FTIR STUDIES OF LOW-TEMPERATURE SULFURIC-ACID AEROSOLS

Fourier transform infrared (FTIR) spectroscopy was used to study low t emperature sulfuric acid aerosols representative of global stratospher ic sulfate aerosols (SSAs). Sub-micrometer sized sulfuric acid (H2SO4) 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 funct ion of time for periods of up to 5 hours. Binary H2SO4/H2O aerosols wi th compositions from 35 to 95 wt % H2SO4 remained liquid for over 3 ho urs at temperatures ranging from 189-240 K. These results suggest that it is very difficult to freeze SSAs via homogeneous nucleation. Attem pts to form aerosols more dilute than 35 wt % H2SO4 resulted in ice fo rmation.