HAZE AND SULFUR
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he cause of visibility degradation by regionalscale haze ill the eastern United States is well established (1-4). ‘l’he haze sources aellerd~lvlie hundreds of iniles or ni& away from the receptor arcas. Hence, it is difficult to attribute haze aerosols to any one source because many distant and local sources contribute to the haze. Chemical analysis reveals that about 40-70yd of the fine particle mass over the easterii Uuited States is composed of sulfates, associated ainiiioiiiuin ion, and water. Based oil their size, sulfates contribute at least their mass share tu light extinction in the atmosphere. For this reason they have been the focus of many iotense studies. Organics are also significant contributors to hare, but difficulties io measurement methods have prevented clear quantification of their contribution. In this paper we present regional and seasonal trends o f eastern United States haze and compare the haze trends to the corresponding SO, euiission treuds. Such a comparison may be of interest for both regulatury and scieotific studies. Haze trend data sets ‘l‘he trend data consist of hourly prevailiog daytime (110011) visibility observations, which are recorded at 1 3 7 U.S. sites (mostly airports). Coniputer-coiiipatible data, which have been collected since about 1948, are suitable for a consistent, long-term trend analysis. The observed visual range (in) is used to calculate the extinction coefficient b,,,. (10P”’ir’ or Mn-’), via the Koschuiieder relationship b,,, = 3.9IV ( 5 ) . The Kuschmieder constant of 3.9 may not be appropriate for airport visibility, but it is used for consistency. Using a different constant wuuld not affect the spatial pattern and trends. ‘The extinction coeffi12
Environ SCI.Trchnol., VoI. 27, NO. 1, 1993
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RUDOLF E. HUSAA Center for Air Pollution Inipact and Trend Analysis Washington University St. Louis, MO 63130
W I L L I A M E. W I L S O N Environmental Protection Agency Atmospheric Research and Exposure Assessment Laboratory Reseorch Triungle Park. NC 2771 I
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cieut, rather than the visual range, is used to facilitate coniparisons with emission trends. In the following discussion. the ternis haze and haziness are used interchangeably with extinction coefficient. Airport visual-range observations pose a significant problem because there is a furthest marker beyond w h i c h t h e visual range i s not known. For example, if the furthest marker is at 20 kin, all visibility observations > 20 km will be recorded as 20 kni (or all extinctions < 195 Mm-’ will be recorded as 195 Mm-’1. ‘This translates to a lower threshold value or truncation for the distribution of the coniputed extinction coefficients. For this reason, nonparametric statistical indices, such as data percentiles, are more useful. The 25th, 50th, 75th, and 90th percentiles of the extinction coefficients were calculated monthly for each station to yield the trend data set ( 4 : Husar, R. B., Washington University, personal communication, 1988). In the data set below, the 75th percentile of the extinction coefficient was used to avoid the visibility threshold anomalies. Also, only data obtained in the absence of fog and precipitation were used. Haze trend maps US.haze trend patterns are summarized in Figure 1. The 16 maps
represent four time periods and four seasons. The selected time periods are five-year averages centered around 1950,1960, 1970, and 1980, whereas the four quarters are calendrical. The first quarter data, shown in the top row of maps, demonstrate that the worst haziness is in the area s u r r o u n d i n g t h e Great Lakes, whereas the least haze is over the Rocky Mountain states. There is evidence of increasing winter haze over the southeastern states. In the second quarter a significant increase in haze is exhibited east of the Rocky Mountains. In about 1950, the hazy region was confined to the Ohio and Mississippi River Valleys and to the Great Lakes. By the 1980s, much of the eastern United States was covered with higher haze. The most significant changes occur in the third quarter (1-3, 6-9, Husar, R. B . , Washington University, personal communication, 1988), particularly south of the Ohio River. In the 1950s, the haziness was the lowest in the Southeast (Georgia, Tennessee, North Carolina, and South Carolina). By the 198Os, this region showed the highest haziness. Fourth quarter and first quarter haziness exhibit similar qualitative and quantitative patterns. The outstanding feature is the haziness over the west coast states and those states surrounding the Great Lakes. Also, haziness has declined in the Great Lakes region and has increased over the southeastern states. The above regional changes in haziness are enlightening because broader regions, such as the Northeast (including Indiana, Ohio, Pennsylvania, New York, Kentucky, West Virginia, and the New England states) and Southeast (states south of the Ohio River and east of the Mississippi River) show coherent but different trends. The differ-
0013-936x19310927-12504.0010 8 1992 American Chemical
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ences in regional and seasonal trends were analyzed. In the Northeast, winter haze shows a 25% decline; in the Southeast there is a 40% increase. The summer haziness in the industrialized Northeast increased until the middle 1970s and showed evidence of a decline since then. However, in the southeastern states summer haziness increased by 80% since the 1950s.
