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 fraction. The 14C/12C ratio is proportional to the fraction of a sample's carbon 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 -7 % to 24 %, from 1300 h to 1600 h was 27 % (n = 4) with a range of 12 % to 39%, and from 1700 h to 2000 h was 34 7 % for a single sample. 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 is 80 41 nmol mol-1 which may be representative of the natural VOC-C background for the Los Angeles air basin.
Citation: Journal of Geophysical Research-Atmospheres
Issue: No. D7-D8
Pub Type: Journals
atmosphere, Azusa, CA, back-trajectories, biogenic, ozone precursors, radiocarbon (14C), source characterization, VOC mixing ratio, volatile organic compounds (VOC)