Trends in air measurements The air is getting better but monitoring data need to be improved
Despite the fact that the air is getting better, many areas in this country still experience pollution levels above the standards established to protect human health. Data from 23 metropolitan areas that have monitored air quality for seven or more years show considerable reductions in pollution levels, according to "State of the Environment—1982" (the Conservation Foundation book reported on in the August issue of ES& T, p. 445A). This conclusion is based on the average number of days in which index readings for the combined 23 cities were in the unhealthful, very unhealthful, and hazardous ranges. From 1974 through 1980, the average number of days of elevated risk declined by 39%, from 97 to 59, in the 23 cities. The national index on air quality is called the Pollution Standards Index (PSl). It is determined by the particulate pollutants (the five criteria pollutants—particulate matter, sulfur dioxide, nitrogen dioxide, ozone, and carbon monoxide) and is based on the highest concentration relative to its primary air quality standard. If the air quality equals the primary standard for that pollutant, the index has a value of 100; if it is twice the standard, the index has a value of 200 and so forth. The index scale is divided into five ranges of air quality ranging from "good" (0-49) to "hazardous" (above 300). But there are always problems with the data. The quality and comparability of data on ambient air quality depend on, among other factors, the proper siting of monitors, the reliability and uniformity of equipment, and the technique used to identify both human error and deficiencies in equipment. But the Conservation Foundation book points out that the number and location of ambient measurements may change substantially over time. Any interpretation of data on ambient air quality, therefore, must recognize these problems. For example, a 1979 EPA study 506A
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reported that 72% of 243 monitors inspected were sited incorrectly; 58% of the equipment in use was not certified by EPA; 81 % of the sites examined had one or more problems that could adversely affect data reliability. The EPA data appear to have improved since the institution of the QA (quality assurance) program by the agency in 1979. But the gathering of reliable trends data is still a real job. At the 75th anniversary meeting of the Air Pollution Control Association in June in New Orleans there were sessions on measurements. There also will be sessions on aerometric data at the fall meeting of the ACS in September in Kansas City. Nitrogen dioxide Michael Claggett of EnviroMeasure, Inc., (Knoxville, Tenn.) presented an overview of current trends in ambient nitrogen dioxide. All sites reporting to the National Air Data Bank were analyzed for the period 1978-80. His analysis showed that there were almost 60% fewer sites
reporting high N 0 2 concentrations in 1 980 than in 1978. Claggett said that this does not necessarily represent an improvement in air quality over the last three years. In fact, it appears that this result may be due to a sharp decline in the quality of air monitoring for N O , . His measurements showed that the populations of 32 counties were at risk during this two-year time period. The total population at risk is 41.7 million persons, of whom 12 million live in the Los Angeles basin. There is no welldefined trend of long-term variations in N 0 2 concentrations that applies to all the sites. In 1978, for example, 32 of 126 sites reported annual average NO2 concentrations exceeding the N A A Q S , the national air quality standard. The problems with monitoring data are legion. Little work, for example, has been reported in the literature concerning the magnitude of public exposure to N 0 2 concentrations. In many cases there is only one N 0 2 monitoring site, and it may not be lo-
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© 1982 American Chemical Society
cated where maximum concentrations occur. In fact, this paper pointed out that most of the U.S. population lives in counties in which no NO2 monitor ing is performed. Nationwide, NO2 levels appear to have risen in recent years. The NO2 measurements from 1974-80 are based on 338 monitors, according to the Conservation Foundation book. Ambient levels of NO2 increased a total of 20% between 1970 and 1980, but there was a slight decline in N 0 2 concentrations in 1979-80. Ozone R.E. DeMandel of the Bay Area Air Quality Management District, San Francisco, Calif., looked at trends in ambient ozone concentrations and re ported that during the May-October ozone season, the mean daily highhour concentration is a suitable index for trend analysis. Since 1975, inland ozone levels have decreased gradually, by about 1%/y. Hydrocarbon emis sions are estimated to have decreased at a rate of about 5%/y. Ambient levels of ozone were 9.9% lower in 1979 than they were in 1974, although they rose slightly in 1980, according to "State of the Environ ment—1982." This trend is based on measurements at 122 sites nationwide. In 1977, more than 140 million people lived in areas exceeding the primary air quality standard for ozone. In 1987, it has been estimated, 35 million people will be exposed to ozone levels above the N A A Q S . William J. Parkhurst of the Ten nessee Valley Authority reported on the atmospheric deposition in the Tennessee Valley, 1979-80. TVA is the largest source of stationary fossilfuel combustion in the Tennessee Valley. W e t / d r y deposition sampling was conducted at each of TVA's 12 coal-fired power plants and at five rural trend stations. Sulfate, nitrate, and p H deposition distributions are similar for all sites, and no significant differences between means could be established. The regional trend stations do not stand out as being different from those located near the power plant monitoring stations. Annual depositions did not indicate regional gradients. Modeling strategies are often used to explain the monitoring data for high levels of pollutants. R.J. Farber et al., of the Southern California Edison Company, classified ozone and nitro gen dioxide episodes in the Los Ange les basin. This basin is among the country's most polluted areas. For the past 30 years, it has experienced the nation's highest ozone levels during the
