ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-4867-2012 Sulfur isotope fractionation during heterogeneous oxidation of SO<sub>2</sub> on mineral dust Harris E. 1 Sinha B. 1 2 Foley S. 3 Crowley J. N. 4 Borrmann S. 1 Hoppe P. 1 Abteilung Partikelchemie, Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany Department of Earth Sciences, Indian Institute for Science Education and Research IISER Mohali, Sector 81, SAS Nagar, Manauli P.O. 140306, India Earth System Science Research Centre, Institute for Geosciences, University of Mainz, Becherweg 21, 55128 Mainz, Germany Abteilung Luftchemie, Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany 04 06 2012 12 11 4867 4884 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/4867/2012/acp-12-4867-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/4867/2012/acp-12-4867-2012.pdf

Mineral dust is a major fraction of global atmospheric aerosol, and the oxidation of SO<sub>2</sub> on mineral dust has implications for cloud formation, climate and the sulfur cycle. Stable sulfur isotopes can be used to understand the different oxidation processes occurring on mineral dust. This study presents measurements of the <sup>34</sup>S/<sup>32</sup>S fractionation factor &alpha;<sub>34</sub> for oxidation of SO<sub>2</sub> on mineral dust surfaces and in the aqueous phase in mineral dust leachate. Sahara dust, which accounts for ~60% of global dust emissions and loading, was used for the experiments. <br><br> The fractionation factor for aqueous oxidation in dust leachate is α<sub>leachate</sub> = 0.9917±0.0046, which is in agreement with previous measurements of aqueous SO<sub>2</sub> oxidation by iron solutions. This fractionation factor is representative of a radical chain reaction oxidation pathway initiated by transition metal ions. Oxidation on the dust surface at subsaturated relative humidity (RH) had an overall fractionation factor of &alpha;<sub>het</sub> = 1.0096&plusmn;0.0036 and was found to be almost an order of magnitude faster when the dust was simultaneously exposed to ozone, light and RH of ~40%. However, the presence of ozone, light and humidity did not influence isotope fractionation during oxidation on dust surfaces at subsaturated relative humidity. All the investigated reactions showed mass-dependent fractionation of <sup>33</sup>S relative to <sup>34</sup>S. <br><br> A positive matrix factorization model was used to investigate surface oxidation on the different components of dust. Ilmenite, rutile and iron oxide were found to be the most reactive components, accounting for 85% of sulfate production with a fractionation factor of &alpha;<sub>34</sub> = 1.012±0.010. This overlaps within the analytical uncertainty with the fractionation of other major atmospheric oxidation pathways such as the oxidation of SO<sub>2</sub> by H<sub>2</sub>O<sub>2</sub> and O<sub>3</sub> in the aqueous phase and OH in the gas phase. Clay minerals accounted for roughly 12% of the sulfate production, and oxidation on clay minerals resulted in a very distinct fractionation factor of &alpha;<sub>34</sub> = 1.085±0.013. The fractionation factors measured in this study will be particularly useful in combination with field and modelling studies to understand the role of surface oxidation on clay minerals and aqueous oxidation by mineral dust and its leachate in global and regional sulfur cycles.

