- Email: [email protected]
Estimate of mercury emission from gasoline and diesel fuel consumption, San Francisco Bay area, California
ARTICLE IN PRESS
Atmospheric Environment 39 (2005) 101–105 www.elsevier.com/locate/atmosenv
Estimate of mercury emission from gasoline and diesel fuel consumption, San Francisco Bay area, California Christopher H. Conawaya,, Robert P. Masonb, Douglas J. Stedinga, A. Russell Flegalb a
Department of Environmental Toxicology, University of California at Santa Cruz, 1156 High Street, Santa Cruz, California, CA 95064, USA b Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, University System of Maryland, P.O. Box 38, Solomons, MD, 20688-0038, USA Received 3 May 2004; accepted 7 September 2004
Abstract Gasoline samples (n ¼ 20) collected from San Francisco Bay area refineries and service stations had mercury concentrations ranging from 0.08 to 1.4 ng g1; diesel samples (n ¼ 19) had concentrations of 0.05–0.34 ng g1. These relatively low levels show little evidence for mercury enrichment or contamination into these fuels from the refining process. Combustion of these fuels in the San Francisco Bay area contributes 0.7–13 kg Hg yr1 to the environment, with an average of 5 kg Hg yr1. Assuming the fate of this emission is to the atmosphere, the total flux from the combustion of these fuels represents less than 3% of the total atmospheric emissions in the San Francisco Bay area. r 2004 Elsevier Ltd. All rights reserved. Keywords: Mercury; Gasoline; Diesel; San Francisco Bay
1. Introduction As a result of widespread and persistent mercury contamination in the San Francisco estuary, there is an interest in developing a detailed understanding of the relevant sources of mercury to that system. There has been a focus on the atmospheric exchange of mercury in the estuary (Conaway et al., 2003; SFEI, 2001) because mercury deposited from the atmosphere is thought to be relatively labile and bioavailable (Benoit et al., 2003). That focus has been partially substantiated by the results of a recent study (Steding and Flegal, 2002) that
Corresponding author.
E-mail address: [email protected] (C.H. Conaway).
indicated the atmospheric deposition of mercury in the surrounding San Francisco Bay area was two-fold greater than in the adjacent coastal area, perhaps due to local differences in atmospheric emissions of industrial mercury. Typically, atmospheric emissions of industrial mercury include the waste products from the combustion of fossil fuels and the incineration of medical wastes, both of which are well-known sources of mercury to the environment. For example, coal combustion alone is reported to account for roughly 20% of total industrial emissions of mercury to the atmosphere in the United States (Porcella et al., 1996). More recently, petroleum production and refined petroleum product (e.g., gasoline and diesel fuel) consumption have come under scrutiny as potential sources of mercury to the environment
1352-2310/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2004.09.025
ARTICLE IN PRESS 102
C.H. Conaway et al. / Atmospheric Environment 39 (2005) 101–105
(Kelly et al., 2003; Liang et al., 1996; Wilhelm, 2001; Wilhelm and Bloom, 2000). Both petroleum production and the consumption of petroleum products are potentially important sources of mercury in the San Francisco Bay area (Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma counties). It is a major refining center in North America, with five major refineries that have the combined capacity to process roughly 95 million liters of crude oil per day, and in 1998 produced about 20 million liters of gasoline and 4.5 million liters of diesel/distillate fuels (Quinn, 2001). This metropolitan area also has a relatively large number of vehicles, with over 4.5 million automobiles, vans, and heavy-duty commercial trucks (Purvis, 1997) that consume about 13 billion liters of gasoline and 2 billion liters of diesel fuel per year (Caltrans, 2002). Because of this sizeable quantity of production and refined product use, even trace quantities of mercury in these petroleum products could result in a relatively large emission to the environment. Mercury and crude oil deposits are known to coexist (Fein and Williams-Jones, 1997; Peabody and Einaudi, 1992), and some economically important petroleum deposits in California, such as the Cymric, have shown relatively high concentrations of mercury, up to 20 mg g1 (Filby and Shah, 1975; Shah et al., 1970). Such values may not be typical of mercury concentrations in crude oil feedstocks used by California refineries (Magaw et al., 1999), which have reported concentrations less than 10 ng g1, excluding data from Cymric samples. Nevertheless, both the volume of petroleum refining and fuel consumption, and the potential for elevated mercury concentration in these matrices, suggest that mercury emission from gasoline and diesel fuel consumption should be evaluated. Data on mercury concentration in gasoline and diesel fuels are limited, and given on a national rather than regional basis (Liang et al., 1996). This limitation is notable in California, where the bulk of its crude oil production is refined and where virtually all gasoline consumed in the San Francisco Bay area is refined locally (Quinn, 2001). Therefore, we conducted a survey of mercury concentrations in gasoline and diesel fuels collected from refineries, terminals, and service stations in the local region surrounding San Francisco Bay in order to more accurately estimate the potential for contamination of refined products from highmercury crudes or from enrichment of mercury in the refining process. The results of this study provide additional data to an existing, but limited, data set. This study is a first attempt at providing a local mercury emission calculation based on local gasoline consumption figures and local gasoline concentrations in a major urban area.
