Evaluation of a particle trap laser desorption mass spectrometer (PT-LDMS) for the quantification of sulfate aerosols

Abstract

AbstractA particle trap laser desorption mass spectrometer (PT-LDMS) has been developed for the online measurements of the chemical composition of submicron aerosol particles. The PT-LDMS was evaluated by both laboratory and ambient measurements, with the focus being the quantification of sulfate aerosols. Ammonium sulfate ((NH4)2SO4) is generally the predominant form of sulfate aerosols in urban air; hence, it is used as a material for laboratory experiments and calibration. Major fragments of (NH4)2SO4 were observed at mass-to-charge ratios (m/z) of 48 (SO+) and 64 (SO2+). The dependence of sensitivity (expressed as the ratio of m/z 48 signal to sulfate mass) on laser power and cell temperature was investigated. An intercomparison of PT-LDMS with a commercial sulfate particle analyzer (SPA) and filter sampling was performed in Tokyo. Good agreement was observed between SPA and filter analysis (slope = 0.98, r2 = 0.99). Although the mass concentration of sulfate measured by PT-LDMS exhibited a tight corr...