Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991) / Chapter Skim
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1 What Is the Problem?
1 What Is the Problem?
Pages 19-40
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From page 19... ...
A plot of ozone partial pressures and atmospheric mixing ratios as a function of altitude is shown in Figure 1-1 for a typical latitude profile (AFGL, 1985~. The bulge shown in Figure 1-1, the stratospheric ozone layer, peaks in ozone concentration (partial pressure)
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From page 20... ...
. : ': 40 60 80 1 00 120 140 PARTIAL PRESSURE (e-bars)
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From page 21... ...
thick. Therefore, it is not surprising that naturally or anthropogenically induced changes in trace chemical emissions might cause changes in atmospheric chemistry which, in turn, could have a significant effect on atmospheric ozone concentrations.
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From page 22... ...
If stratospheric ozone concentrations remained constant, the 10% increase in tropospheric ozone would increase the total column abundance of ozone by about 1%. However, stratospheric ozone concentrations are declining, and increasing amounts of ultraviolet solar radiation are leaking through a thinning stratospheric ozone layer.
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From page 23... ...
The most critical aspect of the tropospheric ozone problem is its formation in and downwind of large urban areas, where, under certain meteorological conditions, emissions of NOX and VOCs can result in ozone concentrations as high as 200-400 ppb. Such production of ozone and related oxidant species is called photochemical air pollution; it was first recognized in the Los Angeles basin in the 1940s, when vegetable crops began to show damage.
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From page 24... ...
There is now a heightened appreciation of the importance of biogenic VOC emissions, whose reaction products react with NOX from anthropogenic and natural sources for regional and urban ozone production (Trainer et al., 1987; Chameides et al., 1988; Cardelino and Chameides, 1990~. Research throughout the 1960s, 1970s, and 1980s focused on several critical aspects of photochemical air pollution (Finlayson-Pitts and Pitts, 1977, 1986; Seinfeld, 1986, 1989)
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From page 25... ...
Organic radicals combine with molecular oxygen to form peroxy radicals (RO2) , a process that usually requires an inert third body, M (e.g., N2 or 02~: M R- + O2 - RO2 (1~)
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From page 26... ...
Because of the importance of precursors in ozone photochemistry, a comprehensive understanding of tropospheric ozone chemistry also requires knowledge of the atmospheric sources and sinks of VOCs and NOX. The sources include VOC emissions from vegetation, industrial and commercial facilities, and motor vehicles and NOx emissions from motor vehicles, power plants, industrial facilities, and to a lesser degree, biomass burning, soil, and lightning.
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From page 27... ...
& ~ FIGURE 1-2 Photochemical air pollution, from emission to deposition. evaluate because, as the relationships between source emissions and their atmospheric chemistry are better understood, certain consistencies in those relationships can provide opportunities for tailoring ozone precursor control strategies to specific cities or canonical regions.
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From page 28... ...
.':~ FIGURE 1-3 Conceptual canonical regions for evaluating tropospheric ozone formation and control. lower population densities, but the people living in these areas rely heavily on motor vehicles for most personal and business transportation.
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From page 29... ...
The canonical regions framework does not provide a rigid format for examining tropospheric ozone, but it does provide necessary building blocks to elucidate both the situations described throughout this report and areas that could be affected by increased ozone concentrations in the future. OZONE AND AIR-QUALITY REGULATIONS The high concentrations of ozone, coupled with lesser, but still serious, concentrations of other smog products, including NO2, nitrate radical (NO3)
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From page 30... ...
EPA has summarized the trends in second-highest daily maximum ozone concentrations from 1978 through 1989. (See Chapters 2 and 3 for a description of the methods used to determine and track compliance with the ozone NAAQS.)
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From page 31... ...
In contrast, in 1989 the number of days on which maximum 1-hour ozone concentrations were above 120 ppb fell to a low for the decade. Although generally reliable data on urban ozone concentrations have been collected, corollary data on ozone precursors (VOCs and NO,`)
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From page 32... ...
bThe monitoring network for ozone has expanded significantly during the past 10 years. According to EPA, the estimates of the number of areas not meeting the ozone NAAQS for 1985 and earlier have not been subject to the same level of quality assurance and monitoring network review as the estimates for more recent years.
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From page 33... ...
These changes must be studied further, but they suggest that the scientific research community must formulate measurement and modeling approaches that can be used in conjunction with health indices to detect or predict annual increments of improvement or degradation of human health. Human Exposure Issues The occurrence of ozone concentrations that exceed 120 ppb in various regions of the United States indicates that many people could be exposed to potentially harmful concentrations of ozone.
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From page 34... ...
34 0.25 l ANNUAL SECOND DAILY MAX 1-HR (PPM) Atlanta 2s;Es ~ 0.2 0.15- at__ 0.1 0.05 o 0.5 Los Angeles 0.4 REIHINKING THE OZONE PROBLEM _ _ _ _ ,,,,,,,,,,, 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 YEAR ANNUAL SECOND DAILY MAX 1-HR (PPM)
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From page 35... ...
In addition, there are multiple opportunities for individuals to be exposed to a 1-hour value above 120 ppb (Figure 1-6~. This fact alone is enough to warrant concern, but as shown in the brief summary on the potential human health effects of ozone, concerns have been raised about public health risks due to exposures to ozone concentrations that are in compliance with the NAAQS.
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From page 36... ...
Controlled human studies and field health studies have indicated that the potential for producing transitory pulmonary effects is greater than originally projected and have indicated the need to consider a demonstration period longer than 1 hour for exposure to ozone. The discussion of ozone's effects must also consider the relative importance of indoor ozone concentrations and the potential duration of exposure.
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From page 37... ...
(1985b) with two varieties of slash pine seedlings suggested that exposures to peak ozone concentrations elicit a greater response than do exposures to mostly lower concentrations over similar time periods.
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From page 38... ...
Based on this current understanding, the committee provides a critique of the scientific basis of current regulatory strategies and lists recommendations for improving the scientific basis of future regulatory strategies. The committee determined that a coherent, integrated research program is needed to clarify further the factors that control tropospheric ozone formation within the context of changing regional and global environmental conditions.
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From page 39... ...
13 What is the interaction between tropospheric ozone concentrations and global change? 14 Is a comprehensive, long-term research program on tropospheric ozone formation and measurement necessary?
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