Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-18
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In addition, there is now a heightened appreciation of the importance of reactive VOCs emitted by vegetation. NOX comes mainly from the combustion of fossil fuels; major sources include motor vehicles and electricity generating stations.
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As the ozone attainment strategy presented in the 1990 amendments to the Clean Air Act is put into effect, the success of efforts to control the precursors of ozone will be of vital concern to Congress, to governmental regulatory agencies, to industry, and to the public. THE CHARGE TO THE COMMITTEE The Committee on Tropospheric Ozone Formation and Measurement was established in 1989 by the Board on Environmental Studies and Toxicology of the National Research Council (NRC)
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Additional funding was provided by the American Petroleum Institute and the Motor Vehicle Manufacturers Association. EPA is expected to provide the committee's report to Congress as partial fulfillment of Section 185B of the Clean Air Act amendments of 1990, which requires EPA to conduct a study in conjunction with the National Academy of Sciences on the role of ozone precursors in tropospheric ozone formation and control.
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Congress set 1975 as the first deadline, but 2 years after this deadline, many areas were still in violation of the NAAQS. The 1977 amendments to the Clean Air Act extended the deadline for compliance until 1982 and allowed certain areas that could not meet the 1982 deadline until 1987.
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process, outlined in the Clean Air Act for developing and implementing ozone reduction strategies, is fundamentally sound in principle but is seriously flawed in practice because of the lack of adequate verification programs. RECOMMENDATION: Reliable methods for monitoring progress in reducing emissions of VOCs and NOx must be established to verify directly regulatory compliance and the effectiveness associated with mandated emission controls.
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Until verification programs are incorporated into the SIP process, the use of unverified emission inventories3 in air-quality models mill continue to involve considerable uncertainties in predicting changes in ozone concentrations resulting from emission controls. ANTHROPOGENIC VOC EMISSIONS FINDING: Current emissions inventories significantly underestimate anthropogenic emissions of VOCs.
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A more profound problem resulting from underestimating VOC emissions is the implication for future emission controls. As discussed in Chapters 6 and 11, the relative effectiveness of VOC and NOX controls for reducing ozone in a particular area depends on the ambient VOC/NOX ratios in that area.
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In addition, air-quality models that use ambient data instead of emissions inventories to identify important precursor sources, to verify emissions algorithms, and to determine ozone precursor relationships could serve as useful checks of models that require the entry of accurate data from emissions inventories. BIOGENIC VOC EMISSIONS FINDING: The combination of biogenic VOCs with anthropogenic NOX can have a significant effect on photochemical ozone formation in urban and rural regions of the United States.
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These measurements can be obtained only by intensive field studies that use validated methods to provide data for evaluating the representation of physical and chemical processes in air-quality models designed to predict the effects of future emissions controls. Past field studies have offered limited spatial coverage; sites in a wide variety of areas must be studied.
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Grid-based models generally have been able to simulate observed 1-hour average ozone concentrations with a gross error of 30~o or less, but known biases in certain inputs, particularly in emissions inventories, have raised the concern that there are uncertainties as yet unknown in other areas such as meteorology. Thus, good predictions of ozone concentrations can result from offsetting errors in inputs.
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The overall influence of initial and boundary conditions on predictions of ozone concentrations can be assessed by performing simulations with initial conditions set to zero and boundary conditions set to zero. Similar calculations can be carried out to assess the uncertainties in ozone predictions that arise from uncertainties in baseyear emissions inventories and projected future emissions.
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might not respond in the same manner as peak ozone to control techniques designed to reduce peak ozone; population exposure should be considered in the design of future control strategies. Many simulations conducted to date have relied on emissions inventories that did not include biogenic emissions and are strongly suspected of significantly underestimating anthropogenic VOC emissions.
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An increase by a factor of two to three in mobile-source VOCs, as suggested by recent studies discussed in Chapter 9, leads to predicted ozone concentrations closer to those observed. If the anthropogenic VOC inventory is as badly underestimated as recent studies indicate, areas that were previously believed to be adversely affected by NOx controls might actually benefit from them.
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Modeling studies show that at relatively low ambient VOC/NOX ratios (in the range of 4 to 6) , the use of natural gas as a motor fuel could reduce ozone formation on a mass basis (grams of ozone formed per gram of VOC emitted)
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effort to address depletion of the stratospheric ozone layer by chlorofluorocarbons.S For this program, EPA is the relevant regulatory agency, but NASA's Upper Atmosphere Research Program was directed in the Clean Air Act amendments of 1977 to "continue programs of research, technology, and monitoring of the phenomena of the stratosphere for the purpose of understanding the physics and chemistry of the stratosphere and for the early detection of potentially harmful changes in the ozone of the stratosphere." The partnership has worked well, and the basic research program has prepared the Ibis program is discussed as an example because it has many features that would be desirable in a tropospheric ozone research program. The committee does not recommend which agency should direct such a program.
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A similar partnership that meets the needs of the research community and those of regulatory agencies will be necessary to establish a reliable scientific basis for the improvement of the nation's air quality.
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Rethinking the Ozone Problem in Urban and Regional Air Pollution
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