2. Methods A suite of gasoline (n ¼ 20) and diesel (n ¼ 19) samples was collected from refineries, distribution stations, and service stations in the San Francisco Bay area. Samples were collected in acid-cleaned PFA Teflons bottles and stored in the dark at 20 1C until analysis. Fuel tanks sampled at refineries were sampled using either a running or all-level sampling technique. Both techniques obtain liquid from the liquid surface to a point about 1 m from the bottom of the tank, sampling a column of liquid that as close as possible represents a total vertical picture of the tank. Mercury was extracted from these samples by BrCl oxidation, and analyzed by SnCl2 reduction, Au-amalgamation, cold vapor atomic fluorescence spectroscopy using established methodologies (Babi et al., 2003; Bloom, 2000; Liang et al., 1996). Matrix spike recoveries in both diesel and gasoline averaged 10176%; the procedural blank for the analyses was 0.01270.002 ng (n ¼ 8); and the recovery was 9577%, based on concurrent analyses of mercury in certified reference material FGS-OIL1 (Mercury Speciation in Petroleum, Frontier Geosciences, HgT=1839 ng g1). Although the reference material is not entirely suitable because of the higher concentration (relative to sample concentrations) and differing matrix (crude oil versus gasoline), it was the closest available material at the time of this study.
3. Results and discussion Gasoline samples from the San Francisco Bay had mercury concentrations ranging from 0.08 to 1.4 ng g1 (Table 1). As shown in Table 2, these data are consistent with other recent measurements of mercury concentrations in gasoline from the US (0.22–1.43 ng g1), but somewhat lower than those from Monaco, Slovenia, and Algeria (0.72–3.20 ng g1), as reported by Liang et al. (1996). Diesel samples in our study had concentrations of 0.05–0.34 ng g1, which are lower than reported by Liang et al. (1996) in a sample from the US (0.4 ng g1) and elsewhere (2.97 ng g1), but higher than that reported by Kelly et al. (2003) for a certified reference material (NIST 2724b, HgT=0.034 ng g1). In addition, the motor fuel concentrations measured in our study are similar to average reported concentrations of mercury (0.04–1.32 ng g1) in other refined petroleum products, including kerosene, light distillates, utility fuel oil, heating oil, and asphalt (Bloom, 2000; Liang et al., 1996). The concentrations observed in gasoline and diesel in this study does not suggest that mercury is enriched from crude oil into these fuels during refining. Concentrations of mercury reported in crude oil have a wide range of reported values (Magaw et al., 1999; Shah et
ARTICLE IN PRESS C.H. Conaway et al. / Atmospheric Environment 39 (2005) 101–105 Table 1 Mercury concentration (ng g1) in gasoline and diesel in samples collected from refineries, service stations, and terminals in San Francisco Bay area County location Diesel Refinery 1 Refinery 2 Refinery 2 Refinery 4 Refinery 5 Refinery 5 Service station 1 Service station 2 Service station 3 Service Station 4 Service station 6 Service station 7 Service station 9 Service station 11 Service station 13 Terminal 2 Terminal 3 Terminal 4 Terminal 5 Gasoline Refinery 1 Refinery 1 Refinery 2 Refinery 2 Refinery 2 Refinery 2 Refinery 3 Refinery 3 Refinery 3 Refinery 4 Refinery 4 Refinery 5 Refinery 5 Service station Service station Service station Service station Service station Service station Terminal 1
3 5 7 8 10 12
Sonoma Sonoma Contra Costa Contra Costa Santa Clara Contra Costa Contra Costa Marin San Mateo
Contra Costa Santa Clara Contra Costa Marin Solano Alameda
[Hg] (ng g1)
0.05 0.20 0.08 0.05 0.10 0.12 0.11 0.12 0.34 0.15 0.11 0.16 0.16 0.15 0.17 0.18 0.11 0.16 0.17 0.26 0.31 0.10 0.08 0.16 0.49 0.54 0.13 0.22 0.69 0.38 1.08 1.39 0.25 0.31 0.24 0.89 0.31 0.82 1.34
Multiple samples taken from the same refinery are from different batches and tanks. For service stations, the county where the sample was collected is indicated.
