Infrared Spectroscopy of Size Resolved Fine Aerosol

This dissertation describes the development and implementation of a new analytical technique for atmospheric aerosols based on infrared spectroscopy. In this technique, aerosols are size segregated and collected using a low pressure impactor (LPI) equipped with ZnSe impaction surfaces, which are transparent to infrared radiation. The LPI samples at a flowrate of 1 L/min, and collects 8 size fractions with aerodynamic diameter cut points of 4.0, 2.0, 1.0, 0.5, 0.26, 0.12, 0.075 and 0.05 mum. Samples are analyzed using transmission Fourier Transform Infrared (FTIR) spectroscopy or microscopy over the spectrum 4000 -575 cm^{-1} (2.5-17.4 μm). Detection limits for each size fraction are as low as 10 picograms. Infrared absorption spectra of ambient urban aerosol contain absorptions due to sulfate, bisulfate, nitrate, ammonium and silicate ions. Organic absorptions due to aliphatic carbon, carbonyl carbons and organonitrates are also observed. Atmospheric loadings of these functional groups are estimated from the infrared absorbance areas based on model compound and field calibrations. Field calibration data were collected during the 1987 Southern California Air Quality Study (SCAQS). Intermethod comparisons were made using SCAQS data. Characteristic loadings and mass size distributions of sulfate ions, bisulfate ions, nitrate ions, aliphatic carbon, carbonyl carbons and organonitrates in Southern California ambient aerosol are reported in this thesis. It is shown that infrared active functional groups account for the majority of the mass present in ambient aerosols. The LPI-FTIR technique can also be applied in the analysis of aerosol generated in smog chamber studies. In separate experiments 1-octene, isoprene and beta -pinene were photooxidized in a flexible outdoor smog chamber. Initial hydrocarbon concentrations ranged from 0.34-20.0 ppm. Hydrocarbon to NO_ {X} ratios ranged from 2.0-10.5. Aerosols were again size segregated and collected using LPIs with ZnSe impaction surfaces for direct analysis. The mole fractions of aliphatic carbon, ketones, aldehydes, carboxylic acids, alcohols and organonitrates in the photooxidation aerosol were quantified. Molecular weights and molecular structures were estimated.