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CMAQ MODELING FOR AIR TOXICS AT FINE SCALES: A PROTOTYPE STUDY
Citation:
Majeed, M. A., J.K S. Ching, T L. Otte, L. Reynolds, AND R. Tang. CMAQ MODELING FOR AIR TOXICS AT FINE SCALES: A PROTOTYPE STUDY. Presented at 2004 Models-3 Conference, Chapel Hill, NC, October 18 - 20, 2004.
Impact/Purpose:
The objective of this task is to develop and evaluate numerical and physical modeling tools for simulating ground-level concentrations of airborne substances in urban settings at spatial scales ranging from ~1-10 km. These tools will support client needs in the areas of air toxics and homeland security. The air toxics tools will benefit the National Air Toxics Assessment (NATA) program and human exposure modeling needs within EPA. The homeland security-related portion of this task will help in developing tools to assess the threat posed by the release of airborne agents. Both sets of tools will consider the effects induced by urban morphology on fine-scale concentration distributions.
Description:
Toxic air pollutants (TAPs) or hazardous air pollutants (HAPs) exhibit considerable spatial and temporal variability across urban areas. Therefore, the ability of chemical transport models (CTMs), e.g. Community Multi-scale Air Quality (CMAQ), to reproduce the spatial and temporal variability is needed to identify and characterize air toxic hot spots, which are the areas that experience high levels of air toxics. These areas are not only impacted by local sources, but also by the secondary production of many air toxics compounds due to photochemistry. For example, formaldehyde and acetaldehyde have secondary components of oxidant photochemistry. The source distribution, photochemistry, dry and wet depositions of these compounds are scale dependent. Therefore, in order to capture the spatial and temporal variability of these compounds and identify air toxic hot spots, it is necessary to perform air quality simulations at fine scales.
To test the ability of air quality models to simulate air toxic concentration at fine scales, and for its application to assess risk, a prototype study is underway with Delaware as the focus. The CMAQ modeling system is selected because it can perform multi-scale, multi-pollutant simulations for air toxics at a neighborhood scale (~1 km). Its preprocessors, the NCAR-PSU Mesoscale Model Version 5 (MM5) and the SMOKE tool provide the meteorological and emission fields, respectively, at 1 km resolution. The air quality simulations will be performed for 1999 emissions and 2001 meteorology; however, the simulations will be limited to the month of July for this demonstration. Air quality simulations are also performed at 36, 12, and 4 km resolution.
Results of this effort will focus on examining the dependency of grid size in the characterization of these air toxic hot spots and also the impact of regional transport and their secondary production by photochemistry.
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 number DW13921548. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.