Atmospheric benzene and toluene

Atmospheric concentrations of benzene (C6H6) and toluene (C7H8) have been observed at nine remote locations of the world ranging in latitude from inside the arctic circle to the south pole. The observations span all seasons at each location. In the northern hemisphere it is observed that C6H6 and C7H8 are most abundant during winter and least abundant during summer. Based on the limited data available, such cycles are not observed in the tropics. These findings are consistent with the expected latitudinal and seasonal variations of OH radicals which cause benzene and toluene to be removed from the atmosphere. The latitudinal distribution shows high concentrations at mid latitudes and low levels in the southern hemisphere. This finding is consistent with the present understanding that the sources of benzene and toluene are primarily anthropogenic. The observed concentration distribution and variability are consistent with the short expected atmospheric lifetime of the order of months for benzene and days for toluene.