Summary and analysis of available PM2.5 measurements in illinois

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Atmospheric Environment Vol. 32, No. 6, pp. 1129—1133, 1998 ( 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain S1352–2310(97)00454–8 1352—2310/98 $19.00#0.00

SHORT COMMUNICATION SUMMARY AND ANALYSIS OF AVAILABLE PM 2.5 MEASUREMENTS IN ILLINOIS CLYDE W. SWEET* and DONALD F. GATZ Illinois State Water Survey, 2204 Griffith Drive, Champaign, IL 61820, U.S.A. (First received 11 July 1997 and in final form 23 September 1997. Published March 1998) Abstract—To provide information necessary for implementation of newly-revised U.S. standards for airborne particulate matter, we have analyzed available data on PM in Illinois. A major component of 2.5the oxidation of SO downwind of PM at locations in Illinois is secondary (NH ) SO that forms from 2.5 4 2of PM 4 2 but is likely the emission sources. Another major component in Illinois is generally unmeasured, 2.5 to be mostly organic and elemental carbon. The secondary oxidation of SO and gas-phase organic compounds is greatest during summer, and the highest concentrations of PM 2also occur then. Analyses of available ambient PM in Illinois indicates that the annual standard of2.515 kg m~3 would likely be exceeded in the Chicago 2.5 and East St. Louis metropolitan areas. Given the preponderance of secondary material in the PM , such exceedances would probably be widespread. The data indicate that the 24 h 2.5 standard of 65 kg m~3 would not likely be exceeded at these locations. At rural and suburban locations statewide neither standard is likely to be exceeded, but current annual means in these locations are within about 10% of the proposed standard. Future reductions in SO emissions may lower PM concentrations 2 and precursors. ( 1998 2.5Elsevier Science in Illinois, barring offsetting increases in other PM components 2.5 Ltd. All rights reserved. Key word index: Fine particles, particulate matter, standards, compliance.

INTRODUCTION

The U.S. Environmental Protection Agency (EPA) has recently revised the primary and secondary national ambient air quality standards (NAAQS) for particulate matter (PM). Two new PM (particles )2.5 km in aerodynamic dia2.5 meter, 50% cutoff ) standards have been added: (1) One at 15 kg m~3, based on the 3 yr average of annual arithmetic mean concentrations, and (2) One at 65 kg m~3, based on the 3 yr average of the 98th percentile of 24 h PM concentra2.5 tions at each population-oriented monitor in an area. In addition, the current PM standard has been revised to be 10 based on the 99th percentile of the 24 h concentrations at each monitor within an area. The revised standards are based on recent health effects studies, which suggest that significant effects, such as premature mortality, hospital admissions, and respiratory illness, occur at PM concentrations below the current standards (U.S. EPA, 1996). Now that revised PM standards have indeed been put in place by the U.S. EPA, the states will be required to monitor to determine compliance, and to devise implementation plans for meeting the standards. To aid Illinois officials in planning for implementing the revised standards, we have compiled, summarized and analyzed available data on PM in Illinois. The available data are typically based 2.5 on the fine particle fraction of samples collected with a dichotomous virtual impactor with a fine particle cutoff at

* Author to whom correspondence should be addressed.

2.5 km. Although it is uncertain whether this sampler will be designated as a reference or equivalent method for PM 2.5 measurement under the revised regulations, the data we have now should be adequate to give a preliminary indication of the annual mean and 24 h mean concentrations that may be expected in the locations where these samples were collected. Further, the data on chemical composition of the PM that are available at some of the sampling locations can be used to give preliminary indications of the kinds of sources that contribute to the observed fine particle concentrations.

RESULTS

Measured concentrations Since there has been no routine measurement program for PM in Illinois, available PM data come from relatively 2.5 2.5 short-term research studies carried out at selected locations by various organizations during several different time periods. Table 1 provides summary data for several of these studies conducted during the past 10 yr. In most cases, particles were collected with dichotomous samplers. Dichotomous samplers use a virtual impactor to separate PM . With this device, the 50% cutpoint diameter for fine 2.5 particles is 2.5 km. Essentially, 100% of particles larger than 3 km in diameter are excluded, and 80—90% of particles between 1 and 2 km are collected (Loo and Cork, 1988). These data strongly suggest that unless conditions have changed very recently, a 3-yr annual average PM limit of 2.5 15 kg m~3 will be exceeded in the heavily urbanized areas in Illinois (Chicago and the St. Louis Metro-East area in

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Short Communication Table 1. Summary of available measurements of PM concentrations in Illinois! 2.5

Location

Type"

Champaign Champaign St. Charles Zion Alsip Blue Island Chicago (IIT)

