Abstract
A new gas chromatographic technique with a modified photoionization detector connected in series with a conventional flame ionization detector was used to determine low concentrations of atmospheric hydrocarbons in remote atmospheres. Average mixing ratios of five aromatic hydrocarbons measured between 42°N and 30°S latitude in the Pacific Ocean in October/November 1983 were highest in the Northern Hemisphere. The average mixing ratios in the northern and southern marine atmospheres were 49±25 ppt (n=35) and 10±2 ppt (n=21) for benzene, 20±12 ppt (n=32) and 5.6±1.6 ppt (n=12) for toluene, 7.6±3.7 ppt (n=35) and 3.7±1.6 ppt (n=21) for ethylbenzene, 25±12 ppt (n=35) and 13±5 ppt (n=20) for the sum of m- and p-xylenes, and 14±6 ppt (n=35) and 6.6±3.0 ppt (n=21) for o-xylene, respectively. The first latitudinal gradients for these five aromatic compounds are reported. Benzene and toluene mixing ratios measured between July 1982 and October 1983 at a rural, mid-latitude continental site in eastern Washington state gave average values of 226±108 ppt and 133±84 ppt, respectively, with higher wintertime than summertime benzene levels. These continental samples gave calculated air mass ages averaging six days based on benzene-to-toluene ratios.
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