Numerical simulation of atmospheric mercury in mid-south USA

Abstract

As a continuation of our recent work that studied temporal patterns of atmospheric mercury (Hg) species in northern Mississippi during 2011–2012, we applied an air quality modeling system, the Community Multi-scale Air Quality (CMAQ), to evaluate model ability in capturing ambient concentration of atmospheric Hg in both summer and winter. The model captured well in the surface ozone and nitrogen dioxide concentrations for both summer and winter months. But it lacked skill in reproducing sulfur dioxide concentration, with significant overestimates in both summer and winter. The model underestimated weekly wet deposition of total Hg partly because of errors in precipitation from the meteorological model. The air quality model overestimated atmospheric ambient elemental Hg (GEM) concentration in summer and slightly underestimated it in winter. The model exhibited good skill in capturing seasonal variability of reactive gaseous mercury (GOM), while it produced a significant overestimate for particulate mercury (PBM) in both summer and winter. Sensitivity tests revealed that anthropogenic emissions had great influences on local/regional ambient concentrations of GEM, GOM, and PBM, with anthropogenic emissions, making a contribution of 10–20 % for ambient GEM, 20–40 % for GOM, and 40–60 % for PBM. The evident influence of anthropogenic sources on Hg concentration suggests that discrepancies between modeled and observed are partly attributable to the uncertainties associated with the anthropogenic emission inventory used in the air quality modeling system. In the future, model performance is expected to be improved by use of 2011 emission data.