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Local haze trends Generally, the haze over large metropolitan areas is higher than that over the surrounding regions. The difference depends on the size and location of the urhan/industrial area, the season, and the decade of observation (3).For example, theregionalllocal trend of the extinction coefficient was analyzed at four locations in the vicinity of New York
City (Newark, NJ; Providence, RI; and JFK and LaGuardia airports in New York City). In the winter season, La Guardia airport shows- the highest haziness and Providence, RI, shows the lowest. A downward trend was observed for each site. The difference between the sites was highest in the 1950s and 1960s and diminished by the 1980s.A factor of 2 difference in winter haziness Environ. Sci. Technol., VoI. 27,No. 1, 1993 13
among these nearby sites prior to 1970 suggest strong local influences that diminished d e r the 1970s.Evidently, the winter haze became more regional in character (4). The summertime haze for the
I 14 Environ. Sci. Technol.. Vol. 27, No. 1. 1993
above four sites showed an upward trend in the 1950s and 1960s and has decreased since then. Historically, the differences in the extinction coefficient among the sites are less pronounced in the summer
than they are in the winter. Evidently, the summertime haziness has been regional i n character since the 1940s; this might be attributed to more intense atmospheric mixing.
Historical data An historical relationship exist, between SO, emissions and haze. Because sulfates are currently the major contributor to light extinction in the eastern United States, haze trends are compared to SO, emission trends. Because of strong regional and seasonal differences, the comparison should be separated by northeast versus southeast and winter versus summer. The SO, emission trends for the comparison have been compiled using historical yearly emission data (10, 11; Husar, R. B., Washington University, personal communication,1988) and historical monthly emission data (12). Figure 2a depicts the trends of winter (January) haze and SO, emissions for the Northeast. The emissions peaked in the 1940s and in the early 1970%and they declined significantly i n the 1980s. Overall, emissions declined during the 40year period. Winter haze also declined overall, but showed more year-to-year fluctuations. Figure 2b illustrates the corresponding trends for the summer season (July). The summer emissions also peaked in the 1940s and early 1970%but the summer peak in the 1970s was more pronounced than the winter peak. Also, the decline in summer emissions after 1970 was not as significant as the decline in winter emissions. The summer haziness in the Northeast was lowest in the 1950s and early 1960s and increased significantly in the late 1960s. Since about 1970, there has been no significant decline except in 1983. Overall, the emission and haze trends corresponded in certain instances, particularly during t h e 1950s a n d 1960%but they deviated somewhat from each other beginning in the 1970s.
The winter haze and emission trends for the Southeast were also analyzed ( 4 ; Husar, R. B., Washington University, personal communication, 1988). Winter emissions rose moderately until the early 1970s and then declined slightly. Winter haziness also increased moderately up until the early 1970s. The 1977 dip in winter haziness did not correspond to the emission trends, but summer SO, emissions and haziness for the Southeast corresponded remarkably. Summer emissions and haze increased from the late 1940s through the early 1970%and then they leveled off. In Figure 2 the extinction coefficient is
Sulfur emissions
Extinction coeflicient
plotted with an offset of 100 Mm-'. This offset may be viewed as a crude estimate for the background extinction coefficient arising from natural sources. Summary and conclusions The data show that trends in seasonal SO, emissions provide a plausible explanation for the observed seasonal trends of atmospheric haze over t h e eastern United States. However, such qualitative comparsons do not provide conclusive evidence of a cause-and-effect relationship. Also, haze and SO, emission patterns for the Northeast and the Southeast tend to deviate at times. The causes of such deviations may include changes in weather, contributions to haze by nonsulfur spe-
cies, or potential errors in both emissions and visibility data. Finally, a one-to-one relationship cannot be expected because the haziness in one region may be influenced somewhat by emissions in neighboring regions. A more detailed emission-haze trend analysis could be conducted using a regional haze model that incorporates the changes in emissions and meteorological data for individual years. Acknowledgments The information in this document has been funded wholly or in part by the U.S. Environmental Protection Agency under CR 813357 to Washington University. It has been subjected to Agency review and approved for publication. Mention of Environ. Sci. Technol., Vol. 27, No. 1. 1993 15
trade names or commercial products does not constitute endorsement or recommendation for use. We are grateful to Janja D.Husar for assistance in emissions data acquisition and analysis.