al., 1970), including those for California crudes that range from as low as 80 ng g1 to over 20,000 ng g1 (Shah et al., 1970) in samples from the Cymric oil field. Recently, Magaw et al. (1999) performed a survey of 26 crude oil types from California refineries, and found that (except in one Cymric sample, 1500 ng g1) mercury concentrations were all less than the method detection
103
limit of 10 ng g1. With this considerable range of reported concentrations, it is not possible to make an evaluation of the loss or enrichment of mercury in the refining process, but given the relatively low concentrations in gasoline and diesel, there is little evidence for mercury enrichment or contamination in the refining process. Using data on gasoline consumption in the San Francisco Bay area, it is possible to estimate the amount of mercury released to the environment by automobile emissions (Table 3). As previously noted, nearly all of the gasoline consumed in the San Francisco Bay area is refined locally (Quinn, 2001), and the total gasoline consumption in nine counties in the area (Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, Sonoma) is now 13 billion liters per year (Caltrans, 2002). Assuming a typical density of gasoline of 0.7 g cm3 (Weast, 1985), this is equivalent to 9 billion kilograms of gasoline. Using the range of mercury concentrations in this study (0.08–1.4 ng g1, average 0.5 ng g1), gasoline consumption in the area contributes 0.7–13 kg yr1 of mercury to the environment, with an estimated average of 5 kg yr1. Because of lower average mercury concentration and consumption, diesel fuel adds little to this estimated emission. Mercury released by gasoline and diesel consumption represents a direct anthropogenic release of mercury to the environment. The fate of this mercury depends on the speciation of the mercury in these products and subsequent transformation when the fuel is combusted. Although we are unaware of any published studies of mercury speciation in gasoline, studies on the speciation of mercury in crude oil and other hydrocarbons (Bloom, 2000; Osborne, 1990) suggest that the mercury can exist as various organic (dialkylmercury, monomethylmercury), inorganic (halide salts, sulfides), and elemental species (Hg0). All of these various forms may be dissolved or adsorbed to particles. The effects of the refining process on mercury speciation have been reviewed (Wilhelm and Bloom, 2000), but insufficient information exists for us to speculate on the relative abundance of mercury species in gasoline or diesel. The high-temperature conditions of the engine and exhaust system are likely to transform any mercury into elemental mercury vapor (Hg0), but some particulate mercury sulfide species may be resistant to thermal decomposition (Wilhelm and Bloom, 2000), and particulate mercury may be an important fraction of automobile emissions. This possibility is supported by a study by Pierson and Brachaczek (1983) that measured particulate mercury in automobile exhaust emissions from neutron activation analysis of particulate filters, but the applicability of this 1983 study to estimating modern day emissions from gasoline combustion is problematic because it foreruns catalytic converters and unleaded gasoline. Based on these studies of mercury
ARTICLE IN PRESS C.H. Conaway et al. / Atmospheric Environment 39 (2005) 101–105
104
Table 2 Summary of mercury concentration (ng g1) in gasoline and diesel in this and other studies n
Range (ng g1) Mean Standard deviation Notes
Gasoline This study 20 0.08–1.4 Liang et al. (1996) 5 0.22–1.43 4 0.72–3.2 Diesel This study 19 0.05–0.34 Liang et al. (1996) 1 0.4 1 2.97 Kelly et al. (2003) 1 0.034a
0.50 0.7 1.5
0.40
Northern California refineries and service stations US Monaco, Slovenia, Algeria
0.15
0.06
Northern California refineries and service stations US Slovenia US, Reference material NIST 2724b (sulfur in diesel fuel oil)
n=number of independent samples. a Based on 6 replicate analyses, standard deviation 0.026 ng g1.
Table 3 Gasoline consumption (billions of liters) in the nine San Francisco Bay area counties, 1993–2001 (Caltrans, 2002) and estimated mercury emission to the environment (kg) based on the range of mercury concentrations (0.08–1.4 ng g1) measured in gasoline in this study Year
1993
1994
1995
1996
1997
1998
1999
2000
2001
Gasoline consumption ( 109 l) Mercury emission (kg) Low (0.08 ng g1) Average (0.50 ng g1) High (1.4 ng g1)
11
11
11
11
12
12
12
13
13
0.6 4 10
0.6 4 10
0.6 4 10
0.6 4 11
0.7 4 11
0.7 4 12
0.7 4 12
0.7 5 12
0.7 5 13
speciation in other petroleum products, we assume that all mercury contained in gasoline is released from the combustion source to the environment as a combination of Hg0 and particulate-bound mercury. Because mercury emitted upon combustion is likely to be a combination of Hg0 and particulate-bound mercury, it will either mix with the global atmospheric reservoir or be deposited locally. Assuming that the mercury released to the environment is primarily to the atmosphere, this mercury represents a small source compared to others in the San Francisco Bay area. Compiled data of total atmospheric emissions to the atmosphere in San Francisco Bay area counties range roughly from 500–2000 kg Hg y1 (USEPA, 2002; CARB, 2000), with the dominant sources being medical waste incineration, Portland cement manufacturing, and geothermal power production. The estimated mercury emission from gasoline consumption represents less than 3% of these total emissions. The typical concentrations of mercury in California gasoline are similar to other reported values, and least similar to or lower that concentrations in crude oil feedstocks purchased by California refineries. Mercury is, therefore, not measurably enriched in gasoline or diesel fuel refining, and there is little evidence of
contamination in motor fuels from high-mercury crude oil in California refineries. In addition, this study demonstrates that mercury from gasoline and diesel consumption is a relatively small (less than 3%) source of mercury to the atmosphere in a major metropolitan area, and suggests that this emission is trivial on a global basis as a contribution to total atmospheric emissions.