 References Adams,~J W., Rodriguez,~D., and Cox,~R A.: The uptake of \chemSO_2 on Saharan dust: a flow tube study, Atmos. Chem. Phys., 5, 2679–2689, http://dx.doi.org/10.5194/acp-5-2679-2005doi:10.5194/acp-5-2679-2005, 2005. Al-Hosney,~H A. and Grassian,~V H.: Water, sulfur dioxide and nitric acid adsorption on calcium carbonate: a transmission and ATR-FTIR study, Phys. Chem. Chem. Phys., 7, 1266–1276, 2005. Alexander,~B., Thiemens,~M H., Farquhar,~J., Kaufman,~A J., Savarino,~J., and Delmas,~R J.: East Antarctic ice core sulfur isotope measurements over a complete glacial-interglacial cycle, J Geophys. Res.-Atmos., 108, 4786, http://dx.doi.org/10.1029/2003JD003513doi:10.1029/2003JD003513, 2003. Alexander, B., Allman, D. J., Amos, H. M., Fairlie, T. D., Dachs, J., Hegg, D. A. and Sletten, R. S.: Isotopic constraints on the formation pathways of sulfate aerosol in the marine boundary layer of the subtropical northeast Atlantic Ocean, J Geophys. Res.-Atmos., 117, D06304, http://dx.doi.org/10.1029/2011JD016773doi:10.1029/2011JD016773, 2012. Baker,~A R., Jickells,~T D., Witt,~M., and Linge,~K L.: Trends in the solubility of iron, aluminium, manganese and phosphorus in aerosol collected over the Atlantic Ocean RID D-1233-2011 RID B-2210-2010 RID B-8095-2008, Mar. Chem., 98, 43–58, http://dx.doi.org/10.1016/j.marchem.2005.06.004doi:10.1016/\breakj.marchem.2005.06.004, 2006. Bogumil,~K., Orphal,~J., Homann,~T., Voigt,~S., Spietz,~P., Fleischmann,~O C., Vogel,~A., Hartmann,~M., Kromminga,~H., Bovensmann,~H., Frerick,~J., and Burrows,~J P.: Measurements of molecular absorption spectra with the SCIAMACHY pre-flight model: instrument characterization and reference data for atmospheric remote-sensing in the 230–2380 nm region, J Photochem. Photobio A, 157, 167–184, 2003. Caquineau,~S., Gaudichet,~A., Gomes,~L., and Legrand,~M.: Mineralogy of Saharan dust transported over northwestern tropical Atlantic Ocean in relation to source regions, J Geophys. Res.-Atmos., 107, 4251, http://dx.doi.org/10.1029/2000JD000247doi:10.1029/2000JD000247, 2002. Cohen,~S., Chang,~S G., Markowitz,~S S., and Novakov,~T.: Role of fly ash in catalytic oxidation of sulfur(IV) slurries, Environ. Sci. Technol., 15, 1498–1502, http://dx.doi.org/10.1021/es00094a013doi:10.1021/es00094a013, 1981. Coude-Gaussen,~G., Rognon,~P., and Le~Coustumer,~M.: Incorporation progressive de poussières sahariennes aux limons des Iles orientales du Cap Vert, C. R. Acad. Sci. II~A, 319, 1343–1349, 1994. Crowley,~J N., Ammann,~M., Cox,~R A., Hynes,~R G., Jenkin,~M E., Mellouki,~A., Rossi,~M J., Troe,~J., and Wallington,~T J.: Evaluated kinetic and photochemical data for atmospheric chemistry: Volume V – heterogeneous reactions on solid substrates, Atmos. Chem. Phys., 10, 9059–9223, http://dx.doi.org/10.5194/acp-10-9059-2010doi:10.5194/acp-10-9059-2010, 2010. Cziczo,~D J., Froyd,~K D., Gallavardin,~S J., Moehler,~O., Benz,~S., Saathoff,~H., and Murphy,~D M.: Deactivation of ice nuclei due to atmospherically relevant surface coatings, Environ. Res. Lett., 4, 044013, http://dx.doi.org/10.1088/1748-9326/4/4/044013doi:10.1088/1748-9326/4/4/044013, 2009. Dentener,~F J., Carmichael,~G R., Zhang,~Y., Lelieveld,~J., and Crutzen,~P J.: Role of mineral aerosol as a reactive surface in the global troposphere, J Geophys. Res.