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MODELING TRANSPORT AND TRANSFORMATION OF HG COMPOUNDS IN CONTINENTAL AIR MASSES
Citation:
BULLOCK, R. MODELING TRANSPORT AND TRANSFORMATION OF HG COMPOUNDS IN CONTINENTAL AIR MASSES. Chapter 14, Dynamics of Mercury Pollution on Regional and Global Scales. Springer Science and Business Media B.V;Formerly Kluwer Academic Publishers B.V., , Germany, , 319-344, (2005).
Impact/Purpose:
The objective of this task is to improve EPA's ability to accurately predict the concentrations and deposition of air pollutants in the atmosphere that are known or suspected to cause cancer or other serious health effects to humans, or adverse environmental effects. It is an essential component of EPA's National Air Toxics Assessment (NATA), which seeks to identify and quantify the concentrations and sources of those hazardous air pollutants which are of greatest potential concern, in terms of contribution to population risk. It is a major contributor to NERL's Air Toxics Research Program.
"Air toxics" or "hazardous air pollutants" (HAPs) is a category that covers a large variety of chemicals, which range from relatively non reactive to extremely reactive; can exist in the gas, aqueous, and/or particle phases; display a large range of volatilities; experience varying deposition velocities, including in some cases revolatilization; and are emitted from a wide variety of sources at a large variety of different scales. In addition, concentrations of air toxics are needed by regulators for both short (days) as well as long (up to a year) time scales. These requirements challenge our current capabilities in air quality models far beyond the needs for other pollutants, such as ozone. The specific work being done under this task involves 1.) developing and testing chemical mechanisms which are appropriate for describing the chemistry of air toxics; 2.) incorporating these chemical and physical mechanisms into EPA's CMAQ modeling system and applying the model at a variety of scales; and 3.) developing the methods for using models to predict HAPs concentrations at subgrid or neighborhood scales; and 4.) using these tools to assess the magnitude and variability of concentrations to which urban populations are exposed.
Description:
The global mercury cycle involves both continental and marine environments. However, there are special considerations for modeling atmospheric mercury over continents. Most anthropogenic sources of atmospheric mercury are on continents and they emit a large fraction in oxidized forms which are most subject to deposition. Continental surfaces can include land and water, and land forms can vary in their vegetation cover and topography. Fine-scale modeling is more necessary for continental domains due to complex wind patterns that are generated by topography and land/sea boundaries. Planetary boundary layer structure is also more dynamic and variable over continents, requiring more detailed information about the time and height of emission for accurate simulation. A number of chemical reactions of mercury are known to involve reactants formed in the photochemistry associated with biogenic and anthropogenic pollutants released mostly in continental regimes. Simulation of atmospheric mercury in continental air masses has been performed using the Community Multi-scale Air Quality (CMAQ) model. The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement DW13921548. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.