Abstract
Abstract. The Community Multiscale Air Quality (CMAQ) model version 4.7.1 was used to simulate mercury wet and dry deposition for a domain covering the continental United States (US). The simulations used MM5-derived meteorological input fields and the US Environmental Protection Agency (EPA) Clear Air Mercury Rule (CAMR) emissions inventory. Using sensitivity simulations with different boundary conditions and tracer simulations, this investigation focuses on the contributions of boundary concentrations to deposited mercury in the Southwest (SW) US. Concentrations of oxidized mercury species along the boundaries of the domain, in particular the upper layers of the domain, can make significant contributions to the simulated wet and dry deposition of mercury in the SW US. In order to better understand the contributions of boundary conditions to deposition, inert tracer simulations were conducted to quantify the relative amount of an atmospheric constituent transported across the boundaries of the domain at various altitudes and to quantify the amount that reaches and potentially deposits to the land surface in the SW US. Simulations using alternate sets of boundary concentrations, including estimates from global models (Goddard Earth Observing System-Chem (GEOS-Chem) and the Global/Regional Atmospheric Heavy Metals (GRAHM) model), and alternate meteorological input fields (for different years) are analyzed in this paper. CMAQ dry deposition in the SW US is sensitive to differences in the atmospheric dynamics and atmospheric mercury chemistry parameterizations between the global models used for boundary conditions.
Highlights
Regional scale simulations of mercury deposition must rely on boundary concentrations to account for fluxes of species, in particular the various mercury species, into the modeling domain from the remainder of the globe
In the North American Mercury Model Intercomparison Study (NAMMIS) Bullock Jr. et al (2008) found that the mercury deposition simulated by regional scale models depends strongly on the initial and boundary concentrations of mercury compounds used for the regional scale simulations
Wet and dry mercury deposition simulated by Community Multiscale Air Quality (CMAQ) for January–February 2002 and July–August 2002 are compared using boundary conditions based on (a) 2002 GEOS-Chem global simulations and (b) the same GEOSChem simulations adjusted based on the results of a 2005 CMAQ hemispheric simulation to keep the spatial and temporal dynamics and non-mercury species constant in the boundary conditions between the simulations
Summary
Regional scale simulations of mercury deposition must rely on boundary concentrations to account for fluxes of species, in particular the various mercury species, into the modeling domain from the remainder of the globe. In the North American Mercury Model Intercomparison Study (NAMMIS) Bullock Jr. et al (2008) found that the mercury deposition simulated by regional scale models depends strongly on the initial and boundary concentrations of mercury compounds used for the regional scale simulations. In order to interpret the results from regional scale simulations of mercury deposition, it is important to understand the influence that the boundary concentrations have on the simulated mercury deposition. The results obtained in the NAMMIS study are expanded by considering, in addition to the effect of using alternate boundary concentrations, the effect of several other factors on simulated mercury deposition. Use of meteorological inputs for a different year; use of an alternative global model as a source of boundary concentrations for the regional scale simulations; changes in the high altitude boundary concentrations; and increased vertical resolution in the regional scale modeling domain are examined. Myers et al.: Investigation of effects of varying model inputs are focused on locations in the Southwest (SW) US where CMAQ model simulations showed high levels of total Hg dry deposition compared to other models considered in the NAMMIS (Bullock Jr. et al, 2008)
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