FTIR double-pass transmittance spectroscopy of size-segregated aerosol deposits

A method based on Fourier transform infrared (FTIR) double-pass transmittance spectroscopy was developed for determining functional group loading in size-segregated ambient aerosol deposits. Atmospheric particulate matter (PM) was sampled during the summer of 2004 in Huntsville, AL, with a rotating-stage Micro-Orifice Uniform Deposit Impactor (MOUDI) equipped with aluminum foil substrates. Each sample was analyzed without extraction using an FTIR spectrometer and a Seagull reflectance accessory. For calibration, solutions of pure ammonium sulfate of varying concentrations were prepared and aerosolized. The resulting PM was collected by the MOUDI and analyzed by the FTIR as the PM from the ambient samples was. The PM from these solutions was also analyzed gravimetrically to establish a relationship between analyte mass and area of the corresponding absorption band. This relationship was used to calculate the mass of the sulfate fraction of the ambient aerosol deposits using the relatively isolated feature at 570-640cm-1.