The Spatial and Source Type Distribution of Emissions of Selected Toxic Volatile Organic Compounds in the United States in 1990 William G. Benjey* Atmospheric Sciences Modeling Division Air Resources Laboratory National Oceanic and Atmospheric Administration Research Triangle Park, North Carolina 27711 ABSTRACT An improved interim toxic emission inventory for the purpose of screening-level regional dispersion and deposition modeling is estimated from a 1990 interim emission inventory of volatile organic compounds (VOCs) for the United States. The VOC emission inventory was derived by updating portions of the 1985 National Acid Precipitation Assessment Program emission inventory. The most current emission factors and speciation profiles available in late 1992 are used to derive emission estimates for specific toxic compounds. Emission factors are used in preference to speciation where possible. The annual anthropogenic emissions, principal contributing source types, and spatial distributions for four selected toxic VOCs, including acrylonitrile, benzene, perchloroethylene, and trichloroethylene, are presented for the United States. The resulting emission estimates are an improvement over an earlier application of this approach, despite necessary heavy reliance on general and default speciation profiles. Emission totals generally exceed national estimates based on partial or top-down inventory approaches by one to two orders of magnitude. The source type and geographical concentrations of toxic VOCs, as well as further emission data needs are discussed. For each toxic compound examined, annual emissions for dominant point, area, and mobile source categories are presented, with the emphasis on demonstrating any distinct geographic patterns. In general, point source toxic emissions are coincident with urban concentrations and chemical industry concentrations. INTRODUCTION The requirements of Title III of the Clean Air Act Amendments of 19901 have created a need for a variety of toxic air emission data, including numerous studies and regulatory activities for specified toxic substances. Title in also requires that the transport and deposition of toxic substances into the "Great Waters" (the Great Lakes, Lake Champlain, Chesapeake Bay, and other specified coastal waters) of the United States be investigated. This requires detailed toxic emission inventories for all sources on at least a national scale. Such an inventory based on traditional facility reporting does not exist. To address the need for regional or national toxic emission inventories, EPA examined existing toxic emission inventory data in the absence of any single inventory with information suitable for regional air quality modeling, and began compilation of an estimated * On assignment to the Atmospheric Research and Assessment Laboratory, U. S. Environmental Protection Agency ------- national interim toxic annual emission inventory.2,3 The initial compilation effort focused on 26 compounds of interest in the Great Lakes area. Because of limited emission factors and activity data for toxic emissions, the emission estimates were based on speciation4 of the base year 1985 total suspended particulate (TSP) and volatile organic compound (VOC) inventories gathered for the National Acid Precipitation Assessment Program (NAPAP).5 The results were generally two or more orders of magnitude larger than existing toxic emission estimates, such as the emissions estimates prepared for the Province of Ontario.6 This was due in part to old data used in NAPAP, in some cases dating to the 1970s; and to uniform application of speciation profiles of different quality to sources with variable characteristics. An effort to improve the interim toxic emission inventory is underway. This paper has three-objectives with respect to the improvement effort. The first objective is to summarize the procedure for expansion and improvement of the interim toxic emission inventory using updated base inventories, the most current chemical and source-type-specific emission factors, and updated speciation profiles. The second objective is to examine the basis of the toxic emission estimates using four examples. Finally, the geographical distribution