Acknowledgements This work was funded in part by the University of California Toxic Substances Research and Teaching Program, and by a grant from USEPA Office of Wetlands, Oceans, and Watersheds as part of the Great Waters Program, and by the W.M. Keck Foundation. The authors are grateful for the support of Geoff Brosseau at the Bay Area Stormwater Management Agencies Association and for the assistance from Fred Schmidt at the California Air Resources Board. This project was also funded in part by the UC Berkeley NIEHS Superfund Basic Research Program Grant 3P432 ES04705 to Principal Investigator Martyn Smith and Project Investigator James Hunt.
ARTICLE IN PRESS C.H. Conaway et al. / Atmospheric Environment 39 (2005) 101–105
References Babi, D., Schaedlich, F., Schneeberger, D., 2003. Total mercury analysis in petroleum products. Journal de Physique IV 107 (Part 2), 1447. Benoit, J., Gilmour, C.C., Heyes, A., Mason, R.P., Miller, C.L., 2003. Geochemical and biological controls over methylmercury production and degradation in aquatic ecosystems. In: Cai, Y., Braids, O.C. (Eds.), Biogeochemistry of Environmentally Important Trace Elements, ACS Symposium Series No. 835. Oxford University Press, Oxford, p. 448. Bloom, N.S., 2000. Analysis and stability of mercury speciation in petroleum hydrocarbons, Fresenius. Journal of Analytical Chemistry 366 (5), 438–443. Caltrans, 2002. Fuel Consumption Estimates by County. Caltrans Office of Transportation Economics, Sacramento, CA. CARB, 2000. California Air Resources Board, 1996 California Toxics Inventory (revised 8/28/00). California Environmental Protection Agency. Conaway, C.H., Squire, S., Mason, R.P., Flegal, A.R., 2003. Mercury speciation in the San Francisco Bay estuary. Marine Chemistry 80 (2–3), 199–225. Fein, J.B., Williams-Jones, A.E., 1997. The role of mercuryorganic interactions in the hydrothermal transport of mercury. Economic Geology & the Bulletin of the Society of Economic Geologists 92 (1), 20–28. Filby, R.H., Shah, K.R., 1975. Neutron activation methods for trace metals in crude oil. In: Yen, T.F. (Ed.), The Role of Trace Metals in Petroleum. Ann Arbor Science Publishers, Ann Arbor, MI. Kelly, W.R., Long, S.E., Mann, J.L., 2003. Determination of mercury in SRM crude oils and refined products by isotope dilution cold vapor ICP-MS using closed-system combustion. Analytical & Bioanalytical Chemistry 376 (5), 753–758. Liang, L., Horvat, M., Danilchik, P., 1996. A novel analytical method for determination of picogram levels of total mercury in gasoline and other petroleum based products. Science of the Total Environment 187 (1), 57–64. Magaw, R., McMillen, S., Gala, W., Trefry, J., Trocine, R., 1999. Risk evaluation of metals in crude oils, SPE/EPA
105
Exploration & Production Environmental Conference. SPE Paper No. 52725. Osborne, S.P., 1990. Quantitation of mercury in petroleum by ETV-ICP-MS. Applied Spectroscopy 44 (6), 1044–1046. Peabody, C.E., Einaudi, M.T., 1992. Origin of petroleum and mercury in the Culver-Baer cinnabar deposit, Mayacmas district, California. Economic Geology 87 (4), 1078–1103. Pierson, N.R., Brachaczek, W.W., 1983. Particulate matter associated with vehicles on the road 2. Aerosol Science and Technology 2 (1), 1–40. Porcella, D., Chu, P., Allan, M.A., 1996. Inventory of North American mercury emissions to the atmosphere, relationship to the global mercury cycle. In: Baeyens, W., Ebinghaus, R., Vasilev, O. (Eds.), Global and Regional Mercury Cycles, Sources, Fluxes, and Mass Balances. NATO-ASI Series 2. Kluwer, Dordrecht, The Netherlands. Purvis, C.L., 1997. Auto Ownership in the San Francisco Bay Area: 1930–2010. Metropolitan Transportation Commission, Oakland, CA. Quinn, T.A., 2000. The San Francisco Bay Petroleum Industry. Western States Petroleum Association, Sacramento, CA. SFEI, 2001. San Francisco Bay Atmospheric Deposition Pilot Study Part 1, Mercury. San Francisco Estuary Institute Regional Monitoring Program for Trace Substances, Oakland, CA. Shah, K.R., Filby, R.H., Haller, W.A., 1970. Determination of trace elements in petroleum by neutron activation analysis. Journal of Radioanalytical Chemistry 6 (413). Steding, D.J., Flegal, A.R., 2002. Mercury concentrations in coastal California precipitation, evidence of local and transPacific fluxes of mercury to North America. Journal of Geophysical Research—Atmospheres 107 (D23). USEPA, 2002. US Environmental Protection Agency. National Toxics Inventory (NTI) Database. Weast, R.C., 1985. CRC Handbook of Chemistry and Physics. CRC Press, Boca Raton, FL. Wilhelm, S.M., 2001. Estimate of mercury emissions to the atmosphere from petroleum. Environmental Science and Technology 35 (24), 4704–4710. Wilhelm, S.M., Bloom, N., 2000. Mercury in petroleum. Fuel Processing Technology 63 (1), 1–27.