-Atmos., 101, 22869–22889, 1996. Derda,~M., Chmielewski,~A G., and Licki,~J.: Sulphur isotope compositions of components of coal and S-isotope fractionation during its combustion and flue gas desulphurization, Isot. Environ. Health~S., 43, 57–63, 2007. Ding,~T., Valkiers,~S., Kipphardt,~H., De~Bievre,~P., Taylor,~P D P., Gonfiantini,~R., and Krouse,~R.: Calibrated sulfur isotope abundance ratios of three IAEA sulfur isotope reference materials and V-CDT with a reassessment of the atomic weight of sulfur, Geochim. Cosmochim. Ac., 65, 2433–2437, 2001. Drake,~N A., Eckardt,~F D., and White,~K H.: Sources of sulphur in gypsiferous sediments and crusts and pathways of gypsum redistribution in Southern Tunisia, Earth Surf. Proc. Land., 29, 1459–1471, http://dx.doi.org/10.1002/esp.1133doi:10.1002/esp.1133, 2004. Falkovich,~A H., Ganor,~E., Levin,~Z., Formenti,~P., and Rudich,~Y.: Chemical and mineralogical analysis of individual mineral dust particles, J Geophys. Res.-Atmos., 106, 18029–18036, 2001. Faust,~B C., Hoffmann,~M R., and Bahnemann,~D W.: Photocatalytic oxidation of sulfur-dioxide in aqueous suspensions of alpha-\chemFe_2O_3, J Phys. Chem., 93, 6371–6381, 1989. Fu,~H B., Wang,~X., Wu,~H B., Yin,~Y., and Chen,~J M.: Heterogeneous uptake and oxidation of \chemSO_2 on iron oxides, J Phys. Chem C, 111, 6077–6085, http://dx.doi.org/10.1021/jp070087bdoi:10.1021/jp070087b, 2007. Gasso,~S., Grassian,~V H., and Miller,~R L.: Interactions between mineral dust, climate, and ocean ecosystems, Elements, 6, 247–252, http://dx.doi.org/10.2113/gselements.6.4.247doi:10.2113/gselements.6.4.247, 2010. Glaccum,~R A. and Prospero,~J M.: Saharan aerosols over the tropical North Atlantic – mineralogy, Mar. Geol., 37, 295–321, http://dx.doi.org/10.1016/0025-3227(80)90107-3doi:10.1016/0025-3227(80)90107-3, 1980. Goldstein,~J., Newbury,~D E., Echlin,~P., Joy,~D., Fiori,~C., and Lifshin,~E.: Scanning Electron Microscopy and X-ray Microanalysis, Plenum Press, New York, USA, 1–820, 1981. Goodman,~A L., Li,~P., Usher,~C R., and Grassian,~V H.: Heterogeneous uptake of sulfur dioxide on aluminum and magnesium oxide particles, J Phys. Chem A, 105, 6109–6120, 2001. Goodsel,~A J., Low,~M J D., and Takezawa,~N.: Reactions of gaseous pollutants with solids II. Infrared study of sorption of sulfur dioxide on magnesium oxide, Environ. Sci. Technol., 6, 268–273, http://dx.doi.org/10.1021/es60062a001doi:10.1021/es60062a001, 1972. Groener,~E. and Hoppe,~P.: Automated ion imaging with the NanoSIMS ion microprobe, Appl. Surf. Sci., 252, 7148–7151, http://dx.doi.org/10.1016/j.apsusc.2006.02.280doi:10.1016/j.apsusc.2006.02.280, 2006. Gustafsson,~R J., Orlov,~A., Badger,~C L., Griffiths,~P T., Cox,~R A., and Lambert,~R M.: A comprehensive evaluation