results from aged photochemical "smog" originating in these distant sources and transported under light wind conditions and surface inversion created by the relatively cool lake. AIR QUALITY MEASUREMENTS The most serious known problem with photochemical "smog" is in Los Angeles County. A great amount of work has been done and much information has been obtained on the problem in this area. In other areas of the country, a large quantity of air quality data obtained by the continuous air monitoring program (CAMP) and other sources indicates that current or potential problems of photochemical "smog" are widespread throughout the United States. Table 2 summarizes data on concentrations of total oxidant (KI method) obtained at CAMP locations. The summary gives yearly means; maximum monthly, daily, and hourly averages; and maximum 5-minute concentrations of this pollutant in each of seven cities where CAMP monitoring was carried out during 1964. Maximum 1-hour average concentrations of oxidant in parts per million were 0.13 (Chicago), 0.26 (Cincinnati), 0.46 (Los Angeles), 0.20 (Philadelphia), 0.17 (San Francisco), 0.26 (St. Louis), and 0.20 (Washington, D.C.). These levels are significantly high and leave little doubt as to the occurrence of photochemical "smog" in eastern cities as well as California cities. Data in table 2 indicate the occurrence of high oxidant values in the cities where CAMP monitoring was done. The data in table 3, based on CAMP values obtained during 1964, indicate the prevalence of elevated oxidant concentrations in these cities. In all the cities the maximum hourly oxidant equalled or exceeded 0.1 part per million on a significant number of days; in all cities except San Francisco maximum hourly oxidant concentrations were 0.05 part per million or greater on at least 43 percent of the total days for which valid data were available. Tables 1 and 2 include data on oxidant concentrations monitored by the CAMP at its site in Washington, D.C. The Metropolitan Washington Council of Governments Oxidant Sampling Network includes seven stations in the metropolitan area at which oxidant samples are taken. Table 4 summarizes datą for the period October 1962 through September 1963 (26). These values were determined by the phenolphthalin method; multiplying by a factor of 0.5 gives the approximate values yielded by the CAMP instrumentation (KI method). The data in table 4 are especially interesting for two reasons. First, they substantiate previously cited CAMP data in showing that on an appreciable number of days there were periods when the oxidant level in the Washington area exceeded levels that could potentially cause smog odor, eye irritation, or plant damage. Secondly, the data indicate the significant variation in concentrations at different locations within a metropolitan area. It seems reasonable to expect that high oxidant concentrations may be localized phenomena; these data support that belief. Since current continuous air monitoring of oxidant concentrations is usually done at only one location within metropolitan areas, the frequency of periods of high oxidant concentrations at other localized areas within a city may be higher than is indicated by the CAMP data in table 3; conversely, in other areas it may be lower. TABLE 2.-Atmospheric concentrations1 of total oxidants (KI method) from continuous air monitoring program—1964 Occurred 8:40 p.m. Nearby source is being investigated for explanation. Next highest value occurred at 7 p.m. TABLE 3.-Prevalence of elevated oxidant concentrations1-Continuous air monitoring program [Days on which maximum hourly oxidant (KI) concentration was equal to or greater than concentration shown, January-December 1964] TABLE 4.-Occurrence of elevated oxidant1 concentrations in Washington, D.C., area (26) [Metropolitan Washington Council of Governments oxidant sampling network] 1 Phenolphthalin (PHTH) method; values are approximately double the values obtained by potassium iodide (KI) method. 2 October 1962-August 1963 only. Highest daily 10-minute sample as recorded by Beckman continuous oxidant analyzer (KI method) multiplied by 2. 31 10-minute sample each day, Monday through Friday, May through September, and 1 10-minute sample each Tuesday and Friday, October through April. 120-minute sample, routine as (3), through June 1963. 1 10-minute sample, routing as (3) beginning July 1963. The Colorado Department of Public Health has obtained oxidant values by use of a Mast instrument in Denver. The Mast is a coulometric instrument, sensitive to several oxidants found in the air. Data from the Colorado study (27) show that during May, June, and July of 1964 periods when the oxidant concentration was equal to or greater than 0.05 part per million occurred on approximately 21 percent of the sampling days. The State of Colorado considers approximately 0.03 part per million oxidant as the possible natural background level and concentrations above that as evidence of photochemical activity. A report to the legislature on air pollution in Colorado (Colorado State Department of Public Health) states that the oxidant level reached a high of 0.13 part per million (KI method) on October 17, 1963. The report concluded that a potential for photochemical "smog" is present. Daines (Rutgers University) has taken oxidant samples at a number of locations in New Jersey for several years. In 1964 (23), he reported oxidant values of 0.05 part per million (KI method) and higher at Carlstadt, N.J. The data, summarized in table 5, are based on samples taken daily over the 4-hour period 1100 to 1500 from May 5, 1961, through November 7, 1963; they probably represent the daily maximum 4-hour concentrations of oxidant for this period. Carlstadt is located 3 or 4 miles west of New York City in an area where some crop production still occurs. These data, table 5, show that on 86 days, or 9.7 percent of the total of 885 sampling days in the period, the 4-hour average concentration of oxidant equaled or exceeded 0.05 part per million (KI). On 23 days, or 2.5 percent of the sampling days, the concentration equaled or exceeded 0.10 part per million. The maximum value recorded during the approximately 3-year study was 0.32 part per million. A review of literature published to July 1963 shows maximum reported oxidant values in a number of communities. Many of these values, listed in table 6, approach or exceed what is generally considered the adverse level of approximately 0.10 to 0.15 part per million oxidant by the potassium iodide method (approximately 0.20 to 0.30 part per million by phenolphthalein method). TABLE 5.