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

Abstract

Abstract. In this study, we have integrated an up-to-date physio-chemical transformation mechanism of Hg into the framework of US EPA's CMAQ model system. In addition, the model adapted detailed calculations of the air-surface exchange for Hg to properly describe Hg re-emissions and dry deposition from and to natural surfaces. The mechanism covers Hg in three categories, elemental Hg (Hg 0 ), reactive gaseous Hg (RGM) and particulate Hg (HgP). With interfacing to MM5 (meteorology processor) and SMOKE (emission processor), we applied the model to a 4-week period in June/July 1995 on a domain covering most of eastern North America. Results indicate that the model simulates reasonably well the levels of total gaseous Hg (TGM) and the specific Hg wet deposition measurements made by the Hg deposition network (MDN). Moreover, results from various scenario runs reveal that the Hg system behaves in a closely linear way in terms of contributions from different source categories, i.e. anthropogenic emissions, natural re-emissions and background. Analyses of the scenario results suggest that 37% of anthropogenically emitted Hg was deposited back in the model domain with 5155 kg of anthropogenic Hg moving out of the domain during the 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 a sensitivity test further rationalized the rate constant for gaseous oxidation of Hg 0 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 its temperature dependence, stands as one of the important issues critical to improving our knowledge on the budget and cycling of Hg.Correspondence to: X. Lin (Xiude. Lin@kinectrics.com)

An assessment of atmospheric mercury in the Community Multiscale Air Quality (CMAQ) model at an urban site and a rural site in the Great Lakes Region of North America

“…Overall, we find that RHg is much too high, whereas wet deposition shows a low bias, even after accounting for low precipitation (∼ 30 % of the wet deposition low bias is attributable to precipitation errors). Taken together, these two results are surprising given that RHg is the dominant contributor to total mercury wet deposition in our simulations and in past studies (Lin and Tao, 2003). These patterns might be explained by compensating errors in CMAQ-Hg.…”

“…A number of studies have used these data to evaluate CMAQ-Hg (Bash, 2010;Bullock and Brehme, 2002;Bullock et al, 2008Bullock et al, , 2009Gbor et al, 2006Gbor et al, , 2007Lin et al, 2007;Lin and Tao, 2003;Pongprueksa et al, 2008;Sunderland et al, 2008;Vijayaraghavan et al, 2007), and other atmospheric chemistry models that include mercury (Cohen et al, 2004;Holmes et al, 2010;Sanei et al, 2010;Seigneur et al, 2003;Selin and Jacob, 2008;Vijayaraghavan et al, 2008). Until recently, most studies that evaluate model estimates of ambient mercury compare with Total Gaseous Mercury (TGM) and/or Hg 0 (Gbor et al, 2006(Gbor et al, , 2007Holmes et al, 2010;Lin and Tao, 2003;Lohman et al, 2008;Selin et al, 2007;Soerensen et al, 2010;Wen et al, 2011).…”

Sensitivity model study of regional mercury dispersion in the atmosphere

“…This model was compiled with the multi-pollutant version of the CBM5 photochemical mechanism (Sarwar et al, 2008) (which includes Hg gaseous reactions with O 3 , OH, H 2 O 2 and Cl 2 as described by Lin and Tao, 2003) with the Euler backward iterative solver and the AERO4 aerosol mechanism (Binkowski and Roselle, 2003). The CMAQ-Hg model uses offline meteorological fields provided by the COSMO-CLM model (Rockel et al, 2008), processed by the Meteorology-Chemistry Interface Processor (MCIP v3.6).…”

Validation of the integrated RAMS-Hg modelling system using wet deposition observations for eastern North America

“…However, the weak relationship between observed and modelled precipitation as well as wet deposited Hg inhibits from any conclusion on model reliability for the summer simulation period. Lin and Tao (2003) have also calculated accumulated wet deposited Hg for the entire summer experimental period as shown in Table 6. These researchers have used CMAQ-Hg with meteorological data generated from MM5 simulations.…”

“…Initial and boundary conditions for Hg 0 , Hg 2 and Hg P : Horizontally homogeneous initial and boundary conditions were used for the three mercury species similar to the ones used by BB and Lin and Tao (2003). The lateral boundary concentrations of all species were fixed throughout the simulations.…”