| Abstract
| - The performance of the real-time single-particle massspectrometer RSMS III is evaluated for ambient fine andultrafine particle number concentration measurements. TheRSMS III couples aerodynamic size selection with laserablation time-of-flight mass spectrometry for single-particleanalysis. It was deployed at the Baltimore particulatematter Supersite for semi-continuous operation over an8-month period. The sampling protocol adopted for this studypermitted the analysis of on average 2000 particles perday. The number of particles analyzed is a tradeoff betweengenerating a statistically significant data set andmaintaining instrument operation over a long period oftime. The optimum particle size range of analysis was foundto be ca. 50−770 nm in diameter, although particles assmall as 45 nm and as large as 1250 nm were also analyzed.While nitrate, sulfate, and carbon (elemental and organic)were found to dominate the ambient aerosol, over 10%of the detected particles contained transition and/or heavymetals. The (size-dependent) detection efficiency, definedas the fraction of particles entering the inlet that areanalyzed, was determined by comparison with scanningmobility particle sizing data. Using the experimentallydetermined detection efficiencies, particle numberconcentrations of specific chemical components wereestimated. While the sampling protocol allowed the particleconcentrations of major chemical components to befollowed as a function of both time and particle size, minorcomponents required averaging over time and/or size toachieve adequate precision.
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