A THERMO OPTIC TECHNIQUE FOR INSITU ANALYSIS OF SIZE-RESOLVED AEROSOL PHYSICOCHEMISTRY

A computer driven heater assembly has been combined with a custom laser aerosol spectrometer to provide continuous data on aerosol volatility for particle diameters from 0.14 to 7.0-mu-m. The size distributions at temperatures of 40-degrees-C, 150-degrees-C and 350-degrees-C are accumulatef for 'dried' aerosol. This allows quantitative intercomparisons of aerosol properties be made independent of variability in ambient relative humidity. Laboratory calibrations for various sulfate species have been used to interpret the resulting fine particle volatility data in terms of sulfate mass and composition. In remote regions where sulfate is known to dominate fine particle mass, our real-time results for the total sulfate mass and the inferred NH4+/SO4(2-) molar ratios compare favorably with concurrent data obtained from filter analysis. Inclusion of a virtual impactor in the sampling system improved coarse particle count statistics and made it possible to obtain representative size distributions during airborne sampling in about one tenth of the time normally required. Unique software features also allow direct assessment of derived aerosol properties.