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INVESTIGATION AND IMPLICATIONS OF SUB GRID VARIABILITY OF CMAQ MODELED CONCENTRATIONS
Citation:
CHING, J. K. AND M. A. MAJEED. INVESTIGATION AND IMPLICATIONS OF SUB GRID VARIABILITY OF CMAQ MODELED CONCENTRATIONS. Presented at 4TH Annual CMAS Models-3 User's Conference, Chapel Hill, NC, September 26 - 28, 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:
This poster introduces a method called SGV adjusted concentrations (SAC) for introducing sub-grid variability (inherent in air quality grid models) into CMAQ for various applications C MAQ was run at 36-, 12-, 4-, and 1 km-grid sizes for July 2001 for the Delaware domain. The SGV descriptors such as the coefficient of variability (COV); were computed for benzene formaldehyde and ozone for 12 km cells based on their km simulations. Potential utility of this method include, (a) exposure assessments, (b) model evaluation studies and (c) weight-of-evidence applications in air quality attainment demonstrations.