Seasonal Variability of Halocarbon Emissions in California and The United States

Ambient concentrations of 8 predominantly anthropogenic halocarbons were measured via in situ gas chromatography in California’s South Coast air basin during both summer and fall as part of the 2005 Study of Organic Aerosols at Riverside (SOAR). Ongoing emissions of methylchloroform, CFC-11, and HCFC-141b, whose production is banned by the Montreal Protocol, were detected by comparison to similar-latitude background measurements at remote AGAGE and NOAA sites. CFC-113 emissions were not detected. Using coincident ambient measurements of carbon monoxide and an emission inventory for carbon monoxide, emission estimates for both California and the United States were estimated for methylchloroform, CFC-11, HCFC-141b, tetrachloroethene, trichloroethylene, dichloromethane, and chloroform of anthropogenic origin. We present evidence for anthropogenic sources of both methylchloroform and chloroform in the Los Angeles region, which show clear seasonal differences in emissions between summer and fall. We compare and contrast our emission estimates to other recently reported estimates.