bons in the Surface of Waters of the Great Basin”, I. V. Olson, Ed., pp 379-400, Nobel Symp. 12, Wiley, 1970. (15) Weiler, R. R., J.Fish. Res. Board Can., 31,329-32 (1974). (16) Emerson, S., Limnol. Oceanogr., 20, No. 5 (Sept. 1975). (17) Liss, P. S., Deep Sea Res., 20,221-38 (1973). (18) Cohen, Y., MASc thesis, University of Toronto, Toronto, Ont., Canada. (19) Mackay, D., Shiu, W. Y., “The Aqueous Solubility and Air-Water Exchange Characteristics of Hydrocarbons under Environmental Conditions”, paper presented to Electrochem. Soc. Symp., Toronto, May 1975, and published in the Proceedings “The Chemistry and Physics of Aqueous Solutions”, pp 93-110. (20) Wilson, B. W., J . Geophys. Res., 65 (lo), 3377-82 (1960). (21) Pollak, M. J., ibid., pp 3383-9. (22) Bird, R. B., Stewart, W. E., Lightfoot, E. W., “Transport Phenomena”, Wiley, New York, N.Y., 1960. (23) Tsivoglou, E. C., “Tracer Measurement of Stream Reaeration”, Fed. Water Pollut. Control Admin., Div. of Technical Services, US. Dept. Interior, Washington, D.C., 1967.
Literature Cited (1) Mackay, D., Leiononen, P. J., Environ. Sci. Technol., 9, 1178
(1975). (2) Dilling, W. L., Tefertiller, N. B., Kallos, G. J., ibid., p 833; ibid., 10,1275 (1976). (3) Dilline. W. L.., ibid.. . 11.405 (1977). (4) NeelyY‘W. B., Proc. 1976 Nat. Conf. on Control of Hazardous Material Spills, pp 197-200, New Orleans, La., Apr. 1976. (5) Lewis, W. K., Whitman, W. G., Ind. Eng. Chem., 16 (12), 1215-20 (1924). (6) Mackay, D., Cohen, Y., “Prediction of Volatilization Rate of Pollutants in Aqueous Systems”, Symp. on Nonbiological Transport and Transformation of Pollutants on Land and Water”, NBS, Gaithersburg, Md., May 1976. (7) Kinsman, B., “Wind Waves”, 2nd printing, Prentice-Hall, Englewood Cliffs, N.J., 1965. (8) Hidy, G. M., Plate, E. J., J . Fluid Mech., 26,651-87 (1966). (9) Plate, E. J., Hidy, G. M., J. Geophys. Res., 72,4627 (1967). (10) Wu, J., J . Fluid Mech., 34,91-122 (1968). (11) Wu, J., J . Geophys. Res., 74,444-55 (1969). (12) Kanwisher, J., ibid., 68,3921 (1963). (13) Broecker, W. S., Peng, T. H., Earth Planet. Lett., 11, 99-108 (1971). (14) Thurber, D. L., Broecker, W. S., “The Behaviour of Radiocar-
Received for review June 7,1977.Accepted November 1,1977.Work supported by Environment Canada (Inland Waters Directorate and Atmospheric Environment Service), Imperial Oil Limited, and the National Research Council of Canada.
Weekday-Weekend Ozone Concentrations in the Northeast United States William S. Cleveland* and Jean E. McRae Bell Laboratories,600 Mountain Avenue, Murray Hill, N.J. 07974 Ozone concentrations a t sites downwind of the New York City metropolitan region decrease on weekends. Concentrations within and upwind of the region are very nearly the same on weekdays and weekends, which agrees with earlier analyses of data in this region. For concentrations above the Federal Standard of 80 ppb, the reduction in Connecticut, which has the highest ozone concentrations in the Northeast, is approximately 20%. This weekend reduction carries over into Monday, which has concentrations approximately the same as those on weekends. This is then followed by a gradual increase on Tuesday to Friday. The reductions in ozone concentrations on Saturdays, Sundays, and Mondays correspond to reductions in traffic which occur on these days of the week. The fitting of a time series model with periodic means, variances, and autocorrelations shows the observed reductions are statistically significant. Photochemical air pollution in the Northeast United States has previously been studied through chemical kinetic modeling (1-3),statistical analysis of ground-level continuous air monitoring data (4-12), and aircraft flights (13, 1 4 ) . Concentrations of O3 on weekdays and Sundays during May to September of 1973 were compared at sites in New Jersey, New York City, and Long Island ( 5 , 6 ) .The conclusion was that while primary pollutant concentrations, such as NO and hydrocarbons, were substantially lower on Sundays than on weekdays, ozone concentration distributions were nearly the same in New Jersey, New York City, and Long Island. This “Sunday effect” was reproduced in a chemical kinetic model of northern New Jersey ( 1 1. In addition, the concept of functional oxygen groups was introduced and used to show that “the Sunday effect results from the tight balance between ozone production through NO2 photodissociation and oxygen scavenging by NO, from the advection of ozone from less urban areas, and from the incorporation of similar quantities of ozone pre-existing above the morning mixed layer.” 558
Environmental Science & Technology
In this paper we shall extend the day of the week data analysis to a larger geographical region (sites in New Jersey, New York, Connecticut, and Massachusetts) and for a longer time period (May to September of 1973,1974, and 1975). The results of this paper substantiate the previous conclusion of no weekend reduction of ozone in New York and New Jersey, but in addition show that there is a weekend reduction of ozone in Connecticut and Massachusetts.