of water uptake on atmospherically relevant mineral surfaces: DRIFT spectroscopy, thermogravimetric analysis and aerosol growth measurements, Atmos. Chem. Phys., 5, 3415–3421, http://dx.doi.org/10.5194/acp-5-3415-2005doi:10.5194/acp-5-3415-2005, 2005. Hanisch,~F. and Crowley,~J N.: Heterogeneous reactivity of gaseous nitric acid on \chemAl_2O_3, \chemCaCO_3, and atmospheric dust samples: a Knudsen cell study, J Phys. Chem A, 105, 3096–3106, 2001. Hanisch,~F. and Crowley,~J N.: Ozone decomposition on Saharan dust: an experimental investigation, Atmos. Chem. Phys., 3, 119–130, http://dx.doi.org/10.5194/acp-3-119-2003doi:10.5194/acp-3-119-2003, 2003. Harris,~E., Sinha,~B., Hoppe,~P., Crowley,~J N., Ono,~S., and Foley,~S.: Sulfur isotope fractionation during oxidation of sulfur dioxide: gas-phase oxidation by OH radicals and aqueous oxidation by \chemH_2O_2, \chemO_3 and iron catalysis, Atmos. Chem. Phys., 12, 407–423, http://dx.doi.org/10.5194/acp-12-407-2012doi:10.5194/acp-12-407-2012, 2012. Heinold,~B., Tegen,~I., Esselborn,~M., Kandler,~K., Knippertz,~P., Mueller,~D., Schadlitz,~A., Tesche,~M., Weinzerl,~B., Ansmann,~A., Althausen,~D., Laurent,~B., Massling,~A., Mueller,~T., Petzold,~A., Schepanski,~K., and Wiedensohler,~A.: Regional Saharan dust modelling during the SAMUM 2006 campaign, Tellus~B, 61, 307–324, http://dx.doi.org/10.1111/j.1600-0889.2008.00387.xdoi:10.1111/j.1600-0889.2008.00387.x, 2009. Herrmann,~H., Ervens,~B., Jacobi,~H W., Wolke,~R., Nowacki,~P., and Zellner,~R.: CAPRAM2.3: a chemical aqueous phase radical mechanism for tropospheric chemistry, J Atmos. Chem., 36, 231–284, 2000. Hong,~A P., Bahnemann,~D W., and Hoffmann,~M R.: Cobalt(ii) tetrasulfophthalocyanine on titanium-dioxide .2. Kinetics and mechanisms of the photocatalytic oxidation of aqueous sulfur-dioxide, J Phys. Chem., 91, 6245–6251, http://dx.doi.org/10.1021/j100308a035doi:10.1021/j100308a035, 1987. Hoppe,~P.: NanoSIMS: a new tool in cosmochemistry, Appl. Surf. Sci., 252, 7102–7106, 2006. Janssen,~A., Geisler,~T., Putnis,~C., and Putnis,~A.: The mechanism of oxidation and \qutleaching of ilmenite during natural and experimental alteration, Geochim. Cosmochim. Ac., 71, A440–A440, 2007. Jayne,~J T., Davidovits,~P., Worsnop,~D R., Zahniser,~M S., and Kolb,~C E.: Uptake of \chemSO_2(g) by aqueous surfaces as a function of pH – the effect of chemical-reaction at the interface, J Phys. Chem., 94, 6041–6048, http://dx.doi.org/10.1021/j100378a076doi:10.1021/j100378a076, 1990. Jickells,~T D., An,~Z S., Andersen,~K K., Baker,~A R., Bergametti,~G., Brooks,~N., Cao,~J J., Boyd,~P W., Duce,~R A., Hunter,~K A., Kawahata,~H., Kubilay,~N., laRoche,~J., Liss,~P S., Mahowald,~N., Prospero,~J M., Ridgwell,~A J., Tegen,~I., and Torres,~R.: Global iron connections between desert dust, ocean biogeochemistry, and climate, Science, 308, 67–71, 2005. Judeikis,~H S., Stewart,~T B., and Wren,~A G.: Laboratory studies of the heterogeneous reactions of \chemSO_2, Atmos. Environ., 12, 1633–1641, 1978. Kaaden,~N., Massling,~A., Schladitz,~A., Mueller,~T., Kandler,~K., Schuetz,~L., Weinzierl,~B., Petzold,~A., Tesche,~M., Leinert,~S., Deutscher,~C., Ebert,~M., Weinbruch,~S., and