R R R R S S U

Chicago (IIT) Chicago (SE) E. St. Louis Granite City

U U U U

Sampling period

No. of samples

Annual mean, $std error (kg m~3)

Maximum 24 h mean (kg m~3)

Reference

1985—87 1994—95 1987—88 1994—95 1995—96 1995—96 1991 (Summer only) 1994—95 1985—87 1985—87 1986—87

43 21 55 21 61 60 12

16$0.9 13$1.1 15$1.2 10$0.6 14$0.8 14$0.9 25$2.6

31 23 48 18 32 28 47

Sweet et al.,1993 Sweet and Gatz, 1997 Gatz, 1989 Sweet and Gatz, 1997 Sprague, 1996a Sprague, 1996a Holsen and Noll, 1992

19 44 42 31

18$1.8 24$1.8 23$1.8 22$2.5

47 49 60 81

Sweet Sweet Sweet Sweet

and Gatz, 1997 et al., 1993 et al., 1993 et al., 1993

! The data are based on 24 h samples except for Sweet and Gatz (1997) (monthly composites of four 24 h samples) and Holsen and Noll (1992) (5 d samples). Except for the data from Holsen and Noll (1992), samples were collected in all seasons of the year. All samples were collected on Teflon filters using virtual dichotomous samplers (Andersen Samplers, Atlanta, GA, or equivalent), except for those collected by Holsen and Noll (1992), using inert substrates in cascade and rotary impactors. " R"rural; S"suburban; U"urban.

Illinois). Recent measurements at the Illinois Institute of Technology (IIT) site south of downtown Chicago by our lab (Sweet and Harlin, 1997) and the IIT lab (Holsen and Noll, 1992) have both detected relatively high concentrations of PM . This site is not near any major industrial facilities 2.5 and should have air quality that is typical of a large part of the Chicago urban area. We also found high annual mean concentrations of PM at industry-influenced sites in East 2.5 St. Louis and Granite City 10 yr ago (Sweet et al., 1993). Available measurements of PM at suburban and rural 2.5 sites in Illinois (Table 1) indicate the annual mean concentrations of PM are very close to 15 kg m~3 in the northern 2.5 half of the state. No measurements were available from suburban or rural locations in southern Illinois; however, measurements in the Missouri suburbs of St. Louis (Sprague, 1996a) suggest that current PM levels are slightly higher 2.5 than at similar suburban locations near Chicago (Sprague, 1996b). Maximum PM values for 24 h samples were below the 2.5 new 65 kg m~3 standard (3-year, 98th percentile) at all of the suburban and rural monitoring sites in Illinois. Only the Granite City site recorded a 24 h concentration '65 kg m~3. This seemingly anomalous value was more than twice the next highest value at that site, so it should not be used to predict future conditions. Presumably new limits on SO emissions in the Midwest 2 will reduce concentrations of fine particulate sulfate over the next few years. At this point it is impossible to say whether such reductions will be enough to meet the 15 kg m~3 standard in urban and suburban areas of Illinois. Any reduction in particulate sulfate could also be offset by an increase in particulate organic materials and their precursors. Statistical distributions The distributions of ambient PM concentrations were 2.5 compared to lognormal and gamma distributions. These two distributions have often been found to best describe air pollutant concentrations in earlier studies. The gamma distribution provided a better fit to the observed data, although neither distribution could be rejected at the 5% level at most sampling sites. The modeled predictions from the statistical distributions suggest that the annual mean fine particle standard will be exceeded, but that the 24 h standard will not be exceeded, at most of the urban sites. Exceedances of the new

standards at the rural and suburban sites in northern Illinois do not appear likely, based on the modeled fits to the available data. Seasonal variations Concentrations of ambient PM tend to be lower in 2.5 winter and higher in summer at most Illinois sampling sites. Figures 1 and 2 illustrate this behavior in monthly values at a rural (Champaign) and an urban (Chicago) site. Direct emissions of fine particles from vehicles and many industrial processes are relatively constant throughout the year. On the other hand, the formation of secondary particulate sulfate and organic compounds in the atmosphere is strongly seasonal. Secondary pollutants form in the atmosphere from reactions of gas-phase pollutants with oxidants. Oxidants are formed by photochemical reactions in the atmosphere and their concentrations are highest in the summer due to high sunlight intensities and elevated temperatures (National Research Council, 1991). Precursor emissions also increase in the summer. Electrical power demand for air conditioning and associated coal combustion lead to slightly higher emissions of sulfur dioxide (SO ). Higher temperatures during 2 the summer also give rise to more evaporative emissions of volatile organics from vehicles and industrial sources. Biogenic emissions of organic compounds from plants are highest during the summer (Lamb et al., 1987). Gas-toparticle reaction rates also increase with temperature. Finally, meteorological conditions that affect atmospheric mixing (wind speed and vertical temperature structure) can also influence the concentration of fine particles in the atmosphere. Chemical composition When sufficient ammonia (NH ) is present, ammonium 3 sulfate, (NH ) SO , is generally the dominant chemical form 42 4 of sulfate in airborne fine particles (Finlayson-Pitts and Pitts, 1986) This chemical is a secondary pollutant derived from SO and NH . The sulfur concentration in airborne fine 2 3 sulfate particles collected in Illinois is consistent with (NH ) SO (Alpert and Hopke, 1981). Other chemical forms 42 4 of sulfate such as sulfuric acid, H SO , and ammonium 2 4 bisulfate, NH HSO , can occur in fine particles; however 4 4 conditions in Illinois generally favor the formation of (NH ) SO . If it is assumed that the sulfate is in the form of 42 4

