Sampling in urban areas

Although highly dependent on many study-specific variables, the compilation suggests that relatively large concentrations of benzene, carbon tetrachloride, decane, and toluene have been detected in air samples in urban areas. The major source of toluene in air samples is fi-om the combustion of gasoline. However, such data must be interpreted cautiously. Although there are no known natural sources of carbon tetrachloride, benzene for example also occurs natiually from crude oil seeps, forest fires, and plant volatiles. ... 

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