summer and the highest nitrogen dioxide concentrations in the winter. During the summer, 1-h ozone read ings are as high as 450 ppb, and nitro gen dioxide climbs to 550 ppb in the winter. For ozone, the national stan dard is 120 ppb; the California firststage episode level is 200 ppb and the second-stage level is 350 ppb. The na tional standard (24-h average) for N 0 2 is 150 ppb. One big problem here is that there is little daily variation in emission levels in the Los Angeles basin, yet there are large differences in ozone and nitrogen dioxide levels during the same period. There is a large collection of data from the Houston 1981 Summer Ozone Study. Walter L. Crow of Ra dian Corporation said that the results of the study are summarized in four volumes. It is hoped that comprehen sive studies will be performed on these data. Robert E. Clark of TVA reported on ozone levels in the Great Smoky Mountains during the summer of 1980. One-hour average ozone con centrations measured at Look Rock exceeded 120 ppb, the national stan dard, on at least 10 days during July and August 1980. The highest 1-h av erage ozone concentration during an episode reached 165 ppb, and this value was recorded in the largest N a tional Park in the eastern U.S.! It was explained that the unusually hot and dry summer weather, combined with several stagnation episodes, created conditions conducive to formation and buildup of photochemical ozone and other pollutants. Particulate matter Promulgation of the revision to the N A A Q S for particulate matter is ex pected during 1983. The new standard may be proposed in terms of particu late matter smaller than 10 μπι aero dynamic diameter. (Particle size is defined in terms of an equivalent aerodynamic diameter, which is the diameter of a unit density sphere that has the same settling rate as the par ticle being classified.) John G. Watson of Environmental Research & Technology, Inc., re ported on the effect of sampling inlets on the IP and T S P concentration ra tios. (IP = inhalable particulate mat ter; TSP = total suspended particulate matter.) Different samplers, i.e., the Hi-Vol, the Hi-Vol with selective-size inlet, and dichotomous samplers, under different ambient conditions measure different fractions of the total suspended particulate matter mass. The Hi-Vol with selective-size inlet and dichotomous samplers collect
equivalent mass concentrations within 5% of each other under typical situa tions. However, under low or high wind speeds, when interferences are present in one or both of these samplers, the mass concentrations of the particles vary more. Thompson G. Pace of the U.S. EPA at Research Triangle Park said that the national IP network of 130 sites has been in operation since 1979. H e attempted to estimate the concentra tions of particulate matter with di ameters less than 10 μιη, from IP and T S P data, but found no relationship between the I P / T S P ratio and type of site and its geographic location. Measurements for the 10-μπι frac tion of particulate matter were re ported for a number of cities including New York. Comparisons of the data with different samplers were reported. R.H. Knuth of the U.S. Department of Energy, New York, reported that on the average at the New York sampling site, 63% of the aerosol mass is con tributed by particles less than 15 μιη; 56% by particles less than 10 μπι, and 36% by particles less than 2.5 μπι. Dale A. Lundgren and coauthor, of the University of Florida at Gaines ville, reported on the ambient aerosol mass distribution of l-100-μπι parti cles in five cities. The purpose of their project was to use the mobile sampling system to obtain ambient mass distri bution data from Birmingham, Ala., Research Triangle Park, N.C., Phoe nix, Ariz., Philadelphia, Pa., and Riv erside, Calif. They compared the re sults to data collected from several conventional ambient aerosol sam plers. Carbon monoxide Measured concentrations of C O have decreased significantly since 1970. Ambient levels of CO, measured at 91 urban sites, decreased 40.6% between 1970 and 1980, according to the Conservation Foundation book, which points out that these measure ments can vary considerably within a region, depending on traffic patterns and the location of monitors. In 1980, C O levels (annual averages) in 145 counties or parts of counties exceeded the health-based ambient standard, 39 of these by more than 100%. The Na tional Commission on Air Quality es timated that 28 metropolitan areas will not meet the ambient standards by 1982. The commission also noted that at least 22 areas have recorded carbon monoxide readings more than 150% higher than the standard, the 1-h standard being 35 ppm, not to be ex ceeded more than once a year. —Stanton Miller Environ. Sci. Technol., Vol. 16, No. 9, 1982
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