Husar. R. E. "Acid Deposition: State of Science and Technology": Report No. 24.1990: National A c i d Precipitat i o n Assessment Program. Washington. DC, 68-76, I51 Koschmieder. H. Reitr. Phys. Freien Atmos. 1925,22.33-53. I61 Trijonis. 1.: Yuan. K. Visibility in the I41
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Northeast: Long-Term Visibility Trends and Vi.~ibility/PollutontRelotionships: Office of Research and Development. U.S. Environmental Pro-
William E. W i l s o n is smior science adviser with EI'A 's Atmospheric Research
1 Rudolf B. H u s a r is o professor of mechanical engineering at Washington University and director of the Center for Air Pollution Impact and Trend Analysis (CAPITA). He attended the University of Zagreb, Croatia, and received a Dipl. Eng. from the Technical University in Berlin. a Ph.D. from the University of Minnesota, and a Postdoctoral Fellowship f r o m the California Institute of Technology. Pasadena. He served on three committees of the National Academy ofsciences His research is devoted to regional air pollution and environmental informatics.
and Exposure Assessment Laboratory in Research Triangle Park, NC. He received a B.A. degree from Hendricks College, a Ph.D. from Purdue University, and he did postdoctoml work at the Technical University of Munich as a Fulbright fellaw. Wilson has had theprimaryresponsibility for EPA's aerosol and visibility research since joining EPA in 1971. His studies o f t h e transport and transformotion of SO, helped establish the regional nature of sulfate aerosols. Wilson is vice-president of the International Aerosol Research Assembly.
References I11
Munn. R. E. Atmos. 1973,1 1 . 156-61. I21 Husar, R. E.: Holloway. J. M.: Patterson. D.E.: Wilson, W. E. Atmos. Environ. 1981.15.1919-28. 13) Trijonis. I. Atmos Environ 1982. 16. 243145.
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tection Agency: Research Triangle Park. NC. 1978: EPA-600/3-78-075. 171 Sloane. C. S. Atmos. Environ. 1982. 26. ~. 2309-21. (81 Sloane. C. S. ~~~
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K. C.: Elridee. K. " H i s t o r i c Emissions o f Suliur and Nitrogen Oxides in the U n i t e d States from 1900 to 1980. Volume I Results." U.S. Environmental Protection Agency: Research T r i a n g l e Park. N C . 1985: EPA- 600/7-85-009a. I111 Husar. R. E. In Acid Deposition: h n g Term Trends: National Academy Press: Washington, DC.1986: pp 48-92, I121 Knudson, D. A. Estimated Monthly Emissions of Sulfur Dioxide and OXides of Nitrogen forthe 48 Contiguous States. 1975-1984. U S Department of Energy. U.S. Government Printing Office: Washington. DC. 1985: A N L / EES-TN-318, Vol 1.
hnsuranium Elements: A Half Century
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eveloped from an international symposium commemorating the 5Gth Anniversary of the discovery of transuranium elements. this volume honors the chemists physicists. materials XlentlStS. and enoineers who were t h P pioneers of transiranium researchinthe 1940s Opening with a comprehensive review by Glenn T. Seaborg of the discovery of transuranium elements and his perspective on the future of the field. the volume offers an outline of the discoveries of transuranium elements and of the chemical io~id3110r.s oi t r m u r n r 'Jresearch. written by the pioneers themselves. The volume also emphasizes contemporary research wlth artlcles on nuclear chemistry and physics: spectroxopy. photophyscs. and photochemlstry: inor. ganic and analytical chemistry: materials physics and chemistry: and solution and enmionmental chemistry of the transuranium elements. Contents 0 HistoricalViewpoints 0 Materials Physics 0 Nuclear Physics and Chemistry 0 Materials Chemistry 0 Chemistry 0 Analytical Chemistry 0 Separations. Thermodynamics ~
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