Wiedensohler,~A.: State of mixing, shape factor, number size distribution, and hygroscopic growth of the Saharan anthropogenic and mineral dust aerosol at Tinfou, Morocco, Tellus~B, 61, 51–63, http://dx.doi.org/10.1111/j.1600-0889.2008.00388.xdoi:10.1111/j.1600-0889.2008.00388.x, 2009. Karge,~H G. and Dalla Lana,~I G.: Infrared studies of \chemSO_2 adsorption on a Claus catalyst by selective poisoning of sites, J Phys. Chem., 88, 1538–1543, 1984. Kim,~B G. and Park,~S U.: Transport and evolution of a winter-time yellow sand observed in Korea, Atmos. Environ., 35, 3191–3201, http://dx.doi.org/10.1016/S1352-2310(00)00469-6doi:10.1016/S1352-2310(00)00469-6, 2001. Krouse,~H R. and Grinenko,~V A. (Eds.): Stable Isotopes: Natural and Anthropogenic Sulphur in the Environment, Vol 43, Wiley, Chichester, 1991. Krouse,~H., Grinenko,~L., Grinenko,~V., Newman,~L., Forrest,~J., Nakai,~N., Tsuji,~Y., Yatsumimi,~T., Takeuchi,~V., Robinson,~B., Stewart,~M., Gunatilaka,~A., Plumb,~L., Smith,~J., Buzek,~F., Cerny,~J., Sramek,~J., Menon,~A., Iyer,~G., Venkatasubramanian,~V., Egboka,~B., Irogbenachi,~M., and Eligwe,~C.: Case studies and potential applications, in: Stable Isotopes: Natural and Anthropogenic Sulphur in the Environment, Chap 8., edited by: Krouse, H. R. and Grinenko, V. A., John Wiley and Sons, Chichester, 307–416, 1991. Kumar,~A. and Sarin,~M M.: Aerosol iron solubility in a semi-arid region: temporal trend and impact of anthropogenic sources, Tellus B – Chem. Phys. Meteorol., 62, 125–132, http://dx.doi.org/10.1111/j.1600-0889.2009.00448.xdoi:10.1111/j.1600-0889.2009.00448.x, 2010. Kumar,~A., Sarin,~M M., and Srinivas,~B.: Aerosol iron solubility over Bay of Bengal: role of anthropogenic sources and chemical processing, Mar. Chem., 121, 167–175, http://dx.doi.org/10.1016/j.marchem.2010.04.005doi:10.1016/j.marchem.2010.04.005, 2010. Lee,~C C W. and Thiemens,~M H.: The $\delta $O-17 and $\delta $O-18 measurements of atmospheric sulfate from a coastal and high alpine region: a mass-independent isotopic anomaly, J Geophys. Res.-Atmos., 106, 17359–17373, 2001. Levin,~Z., Ganor,~E., and Gladstein,~V.: The effects of desert particles coated with sulfate on rain formation in the Eastern Mediterranean, J. of Appl. Meteorol., 35, 1511–1523, 1996. Li,~L., Chen,~Z M., Zhang,~Y H., Zhu,~T., Li,~J L., and Ding,~J.: Kinetics and mechanism of heterogeneous oxidation of sulfur dioxide by ozone on surface of calcium carbonate, Atmos. Chem. Phys., 6, 2453–2464, http://dx.doi.org/10.5194/acp-6-2453-2006doi:10.5194/acp-6-2453-2006, 2006. Li,~L., Chen,~Z M., Zhang,~Y H., Zhu,~T., Li,~S., Li,~H J., Zhu,~L H., and Xu,~B Y.: Heterogeneous oxidation of sulfur dioxide by ozone on the surface of sodium chloride and its mixtures with other components, J Geophys. Res.-Atmos., 112, D18301, http://dx.doi.org/10.1029/2006JD008207doi:10.1029/2006JD008207, 2007. Liao,~H. and Seinfeld,~J H.: Global impacts of gas-phase chemistry-aerosol interactions on direct radiative forcing by anthropogenic aerosols and ozone, J Geophys. Res.