Characterization of ambient volatile organic compounds at the western boundary of the SCOS97-NARSTO modeling domain

Speciated volatile organic compounds (VOCs) measurements were made at remote upwind locations in order to establish the boundary conditions for input into air quality simulation modeling for the 1997 Southern California Ozone Study (SCOS97-NARSTO). These measurements were made on two islands off the coast of Southern California and two coastal sites on the northern and southern end of the modeling domain. Results show that the mixing ratios and composition of VOC are impacted at these sites by local emissions as well as transported aged emissions. Of the four sites, San Nicolas Island is most representative of the boundary conditions at the western edge of the modeling domain with total identified non-methane hydrocarbons, identified oxygenated compounds (excluding formaldehyde), and unidentified hydrocarbons at about 12, 10, and 6 ppbC, respectively. Formaldehyde and acetaldehyde are on the order of 0.5 ppbv each, and C6–C9 aldehydes account for a majority of the oxygenated compounds. Comparable measurements at remote downwind locations also show that oxygenated compounds, especially C6–C9 aldehydes account for a significant fraction of total oxygenated VOC in downwind locations.