Atmospheric Environment 39 (2005) 101–105 www.elsevier.com/locate/atmosenv
Estimate of mercury emission from gasoline and diesel fuel consumption, San Francisco Bay area, California Christopher H. Conawaya,, Robert P. Masonb, Douglas J. Stedinga, A. Russell Flegalb a
Department of Environmental Toxicology, University of California at Santa Cruz, 1156 High Street, Santa Cruz, California, CA 95064, USA b Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, University System of Maryland, P.O. Box 38, Solomons, MD, 20688-0038, USA Received 3 May 2004; accepted 7 September 2004
Abstract Gasoline samples (n ¼ 20) collected from San Francisco Bay area refineries and service stations had mercury concentrations ranging from 0.08 to 1.4 ng g1; diesel samples (n ¼ 19) had concentrations of 0.05–0.34 ng g1. These relatively low levels show little evidence for mercury enrichment or contamination into these fuels from the refining process. Combustion of these fuels in the San Francisco Bay area contributes 0.7–13 kg Hg yr1 to the environment, with an average of 5 kg Hg yr1. Assuming the fate of this emission is to the atmosphere, the total flux from the combustion of these fuels represents less than 3% of the total atmospheric emissions in the San Francisco Bay area. r 2004 Elsevier Ltd. All rights reserved. Keywords: Mercury; Gasoline; Diesel; San Francisco Bay
1. Introduction As a result of widespread and persistent mercury contamination in the San Francisco estuary, there is an interest in developing a detailed understanding of the relevant sources of mercury to that system. There has been a focus on the atmospheric exchange of mercury in the estuary (Conaway et al., 2003; SFEI, 2001) because mercury deposited from the atmosphere is thought to be relatively labile and bioavailable (Benoit et al., 2003). That focus has been partially substantiated by the results of a recent study (Steding and Flegal, 2002) that
Corresponding author.
E-mail address: [email protected] (C.H. Conaway).
indicated the atmospheric deposition of mercury in the surrounding San Francisco Bay area was two-fold greater than in the adjacent coastal area, perhaps due to local differences in atmospheric emissions of industrial mercury. Typically, atmospheric emissions of industrial mercury include the waste products from the combustion of fossil fuels and the incineration of medical wastes, both of which are well-known sources of mercury to the environment. For example, coal combustion alone is reported to account for roughly 20% of total industrial emissions of mercury to the atmosphere in the United States (Porcella et al., 1996). More recently, petroleum production and refined petroleum product (e.g., gasoline and diesel fuel) consumption have come under scrutiny as potential sources of mercury to the environment
1352-2310/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2004.09.025
ARTICLE IN PRESS 102
C.H. Conaway et al. / Atmospheric Environment 39 (2005) 101–105
(Kelly et al., 2003; Liang et al., 1996; Wilhelm, 2001; Wilhelm and Bloom, 2000). Both petroleum production and the consumption of petroleum products are potentially important sources of mercury in the San Francisco Bay area (Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma counties). It is a major refining center in North America, with five major refineries that have the combined capacity to process roughly 95 million liters of crude oil per day, and in 1998 produced about 20 million liters of gasoline and 4.5 million liters of diesel/distillate fuels (Quinn, 2001). This metropolitan area also has a relatively large number of vehicles, with over 4.5 million automobiles, vans, and heavy-duty commercial trucks (Purvis, 1997) that consume about 13 billion liters of gasoline and 2 billion liters of diesel fuel per year (Caltrans, 2002). Because of this sizeable quantity of production and refined product use, even trace quantities of mercury in these petroleum products could result in a relatively large emission to the environment. Mercury and crude oil deposits are known to coexist (Fein and Williams-Jones, 1997; Peabody and Einaudi, 1992), and some economically important petroleum deposits in California, such as the Cymric, have shown relatively high concentrations of mercury, up to 20 mg g1 (Filby and Shah, 1975; Shah et al., 1970). Such values may not be typical of mercury concentrations in crude oil feedstocks used by California refineries (Magaw et al., 1999), which have reported concentrations less than 10 ng g1, excluding data from Cymric samples. Nevertheless, both the volume of petroleum refining and fuel consumption, and the potential for elevated mercury concentration in these matrices, suggest that mercury emission from gasoline and diesel fuel consumption should be evaluated. Data on mercury concentration in gasoline and diesel fuels are limited, and given on a national rather than regional basis (Liang et al., 1996). This limitation is notable in California, where the bulk of its crude oil production is refined and where virtually all gasoline consumed in the San Francisco Bay area is refined locally (Quinn, 2001). Therefore, we conducted a survey of mercury concentrations in gasoline and diesel fuels collected from refineries, terminals, and service stations in the local region surrounding San Francisco Bay in order to more accurately estimate the potential for contamination of refined products from highmercury crudes or from enrichment of mercury in the refining process. The results of this study provide additional data to an existing, but limited, data set. This study is a first attempt at providing a local mercury emission calculation based on local gasoline consumption figures and local gasoline concentrations in a major urban area.
