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BIOGENIC CONTRIBUTIONS TO ATMOSPHERIC VOLATILE ORGANIC COMPOUNDS IN AZUSA CA
Citation:
Klouda, G. A., C W. Lewis, D. C. Stiles, J. L. Marolf, W. D. Ellenson, AND W A. Lonneman. BIOGENIC CONTRIBUTIONS TO ATMOSPHERIC VOLATILE ORGANIC COMPOUNDS IN AZUSA CA. JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES 107(D8):7-1-7-13, (2002).
Impact/Purpose:
To use the tools of radiocarbon (14C) and gas chromatographic (GC) analysis combined with various receptor models to determine the contributions of sources to ambient VOC, and indirectly their contribution to tropospheric ozone via their role as sources of ozone precursors.
Description:
An objective of the 1997 Southern California Ozone Study (SCOS97) was to provide an up-to-date assessment of the importance of biogenic emissions for tropospheric ozone production in the South Coast Air Basin. To this end ambient air samples were collected during September 1997 at the Azusa air monitoring station for subsequent measurement of their radiocarbon (14C) content of the atmospheric non-methane volatile organic compound (VOC) fraction. The 14C/12C ratio is proportional to the fraction of a sample's caarbon that is biogenic. The proportionality constant was determined from local samples of vegetation, gasoline and ambient CO2 collected during the same period. The median fraction of biogenic VOC observed from 0600 h to 0900 h was 7 % (n = 5) with a range of -8 % to 24 %, from 1300 h to 1600 h it was 27 % (n = 4) with a range of 11 % to 39%, and from 1700 h to 2000 h it was 34 + or - 7 % for a single sample. Based on calculated 24-h back-trajectories, the dominant source region for the air masses associated with periods of high biogenic VOC levels was a sector extending from the north to the east. Over all time and space that the samples represent, the median fraction of biogenic VOC was 18 % (n = 10). Expressed as an atmospheric mixing ratio, the overall (median and 95 % confidence interval) biogenic VOC-carbon contribution was 80 + or - 50 nmol mol-1 which may be representative of the natural VOC-carbon background for the Los Angeles air basin.
This work was supported by the U.S. Environmental Protection Agency under Contract No. 68D50049, Interagency Agreement DW13937923-01-0, and by the National Institute of Standards and Technology. It has been subjected to Agency review and approved for publication. Certain commercial equipment, instruments, or materials are identified in this paper to specify adequately the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.