FTIR studies of low temperature sulfuric acid aerosols

Abstract

Fourier transform infrared (FTIR) spectroscopy was used to study low temperature sulfuric acid aerosols representative of global stratospheric sulfate aerosols (SSAs). Sub‐micrometer sized sulfuric acid (H 2 SO 4 ) particles were generated using a constant output atomizer source. The particles were then exposed to water vapor before being injected into a low temperature cell. Multipass transmission FTIR spectroscopy was used to determine the phase and composition of the aerosols as a function of time for periods of up to 5 hours. Binary H 2 SO 4 /H 2 O aerosols with compositions from 35 to 95 wt % H 2 SO 4 remained liquid for over 3 hours at temperatures ranging from 189–240 K. These results suggest that it is very difficult to freeze SSAs via homogeneous nucleation. Attempts to form aerosols more dilute than 35 wt % H 2 SO 4 resulted in ice formation.