To put these mass fractions into context, we reviewed published work concerning Hg mass fractions in volcanic fine particles and suspended fine particles (< 10 µm in diameter) in urban environments (this review does not intend to be exhaustive). Assuming complete uptake of all the "missing" GEM onto PM0.7DMPS leads to Hg mass fractions that are quite large compared to published work (see Figure ). On the other hand, if we assume complete uptake onto PM0.95sulfate proxy, which arguably captures a much larger fraction of the suspended submicron particle mass than PM0.7DMPS, Hg mass fractions fall well into the range of values reported elsewhere.