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Fig. 1. Seasonal variation in the chemical composition of PM in rural Champaign, Illinois. 2.5

Fig. 2. Seasonal variation in the chemical composition of PM at Chicago, Illinois. 2.5

(NH ) SO , Table 2 shows that this compound makes up 42 4 between 35% and 48% of the fine mass at Illinois sampling sites where chemical composition has been measured. The concentration of (NH ) SO is highest in summer (Figs 42 4 1 and 2). Although Illinois SO emissions are only slightly 2 higher in summer than in other seasons, oxidation of SO to 2 sulfate is more rapid and complete in the summer when oxidant concentrations are highest (Venkatram et al., 1990). Inorganic matter derived from crustal dust and metals makes up between 6% and 12% of the fine particle mass in

Illinois (Table 1). In addition, road salt contributes up to 3% of the fine mass averaged over a calendar year at urban locations. After accounting for these inorganic constituents, 43—56% of the fine particle mass remains unexplained in Illinois air samples (Table 2). Nitrates and water are expected to account for roughly 10% of the total airborne fine particle mass (Wolff, 1984), or perhaps 20% of this remainder. The rest is likely to be carbonaceous material, including elemental carbon (soot) and particulate organic chemicals

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Short Communication Table 2. Chemical Composition (percent of total mass$std.dev.) of PM in Illinois 2.5 Location

Ammonium sulfate

Crustal material

Trace metals

Road salt

Other

48$17 35$13 36$12 37$15 45$15 43$10

5$7 5$3 6$3 8$8 8$6 5$2

1$1 3$1 5$4 4$3 3$2 2$1

(1 1$2 3$3 2$3 (1 (1

45$15 56$10 51$13 49$18 43$16 51$10

Champaign Chicago (IIT) Chicago (SE) E. St. Louis Granite City Zion

(Shah et al., 1986; Malm et al., 1994). Although there have been few measurements of carbon and organic chemicals in PM , these materials probably comprise the second most 2.5 important component of PM , making up about one-third 2.5 of the airborne fine particle mass. Elemental carbon is emitted directly from combustion sources such as diesel engines. Particulate organic chemicals can be emitted directly from sources or formed as secondary particles by the oxidation of gas-phase organic chemicals in the atmosphere. Receptor modeling results for PM2.5 Several receptor modeling studies of PM have pre2.5 viously been conducted in Illinois. Sweet et al. (1993) identified regional background, steel, and combustion-related activities as important sources of trace elements in fine particles in southeast Chicago. They did not measure carbon in the samples or apportion the total PM mass. Glover 2.5 et al. (1991) found that regional sulfate, steel sources, secondary smelters, and urban fugitive dust contributed to the PM mass in Granite City. They could account for only 2.5 about half of the PM mass from these sources and cited 2.5 the need for carbon data to adequately characterize PM in 2.5 Granite City. Both of these studies were based on samples collected between 1985 and 1987. Scheff et al. (1994) found that 30% of the PM collected at the University of Illinois 10 in Chicago was organic and elemental carbon. Assuming that most of this carbon was in the PM fraction and that 2.5 PM was about 60% of PM , then carbon made up about 2.5 10 50% of PM at this site. The carbon was attributed to 2.5 mobile sources, diesel engines, and wood smoke. An extensive air monitoring project in the St. Louis area, the Regional Air Pollution Study (RAPS), included CMB analysis of fine particles (Dzubay, 1980). Samples of PM 2.5 collected between 1975 and 1977 consisted of 50—60% (NH ) SO . Crustal material and motor vehicle emissions 42 4 were also important contributors to PM . Approximately 2.5 25% of the PM could not be attributed to sources. This is 2.5 presumably carbon-based material because it was not detectable by X-ray fluorescence. Using the same database, Altshuller (1987) concluded that most of the (NH ) SO 42 4 measured in PM in the St. Louis area came from oxida2.5 tion of SO in the atmosphere. Because this process is rela2 tively slow, the material found in PM collected in St. 2.5 Louis was judged to have originated outside the metro area and to have been transported by air movements to the sampling sites. Highest levels of (NH ) SO and PM 42 4 2.5 were measured when air movement was from Illinois (E and S).

