Observations of supersaturated MgSO 4 and NaClO 4 aerosols by FTIR/ATR spectroscopy

Abstract

FTIR/ATR (attenuated total reflection) spectroscopy has been used to investigate supersaturated MgSO 4 and NaClO 4 aerosols. The experimental ATR spectra of MgSO 4 and NaClO 4 aerosols were found to show little disturbance from water vapor, and thus were always of high quality independent of relative humidity (RH). Some relatively weak absorbing bands, such as the v 1 and v 3 bands of SO 4 2− in supersaturated MgSO 4 aerosols and the v 1 band of ClO 4 − and the residual bands of the water O–H stretching envelope in supersaturated NaClO 4 aerosols, could be identified by their peak positions comparable with those obtained by other experimental methods. In contrast, the relatively strong absorbing v 3 band of ClO 4 − in supersaturated NaClO 4 aerosols could be distorted very seriously, so that quantitative analysis with regard to band shape and peak position should be avoided. The above observations for MgSO 4 and NaClO 4 aerosols by FTIR/ATR spectroscopy could be understood, primarily in terms of the effects on weak and strong absorbing bands of anomalous dispersion and penetration depth ( d p) dependence on wavelength ( λ) inherent in FTIR/ATR technique. Though rather limited in straightforward spectral analysis, the experimental high quality ATR spectra obtained under given conditions may be used to derive the optical constants of supersaturated aerosols.