-Atmos., 110, D18208, http://dx.doi.org/10.1029/2005JD005907doi:10.1029/2005JD005907, 2005. Lin,~Y., Sim,~M S., and Ono,~S.: Multiple-sulfur isotope effects during photolysis of carbonyl sulfide, Atmos. Chem. Phys., 11, 10283–10292, http://dx.doi.org/10.5194/acp-11-10283-2011doi:10.5194/acp-11-10283-2011, 2011. Low,~M J D., Goodsel,~A J., and Takezawa,~N.: Reactions of gaseous pollutants with solids I. Infrared study of the sorption of sulfur dioxide on calcium oxide, Environ. Sci. Technol., 5, 1191–1195, http://dx.doi.org/10.1021/es60059a003doi:10.1021/es60059a003, 1971. Mamane,~Y. and Gottlieb,~J.: Heterogeneous reactions of minerals with sulfur and nitrogen oxides, J. Aerosol Sci., 20, 303–311, 1989. Mariotti,~A., Germon,~J C., Hubert,~P., Kaiser,~P., Letolle,~R., Tardieux,~A., and Tardieux,~P.: Experimental-determination of nitrogen kinetic isotope fractionation – some principles – illustration for the denitrification and nitrification processes, Plant Soil, 62, 413–430, 1981. Mayer,~B., Feger,~K H., Giesemann,~A., and Jäger,~H. J.: Interpretation of sulfur cycling in two catchments in the Black Forest (Germany) using stable sulfur and oxygen isotope data, Biogeochemistry, 30, 31–58, 1995. McCabe,~J R., Savarino,~J., Alexander,~B., Gong,~S L., and Thiemens,~M H.: Isotopic constraints on non-photochemical sulfate production in the Arctic winter, Geophys. Res. Lett., 33, L05810, http://dx.doi.org/10.1029/2005GL025164doi:10.1029/2005GL025164, 2006. Morales,~C.: The airborne transport of Saharan dust: a review, Climatic Change, 9, 219–241, http://dx.doi.org/10.1007/BF00140538doi:10.1007/BF00140538, 1986. Mukai,~H., Tanaka,~A., Fujii,~T., Zeng,~Y Q., Hong,~Y T., Tang,~J., Guo,~S., Xue,~H S., Sun,~Z L., Zhou,~J T., Xue,~D M., Zhao,~J., Zhai,~G H., Gu,~J L., and Zhai,~P Y.: Regional characteristics of sulfur and lead isotope ratios in the atmosphere at several Chinese urban sites, Environ. Sci. Technol., 35, 1064–1071, 2001. Ndour,~M., Nicolas,~M., D'Anna,~B., Ka,~O., and George,~C.: Photoreactivity of \chemNO_2 on mineral dusts originating from different locations of the Sahara desert, Phys. Chem. Chem. Phys., 11, 1312–1319, 2009. Nicolas,~M., Ndour,~M., Ka,~O., D'Anna,~B., and George,~C.: Photochemistry of atmospheric dust: ozone decomposition on illuminated titanium dioxide, Environ. Sci. Technol., 43, 7437–7442, 2009. Norman,~A L., Barrie,~L A., Toom-Sauntry,~D., Sirois,~A., Krouse,~H R., Li,~S M., and Sharma,~S.: Sources of aerosol sulphate at alert: apportionment using stable isotopes, J Geophys. Res.-Atmos., 104, 11619–11631, 1999. Norris,~G., Vedantham,~R., Wade,~K., Brown,~S., Prouty,~J., and Foley,~C.: EPA Positive Matrix Factorization (PMF) 3.0 Fundamentals and User Guide, US Environmental Protection Agency, Office of Research and Development, Washington, DC, 2008. Novak,~M., Jackova,~I., and Prechova,~E.: Temporal trends in the isotope signature of air-borne sulfur in Central Europe, Environ. Sci. Technol., 35, 255–260, 2001. Pacchioni,~G., Clotet,~A., and Ricart,~J M.: A theoretical study of the absorption and reaction of \chemSO_2 at surface and step sites of the MgO(100) surface, Surf. Sci., 315, 337–350, 1994. Park,~S H., Song,~C B., Kim,~M C., Kwon,~S