Atmos. Chem. Phys. Discuss., 9, 9879-9926, 2009
© Author(s) 2009. This work is distributed
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Closing the peroxy acetyl (PA) radical budget: observations of acyl peroxy nitrates (PAN, PPN, and MPAN) during BEARPEX 2007
B. W. LaFranchi1, G. M. Wolfe2, J. A. Thornton3, S. A. Harrold3, E. C. Browne1, K. E. Min4, P. J. Wooldridge1, J. B. Gilman5, W. C. Kuster5, P. D. Goldan5, J. A. deGouw5, M. McKay6,*, A. H. Goldstein6, X. Ren7,**, J. Mao7,***, and R. C. Cohen1,4
1Department of Chemistry, University of California, Berkeley, Berkeley, CA, USA
2Department of Chemistry, University of Washington, Seattle, WA, USA
3Department of Atmospheric Sciences, University of Washington, Seattle, WA, USA
4Department of Earth and Planetary Science, University of California, Berkeley, CA, USA
5NOAA/ESRL Chemical Sciences Division, Boulder, CO, USA
6Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA
7Department of Meteorology, Penn State University, University Park, PA, USA
*now at: California Air Resources Board, Sacramento, CA, USA
**now at: Rubenstein School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA
***now at: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

Abstract. Acyl peroxy nitrates (APNs, also known as PANs) are formed from the oxidation of aldehydes and other oxygenated VOC (oVOC) in the presence of NO2. Formation of APNs suppresses NOx (NOx≡NO+NO2) in urban areas and enhances NOx downwind in urban plumes, increasing the rate of ozone production throughout an urban plume. APNs also redistribute NOx on global scales, enhancing NOx and thus ozone production. There are both anthropogenic and biogenic oVOC precursors to APNs, but a detailed evaluation of their chemistry against observations has proven elusive. Here we describe measurements of PAN, PPN, and MPAN along with the majority of chemicals that participate in their production and loss, including OH, HO2, numerous oVOC, and NO2. Observations were made during the Biosphere Effects on AeRosols and Photochemistry Experiment (BEARPEX 2007) in the outflow of the Sacramento urban plume. These observations are used to evaluate a detailed chemical model of APN ratios and concentrations. We find the ratios of APNs are nearly independent of the loss mechanisms and thus an especially good test of our understanding of their sources. We show that oxidation of methylvinyl ketone, methacrolein, methyl glyoxal, biacetyl and acetaldehyde are all significant sources of the PAN+peroxy acetyl (PA) radical reservoir, with methylvinyl ketone (MVK) often being the primary non-acetaldehyde source. At high temperatures, oxidation of non-acetaldehyde PA radical sources contributes over 60% to the total PA production rate. An analysis of absolute APN concentrations reveals a missing APN sink that can be resolved by increasing the PA+∑RO2 rate constant by a factor of 3.

Citation: LaFranchi, B. W., Wolfe, G. M., Thornton, J. A., Harrold, S. A., Browne, E. C., Min, K. E., Wooldridge, P. J., Gilman, J. B., Kuster, W. C., Goldan, P. D., deGouw, J. A., McKay, M., Goldstein, A. H., Ren, X., Mao, J., and Cohen, R. C.: Closing the peroxy acetyl (PA) radical budget: observations of acyl peroxy nitrates (PAN, PPN, and MPAN) during BEARPEX 2007, Atmos. Chem. Phys. Discuss., 9, 9879-9926, doi:10.5194/acpd-9-9879-2009, 2009.
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