Experimental investigation of homogeneous freezing of sulphuric acid particles in the aerosol chamber AIDA

[摘要] The homogeneous freezing of supercooledH₂SO₄/H₂O solution droplets was investigated in the aerosol chamber AIDA(Aerosol Interactions and Dynamics in the Atmosphere) of ForschungszentrumKarlsruhe. 24 freezing experiments were performed at temperatures between189 and 235 K with aerosol particles in the diameter range 0.05 to 1 µm. Individual experiments started at homogeneous temperatures andice saturation ratios between 0.9 and 0.95. Cloud cooling rates up to -2.8K min^-1 were simulated dynamically in the chamber by expansion cooling using a mechanical pump. Depending onthe cooling rate and starting temperature, freezing threshold relative humidities were exceeded after expansion time periodsbetween about 1 and 10 min. The onset of ice formation was measured with three independent methods showing good agreementamong each other. Ice saturation ratios measured at the onset of ice formation increased from about1.4 at 231 Kto about 1.75 at 189 K. The experimental data set includingthermodynamic parameters as well as physical and chemical aerosol analysis provides a good basis for microphysical model applications.

[学科分类] 大气科学