-Days in Carlstadt, N.J. (May 18, 1961, through Nov. 7, 1963) when oxidant concentration1 equaled or exceeded 0.05 p.p.m. (23) Number of days when oxidant≥0.05 p.p.m__-. Percent of sampling days when oxidant≥0.05 p.p.m.2 Number of days when oxidant≥0.10 p.p.m--- Percent of sampling days when oxidant≥0.10 p.p.m.2_ Maximum concentration (p.p.m.) 86 9.7 23 2.5 0.32 1 Analyses done by potassium iodide method (KI). Samples taken daily between 1100 and 1500. 2 885 sampling days in this period. TABLE 6.-Maximum oxidant values reported in a number of American cities Figure 1 shows plots of 2-year (1962-63) average concentrations of total hydrocarbon total oxidant, nitric oxide, and nitrogen dioxide in Cincinnati. These data, taken at the CAMP station located in the downtown area, show a diurnal pattern typical of photochemical smog development. This pattern is similar to those occurring in other eastern cities as well as in Los Angeles. The buildup in oxidant is preceded by a buildup in nitrogen dioxide and a decrease in nitric oxide and hydrocarbons. Figures 2 and 3 are plots of time versus concentrations of nitric oxide, hydrocarbon, oxidant, and nitrogen dioxide in the ambient air at CAMP stations in Cincinnati and Washington, D.C. Photochemical "smog" occurred on the dates represented in these graphs; the data were selected as examples of such inci dents, which are not uncommon among cities monitored by the CAMP. These naturally occurring patterns of photochemical smog reactions are typical of laboratory irradiation chamber patterns, such as the example shown in figure 4. NITROGEN DIOXIDE The atmospheric concentration of nitrogen dioxide is useful as an indicator of photochemical activity; it has been well established that nitrogen dioxide is formed rapidly in "smog" reactions from the primary exhaust pollutant, nitric oxide. Table 7 shows the mean yearly concentrations; maximum monthly, daily, and hourly averages; and maximum 5-minute concentrations of nitrogen dioxide measured in seven cities by CAMP instrumentation. Table 8 lists the maximum 24-hour concentrations of nitrogen dioxide for 1962 or 1963 and the average 24-hour values for 1962 and 1963 in several cities. These data in table 8 are from the National Air Sampling Network (NASN), which samples on a random schedule 1 day in each 2-week period. The concentrations reach significantly high levels in a number of cities. CARBON MONOXIDE Carbon monoxide also is considered an excellent source indicator for pollution of the air by motor vehicle exhaust. Tables 7 and 9, based on CAMP data, show average concentrations in seven cities for 1962 and/or 1963 and for 1964. These data indicate that although the magnitude of the problem varies from one area to another, motor vehicles produce appreciable contamination in communities that are widely separated geographically. EMISSION ESTIMATES Emission estimates help to reveal important sources of air pollutants. Nitrogen oxides, carbon monoxide, and hydrocarbons are major gaseous pollutants emitted by motor vehicles, although they are also emitted in various amounts by other sources in urban areas. Table 10 has been prepared from published material to allow an evaluation of the relative importance of vehicular contributions to the total emissions of these gases in several urban communities. Typically, in large metropolitan areas, motor vehicles account for 30 to 50 percent of the nitrogen oxides, 40 to 80 percent of the hydrocarbons, and almost all of the carbon monoxide. SUMMARY AND CONCLUSIONS The evidence of photochemical smog reaction products in metropolitan areas outside of California is clear. Data from large urban areas other than Los Angeles indicate that oxidant concentrations equaling or exceeding 0.10 p.p.m. occurred for at least 1 hour on 4 to 14 percent of the days during 1964. This condition occurred on 42 percent of the days in Los Angeles. Significantly high concentrations of carbon monoxide and nitrogen oxides are now occurring in all metropolitan areas where pollutants are monitored. Diurnal patterns of concentrations of photochemical "smog" precursors and reaction products in eastern cities are similar to those in Los Angeles. Plant damage from oxidants have been reported in most regions of the United States. Current evidence indicates the widespread occurrence of photochemically produced pollutants and their deleterious effects. The problem is significant now and will become more severe with increases in population density and use of automobiles. The projected large increase in urban population depicted in figure 5 will greatly intensify the pollution problem, since levels of "smog" pollutants as well as other pollutants are known to rise with increasing concentrations of human activity. Figure 6 projects a much greater increase in urban than in rural travel and further emphasizes the potential aggravation of pollution problems throughout the country. Present and projected automobile registrations and miles of travel shown in figure 7 also point to a serious increase in problems from pollution by automotive vehicles. |