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Human Exposure and Atmospheric Sciences

Research in Action

Computational atmospheric chemistry helps EPA scientists forecast future atmospheric conditions

The concentrations of compounds, such as nitrogen oxides, sulfur oxides, ozone, particulate matter, and other hazardous air toxics, must be closely monitored to ensure that their concentrations do not exceed those allowed by the National Ambient Air Quality Standards. Additionally, there is a need to understand and measure how air pollutants from various sources, such as motor vehicles, industry, wildfires, and vegetation combine with nitrogen oxides in the urban air to form secondary organic aerosols.

Laboratory studies used to acquire data on these hazardous compounds can be lengthy and expensive, making it difficult to meet regulatory schedules. Furthermore, in some cases, there are no laboratory methods available for doing these measurements. Therefore, methods are needed that are capable of predicting, in a timely and cost effective manner, the chemical mechanisms and processes that affect the composition and concentrations of gas phase and particulate phase compounds in the air that could adversely impact human health or damage sensitive ecosystems.

EPA scientists developed COMPCHEM, a new and innovative computational chemistry-based method for predicting lifetimes and fates of atmospheric compounds. COMPCHEM consists of a set of well-established, state of the science, quantum chemistry and gas phase kinetic codes, all of which have been used in numerous studies reported in peer-reviewed literature.

The focus of this project is to develop the methods and determine the utility of computational atmospheric chemistry methods for characterizing the chemical reactions that control the formation and fates of gas-phase and aerosol-phase compounds affecting climate change and atmospheric toxicity. Researchers will compare predicted reaction rate constants and chemical pathways to experimental laboratory measurements to assess the computational methods. These methods have the potential to provide EPA with a cost-effective tool for generating data that can supplement lab data and help it meet its regulatory responsibilities in a timely manner.

Computational chemistry is expected to play a major role in atmospheric chemistry. The computational methods of COMPCHEM have the potential to significantly improve our understanding of atmospheric chemistry similar to what has been done over the past decade to dramatically improve our understanding of combustion chemistry through computational chemistry calculations.

It is anticipated that COMPCHEM will provide a timely and cost effective tool for supplementing the experimental data on atmospheric chemistry generated through laboratory studies, thereby significantly enhancing EPA’s ability to develop and implement air quality standards. COMPCHEM should significantly improve the chemical mechanisms used in EPA air quality forecasting models such as EPA's Community Multiscale Air Quality (CMAQ) modeling system. The tool will enhance our ability to forecast future atmospheric conditions, thereby making it possible for EPA to take pro-active approaches for addressing the major atmospheric chemistry issues of the 21st century. The computational methods and results generated in this program are expected to be used by other U.S. and international research groups to further expand our understanding of atmospheric chemistry and its impact on human health and ecosystems.

Technical Contact:
Edward O. Edney, Ph.D.

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