Se. Anthony et al., LABORATORY STUDIES OF TERNARY H2SO4 HNO3/H2O PARTICLES - IMPLICATIONSFOR POLAR STRATOSPHERIC CLOUD FORMATION/, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 102(D9), 1997, pp. 10777-10784
It has recently been suggested that type Ib polar stratospheric clouds
are composed of supercooled ternary-solutions of sulfuric acid (H2SO4
), nitric acid (HNO3), and water (H2O). We have studied the low-temper
ature behavior of ternary-solution aerosols to determine if they will
undergo homogeneous freezing nucleation under polar stratospheric cond
itions. Ternary-solution aerosols were injected into a low-temperature
chamber and observed for periods of up to 3 hours. Fourier transform
infrared spectroscopy was used to determine the aerosol composition an
d phase as a function of time. We found that ternary-solution aerosols
with compositions similar to those expected in the polar stratosphere
remained supercooled for the duration of our experiments. Homogeneous
freezing of the particles was never observed, even after warming from
190 to 204 K. However, heterogeneous freezing was occasionally observ
ed for particles adhering to the infrared optics within the chamber.