Development of diffuse reflectance infrared Fourier transform spectroscopy for the rapid characterization of aerosols

In this study, the viability of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) for quantitative analysis of atmospheric aerosols is assessed. DRIFTS-derived absorption frequencies of the functional groups contained in aerosols are calibrated using ion chromatography (IC) and the calibrated concentrations are applied in an analysis of the major salt species contained in aerosols of various diameters collected in the city of Tainan in southern Taiwan. We found that the average discrepancy between measurements of SO42−, NH4+ and NO3− content from IC and DRIFTS was always <2% (1.21% for SO42−, 0.41% for NH4+, and 0.61% for NO3−), indicating that these two methods yield similar results and thus demonstrating that DRIFTS is a practical method for measuring these inorganic salts in aerosols. Results of the DRIFTS measurements indicate that the wavenumber absorbed by SO42− changes with increasing or decreasing SO32−, demonstrating that SO42− is formed from SO32− via SO2. Additionally, (NH4)2SO4 and NH4NO3, distributed in 0.10–0.32 μm (condensation mode) and 0.56–1.8 μm (droplet mode) particles, are shown to be the combination forms of secondary aerosols in the study area.