CONCLUSIONS

The largest identified component of PM at locations in 2.5 Illinois is secondary (NH ) SO that forms from the relative42 4 ly slow oxidation of SO downwind of the emission sources. 2 Another major component of PM in Illinois is of un2.5

measured composition but is likely to be mostly organic and elemental carbon. Particulate organic materials can be emitted directly by combustion sources, and they are also formed from the gas phase by secondary reactions in the atmosphere. The secondary oxidation of SO and VOCs maxi2 mizes in the summer, and peak concentrations of PM can 2.5 be expected then. Analyses of available ambient PM in Illinois indicates 2.5 that the annual standard of 15 kg m~3 would likely be exceeded in the Chicago and East St. Louis metropolitan areas. Given the preponderance of secondary material in the PM , such exceedances would probably be widespread. 2.5 The data indicate that the 24 h standard of 65 kg m~3 would not likely be exceeded at these locations. At rural and suburban locations statewide neither standard is likely to be exceeded, but current annual means in these locations are within about 10% of the proposed standard. Future reductions in SO emissions may lower PM concentrations in 2 2.5 Illinois, barring offsetting increases in other PM compo2.5 nents and precursors. Acknowledgment and Disclaimer—Although funding for this work was provided by the Illinois Environmental Protection Agency (Grant CS 1320), this paper does not necessarily reflect the views of the Agency and no official endorsement should be inferred.

REFERENCES

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Short Communication Lamb, B., Guenther, A. and Westberg, H. (1987) A national inventory of biogenic hydrocarbon emissions. Atmospheric Environment 21(8), 1695—1705. Loo, B. W. and Cork, C. P. (1988) Development of high efficiency virtual impactors. Aerosol Science and ¹echnology 9, 167—176. Malm, W. C., Sisler, J. F., Huffman, D., Eldred, R. A. and Cahill, T. A. (1994) Spatial and seasonal trends in particle concentration and optical extinction in the United States. Journal of Geophysical Research 99, 1346—1370. National Research Council (1991) Rethinking the Ozone Problem in ºrban and Regional Air Pollution. National Academy Press, Washington, D.C. p. 500. Scheff, P. A., Wadden, R. A., and Lin, J. (1994) Source allocation of hazardous air pollutants in Chicago. Paper 94-TP26B.04, Proceedings of the 87th Annual Meeting of the Air and ¼aste Management Association, Air and ¼aste Management Association, Pittsburgh, Pennsylvania. Shah, J. J., Johnson, R. L., Heyerdahl, E. K. and Huntzicker, J. J. (1986) Carbonaceous aerosol at urban and rural sites in the United States. Journal of Air Pollution Control Association 36, 254—257. Sprague, J. (1996a) Illinois EPA, St. Louis County Air Pollution Control unpublished data. Personal communication. Sprague, J. (1996b) Illinois EPA, Robbins project preliminary data. Personal communication.

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Sweet, C. W. and Gatz, D. F. (1997) Scoping study for PM-2.5 in Illinois. Contract report prepared for the Illinois EPA, Bureau of Air, Air Quality Planning Section. Illinois State Water Survey, Champaign. Sweet, C. W., Vermette, S. J. and Landsberger, S. (1993) Sources of toxic trace elements in urban air in Illinois. Environmental Science and ¹echnology 27(12), 2502—2510. Sweet, C. W. and Harlin, K. S. (1997) Toxic organics and trace metals in air and precipitation at sites near Lake Michigan. Paper presented at the 90th Annual Meeting of the Air and ¼aste Management Association, 8—13 June, Toronto, Ontario. U.S. EPA (1996) Fact Sheet——EPA’s proposal on the particulate matter standard. U.S. EPA Office of Air and Radiation, Office of Air Quality Planning and Standards. 29 November 1996. Venkatram, A., McNaughton, D. and Karamchandanai, P. K. (1990) Factors influencing source—receptor relationships. In Relationships Between Atmospheric Emissions and Deposition/Air Quality, National Acid Precipitation Assessment Program, State of Science and Technology Report 8, U.S. Government Printing Office, Washington, D.C. Wolff, G. T. (1984) On the nature of nitrate in coarse continental aerosols. Atmospheric Environment 18(5), 977—981.