B., and Lee,~K W.: Study on size distribution of total aerosol and water-soluble ions during an Asian dust storm event at Jeju Island, Korea, Environ. Monitor. Assess., 93, 157–183, http://dx.doi.org/10.1023/B:EMAS.0000016805.04194.56doi:10.1023/B:EMAS.0000016805.04194.56, 2004. Pruppacher,~H. and Klett,~J.: Microphysics of Clouds and Precipitation, 2nd edn., Kluwer Academic Publishers, Dordrecht, The Netherlands, 309–360, 1997. Putnis,~A.: Mineral replacement reactions: from macroscopic observations to microscopic mechanisms, Mineralogical Magazine, 66, 689–708, http://dx.doi.org/10.1180/0026461026650056doi:10.1180/0026461026650056, 2002. Rani,~A., Prasad,~D S N., Madnawat,~P V S., and Gupta,~K S.: The role of free-fall atmospheric dust in catalyzing autoxidation of aqueous sulfur-dioxide, Atmos. Environ A-Gen., 26, 667–673, 1992. Roithner: Preliminary Information: Hexagonal High-Power UV LED H2A1 UV Series, Roithner Lasertechnik GmbH, Vienna, Austria, available at: http://www.roithner-laser.com/datasheets/led_single/hexagonal/h2a1-uv.pdf, last access: August 2011. Rubasinghege,~G., Elzey,~S., Baltrusaitis,~J., Jayaweera,~P M., and Grassian,~V H.: Reactions on atmospheric dust particles: surface photochemistry and size-dependent nanoscale redox chemistry, J Phys. Chem. Lett., 1, 1729–1737, 2010. Rufus,~J., Stark,~G., Smith,~P L., Pickering,~J C., and Thorne,~A P.: High-resolution photoabsorption cross section measurements of \chemSO_2, 2: 220 to 325 nm at 295 K, J Geophys. Res., 108, 5011, http://dx.doi.org/10.1029/2002JE001931doi:10.1029/2002JE001931, 2003. Saltzman,~E S., Brass,~G., and Price,~D.: The mechanism of sulfate aerosol formation: chemical and sulfur isotopic evidence, Geophys. Res. Lett., 10, 513–516, 1983. Savarino,~J., Lee,~C C W., and Thiemens,~M H.: Laboratory oxygen isotopic study of sulfur (IV) oxidation: origin of the mass-independent oxygen isotopic anomaly in atmospheric sulfates and sulfate mineral deposits on Earth, J Geophys. Res.-Atmos., 105, 29079–29088, 2000. Sofen,~E D., Alexander,~B., and Kunasek,~S A.: The impact of anthropogenic emissions on atmospheric sulfate production pathways, oxidants, and ice core Δ\chem^17O(SO_4^2-), Atmos. Chem. Phys., 11, 3565–3578, http://dx.doi.org/10.5194/acp-11-3565-2011doi:10.5194/acp-11-3565-2011, 2011. Sullivan,~R C., Guazzotti,~S A., Sodeman,~D A., and Prather,~K A.: Direct observations of the atmospheric processing of Asian mineral dust, Atmos. Chem. Phys., 7, 1213–1236, http://dx.doi.org/10.5194/acp-7-1213-2007doi:10.5194/acp-7-1213-2007, 2007. Tanaka,~T Y. and Chiba,~M.: A numerical study of the contributions of dust source regions to the global dust budget, Global Planet. Change, 52, 88–104, http://dx.doi.org/10.1016/j.gloplacha.2006.02.002doi:10.1016/j.gloplacha.2006.02.002, 2006. Tanaka,~N., Rye,~D M., Xiao,~Y., and Lasaga,~A C.: Use of stable sulfur isotope systematics for evaluating oxidation reaction pathways and in-cloud scavenging of sulfur-dioxide in the atmosphere, Geophys. Res. Lett., 21, 1519–1522, 1994. Tilly,~J., Lewicki,~M., Tomaszewski,~Z., and Toczkowski,~J.: Use of ilmenite decomposition products in a gas