of the example toxic emissions are presented as examples of the magnitude and spatial variability of toxic emissions. METHODOLOGY The updated interim annual toxic emission inventory uses the 1990 EPA interim national emission inventory7 as the basis for VOC-related toxic emissions. Because the-1990 inventory does not address particulate matter, the updated toxic emission inventory will use the 1985 NAPAP inventory for particulate-related toxic emissions. The 1990 interim inventory will be improved as 1990 emission data from the states are completed under the State Implementation Program for ozone precursor pollutants. There is generally insufficient information at this time to perform temporal allocation of the estimated emissions to seasonal, daily, or hourly values. Sixty compounds, including the 26 previously addressed, were tentatively selected for the updated toxic emission inventory, based on a draft ranking of Agency program needs and compound toxicity. Current information was examined to extract emission factors for each toxic pollutant-emission source category pair. Where there was no emission factor information, the best available speciation profile information was determined for speciation profile-emission source category pairs. Although the information available is improved from 1991, in most instances it was necessary to use a default profile. The default profiles are average representations of all profiles currently available, and although improved, are of low quality when applied to specific sources. Emission estimates attributable to default profiles were tracked to help define uncertainty in the interim toxic emission inventory. The estimated annual emissions of each toxic compound were calculated by following similar, but slightly different procedures for point, area and mobile sources. Point Sources To estimate point source emissions, it was necessary to determine if an emission factor existed for each compound-source type combination. If so, emissions were estimated by multiplying the emission factor with the corresponding activity data for each source. If not, available information was investigated to determine if a source type-speciation profile pair was available for the toxic compound. If so, the speciation factor in the profile for the toxic compound was multiplied against the total VOC or TSP for the source, as appropriate. ------- If there was neither an emission factor nor directly applicable speciation profile, a general default profile was used. Area Sources Because of a lack of appropriate emission factors and area source activity data, area source emissions were estimated by speciation. If a source type-speciation profile pair was available that included the toxic compound, the speciation weight factor was multiplied with the VOC emission for the source. If no directly applicable source type-speciation profile wa available, a speciation weight factor from a general default profile was used. Mobile Sources Mobile source emissions for criteria pollutants are calculated for specific vehicle types, road use, and environmental conditions. This procedure is not available for direct determination of toxic emissions. Consequently, mobile source emissions were estimated by speciation. Speciation profiles specific to vehicle exhaust and portions of evaporative loss were used where available. If the specific profiles were not applicable, more general profile linked to mobile source types were used. In the absence of either kind of emission profile, ; general default speciation profile was used. BASIS OF INFORMATION This paper presents example preliminary emission estimates for each state for the VOC-based toxic compounds acrylonitrile, benzene, perchloroethylene and trichloroethylene (Table 1). These compounds were selected because of their common use. Benzene is a constituent of fuels, while perchloroethylene and trichloroethylene are solvents often used in degreasing. Emission estimates for these examples are based on the VOC emissions in the 1990 EPA interim emission inventory. In each case, the point source emissions were estimated using a combination of emission factors and speciation. The results are of the same order of magnitude as