FREEZING BEHAVIOR OF SINGLE SULFURIC-ACID AEROSOLS SUSPENDED IN A QUADRUPOLE TRAP

The freezing properties of sulfuric acid droplets were studied by susp ending single 20- to 30-mu m-diameter particles in a quadrupole trap a nd cooling them to stratospheric temperatures (greater than or equal t o 191.5 K). Each particle's de balance voltage was measured to determi ne the particle composition as a function of temperature and map out t he particle's trajectory relative to the sulfuric acid phase diagram. Angularly resolved optical scattering patterns were monitored to detec t freezing events. Particles cooled through the sulfuric acid tetrahyd rate region (35-70 wt % H2SO4) did not freeze and remained spherical l iquid droplets for several hours. Only particles cooled through the ic e-liquid equilibrium region (<35 wt % H2SO4) showed evidence of freezi ng. This supports previous experimental and field observations that st ratospheric sulfuric acid aerosols are likely to remain liquid to with in a few degrees of the ice frost point.