desulfurization process, J Chem. Technol. Biot., 52, 301–310, 1991. Torfs,~K M., VanGrieken,~R., and Buzek,~F.: Use of stable isotope measurements to evaluate the origin of sulfur in gypsum layers on limestone buildings, Environ. Sci. Technol., 31, 2650–2655, 1997. Ullerstam,~M., Vogt,~R., Langer,~S., and Ljungstrom,~E.: The kinetics and mechanism of \chemSO_2 oxidation by O-3 on mineral dust, Phys. Chem. Chem. Phys., 4, 4694–4699, 2002. Ullerstam,~M., Johnson,~M S., Vogt,~R., and Ljungström,~E.: DRIFTS and Knudsen cell study of the heterogeneous reactivity of \chemSO_2 and \chemNO_2 on mineral dust, Atmos. Chem. Phys., 3, 2043–2051, http://dx.doi.org/10.5194/acp-3-2043-2003doi:10.5194/acp-3-2043-2003, 2003. Umann,~B., Arnold,~F., Schaal,~C., Hanke,~M., Uecker,~J., Aufmhoff,~H., Balkanski,~Y., and Dingenen,~R V.: Interaction of mineral dust with gas phase nitric acid and sulfur dioxide during the MINATROC II field campaign: first estimate of the uptake coefficient γ\chem(HNO_3) from atmospheric data, J Geophys. Res.-Atmos., 110, D22306, http://dx.doi.org/10.1029/2005JD005906doi:10.1029/2005JD005906, 2005. Usher,~C R., Al-Hosney,~H., Carlos-Cuellar,~S., and Grassian,~V H.: A laboratory study of the heterogeneous uptake and oxidation of sulfur dioxide on mineral dust particles, J Geophys. Res.-Atmos., 107, 4713, http://dx.doi.org/10.1029/2002JD002051doi:10.1029/2002JD002051, 2002. Wagner,~F., Bortoli,~D., Pereira,~S., Costa,~M., Silva,~A., Weinzierl,~B., Esselborn,~M., Petzold,~A., Rasp,~K., Heinold,~B., and Tegen,~I.: Properties of dust aerosol particles transported to Portugal from the Sahara desert, Tellus~B, 61, 297–306, http://dx.doi.org/10.1111/j.1600-0889.2008.00393.xdoi:10.1111/j.1600-0889.2008.00393.x, 2009. Winterholler,~B.: Sulfur Isotope Analysis of Aerosol Particles by NanoSIMS, Ph.D. thesis, Johannes Gutenberg-Universität, Mainz, Germany, 2007. Winterholler,~B., Hoppe,~P., Andreae,~M O., and Foley,~S.: Measurement of sulfur isotope ratios in micrometer-sized samples by NanoSIMS, Appl. Surf. Sci., 252, 7128–7131, 2006. Winterholler,~B., Hoppe,~P., Foley,~S., and Andreae,~M O.: Sulfur isotope ratio measurements of individual sulfate particles by NanoSIMS, Int J. Mass Spectrom., 272, 63–77, 2008. Xiao,~H., Carmichael,~G R., Durchenwald,~J., Thornton,~D., and Bandy,~A.: Long-range transport of \chemSO_x and dust in East Asia during the PEM~B experiment, J Geophys. Res.-Atmos., 102, 28589–28612, 1997. Zender,~C., Newman,~D., and Tegen,~I.: Quantifying mineral dust mass budgets: terminology, constraints, and current estimates, EOS~T. Am. Geophys. Un., 85, 509–512, http://dx.doi.org/10.1029/2004EO480002doi:10.1029/2004EO480002, 2004. Zhang,~X Y., Zhuang,~G S., Chen,~J M., Wang,~Y., Wang,~X., An,~Z S., and Zhang,~P.: Heterogeneous reactions of sulfur dioxide on typical mineral particles, J Phys. Chem B, 110, 12588–12596, 2006. Zhu,~S., Butler,~T., Sander,~R., Ma,~J., and Lawrence,~M G.: Impact of dust on tropospheric chemistry over polluted regions: a case study of the Beijing megacity, Atmos. Chem. Phys., 10, 3855–3873, http://dx.doi.org/10.5194/acp-10-3855-2010doi:10.5194/acp-10-3855-2010, 2010.