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Speciation of sulfur compounds in individual aerosol particles
J. Aerosol Sci., Vol. 26. Suppl 1, p. S193, 1995 Elsevier Science Ltd Printed in Great Britain 0021 8502/95 $9.50 + 0.00
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S P E C I A T I O N O F S U L F U R C O M P O U N D S IN I N D I V I D U A L A E R O S O L PARTICLES Kenneth R. Neubauer*, Murray V. Johnston*, and Anthony S. Wexler'~ *Department of Chemistry and Biochemistry, and tDepartment of Mechanical Engineering, University of Delaware, Newark, DE 19716, U.S.A. INTRODUCTION Sulfur aerosols play an important role in acid deposition and the earth's energy balance; important species include methanesulfonates, hydroxymethanesulfonates, sulfates, and sulfites. Because their presence and relative amounts indicate processes operating in the atmosphere, it is important to distinguish each class of compounds. To accomplish this task, we use rapid singleparticle mass spectrometry (RSMS), a technique which analyzes individual particles in an on-line mode. Particles are drawn into the source regio of a mass spectrometer through a differentially pumped nozzle which forms a particle beam and removes the gas. Particles are sequentially detected by light scattering of a helium-cadmium laser beam. A pulsed laser is then triggered which ablates and ionizes each particle in flight. Since individual particles are analyzed, particleto-particle composition variations can be assessed, and consequently their source. The rapid time between sampling and analysis, about 1 millisecond, minimizes particle composition changes due to condensation, evaporation, or chemical reactions. RESULTS Each compound can be identified on the basis of peak area ratios of sulfur-containing ions in the mass spectra. In simulated marine and urban aerosols the relative amounts of methansulfonic acid (MSA) and sodium hydroxymethanesulfonate (NaHMSA) in a single particle can be qualitatively determined by measuring peak area ratios. Improved quantitation is possible by application of the classification and regression tree (CART) algorithm to distinguish the mass spectra of particles having different compositions. Many factors must be taken into account when performing field measurements on ambient aerosols. These include particle size and morphology, laser fluence, and the physical distribution of components within a particle.
S193
Peroamon A m
S P E C I A T I O N O F S U L F U R C O M P O U N D S IN I N D I V I D U A L A E R O S O L PARTICLES Kenneth R. Neubauer*, Murray V. Johnston*, and Anthony S. Wexler'~ *Department of Chemistry and Biochemistry, and tDepartment of Mechanical Engineering, University of Delaware, Newark, DE 19716, U.S.A. INTRODUCTION Sulfur aerosols play an important role in acid deposition and the earth's energy balance; important species include methanesulfonates, hydroxymethanesulfonates, sulfates, and sulfites. Because their presence and relative amounts indicate processes operating in the atmosphere, it is important to distinguish each class of compounds. To accomplish this task, we use rapid singleparticle mass spectrometry (RSMS), a technique which analyzes individual particles in an on-line mode. Particles are drawn into the source regio of a mass spectrometer through a differentially pumped nozzle which forms a particle beam and removes the gas. Particles are sequentially detected by light scattering of a helium-cadmium laser beam. A pulsed laser is then triggered which ablates and ionizes each particle in flight. Since individual particles are analyzed, particleto-particle composition variations can be assessed, and consequently their source. The rapid time between sampling and analysis, about 1 millisecond, minimizes particle composition changes due to condensation, evaporation, or chemical reactions. RESULTS Each compound can be identified on the basis of peak area ratios of sulfur-containing ions in the mass spectra. In simulated marine and urban aerosols the relative amounts of methansulfonic acid (MSA) and sodium hydroxymethanesulfonate (NaHMSA) in a single particle can be qualitatively determined by measuring peak area ratios. Improved quantitation is possible by application of the classification and regression tree (CART) algorithm to distinguish the mass spectra of particles having different compositions. Many factors must be taken into account when performing field measurements on ambient aerosols. These include particle size and morphology, laser fluence, and the physical distribution of components within a particle.
S193