Fourier Transform Infrared Spectroscopy of Aerosol Collected in a Low Pressure Impactor (LPI/FTIR): Method Development and Field Calibration

A method for determining the loadings of organic and inorganic functional groups in size segregated ambient aerosol has been developed and demonstrated. The method uses a Hering Low Pressure Impactor (LPI), equipped with ZnSe impaction surfaces, to sample the aerosol. The aerosol samples are analyzed directly, without extraction, using transmission infrared spectroscopy. The resulting spectra of aerosol size fractions are used to determine loadings of sulfate ion, nitrate ion, aliphatic carbon, carbonyl and organonitrate groups, using calibration factors developed in field and model compound studies. This paper describes, in detail, the data interpretation and calibration methods used to obtain these functional group loadings from the infrared spectra. The functional group loadings, particularly the size distributions of organic compound classes, provide new insights into the composition of atmospheric aerosol.