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A study of type I polar stratospheric cloud formation
Author(s) -
Tabazadeh A.,
Turco R. P.,
Drdla K.,
Jacobson M. Z.,
Toon O. B.
Publication year - 1994
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/94gl01368
Subject(s) - nucleation , nitric acid , sulfate , dissolution , ice nucleus , cloud condensation nuclei , condensation , supercooling , polar , aerosol , chemical physics , aqueous solution , chemistry , mineralogy , chemical engineering , materials science , inorganic chemistry , meteorology , organic chemistry , physics , astronomy , engineering
Mechanisms for the formation of Type I (nitric acid‐based) polar stratospheric clouds (PSCs) are discussed. If the pre‐existing sulfate aerosols are liquid prior to PSC formation, then nitric acid particles (Type Ib) form by HNO 3 dissolution in aqueous H 2 SO 4 solution droplets. This process does not require a nucleation step for the formation of HNO 3 aerosols, so most pre‐existing aerosols grow to become relatively small HNO 3 ‐containing particles. At significantly lower temperatures, the resulting supercooled solutions (Type Ib) may freeze to form HNO 3 ice particles (Type Ia). If the preexisting sulfate aerosols are initially solid before PSC formation, then HNO 3 vapor can be deposited directly on the frozen sulfate particles. However, because an energy barrier to the condensation exists a nucleation mechanism is involved. Here, we suggest a unique nucleation mechanism that involves formation of HNO 3 /H 2 O solutions on the sulfate ice particles. These nucleation processes may be highly selective, resulting in the formation of relatively small number of large particles.