A numerical modelling study on regional mercury budget for eastern North America

[摘要] In this study, we have integrated an up-to-datephysio-chemical transformation mechanism of Hg into the framework of US EPA's CMAQ model system.In addition, themodel adapted detailed calculations of the air-surface exchange for Hg to properlydescribe Hg re-emissions and dry deposition from and to natural surfaces.Themechanism covers Hg in three categories, elemental Hg (Hg⁰), reactive gaseous Hg(RGM) and particulate Hg (HgP).With interfacing to MM5 (meteorology processor) andSMOKE (emission processor), we applied the model to a 4-week period in June/July1995 on a domain covering most of eastern North America.Results indicate that themodel simulates reasonably well the levels of total gaseous Hg (TGM) and the specificHg wet deposition measurements made by the Hg deposition network (MDN). Moreover, results from various scenario runs reveal that the Hg system behaves in aclosely linear way in terms of contributions from different source categories, i.e.anthropogenic emissions, natural re-emissions and background.Analyses of thescenario results suggest that 37% of anthropogenically emitted Hg was deposited backin the model domain with 5155 kg of anthropogenic Hg moving out of the domain duringthe simulation period.Overall, the domain served as a net source, which supplied~a half ton of Hg to the global background pool over the period.Our model validation and asensitivity test further rationalized the rate constant for gaseous oxidation ofHg⁰ by hydroxyl radical OH used in the global scale modelling study by Bergan and Rodhe(2001).A further laboratory determination of the reaction rate constant, including itstemperature dependence, stands as one of the important issues critical to improving ourknowledge on the budget and cycling of Hg.

[学科分类] 大气科学