2. Methods A suite of gasoline (n ¼ 20) and diesel (n ¼ 19) samples was collected from refineries, distribution stations, and service stations in the San Francisco Bay area. Samples were collected in acid-cleaned PFA Teflons bottles and stored in the dark at 20 1C until analysis. Fuel tanks sampled at refineries were sampled using either a running or all-level sampling technique. Both techniques obtain liquid from the liquid surface to a point about 1 m from the bottom of the tank, sampling a column of liquid that as close as possible represents a total vertical picture of the tank. Mercury was extracted from these samples by BrCl oxidation, and analyzed by SnCl2 reduction, Au-amalgamation, cold vapor atomic fluorescence spectroscopy using established methodologies (Babi et al., 2003; Bloom, 2000; Liang et al., 1996). Matrix spike recoveries in both diesel and gasoline averaged 10176%; the procedural blank for the analyses was 0.01270.002 ng (n ¼ 8); and the recovery was 9577%, based on concurrent analyses of mercury in certified reference material FGS-OIL1 (Mercury Speciation in Petroleum, Frontier Geosciences, HgT=1839 ng g1). Although the reference material is not entirely suitable because of the higher concentration (relative to sample concentrations) and differing matrix (crude oil versus gasoline), it was the closest available material at the time of this study.
3. Results and discussion Gasoline samples from the San Francisco Bay had mercury concentrations ranging from 0.08 to 1.4 ng g1 (Table 1). As shown in Table 2, these data are consistent with other recent measurements of mercury concentrations in gasoline from the US (0.22–1.43 ng g1), but somewhat lower than those from Monaco, Slovenia, and Algeria (0.72–3.20 ng g1), as reported by Liang et al. (1996). Diesel samples in our study had concentrations of 0.05–0.34 ng g1, which are lower than reported by Liang et al. (1996) in a sample from the US (0.4 ng g1) and elsewhere (2.97 ng g1), but higher than that reported by Kelly et al. (2003) for a certified reference material (NIST 2724b, HgT=0.034 ng g1). In addition, the motor fuel concentrations measured in our study are similar to average reported concentrations of mercury (0.04–1.32 ng g1) in other refined petroleum products, including kerosene, light distillates, utility fuel oil, heating oil, and asphalt (Bloom, 2000; Liang et al., 1996). The concentrations observed in gasoline and diesel in this study does not suggest that mercury is enriched from crude oil into these fuels during refining. Concentrations of mercury reported in crude oil have a wide range of reported values (Magaw et al., 1999; Shah et
ARTICLE IN PRESS C.H. Conaway et al. / Atmospheric Environment 39 (2005) 101–105 Table 1 Mercury concentration (ng g1) in gasoline and diesel in samples collected from refineries, service stations, and terminals in San Francisco Bay area County location Diesel Refinery 1 Refinery 2 Refinery 2 Refinery 4 Refinery 5 Refinery 5 Service station 1 Service station 2 Service station 3 Service Station 4 Service station 6 Service station 7 Service station 9 Service station 11 Service station 13 Terminal 2 Terminal 3 Terminal 4 Terminal 5 Gasoline Refinery 1 Refinery 1 Refinery 2 Refinery 2 Refinery 2 Refinery 2 Refinery 3 Refinery 3 Refinery 3 Refinery 4 Refinery 4 Refinery 5 Refinery 5 Service station Service station Service station Service station Service station Service station Terminal 1
3 5 7 8 10 12
Sonoma Sonoma Contra Costa Contra Costa Santa Clara Contra Costa Contra Costa Marin San Mateo
Contra Costa Santa Clara Contra Costa Marin Solano Alameda
[Hg] (ng g1)
0.05 0.20 0.08 0.05 0.10 0.12 0.11 0.12 0.34 0.15 0.11 0.16 0.16 0.15 0.17 0.18 0.11 0.16 0.17 0.26 0.31 0.10 0.08 0.16 0.49 0.54 0.13 0.22 0.69 0.38 1.08 1.39 0.25 0.31 0.24 0.89 0.31 0.82 1.34
Multiple samples taken from the same refinery are from different batches and tanks. For service stations, the county where the sample was collected is indicated.
