Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991) / Chapter Skim
Currently Skimming:
2 Trends In Tropospheric Concentration of Ozone
2 Trends In Tropospheric Concentration of Ozone
Pages 41-66
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 41... ...
Despite comprehensive local, state, and national regulatory initiatives over the past 20 years, ambient ozone concentrations in urban, suburban, and rural areas of the United States continue to be a major environmental and health concern. Sixty-three areas did not meet the ozone NAAQS in 1987; 101 areas were out of compliance in 1988, 96 areas in 1989, and 98 areas in 1990 (see Table 1-1 and Figure 2-1)
|
From page 42... ...
42 ~D Q In C ~ O a' ·- Cat G ~ ~ ~ c I _, ' r!
|
From page 43... ...
Meteorologically induced variability makes it difficult to identify underlying trends in ozone concentrations that could result from changes in the amount, type, and geographical distribution of precursor emissions. This chapter outlines the existing form of the ozone NAAQS, summarizes studies on ozone trends, evaluates recent efforts to screen meteorological influences on ozone trends, and highlights research needs for more robust indicators of progress in reducing ozone concentrations.
|
From page 44... ...
The first, second, and fifth attributes shown in Table 2-1 are those most commonly considered in relation to the ozone NAAQS. For the existing ozone NAAQS, the averaging time is 1 hour, but ozone trends have been examined using averaging times of 7, 12, and 24 hours for a given day, and the Occupational Safety and Health Administration exposure standard for ozone is based on an 8-hour averaging period.
|
From page 45... ...
o a o · ct In at .2 Cal O' A: o a Ct o .c D Ct Cal C D .c I: ._ Ct .
|
From page 46... ...
. EPA's principal statistical measure of ozone concentrations is the composite nationwide average of second highest 1-hour daily maximum concentrations in a given year.
|
From page 47... ...
1 1 ~NMOS Z 0.15 O 0.10 z 0.05o 0 0.00- 1 1 1 1 1 1 1 1 ~ 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 YEAR FIGURE 2-2. Boxplot comparisons of trends in annual second highest daily maximum 1-hour ozone concentration at 431 monitoring sites, 1980-1989.
|
From page 48... ...
O 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 YEAR FIGURE 2-3. National trend in the composite average of the estimated number of days exceeding the ozone NAAQS concentration during the ozone season at monitoring sites, with 95% confidence intervals, 19801989.
|
From page 49... ...
For example, in the California South Coast air basin, Kuntasal and Chang (1987) estimated that NOX emissions decreased by only 1% between 1970 and 1985, whereas ambient concentrations of NOX decreased by 30%.
|
From page 50... ...
As discussed above, the current principal statistical measure of ozone concentrations, the composite average of second highest daily maximum 1-hour
|
From page 51... ...
This measure masks underlying trends and is therefore not a reliable indicator of an area's progress in reducing ozone over several years. The following sections discuss various approaches to obtaining a measure of ozone concentrations that accounts for variations in meteorology.
|
From page 52... ...
, chartered under the California Clean Air Act of 1988, characterized the intrinsic uncertainty or "native variability" of 27 air-quality-related indicators in 43 areas within the state and determined the uncertainty intrinsic to each indicator in the absence of reduction of ozone concentrations. From this characterization, a list of approved indicators could be used to estimate progress in the attainment of air quality standards.
|
From page 53... ...
. The robustness of an ozone trends indicator depends on its separation from the extreme values associated with the NAAOS.
|
From page 54... ...
o o 0 1 en o Q en 0.5 I RETHINKING THE OZONE PROBLEM 2 1.6 nag 1.5 _ 0 ~ ~ 2 go 59 ~ for ~°~ ~° on or of or Years of averaging period 1.6 1 1.3 0.8 o I ~ L ~ 1 so 59 or no on on oh's or' or or 0.5 Years of averaging period FIGURE 2-8 Three-year running mean of South Coast basin population weighted ozone exposure hours for the average resident. Source: SCAQMD, 1989.
|
From page 55... ...
The first step necessary to account for meteorological effects is to determine what ozone data should be used in an analysis. Data often are selected to reduce the dependence of the analysis on the extreme values generally associated with the existing ozone NAAQS.
|
From page 56... ...
Three-month averages of the 1-hour daily maxima for 6, 9, and 13 stations in the South Coast Air Quality Management District (Kuntasal and Chang, 1987) The basinwide daily maximum oxidant concentrations (Chock et al., 1982; Kumar and Chock, 1984)
|
From page 57... ...
Apparently, the ozone-conducive days of June 1987 were more prone to ozone formation than were the ozone-conducive days of June 1984. An important problem that impedes the routine prediction of ozone concentrations is that the ozone associated with transport cannot always be related to weather.
|
From page 58... ...
The binary splits continue until the data are subdivided such that the ozone concentrations on days within each final group are sufficiently uniform. While the regression tree does not re~duce all the year-to-year variability, it does highlight the results from individual years that have unusual meteorological conditions, such as 1980, 1983, and 1988.
|
From page 59... ...
~oo~<~o~oo3~oooo~'oooo~oooo~ooooA~oo FIGURE 2-10 Number of days exceeding the ozone NAAQS concentration in the Chicago area, 1977-1989. Normalized data were obtained by removing meteorological variability.
|
From page 60... ...
for the California South Coast air basin and reduced variability in the ozone concentration trend for the period from 1968 to 1985 (Figure 2-12~. Wakim (1989)
|
From page 61... ...
The current principal statistical measure of ozone trends-the second-highest daily maximum 1-hour concentration-is highly sensitive to fluctuations in weather patterns and therefore is not a reliable measure of underlying trends. If the effectiveness of a program to reduce ozone concentrations in a particular area is to be tracked over a period of several years, then some way is needed to account for the effects of meteorological fluctuations.
|
From page 62... ...
For each city, the number of days per year with ozone concentration greater than 0.12 ppm is shown in a. The number of days per year with temperatures greater than 90°F is shown in b.
|
From page 63... ...
TRENDS IN CONCENTRATION (a) 70 ~ Boston (a)
|
From page 64... ...
adjusted O : 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 Year FIGURE 2-12 Trends in ozone concentrations (temperature-adjusted and unadjusted) at nine sites in the California South Coast air basin, 1968 1985.
|
From page 65... ...
x variations is first to classify days as ozone-conducive or nonconducive and then further subdivide the conducive days using a binary decision tree or a regression equation to measure the degree to which the weather conditions of each conducive day deviate from the norm.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.