the previous version of the interim toxic emission inventory. Decreases and increases varied from none to a factor of eight, reflecting changes in emissior factors and speciation profiles. The fraction of estimated emissions for point, area, and mobile sources for each compound derived from emission factors, speciation with source- type-specific profiles, and general default profiles is given in Tables 2 and 3. Despite substantial new information, the frequency of use of general default speciatioi profiles ranges between 90 and 100 percent of all sources for most toxic emissions. Benzent is an exception because more emission factors are available. The emission estimates in this paper for acrylonitrile and benzene are more than two orders of magnitude larger than emission estimates by the 1991 Toxic Chemical Release Inventory System (TRIS).8 The trichloroethylene emission estimates are one order of magnitude larger than the TRIS estimate. The differences are attributable to several factors. The TRIS does not include are; or mobile sources in estimating emissions, or many non-manufacturing point sources. Because area sources are extremely important for emissions of three of the four toxic air pollutants addressed in this paper, it is to be expected that the emission estimates will be larger than the TRIS estimates. There is evidence that, even when only point sources from <. reported facility-level inventory are compared to TRIS, TRIS emissions are at least an order of magnitude too low.9 Limited measured emission data makes it difficult to quantify the accuracy of the estimates presented in this paper. The estimates may be somewhat high, ------- despite the use of new emission factors and profiles, because of the continued need to use generalized speciation or default profiles for many source categories. Application of averaged speciation profiles to many small sources tends to increase the total emissions. Small sources can not be ignored in a comprehensive inventory. However, use of averaged or default speciation profiles tends to overestimate emissions because all existing speciation profiles are not complete (which may inflate the relative percentage weight of compounds that are in the profile), and averaged profiles are probably not applicable to some of the sources. Tables 2 and 3 illustrate the heavy reliance on speciation profiles, both in terms of the number of sources addressed and in terms of the amount of emissions. The basis for estimating overall emissions will improve as more air toxic emission factors are developed and used. In the meantime, estimates made using the approach described here provide a first order working estimate of toxic emissions from all sources and the means by which screening-level dispersion and deposition modeling can begin. DISTRIBUTION OF EMISSIONS As expected, the geographical distribution of emissions reflects population, manufacturing, and petrochemical industry concentrations. States with large chemical industries generally have the greatest point source emissions of the selected toxic compounds (Table 4). Benzene emissions are a factor of two to three larger than emissions of the other three chemicals because of the prevalence of benzene in fuels and chemical processes. Emissions from area sources (Table 5) and mobile sources (Table 6) reflect the relative populations and concomitant economic activity levels of the states, consistent with estimates of VOC for area and point sources. Mobile and area sources of vehicle exhaust and evaporative loss, fuel transport and storage, degreasing, and cleaning are the predominant emission sources of acrylonitrile, benzene, and perchloroethylene (Table 7). Trichloroethylene emissions are principally from point sources of cleaning, degreasing and adhesive application. The manufacture of these compounds is also an important emission source. The locations of the dominant source types are consistent with the geographical distribution of the emissions mentioned previously. CONCLUSIONS This paper presents an estimation procedure and resulting national and state estimates of annual anthropogenic emissions of four example toxic compounds from the 60 compounds for which emission estimates are being