Open AccessThe nucleation rate constants and freezing mechanism of nitric acid trihydrate aerosol under stratospheric conditions
Author(s) -
Bertram A. K.,
Sloan J. J.
Publication year - 1998
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/98jd00921
Subject(s) - nucleation , aerosol , crystallization , materials science , extinction (optical mineralogy) , stratosphere , nitric acid , atmospheric temperature range , ice nucleus , analytical chemistry (journal) , chemistry , mineralogy , atmospheric sciences , thermodynamics , chromatography , geology , organic chemistry , physics , metallurgy
The nucleation rates for submicron‐diameter nitric acid trihydrate (NAT) aerosol particles were measured under stratospheric conditions using a temperature‐programed flow tube and Fourier transform infrared extinction spectroscopy to detect the phase change from liquid to solid. The temperature range from 175 to 155 K was examined. The measured nucleation rate constants (in units of cm −3 s −1 ) are between 3.8±1.8 × 10 10 and 9.7±6.3 × 10 12 for the temperature range between 167.2 and 163.5 K. The experiments show directly that critical nuclei form rapidly in NAT droplets at these temperatures, but subsequent crystallization is very slow, so the nucleated droplets can persist as liquids for long times unless their temperature is raised to increase the crystal growth rate. In these experiments, complete crystallization of the nucleated droplets was achieved in the observation time (about 10 s) by raising their temperature to near 180 K. Although demonstrable in the laboratory, the freezing of NAT by homogeneous nucleation at low temperature and subsequent warming are unlikely to be important for type 1 polar stratospheric cloud formation because the temperatures required for nucleation are lower than those commonly found in the lower stratosphere.