Open AccessComposition‐dependent freezing nucleation rates for HNO 3 /H 2 O aerosols resembling gravity‐wave‐perturbed stratospheric particles
Author(s) -
Prenni Anthony J.,
Onasch Timothy B.,
Tisdale Robert T.,
Siefert Ronald L.,
Tolbert Margaret A.
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 - 10.1029/98jd02851
Subject(s) - nucleation , aerosol , analytical chemistry (journal) , atmospheric temperature range , melting point , diffusion , reaction rate constant , chemistry , materials science , thermodynamics , mineralogy , kinetics , chromatography , physics , organic chemistry , quantum mechanics
Laboratory measurements are presented for the freezing kinetics of H 2 O/HNO 3 aerosols over the temperature range of 188–204 K. For 2:1 H 2 O:HNO 3 aerosols crystallizing to NAD we observed a maximum nucleation rate of J = 9.3×10 9 cm −3 s −1 at 194 K. This temperature is between the glass point of 161 K [ Ji et al ., 1993] and the melting point of 235.5 K [ Ji et al ., 1996]. This can be compared to a previous measurement of J = 6.7×10 9 cm −3 s −1 at 193 K [ Disselkamp et al ., 1996] and lower temperature measurements of J ≈ 10 10 –10 12 cm −3 s −1 at 178.8 ‐ 175.8 K [ Bertram and Sloan , 1998a]. Measured nucleation rates decrease as the aerosol becomes dilute, but NAD formation is still observable for 2.5:1 H 2 O:HNO 3 at temperatures near 195 K. In contrast, freezing of 3:1 H 2 O:HNO 3 aerosol was not observed for constant temperature experiments throughout this temperature range, yielding an upper limit of J <1.5×10 9 cm −3 s −1 . This is the lowest experimental value determined for 3:1 H 2 O:HNO 3 freezing rates at these temperatures. From the measured freezing rates and knowledge of the free energy of diffusion the average interfacial free energy for NAD in a 2:1 H 2 O:HNO 3 solution was determined to be σ = 25.2 ergs cm −2 . A limit for the interfacial free energy was placed on 3:1 H 2 O:HNO 3 particles, for which freezing was not observed. These data imply that if aerosols reach compositions more concentrated than 3:1 H 2 O:HNO 3 in the atmosphere, NAD may play a role in polar stratospheric cloud formation.