prepared. Although heavily dependent upon default speciation profiles, these emission estimates represent an improved first order, possibly large estimate for a regional dispersion modeling inventory including most sources. The TRIS estimates are by definition less than the total emissions of any given toxic air emission. The uncertainty in the emission estimates provides an accuracy limitation on regional dispersion modeling efforts, and limits modeling results to relative transport and deposition patterns demonstrating ranges of quantitative results. DISCLAIMER This paper has been reviewed in accordance with the U. S. Environmental Protection Agency's peer and administrative review policies and approved for presentation and publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. ------- REFERENCES 1. United States Code; Clean Air Act Amendments of 1990, Public Law 99-499; Washington, D.C.; 1990. 2. Benjey, W.G.; "Status and Needs for Toxic Emission Inventories for Regional Dispersion and Deposition Modeling," in Proceedings of the EPA/AWMA International Specialty Conference on Emission Inventory Issues in the 1990's\ Air and Waste Management Association: Pittsburgh, PA. 1991; pp. 221-231. 3. Benjey, W.G. and Coventry, D.H.; "Geographical Distribution and Source Type Analysis of . Toxic Metal .Emissions," in Proceedings of the 1992 U.S. EPA/A&WMA International Symposium on Measurement of Toxic and Related Air Pollutants, VIP-25; Air and Waste Management Association: Pittsburgh, PA, 1992; pp. 1029-1034. 4. Radian Corporation; Volatile Organic Compound (VOC)/Particulate Matter (PM) Speciation Data System Documentation and User's Guide, EPA Contract No. 68-02-4286, WA No. 115; U. S. Environmental Protection Agency, Research Triangle Park, 1990; 59 pp. 5. Saeger, M., Langstaff, J., Walters, R., Modica, L., Zimmerman, Pratt, D., Dulleba,_D. and Werner, A.S.; The 1985 NAPAP Emissions Inventory (Version 2): Development of the Annual Data and Modeler's Tapes, EPA-600/7-89-012a; U. S. Environmental Protection Agency: Research Triangle Park, 1989; 692 pp. 6. Johnson, N.D., Scholtz, M.T., Cassaday, V., Davidson, K., and Ord, DMOE Toxic Chemical Emission Inventory for Ontario and Eastern North America, Report No. P.92-T61- 5429/OG, Ontario Ministry of the Environment: Rexdale, Ontario, 1992, 402 pp. 7. Office of Air Quality Planning and Standards; Regional Interim Emission Inventories (1987- 1991): Volume I: Development Methodologies, EPA-454/R-93-021a; U.S. Environmental Protection Agency: Research Triangle Park, 1993; 109 pp. 8. Office of Pollution Prevention and Toxics; 1991 Toxics Release Inventory: Public Data. Release, EPA 745-R-93-003; U.S. Environmental Protection Agency: Washington, D.C., 1993; 363 pp. 9. Marty, M.A., Alexseff, G.V., and Collins, J.F.; "Air Emissions and Associated Cancer Risks of Selected Carcinogens in California," in Proceedings of the International Specialty Conference on the Emission Inventory: Perception and Reality, Air and Waste Management Association: Pittsburgh, PA. (in press). ------- Table 1. Selected annual state total toxic volatile organic compound emissions (tons per year) based on 1990 interim emissions inventory. State Aciylo- nitrile AL 3589 AZ 1539 AR 1381 CA 11349 CO 1317 ~ CT 1168 DE 678 DC 144 FL 5121 GA 3813 ID 1017 IL 6135 IN 3697 LA 1370 KS 1380 KY 2143 LA 4221 ME 537 MD 1692 MA 2374 MI 4493 MN 2335 MS 1863 MO 3114 MT 796 NE 764 NV 485 NH 435 NJ 3551 NM 813 NY 7305 NC 4787 ND 457 OH 5893 OK 1723 OR 1582 PA 5871 RI 418 SC 4103 SD 537 TN 3673 TX 34088 UT 794 VT 246 VA 4726 WA 2726 WV 3873 W1 2838 WY 360 TOTAL 159314 Perchloro- Trichloro- ethylene ethylene 3909 2666 1796 1141 1620 1027 13921 25527 1580 ' 2830 1335 829 813 499 173 106 6165 5466 4055 2817 1227 754 8196 62270 1202 10896 1608 1492 1645 1177 2566 1525 4086 39333 645 397 1980 1231 * 2867 52725 5577 4309 2807 2115 2422 1992 3991 5614 958 588 928 592 537 360 531 11860 3734 2541 978 601 7002 4376 5498 4668 540 336 6214 4231 2441 4771 1901 1179 5956 4450 519 299 2739 3308 648 399 4290 4977 24840 . 