al., 1970), including those for California crudes that range from as low as 80 ng g1 to over 20,000 ng g1 (Shah et al., 1970) in samples from the Cymric oil field. Recently, Magaw et al. (1999) performed a survey of 26 crude oil types from California refineries, and found that (except in one Cymric sample, 1500 ng g1) mercury concentrations were all less than the method detection
103
limit of 10 ng g1. With this considerable range of reported concentrations, it is not possible to make an evaluation of the loss or enrichment of mercury in the refining process, but given the relatively low concentrations in gasoline and diesel, there is little evidence for mercury enrichment or contamination in the refining process. Using data on gasoline consumption in the San Francisco Bay area, it is possible to estimate the amount of mercury released to the environment by automobile emissions (Table 3). As previously noted, nearly all of the gasoline consumed in the San Francisco Bay area is refined locally (Quinn, 2001), and the total gasoline consumption in nine counties in the area (Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, Sonoma) is now 13 billion liters per year (Caltrans, 2002). Assuming a typical density of gasoline of 0.7 g cm3 (Weast, 1985), this is equivalent to 9 billion kilograms of gasoline. Using the range of mercury concentrations in this study (0.08–1.4 ng g1, average 0.5 ng g1), gasoline consumption in the area contributes 0.7–13 kg yr1 of mercury to the environment, with an estimated average of 5 kg yr1. Because of lower average mercury concentration and consumption, diesel fuel adds little to this estimated emission. Mercury released by gasoline and diesel consumption represents a direct anthropogenic release of mercury to the environment. The fate of this mercury depends on the speciation of the mercury in these products and subsequent transformation when the fuel is combusted. Although we are unaware of any published studies of mercury speciation in gasoline, studies on the speciation of mercury in crude oil and other hydrocarbons (Bloom, 2000; Osborne, 1990) suggest that the mercury can exist as various organic (dialkylmercury, monomethylmercury), inorganic (halide salts, sulfides), and elemental species (Hg0). All of these various forms may be dissolved or adsorbed to particles. The effects of the refining process on mercury speciation have been reviewed (Wilhelm and Bloom, 2000), but insufficient information exists for us to speculate on the relative abundance of mercury species in gasoline or diesel. The high-temperature conditions of the engine and exhaust system are likely to transform any mercury into elemental mercury vapor (Hg0), but some particulate mercury sulfide species may be resistant to thermal decomposition (Wilhelm and Bloom, 2000), and particulate mercury may be an important fraction of automobile emissions. This possibility is supported by a study by Pierson and Brachaczek (1983) that measured particulate mercury in automobile exhaust emissions from neutron activation analysis of particulate filters, but the applicability of this 1983 study to estimating modern day emissions from gasoline combustion is problematic because it foreruns catalytic converters and unleaded gasoline. Based on these studies of mercury
ARTICLE IN PRESS C.H. Conaway et al. / Atmospheric Environment 39 (2005) 101–105
104
Table 2 Summary of mercury concentration (ng g1) in gasoline and diesel in this and other studies n
Range (ng g1) Mean Standard deviation Notes
Gasoline This study 20 0.08–1.4 Liang et al. (1996) 5 0.22–1.43 4 0.72–3.2 Diesel This study 19 0.05–0.34 Liang et al. (1996) 1 0.4 1 2.97 Kelly et al. (2003) 1 0.034a
0.50 0.7 1.5
0.40
Northern California refineries and service stations US Monaco, Slovenia, Algeria
0.15
0.06
Northern California refineries and service stations US Slovenia US, Reference material NIST 2724b (sulfur in diesel fuel oil)
n=number of independent samples. a Based on 6 replicate analyses, standard deviation 0.026 ng g1.
Table 3 Gasoline consumption (billions of liters) in the nine San Francisco Bay area counties, 1993–2001 (Caltrans, 2002) and estimated mercury emission to the environment (kg) based on the range of mercury concentrations (0.08–1.4 ng g1) measured in gasoline in this study Year
1993
1994
1995
1996
1997
1998
1999
2000
2001
Gasoline consumption ( 109 l) Mercury emission (kg) Low (0.08 ng g1) Average (0.50 ng g1) High (1.4 ng g1)
11
11
11
11
12
12
12
13
13
0.6 4 10
0.6 4 10
0.6 4 10
0.6 4 11
0.7 4 11
0.7 4 12
0.7 4 12
0.7 5 12
0.7 5 13
speciation in other petroleum products, we assume that all mercury contained in gasoline is released from the combustion source to the environment as a combination of Hg0 and particulate-bound mercury. Because mercury emitted upon combustion is likely to be a combination of Hg0 and particulate-bound mercury, it will either mix with the global atmospheric reservoir or be deposited locally. Assuming that the mercury released to the environment is primarily to the atmosphere, this mercury represents a small source compared to others in the San Francisco Bay area. Compiled data of total atmospheric emissions to the atmosphere in San Francisco Bay area counties range roughly from 500–2000 kg Hg y1 (USEPA, 2002; CARB, 2000), with the dominant sources being medical waste incineration, Portland cement manufacturing, and geothermal power production. The estimated mercury emission from gasoline consumption represents less than 3% of these total emissions. The typical concentrations of mercury in California gasoline are similar to other reported values, and least similar to or lower that concentrations in crude oil feedstocks purchased by California refineries. Mercury is, therefore, not measurably enriched in gasoline or diesel fuel refining, and there is little evidence of
contamination in motor fuels from high-mercury crude oil in California refineries. In addition, this study demonstrates that mercury from gasoline and diesel consumption is a relatively small (less than 3%) source of mercury to the atmosphere in a major metropolitan area, and suggests that this emission is trivial on a global basis as a contribution to total atmospheric emissions.
