turnipseed, A., Cantrell, C., Lefer, B. L., and Grossberg, N.: Observations of gas- and aerosol-phase organic nitrates at BEACHON-RoMBAS 2011, Atmos. Chem. Phys., 13, 8585-8605, doi:10.5194/acp-13-8585-2013, 2013.