14811 932 580 296 211 4247 2887 3213 2008 1976 36872 3956 18329 431 265 165956 354237 Benzene 17949 8242 8003 64284 7547 6473 3694 832 27836 20966 5285 39443 20898 7116 7811 12898 26191 3295 9395 13237 26395 13541 9948 16422 4911 4061 2802 2552 21472 4979 35116 26046 2478 28352 9818 8711 31186 2451 19668 2815 21993 144786 4602 1468 19056 15965 22866 15736 2624 834216 ------- Table 2. Frequency of emission estimation method use. Acrvlonitrile Emission factors Number of times used Percent of total Specified emission profiles Number of times used Percent of total Default profile Number of times used Percent of total Total number of sources Benzene Emission factors Number of times used Percent of total Specified emission profiles Number of times used Percent of total Default profile Number of times used Percent of total Total number of sources Perchloroethvlene Emission factors Number of times used Percent of total Specified emission profiles Number of times used Percent of total Default profile Number of times used Percent of total Total number of sources Trichloroethvlene Emission factors Number of times used Percent of total Specified emission profiles Number of times used Percent of total Default profile Number of times used Percent of total Total number of sources Point sources 7 0.1 4275 9.0 41132 90.9 45414 122 0.3 27242 60.0 18050 39.7 45414 77 0.2 916 2.0 44421 97.8 45414 230 1.0 853 2.0 44331 97.0 45419 Area sources 0 0 618 0.3 207692 99.7 208310 0 0 5660 3.0 202650 97.0 208310 0 0 1886 1.0 206424 99.0 208310 0 0 0 0 208310 100.0 45419 Mobile sources 0 0 0 0 187744 100.0 187744 0 0 187744 100.0 0 0 187744 0 0 0 0 187744 100.0 187744 0 0 0 0 187744 100.0 45419 ------- Table 3. Estimation basis of emission amounts (tons per year). Point sources profiles i profiles Acrvlonitrile Emission factors Amount due to emission factors Percent of total Specified emission "Amount due to Percent of total Default profile Amount due to Percent of total Total amount Benzene Emission factors Amount due to Percent of total Specified emission Amount due to Percent of total Default profile Amount due to Percent of total Total amount Perchloroethvlene Emission factors Amount due to Percent of total Specified emission Amount due to Percent of total Default profile Amount due to Percent of total Total amount Trichloroethvlene Emission factors Amount due to Percent of total Specified emission Amount due to Percent of total Default profile Amount due to Percent of total Total amount 53 0.1 "27603 - 58.0 default profile 19583 41.9 47240 . emission factors 2313 1.0 profiles profiles 150488 70.0 default profile 61602 29.0 214403 emission factors 3776 9.0 profiles profiles 9830 23.0 default profile 29207 97.8 42813 emission factors 246023 91.0 profiles profiles 7287 3.0 default profile 17857 6.0 271167 Area sources 0 0 1.131 4.0 '0160 96.0 72897 0 0 84198 24.0 264303 76.0 348501 0 0 1940 3.0 73921 99.0 75861 0 0 0 0 53749 100.0 53749 Mobile sources 0 0 0 0 39315 100.0 39315 0 0 272965 100.0 0 0 272965 0 0 0 0 47450 100.0 47450 0 0 0 0 29148 100.0 29148 ------- Table 4. Annual estimated point source emissions of selected toxic volatile organic compounds (tons per year) based on the 1990 interim emissions inventory. State Acrylo- nitrile AL 1285 AZ 13 AR 238 CA . ..720 CO 35 CT 85 DE 78 DC 4 FL 130 GA 292 ID 4 IL 2081 IN 940 IA 99 KS 177 KY 599 LA 999 ME 32 MD 175 MA 347 MI 606 MN 335 MS 342 MO 867 MT 35 NE 27 NV 4 NH 28 NJ 672 NM 47 NY 2355 NC 1299 ND 11 OH 1511 OK 144 OR 257 PA 1236 RI 69 SC 177 SD 45 TN 1273 TX 23060 UT 63 VT 6 VA 2095 WA 314 WV 1220 WI 711 WY 98 TOTAL 47240 Perchloro- Trichloro- ethylene ethylene 1489 962 16 10 269 182 1673 17687 42 1607 57 27 93 57 5 3 156 1770 347 213 5 3 3429 59286 2515 8860 79 551 211 289 732 384 998 36971 39 24. 167 109 438 51225 1050 1432 405 637 631 873 1300 3952 42 26 42 47 4 3 41 11558 644 416 57 35 1105 714 1367 2089 11 7 1250 995 632 3609 312 198 882 1033 101 42 214 398 55 34 1428 3203 14690 6672 65 40 7 33 1092 940 339 228 748 34906 1421 16756 118 72 42812 271167 Benzene 6077 274 2247 .. 