1Department of Chemistry, University of Wisconsin-Madison, Madison, WI, USA
2Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
3Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
4Chemical Sciences Division, National Oceanic and Atmospheric Administration, Boulder, CO, USA
5Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
6Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA
7Department of Physics, University of Helsinki, Helsinki, Finland
8Division of Applied Chemistry, Faculty of Urban Environmental Sciences, Tokyo Metropolitan University, Tokyo, Japan
9Department 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
Received: 27 Jan 2012 – Discussion started: 24 Feb 2012
Abstract. 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, RGF, displayed a very regular diurnal cycle over nearly 2 weeks of measurements. The only deviations in RGF 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 RGF and could reflect transitions between low and high NO regimes. The trend of increased RGF 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 RGF occurred. Satellite retrievals, which suggest higher RGF 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 RGF 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 NOx. In particular, RGF 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.
Revised: 24 Aug 2012 – Accepted: 19 Sep 2012 – Published: 22 Oct 2012
DiGangi, J. P., Henry, S. B., Kammrath, A., Boyle, E. S., Kaser, L., Schnitzhofer, R., Graus, M., Turnipseed, A., Park, J.-H., Weber, R. J., Hornbrook, R. S., Cantrell, C. A., Maudlin III, R. L., Kim, S., Nakashima, Y., Wolfe, G. M., Kajii, Y., Apel, E. C., Goldstein, A. H., Guenther, A., Karl, T., Hansel, A., and Keutsch, F. N.: Observations of glyoxal and formaldehyde as metrics for the anthropogenic impact on rural photochemistry, Atmos. Chem. Phys., 12, 9529-9543, doi:10.5194/acp-12-9529-2012, 2012.