ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-9529-2012 Observations of glyoxal and formaldehyde as metrics for the anthropogenic impact on rural photochemistry DiGangi J. P. 1 10 Henry S. B. 1 Kammrath A. 1 11 Boyle E. S. 1 Kaser L. 2 Schnitzhofer R. 2 Graus M. 3 4 Turnipseed A. 5 Park J-H. 6 Weber R. J. 6 Hornbrook R. S. 5 Cantrell C. A. 5 Maudlin III R. L. 5 7 12 Kim S. 5 Nakashima Y. 8 Wolfe G. M. 1 Kajii Y. 8 Apel E.C. 5 Goldstein A. H. 6 9 Guenther A. 5 Karl T. 5 Hansel A. 2 Keutsch F. N. 1 Department of Chemistry, University of Wisconsin-Madison, Madison, WI, USA Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA Chemical Sciences Division, National Oceanic and Atmospheric Administration, Boulder, CO, USA Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA Department of Physics, University of Helsinki, Helsinki, Finland Division of Applied Chemistry, Faculty of Urban Environmental Sciences, Tokyo Metropolitan University, Tokyo, Japan Department of Civil and Environmental Engineering, University of California, Berkeley, CA, USA now at: Department of Civil & Environmental Engineering, Princeton University, Princeton, NJ, USA now at: Kimberly Clark Corporation, Neenah, WI, USA now at: Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, USA 22 10 2012 12 20 9529 9543 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/9529/2012/acp-12-9529-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/9529/2012/acp-12-9529-2012.pdf

We present simultaneous fast, in-situ measurements of formaldehyde and glyoxal from two rural campaigns, BEARPEX 2009 and BEACHON-ROCS, both located in Pinus Ponderosa forests with emissions dominated by biogenic volatile organic compounds (VOCs). Despite considerable variability in the formaldehyde and glyoxal concentrations, the ratio of glyoxal to formaldehyde, R<sub>GF</sub>, displayed a very regular diurnal cycle over nearly 2 weeks of measurements. The only deviations in R<sub>GF</sub> were toward higher values and were the result of a biomass burning event during BEARPEX 2009 and very fresh anthropogenic influence during BEACHON-ROCS. Other rapid changes in glyoxal and formaldehyde concentrations have hardly any affect on R<sub>GF</sub> and could reflect transitions between low and high NO regimes. The trend of increased R<sub>GF</sub> from both anthropogenic reactive VOC mixtures and biomass burning compared to biogenic reactive VOC mixtures is robust due to the short timescales over which the observed changes in R<sub>GF</sub> occurred. Satellite retrievals, which suggest higher R<sub>GF</sub> for biogenic areas, are in contrast to our observed trends. It remains important to address this discrepancy, especially in view of the importance of satellite retrievals and in situ measurements for model comparison. In addition, we propose that R<sub>GF</sub> represents a useful metric for biogenic or anthropogenic reactive VOC mixtures and, in combination with absolute concentrations of glyoxal and formaldehyde, furthermore represents a useful metric for the extent of anthropogenic influence on overall reactive VOC processing via NO<sub>x</sub>. In particular, R<sub>GF</sub> yields information about not simply the VOCs dominating reactivity in an airmass, but the VOC processing itself that is directly coupled to ozone and secondary organic aerosol production.

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