3168 167 399 461 21 1189 2069 97 15092 5231 336 1029 4071 7985 317 670 1478 3330 1943 1737 3977 735 110 14 157 5718 361 6497 8029 63 2982 560 1394 4815 465 949 227 9110 87164 245 37 4614 1836 10496 3430 1030 214403 ------- Table 5. Annual estimated area source emissions of selected volatile organic compounds (tons per year) based on the 1990 interim emission inventory. State Acrylo- Benzene Perchloro- Trichloro- nitrile ethylene ethylene AL 1394 6398 1322 1030 AZ 858 4017 974 636 AR 732 3193 856 541 CA 6402 32305 7146 4706 CO 793 3745 948 587 CT 694 3235 809 514 DE 489 2420 586 360 DC 82 396 98 60 FL 2731 12807 3282 2021 GA 2189 10171 2100 1616 ID 828 3862 999 614 IL 2532 13009 2930 1855 IN 1761 8310 1951 1298 IA 841 3723 1010 622 KS 785 3783 930 578 KY 942 4604 1107 694 LA 2424 13238 2125 1770 ME 289 1300 346 213 ME 837 3925 992 618" MA 1271 6062 1516 939 MI 2279 10736 2586 1685 MN 1277 6012 1529 942 MS 1031 5278 1200 756 MO 1323 5857 1576 977 MT 604 2974 726 446 NE 485 2116 581 358 NV 280 1296 291 208 NH 234 1082 282 174 NJ 1943 9144 1960 1431 NM 403 1911 483 297 NY 3040 14179 3591 2246 NC 2261 10177 2650 1669 ND 318 1453 374 234 OH 2715 13343 2952 2000 OK 966 5109 1069 707 OR 866 4042 1035 640 PA 3024 14633 3130 2223 RI 224 1045 267 165 SC 3264 14744 1725 2419 SD 352 1552 424 261 TN 1487 7051 1760 1097 TX 7846 37744 6310 5780 UT 428 2135 501 315 VT 135 612 162 100 VA 1682 7779 2010 1243 WA 1578 8059 1867 1161 WV 2386 10529 906 1768 WI 1302 5993 1540 962 WY 153 758 182 112 TOTAL 72760 347847 75696 53648 ------- Table 6. Annual estimated mobile source emissions of selected volatile organic compounds (tons per year) based on 1990 interim emissions inventory. State Acrylo- Benzene Perchloro- Trichloro- litrile ethylene ethylene AL 910 5474 1098 ' 674 AZ 668 3951 806 495 AR 411 2563 495 304 CA mi 28811 5102 3134 CO 489 3635 590 363 CT 389 2839 469 288 DE 111 813 134 82 DC 58 415 70 43 FL 2260 13840 2727 1675 GA 1332 8726 1608 988 ID 185 1326 223 137 IL 1522 11342 1837 1129 IN . 996 7357 1202 738 IA 430 3057 519 319 KS 418 2999 504 310 KY 602 4223 727 447 LA 798 4968 963 592 ME 216 1678 260 160 MD 680 4800 821 504 . MA 756 5697 913 561 MI 1608 12329 1941 1192 MN 723 5586 873 536 MS 490 2933 591 363 MO 924 6588 1115 685 MT 157 1202 190 117 NE 252 1835 305 187 NV 201 1492 242 149 NH 173 1313 208 128 NJ 936 6610 1130 694 NM 363 2707 438 269 NY 1910 14440 2306 1416 NC 1227 7840 1481 910 ND 128 962 155 95 OH 1667 12027 2012 1236 OK 613 4149 740 455 OR 459 3275 554 341 PA 1611 11738 1944 1194 RI 125 941 151 92 sc 662 3975 800 491 SD 140 1036 169 104 TN 913 5832 1102 677 TX 3182 19878 3840 2359 UT 303 2222 366 225 VT 105 819 127 78 VA 949 6663 1145 704 WA 834 6070 1007 619 WV 267 1841 322 198 WI 825 6313 995 611 WY 109 836 131 81 TOTAL 39314 271966 47448 29149 ------- Table 7. Source category codes* associated with the greater portion of emissions from selected toxic volatile organic compounds. Percent of Estimated Annual Total Emissions in the United States ACRVT.ONTTRTT.F. BENZENE PERCHLOROETHYLENE TRICHLOROETHYLEN SCC j/k. SCC % SCC % SCC & 30 11 30 14 30 13 40100306 23 109 7 28 6 95 8 40200701 21 95 7 95 6 28 6 30101801 17 30125405 6 109 6 39 5 40100205 8 28 5 34 5 40100203 5 30 4 39 4 39 4 34 4 109 2 34 4 30199999 4 54 3 95 2 30190099 3 104 3 93 3 28 2 30101899 3 32 3 78 3 39 1 54 3 54 2 103 2 34 1 Subtotal 53 53 52 81 Others 47 47 48 19 Total 100 100 100 100 Percent of total emissions by general source group Point 30 26 26 77 Area 46 42 46 15 Mobile 24 32 28 8 * Source Category Code (SCC Code) key. Two codes are point sources. 28 - Lgt. duty gas vehicles, rural roads 32 - Lgt. duty gas. trucks, rural roads 39 - Off-highway gasoline vehicles 78 - Degreasing 95 - Misc. nonindustrial solvent use 104 - Fugitive emiss., petrol.refmeries 30100801 - Chloro-alkali production 30101899 - Misc. general plastics production 30190099 - Waste gas flares 40100203 - Perchloroethylene degreasing 40100306 - Trichloroethylene cleaning three-digit codes are area or mobile sources, seven-digit 30 - Lgt. duty gas vehicles, urban roads 34 - Lgt. duty gas trucks, urban roads 54 - Gasoline marketing 93 - Misc. industrial manufacturing 103 - Bulk terminals and plants 109 - Hazard, waste treatment and storage 30101801 - Polyvinyl chloride production 30125405 - Aciylonitrile production 30199999 - Misc. chemical manufacturing 40100205 - Trichloroethylene degreasing 40200701 - General adhesive application ------- KEY WORDS emission inventory emission factors acrylonitrile benzene perchloroethylene trichloroethylene ------- |