NERL Research Abstract KPA's Vilionnl Ucscnrch Lnhomlorv (il'UA (.(.ill I - Clean Air APM #442 Significant Research Findings Role of Anthropogenic Nitrogen Oxides and Volatile Organic Compounds as Ozone Precursors Scientific Problem and Policy Issues In the 1991 National Research Council (NRC) Report Rethinking the Ozone Problem in Regional and Urban Pollution, a panel of national experts concluded that the previous U.S. emission control efforts may have focused too heavily on control of volatile organic compounds (VOCs) for reducing ozone pollution. The reviewers recommended that more research and control attention be directed to nitrogen oxides (NOx) as an ozone precursor. The atmospheric chemistry by which VOCs and NOx form ozone is complex, especially since VOCs and NOx may both create and destroy ozone in the air. In response to the NRC Report, EPA funded the Southern Oxidants Study (SOS) to explore the scientific issues underpinning the roles of VOCs and NOx as ozone precursors. The SOS was been designed to investigate such issues in urban and regional atmospheres within southern environments. Research The recent focus of the SOS research has compared the use of Observation- Approach Based Models (OBM) to the traditionally used Emissions-Based Model (EBM) methods. OBMs use real-world observations to estimate the relative influence of VOCs versus NOx in creating ozone, whereas EBMs use emission inventories and air quality models to estimate the relative roles of the two classes of precursors. As a part of the SOS efforts, observational data have been collected in extensive ambient monitoring networks covering the southeastern region of the country, as well as in specially designed urban and regional field campaigns. The observational data are used to develop OBMs and also to test and refine EBMs. Critical technical issues are explored through combined use of OBM and EBM methods. Results A number of OBM methods were developed for comparison with traditional and _ _ EBMs. Some of these OBM methods are empirical in nature, while others were Implications developed with the help of modeling derivations. This research used OBM methods to investigate the relative effectiveness of VOC and NOx controls for reducing ozone in urban and rural areas in the southeast, as well as the relative National Exposure Research Laboratory - September 2000 ------- effectiveness of controls of NOx emissions from different source types (e.g., autos, power plants, biogenic). Based upon data obtained in a variety of urban and rural areas, a general trend was detected: center-city sections of an urban area were usually VOC-limited—that is, control of VOCs would be more effective in reducing ozone than would control of NOx. Farther downwind away from the center-city sections, the ozone formation process becomes less VOC-limited and more NOx-limited. In rural areas, and also in those urban areas where the biogenic VOC emissions are dominant, ozone formation is clearly NOx-limited. These findings are significant because they provide invaluable guidance about the most effective emission control efforts. The data suggest that in most urban areas both VOCs and NOx should be controlled, whereas in rural areas control of the NOx emission sources would be more effective. The report meets the requirement of Annual Performance Measure (APM) 442 under GPRA Annual Performance Goal (APG) 01 (Recommend methods for measuring NOx [nitrogen oxides and their products]). Results of the report are directly relevant to the improvement of instrumentation for national monitoring networks including the Photochemical Assessment Monitoring Stations (PAMS) and regulatory networks associated with the National Ambient Air Quality Standards. Research The Southern Oxidant Study is been a collaborative effort involving EPA, Collaboration Georgia Institute of Technology, North Carolina State University, the Publications University of Alabama at Huntsville, the University Corporation for Atmospheric Research (UCAR), the National Center for Atmospheric Research (NCAR), the Brookhaven National Laboratory, and the Tennessee Valley Authority. Examples of recent publications from this study follow. Meagher, J.F., Cowling, E.B., Fehsenfeld, F.C., Parkhurst, W.J. Ozone formation and transport in southeastern United States: Overview of the SOS Nashville/Middle Tennessee Ozone Study. Journal of Geophysical Research D: Atmospheres 103: 22,213-22,223, 1998. Tonnesen, G.S., Dennis, R.L. Analysis of radical propagation efficiency to assess ozone sensitivity to hydrocarbons and NOx. Part 1. Local indicators of instantaneous odd oxygen production sensitivity. Journal of Geophysical Research D: Atmospheres 105: 9213-9225. Tonnesen, G.S., Dennis, R.L. Analysis of radical propagation efficiency to assess ozone sensitivity to hydrocarbons and NOx. Part 2. Long-lived species as indicators of ozone concentration sensitivity. Journal of Geophysical Research D: Atmospheres 105: 9227-9241. Daum, P.H., Kleinman, L.I., Imre, D., Nunnermacker, L.J., Lee, Y.-N., Springston, S.R., Newman, L., Weinstein-Lloyd, J., Valente, R.J., Imhoff, R.E., Tanner, R.L., Meagher, J.R. Analysis of 03 formation during a stagnation episode in central Tennessee in summer 1995. Journal of Geophysical Research D: Atmospheres 105: 9107-9119, 2000. National Exposure Research Laboratory - September 2000 ------- The SOS Study is nearing the end of its second 5-year period (1991-1196 and 1996-2001). A third 5-year phase of the effort is being considered. Such a future effort, if funded, will focus on completing the analysis of the field programs mounted through 2001, including an expanded collaborative effort with the State of Texas, the TEXAS2000 Study, conducted in Houston and its surrounding area. Inquiries concerning this project should be directed to: Dr. Paul Solomon U.S. Environmental Protection Agency National Exposure Research Laboratory P.O. Box 93478 Las Vegas, Nevada 89193-3478 Phone: (702)798-2280 E-mail: solomon.paul@epa.gov Federal funding for this research was administered under EPA cooperative agreements CR824839 with the North Carolina State University, CR824840 with the University of Alabama at Huntsville, CR824843 and CR824849 with the Georgia Institute of Technology, CR824833 with UCAR/NCAR, and interagency agreements DW89938059 with DOE's Brookhaven National Laboratory, and DW64938057 with the Tennessee Valley Authority. Future Research National Exposure Research Laboratory - September 2000 ------- |