Acknowledgements This work was funded in part by the University of California Toxic Substances Research and Teaching Program, and by a grant from USEPA Office of Wetlands, Oceans, and Watersheds as part of the Great Waters Program, and by the W.M. Keck Foundation. The authors are grateful for the support of Geoff Brosseau at the Bay Area Stormwater Management Agencies Association and for the assistance from Fred Schmidt at the California Air Resources Board. This project was also funded in part by the UC Berkeley NIEHS Superfund Basic Research Program Grant 3P432 ES04705 to Principal Investigator Martyn Smith and Project Investigator James Hunt.
ARTICLE IN PRESS C.H. Conaway et al. / Atmospheric Environment 39 (2005) 101–105
References Babi, D., Schaedlich, F., Schneeberger, D., 2003. Total mercury analysis in petroleum products. Journal de Physique IV 107 (Part 2), 1447. Benoit, J., Gilmour, C.C., Heyes, A., Mason, R.P., Miller, C.L., 2003. Geochemical and biological controls over methylmercury production and degradation in aquatic ecosystems. In: Cai, Y., Braids, O.C. (Eds.), Biogeochemistry of Environmentally Important Trace Elements, ACS Symposium Series No. 835. Oxford University Press, Oxford, p. 448. Bloom, N.S., 2000. Analysis and stability of mercury speciation in petroleum hydrocarbons, Fresenius. Journal of Analytical Chemistry 366 (5), 438–443. Caltrans, 2002. Fuel Consumption Estimates by County. Caltrans Office of Transportation Economics, Sacramento, CA. CARB, 2000. California Air Resources Board, 1996 California Toxics Inventory (revised 8/28/00). California Environmental Protection Agency. Conaway, C.H., Squire, S., Mason, R.P., Flegal, A.R., 2003. Mercury speciation in the San Francisco Bay estuary. Marine Chemistry 80 (2–3), 199–225. Fein, J.B., Williams-Jones, A.E., 1997. The role of mercuryorganic interactions in the hydrothermal transport of mercury. Economic Geology & the Bulletin of the Society of Economic Geologists 92 (1), 20–28. Filby, R.H., Shah, K.R., 1975. Neutron activation methods for trace metals in crude oil. In: Yen, T.F. (Ed.), The Role of Trace Metals in Petroleum. Ann Arbor Science Publishers, Ann Arbor, MI. Kelly, W.R., Long, S.E., Mann, J.L., 2003. Determination of mercury in SRM crude oils and refined products by isotope dilution cold vapor ICP-MS using closed-system combustion. Analytical & Bioanalytical Chemistry 376 (5), 753–758. Liang, L., Horvat, M., Danilchik, P., 1996. A novel analytical method for determination of picogram levels of total mercury in gasoline and other petroleum based products. Science of the Total Environment 187 (1), 57–64. Magaw, R., McMillen, S., Gala, W., Trefry, J., Trocine, R., 1999. Risk evaluation of metals in crude oils, SPE/EPA
105
Exploration & Production Environmental Conference. SPE Paper No. 52725. Osborne, S.P., 1990. Quantitation of mercury in petroleum by ETV-ICP-MS. Applied Spectroscopy 44 (6), 1044–1046. Peabody, C.E., Einaudi, M.T., 1992. Origin of petroleum and mercury in the Culver-Baer cinnabar deposit, Mayacmas district, California. Economic Geology 87 (4), 1078–1103. Pierson, N.R., Brachaczek, W.W., 1983. Particulate matter associated with vehicles on the road 2. Aerosol Science and Technology 2 (1), 1–40. Porcella, D., Chu, P., Allan, M.A., 1996. Inventory of North American mercury emissions to the atmosphere, relationship to the global mercury cycle. In: Baeyens, W., Ebinghaus, R., Vasilev, O. (Eds.), Global and Regional Mercury Cycles, Sources, Fluxes, and Mass Balances. NATO-ASI Series 2. Kluwer, Dordrecht, The Netherlands. Purvis, C.L., 1997. Auto Ownership in the San Francisco Bay Area: 1930–2010. Metropolitan Transportation Commission, Oakland, CA. Quinn, T.A., 2000. The San Francisco Bay Petroleum Industry. Western States Petroleum Association, Sacramento, CA. SFEI, 2001. San Francisco Bay Atmospheric Deposition Pilot Study Part 1, Mercury. San Francisco Estuary Institute Regional Monitoring Program for Trace Substances, Oakland, CA. Shah, K.R., Filby, R.H., Haller, W.A., 1970. Determination of trace elements in petroleum by neutron activation analysis. Journal of Radioanalytical Chemistry 6 (413). Steding, D.J., Flegal, A.R., 2002. Mercury concentrations in coastal California precipitation, evidence of local and transPacific fluxes of mercury to North America. Journal of Geophysical Research—Atmospheres 107 (D23). USEPA, 2002. US Environmental Protection Agency. National Toxics Inventory (NTI) Database. Weast, R.C., 1985. CRC Handbook of Chemistry and Physics. CRC Press, Boca Raton, FL. Wilhelm, S.M., 2001. Estimate of mercury emissions to the atmosphere from petroleum. Environmental Science and Technology 35 (24), 4704–4710. Wilhelm, S.M., Bloom, N., 2000. Mercury in petroleum. Fuel Processing Technology 63 (1), 1–27.