Volatile Organic Compounds and Secondary Organic
Shared by: zeb19689
Volatile Organic Compounds and Secondary Organic Aerosol Joost de Gouw NOAA Earth System Research Laboratory & Cooperative Institute for Research in Environmental Sciences, CU Boulder Volatile Organic Compounds (VOCs) are emitted from a wide variety of natural and man-made sources. In the atmosphere, the photo-oxidation of VOCs leads to the formation of ozone and secondary organic aerosol (SOA) that are both important for air quality and climate forcing. In this talk, I will give an overview of our recent studies on the emissions and chemical transformation of VOCs. We studied the direct emissions and secondary formation of VOCs at a sub-urban ground site in Mexico City and compared the results with previous studies in the U.S. VOC emission ratios relative to combustion tracers such as CO and CO2 are higher in Mexico City than in the U.S. The formation of SOA was found to be significant in the afternoon and much higher than can be explained from the measured precursors and their particulate mass yields determined from smog chambers. In an effort to quantify the contribution from biogenic VOCs to the formation of SOA, we studied if measurements of carbonyl sulfide (COS) can be used as an inert, inverted tracer of biogenic emissions. COS is a long-lived trace gas in the atmosphere with an oceanic source and a surface sink through the uptake by vegetation and soils. We demonstrate that air masses with reduced COS were, on average, enriched in biogenic VOCs and their oxidation products. The enrichment was only small for water-soluble organic carbon (WSOC), however, suggesting that biogenic VOCs only contributed a small amount of SOA. We summarize the recent insights into the emissions and formation of organic aerosol. Different studies of SOA formation in urban air consistently reveal a strong growth in the first day after emission. The results on SOA formation in biomass burning plumes are less clear. We combined the evidence to construct a zonally averaged distribution of organic aerosol sources. The analysis suggests that biomass burning and biogenic SOA dominate in the tropics, but that SOA formation from urban VOCs may be a significant source of aerosol at northern mid-latitudes.