Cycling of gaseous elemental mercury: Importance of water vapor

Gaseous elemental mercury is typically not thought of as a soluble compound, but its Henry’s law constant of 0.11 - 0.14 M atm-1 at 298K indicates enough water solubility that it must be considered in chemical cycling of Hg(0). We included mass transfer between the gaseous-aqueous phases and mercury aqueous reactions into our gas phase mercury chemical box model in order to better understand loss of Hg0 during nighttime. Mass transfer between the gaseous-aqueous phases was significantly influenced by water solubility of Hg(0) and the amount of liquid water content (LWC). The impact of water solubility of Hg(0) was examined through two sensitivity experiments; with and without aerosol chemistry. Ten hours of simulation showed that ~3.8 ppqv and ~11.5 ppqv of Hg(0) were decreased without and with aerosol chemistry respectively. The amount of Hg(0) lost indicated that aerosol uptake into its liquid water could be very important to mercury cycling compared to loss by dry deposition of Hg(0) alone. The sensitivity experiments showed also that Hg(aq) was increased to 9-102 ppqv with variable LWC ranging from 2exp(-12)-2exp(-10) after 10 hours of simulation. Finally, we conducted sensitivity experiments with consideration of dry deposition of speciated mercury. The sensitivity experiments indicated that dry deposition of particulate mercury (PHg) is critical to generate typical ambient levels of PHg compared to Hg0 and RGM. The loss of Hg(0) by aerosol uptake and dry deposition suggested that aerosol uptake of Hg(0) could play an important role in mercury cycling in the atmosphere.