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A BIOGENIC ROLE IN EXPOSURE TO TWO TOXIC COMPOUNDS
Citation:
Hutzell, W T., G L. Gipson, G Pouliot, AND T. Pierce. A BIOGENIC ROLE IN EXPOSURE TO TWO TOXIC COMPOUNDS. Presented at American Geophysical Union, San Francisco, CA, December 8-12, 2003.
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:
Biogenic sources play an important role in ozone and particulate concentrations through emissions of volatile organic compounds. The same emissions also contribute to chronic toxic exposures from formaldehyde and acetaldehyde because each compound arises through primary and secondary processes. Anthropogenic sources may dominate over biogenic sources in both processes. Modeling tools are becoming able to compare how biogenic and anthropogenic sources contribute to both processes. Emissions models can predict formaldehyde and acetaldehyde emissions. Photochemical models can isolate how biogenic emissions contribute to the primary and secondary components of formaldehyde and acetaldehyde concentrations. Initial modeling results show that biogenic versus anthropogenic contributions depend on the pollutant and location. For the primary component, anthropogenic sources determine formaldehyde concentrations over most locations but acetaldehyde has large contribution from biogenic sources over rural locations. For the secondary component, both pollutants have a significant contribution from biogenic sources outside urban areas. This presentation discusses these contributions and their evaluation based on a model system called Community Multiscale Air Quality model.
This work has been funded wholly by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for publication.