Data Analysis Data Analyzed. The ozone data analyzed in this paper consist of daily maximum O3concefitrations at 28 sites in New Jersey, New York, Connecticut, and Massachusetts. The time period covered is May through September for the years 1974-75 at 21 sites, 1973-75 at 6 sites, and 1970-75 at 1site. With the exception of one site, where a colorimetric method was used, all monitors were of the gas phase, ozone-ethylene type. In addition, hourly carbon monoxide concentrations a t 10 sites and traffic counts at the Lincoln Tunnel between New Jersey and New York City are analyzed to characterize traffic according to the day of the week. These data are from the time periods May through September for the years 1974 and 1975. The data were obtained from the New Jersey Department of Environmental Protection, the New York State Department of Environmental Conservation, the Connecticut Department of Environmental Protection, the Massachusetts Department of Public Health, Boyce Thompson Institute, Yonkers, N.Y., and the New York Port Authority. Method of Analysis. Consider the following two sets of 0 3 concentrations in ppb: (50,70,90,90,100,120,140,160,250, 370) and ~50,70,90,90,100,120,140,160,200,250). The two sets differ in that the two highest concentrations are considerably reduced in the second set. However, the averages of the first and second sets are 144 and 127, respectively. Thus, the reduction that occurs in the high concentrations is far larger than the reduction in the averages since the majority of ob0013-936X/78/0912-0558$01.00/0
0 1978 American Chemical Society
servations do not change. This, in fact, happens for O3 concentrations in the Los Angeles Basin where the reduction in the very highest 0 3 concentrations which occurs on weekends is “washed out” when averages are taken. For example, Tiao et al. (15) have reported the percentage of times O3 daily maxima a t five sites in the Los Angeles Basin (Burbank, West Los Angeles, downtown Los Angeles, Pasadena, and Azusa from 1962 to 1972) which were above 500 ppb, occurred on each day of the week. These values, shown in Figure 1 (top panel) reveal a rather dramatic reduction in the number of concentrations above 500 ppb on weekends. In contrast, Elkus and Wilson (16) have reported averages of daily maxima during the summer months of 1965-72 for several California sites. The values for Azusa, shown in Figure 1 (bottom panel), reveal a less dramatic reduction. Finally, similar averages taken over the entire year, which include the low winter months, show only very slight weekend reductions. In this paper, one of the tools used to analyze the data, empirical quantile-quantile plots (17), will allow us to compare the entire range of 0 3 concentrations from smallest to largest. Analysis of Each Day of Week. The behavior of the high 0 3 concentrations for individual days of the week at Bridgeport, Conn., is illustrated in Figure 2 (top panel) which shows a robust upper quarter mean of the daily maxima for each day of the week. Upper quarter means are, roughly, an “average” of the highest 25% of the observations and therefore summarize the upper tails of the ozone concentration distributions for each day of the week. A precise definition is given in the Appendix. It is quite interesting that, just as in Azusa, Calif. (Figure l),there appears to be a reduction on weekends which carries over into Monday, and then a gradual increase on Tuesday to Friday.
To characterize traffic patterns, the average carbon monoxide concentration from 6 a.m. to 1 p.m. for each day of the week a t each site was computed. The averaging was carried out for all days with available data from May through September of 1974 and 1975. Similar averages were computed for the Lincoln Tunnel traffic counts. The results show that the traffic pattern is similar to the pattern of the ozone concentrations-there is a reduction on Saturday, Sunday, and Monday. This is illustrated in Figure 2 (bottom panel) where the carbon monoxide averages at a measuring site in Elizabeth, N.J., are plotted. Weekends vs. Tuesday-Friday. In this and the following sections we shall compare concentrations of daily maximum O3 on three types of days-weekends, Mondays, and Tuesdays to Fridays-using descriptive statistics and empirical quantile-quantile (EQQ) plots (17). Monday has been selected for separate analysis as a result of the upper quarter mean analysis discussed earlier. The p t h percentile (quantile) of a set of data is a value such that p percent of the data is less than or equal to the value. For instance, the median is the 50th percentile. On the EQQ plot percentiles of one set of data (for example, weekends) are plotted against the corresponding percentiles of the other set of data (for example, Tuesdays to Fridays). In the special case when both sets of data have the same number of observations, this amounts to plotting the largest concentration from one data set against the largest from the other, the next largest against the next largest, etc. If the distributions are nearly the same, then the points of the plot lie close to the line Y = X , which is drawn on all plots. The most important feature of the EQQ plot is that it allows comparison of values of the Concentration distributions across the entire range of values from smalle& to largest.
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