Monoaromatic compounds in ambient air of various cities: a focus on correlations between the xylenes and ethylbenzene

Speciation of o-xylene, m-xylene, p-xylene and ethylbenzene was performed b y gas chromatography from ambient air and liquid fuel samples collected at various locations in 19 cities in Europe, Asia and South America. The xylen e's mixing ratios were compared to each other from the various locations, w hich included urban air, traffic air and liquid fuel. For all samples, the xylenes exhibited robust correlations, and the slopes remained constant. Th e m-xylene/p-xylene ratio was found to be 2.33 +/- 0.30, and the m-xylene/o -xylene ratio was found to be 1.84 +/- 0.25. These ratios remain persistent even in biomass combustion experiments (in South America and South Africa) . Comparing the xylenes to toluene and benzene indicate that combustion, bu t not fuel evaporation, is the major common source of the xylenes in areas dominated by automotive emissions. Although a wide range of combustion type s and combustion efficiencies were encountered throughout all the locations investigated, xylenes and ethylbenzene ratios remained persistent. We disc uss the implications of the constancies in the xylenes and ethylbenzene rat ios on atmospheric chemistry. (C) 2000 Elsevier Science Ltd. All rights res erved.