On the other hand, many studies have explored PBM in urban smog, a similarly fine-particle-loaded and sulfurrich, albeit less extreme environment. Measurements in polluted urban environments suggest strong Hg enrichment in suspended fine particles, with Hg mass fractions in the PPM range . While these high Hg contents have been associated with direct PBM emission from industry and traffic , they may also result from gas-particleinteractions, for example from heterogeneous GEM oxidation and Hg uptake by particles . As most oxidized Hg species are semi-volatile, they partition between the gas phase and the particulate phase 89 .