Atmos. Chem. Phys. Discuss., 13, 11863-11918, 2013
www.atmos-chem-phys-discuss.net/13/11863/2013/
doi:10.5194/acpd-13-11863-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Biogenic VOC oxidation and organic aerosol formation in an urban nocturnal boundary layer: aircraft vertical profiles in Houston, TX
S. S. Brown1, W. P. Dubé1,2, R. Bahreini1,2,*, A. M. Middlebrook1, C. A. Brock1, C. Warneke1,2, J. A. de Gouw1,2, R. A. Washenfelder1,2, E. Atlas3, J. Peischl1,2, T. B. Ryerson1, J. S. Holloway1,2, J. P. Schwarz1,2, R. Spackman1,2, M. Trainer1, D. D. Parrish1, F. C. Fehshenfeld1,2, and A. R. Ravishankara1
1NOAA Earth System Research Laboratory, Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, USA
2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA
3RSMAS/MAC, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA
*now at: Department of Environmental Sciences, University of California, Riverside, CA 92521, USA

Abstract. Organic compounds are a large component of aerosol mass, but organic aerosol (OA) sources remain poorly characterized. Recent model studies have suggested nighttime oxidation of biogenic hydrocarbons as a potentially large OA source, but analysis of field measurements to test these predictions is sparse. We present nighttime vertical profiles of nitrogen oxides, ozone, VOCs and aerosol composition measured during low approaches of the NOAA P-3 aircraft to airfields in Houston, TX. This region has large emissions of both biogenic hydrocarbons and nitrogen oxides. The latter serves as a source of the nitrate radical, NO3, a key nighttime oxidant. Biogenic VOCs (BVOC) and urban pollutants were concentrated within the nocturnal boundary layer (NBL), which varied in depth from 100–400 m. Despite concentrated NOx at low altitude, ozone was never titrated to zero, resulting in rapid NO3 radical production rates of 0.2–2.7ppbv h-1 within the NBL. Monoterpenes and isoprene were frequently present within the NBL and underwent rapid oxidation (up to 1ppbv h−1), mainly by NO3 and to a lesser extent O3. Concurrent enhancement in organic and nitrate aerosol on several profiles was consistent with primary emissions and with secondary production from nighttime BVOC oxidation, with the latter equivalent to or slightly larger than the former. Ratios of organic aerosol to CO within the NBL ranged from 14 to 38 μg m−3 OA/ppmv CO. A box model simulation incorporating monoterpene emissions, oxidant formation rates and monoterpene SOA yields suggested overnight OA production of 0.5 to 9 μg m−3.

Citation: Brown, S. S., Dubé, W. P., Bahreini, R., Middlebrook, A. M., Brock, C. A., Warneke, C., de Gouw, J. A., Washenfelder, R. A., Atlas, E., Peischl, J., Ryerson, T. B., Holloway, J. S., Schwarz, J. P., Spackman, R., Trainer, M., Parrish, D. D., Fehshenfeld, F. C., and Ravishankara, A. R.: Biogenic VOC oxidation and organic aerosol formation in an urban nocturnal boundary layer: aircraft vertical profiles in Houston, TX, Atmos. Chem. Phys. Discuss., 13, 11863-11918, doi:10.5194/acpd-13-11863-2013, 2013.
 
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