Chemical compositional bulk analysis of size-segregated aerosol particles using ATR-FTIR

초록

The bulk chemical composition of size-segregated aerosol particles can provide valuable insights into their reactivity, sources, and fate in the troposphere. In this work, aerosol samples were collected at the roof of a building in KRISS (Korea Research Institute of Standards and Science; 36.39˚N, 127.37˚E) located at Daejeon city, Korea, where industrial and anthropogenic activities are expected to mainly influence the chemical compositions of aerosol particles. Size-segregated aerosol particles were collected on Ag foil using a seven-stage May cascade impactor with aerodynamic cut-off diameters of 16, 8, 4, 2, 1, 0.5, and 0.25 μm for stages 1-7, respectively. The sampling duration for each stage was set differently to collect enough particles for bulk analysis using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) technique [1], [2], [3]. A Universal ATR single reflection accessory, comprising a diamond/KRS-5 internal reflection element (IRE) crystal with a diameter of 1.8 mm, installed in Perkin Elmer Spectrum 100 FTIR spectrometer, was used for the bulk analysis. A home-made curve-fitting program was utilized for deconvolution of asymmetric ATR-FTIR peaks in order to obtain areas of the characteristic IR peaks for relative quantitative analysis. Quantitative low-Z particle EPMA (energy dispersive electron probe X-ray microanalysis) provides complementary information on elemental concentrations, including IR inactive species such as NaCl [4]. For supermicron particles (stages 1?4), major chemical species are aluminosilicates, carbonates, and organics, while submicron particles (stages 5?7) are abundant with (NH4)2SO4, NH4NO3, and organics. The mixing ratios of chemicals varies with particle size and time. For example, for the submicron fraction, nitrate peak relative intensity increases during peak office hours, due to increased traffic emissions compared to other time in the day or night. Further analyses involving variation