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INITIAL STUDY OF HPAC MODELED DISPERSION DRIVEN BY MM5 WITH AND WITHOUT URBAN CANOPY PARAMETERIZATIONS
Citation:
KILEY, C., J. K. CHING, AND S. HAMILTON. INITIAL STUDY OF HPAC MODELED DISPERSION DRIVEN BY MM5 WITH AND WITHOUT URBAN CANOPY PARAMETERIZATIONS. Presented at 5th Annual CMAS Conference, Chapel Hill, NC, October 16 - 18, 2006.
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:
Improving the accuracy and capability of transport and dispersion models in urban areas is essential for current and future urban applications. These models must reflect more realistically the presence and details of urban canopy features. Such features markedly influence the flow circulation patterns, turbulence fields, and energy budgets at mesoscale; they also have a dominant influence of the fine scale flow and corresponding dispersion within and above the building elements and their canopy. Current advancements in mapping these urban features with a high degree of horizontal and vertical resolution is making possible (a) improved urban meteorological simulations with advanced urban canopy parameterizations in mesoscale models and (b) in advanced models of flow and dispersion within and above urban canopies at building scales. For this study, we utilize outputs of simulations from an urbanized version of the well known Mesoscale Model (Version 5) or MM5 to drive the Hazard Prediction and Assessment Capability (HPAC) model. The building data set is derived from airborne lidar mappings providing resolution at 1 to 5 meter resolution. HPAC incorporates such data as shape files; MM5 utilizes these data in aggregated form as urban canopy parameters (UCPs) gridded at 1 km resolution. The study venue is Houston Texas. This sensitivity study provides a comparative of HPAC driven by both the UCP and the standard versions of MM5.