UC Irvine

Spatial and temporal distributions of atmospheric CH3Cl, CH3Br, C2H5Cl, and C2H5Br were determined by gas chromatography/mass spectrometry measurements at coastal California and inland sites from 1996 through 1999. The median concentrations observed at a clean coastal site were 585, 13.1, 3.3, and 0.3 ppt (parts per trillion) for CH3Cl, CH3Br, C2H5Cl, and C2H5Br, respectively. To our knowledge, these represent the first quantitative measurements of atmospheric C2H5Cl. High variation was seen in CH3Br and C2H5Cl measurements from the other two California sites, a rural inland site and a coastal site with urban influence. When compared to the California stationary sites, the median Northern Hemispheric results from measurements taken along Pacific Ocean transects between California and New Zealand from 1996 through 1999 were similar for CH3Cl (594 ppt) and C2H5Br (0.3 ppt) but lower for CH3Br (10.4 ppt) and C2H5Cl (2.6 ppt). Median concentrations of Southern Hemispheric CH3Br (9.4 ppt), C2H5Cl (1.6 ppt), and C2H5Br (less than 0.2 ppt) were lower than the Northern Hemispheric results. No significant correlation was found between the atmospheric concentrations of the methyl halides with the ethyl halides.