Trans-Pacific Transport of Mercury

We examine the trans-Pacific transport of mercury using a global chemical transport model. Using existing anthropogenic inventories, the model reproduces the observed Hg/CO ratio in Asian long-range transport events observed at a surface site in Okinawa, Japan and Mount Bachelor, Oregon, with an underestimate of 18-26% in the ratio. This is in contrast with previous studies that inferred a factor of two underestimate in Asian anthropogenic emissions. We find that mercury from land emissions and re-emissions, which are largely co-located with anthropogenic emissions, account for a significant fraction of the observed Hg/CO ratio. Increasing Asian anthropogenic emissions by 50% while holding land emissions constant, or further increasing anthropogenic emissions while decreasing land emissions, corrects the remaining model bias in the Hg/CO ratio. We thus find that a total Asian source of 1260-1450 Mg/yr Hg is consistent with observations. Hg emissions from Asia are transported northwestward across the Pacific,