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AIR TOXICS MODELING FROM LOCAL TO REGIONAL SCALES TO SUPPORT THE 2002 MULTIPOLLUTANT ASSESSMENT
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:
This research focuses on developing models that can describe the chemical and physical processes affecting concentrations of toxic air pollutants in the atmosphere, at spatial scales, ranging from local (< 1 km) to regional (36 km). One objective of this task is to extend the capabilities of EPA's Community Multiscale Air Quality (CMAQ) to include the capability to model high-priority toxic air pollutants. With these improvements, CMAQ will be able to handle the wide variety of processes that toxic air pollutants are subjected to, including gas and aqueous phase photochemistry, heterogeneous chemistry, transport, deposition, and re-emission from the surface. Another objective of this task is develop methods and tools for incorporating sources of information on concentrations at scales finer than CMAQ grid resolutions, including Gaussian plume dispersion models, computational fluid dynamics (CFD) models, large eddy simulation (LES) techniques, and computational methods for determining subgrid variability. With these tools, we will be able to combine information from a number of sources in order to more accurately model the temporal and spatial variability of ground-level concentrations of toxic air pollutants that occur in both rural and urban settings, and capture hot spots in concentrations. By developing improved regional and neighborhood-scale modeling tools, and linking them to human exposure models, we can improve assessments of the exposure of humans and ecosystems to air toxics and hazardous releases.
The research performed under this task includes the development and incorporation of improved chemical mechanisms to predict the concentrations of toxic chemicals that are not available in standard chemical mechanisms, application of these models at a variety of scales, and analysis of the results. We have chosen applications that are coordinated with ongoing applications of HEASD's advanced exposure model, SHEDS, and that are of high importance to OAQPS' National Air Toxics Assessment (NATA). A critical portion of this research is the development of methods that can be used to apply these models at finely-resolved or "neighborhood" scales, so that we can predict hot spots in toxic concentrations and the environmental variability of exposure to air toxics. It is closely tied with EPA/AMD's research in the development of EPA's Models-3/CMAQ. It incorporates ongoing improvements in the CMAQ representation of gas phase chemistry, cloud dynamics and aqueous chemistry, photolysis rates and radiative transfer, aerosol transport, and wet and dry and deposition that are being performed in these related tasks. Improvements in CMAQ, such as as the fine-scale modeling techniques, which are developed under this task also benefit other CMAQ tasks. It is closely coordinated with EPA/HEASD Task 15388 which performs research to improve the mechanistic and physical parameters used to describe air toxic compounds, and EPA/HEASD Task 20595 which develops improved models of human exposure to toxic air pollutants.
This task utilizes the high performance computing and scientific visualization resources provided by EPA's National Environmental Scientific Computing Center (NESC2).