Citation:

SARWAR, G. AND G. L. GIPSON. THE EFFECT OF CHLORINE EMISSIONS ON TROPOSPHERIC OZONE IN THE UNITED STATES. Presented at Air and Waste Management Association 2005 Annual Conference, Minneapolis, MN, June 21 - 25, 2005.

Impact/Purpose:

The objectives of this task are to develop, improve, and evaluate EPA's Community Multiscale Air Quality (CMAQ) model, as an air quality management and NAAQS implementation tool. CMAQ is a multiscale and multi-pollutant chemistry-transport model (CTM) that includes the necessary critical science process modules for atmospheric transport, deposition, cloud mixing, emissions, gas- and aqueous-phase chemical transformation processes, and aerosol dynamics and chemistry. To achieve the advances in CMAQ, research will be conducted to develop and test appropriate chemical and physical mechanisms, improve the accuracy of emissions and dry deposition algorithms, and to develop and improve state-of-the-science meteorology models and contributing process parameterizations.

The model will be tested and evaluated to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the CMAQ system, with an emphasis on the chemical/transport model, CMAQ. Emissions-based models are composed of highly complex scientific hypotheses concerning natural processes that can be evaluated through comparison with observations, but not truly validated. Both operational and diagnostic evaluations, together with sensitivity analyses are needed to both establish credibility and build confidence within the client and scientific community in the simulation results for policy and scientific applications. The characterization of the performance of Models-3/CMAQ is also a tool for the model developers to identify aspects of the modeling system that require further improvement.

Description:

The effect of chlorine emissions on atmospheric ozone in the continental United States was evaluated. Atmospheric chlorine chemistry was combined with the carbon bond mechanism and incorporated into the Community Multiscale Air Quality model. Sources of chlorine included anthropogenic emissions obtained from the 1999 National Emissions Inventory for Hazardous Air Pollutants, and chlorine released from the reactions of chlorides in sea-salt aerosols. Results from the photochemical model were evaluated for five days during the summer of 2001. Model results show that chlorine chemistry increased morning ozone mixing ratio by as much as 19 parts per billion by volume near the Great Salt Lake. However, the chlorine chemistry did not affect ozone mixing ratio in other areas of the continental United States. The enhancement of morning ozone mixing ratio was accompanied by a decrease in volatile organic compound mixing ratio. Chlorine radical levels peaked in the morning hours whereas maximum hydroxyl radical levels occurred in the afternoon hours. During morning hours, peak chlorine radical levels were approximately 5-10% of hydroxyl radical levels, and the volatile organic compound oxidation rate via chlorine radical pathway was comparable to the VOC oxidation rate via hydroxyl radical pathway. During afternoon hours, chlorine radical levels were typically less than 0.5% of the hydroxyl radical levels, and the VOC oxidation rate via chlorine radical pathway was lower than the VOC oxidation rate via hydroxyl radical pathway.

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.

Record Details: