Open AccessEvolution and stoichiometry of heterogeneous processing in the Antarctic stratosphere
Author(s) -
Jaeglé L.,
Webster C. R.,
May R. D.,
Scott D. C.,
Stimpfle R. M.,
Kohn D. W.,
Wennberg P. O.,
Hanisco T. F.,
Cohen R. C.,
Proffitt M. H.,
Kelly K. K.,
Elkins J.,
Baumgardner D.,
Dye J. E.,
Wilson J. C.,
Pueschel R. F.,
Chan K. R.,
Salawitch R. J.,
Tuck A. F.,
Hovde S. J.,
Yung Y. L.
Publication year - 1997
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 - 10.1029/97jd00935
Subject(s) - stratosphere , chlorine , ozone , hydrochloric acid , sulfate , polar vortex , atmospheric chemistry , sulfate aerosol , atmospheric sciences , troposphere , aerosol , plume , trace gas , southern hemisphere , box model , stoichiometry , chemistry , climatology , geology , inorganic chemistry , meteorology , physics , organic chemistry
Simultaneous in situ measurements of HCl and ClO have been made for the first time in the southern hemisphere, allowing a systematic study of the processes governing chlorine activation between 15 and 20 km in the 1994 Antarctic winter. Data for several other gases (O 3 , NO, NO y , OH, HO 2 , N 2 O, CH 4 , CO, H 2 O, CFCs), particulates, and meteorological parameters were collected from the ER‐2 aircraft out of New Zealand as part of the 1994 Airborne Southern Hemisphere Ozone Experiment/Measurements of Atmospheric Effects of Stratospheric Aircraft (ASHOE/MAESA) campaign. Observations from the ER‐2 in the fall (April–May), prior to polar night, show that chlorine activation begins with 60–75% of inorganic chlorine as HCl. By midwinter (July–August), near‐total removal of HCl is observed. The wintertime loss of HCl in air recently exposed to extreme temperatures is found to be correlated with high levels of reactive chlorine (ClO and its dimer, Cl 2 O 2 ) in the linear fashion expected from the stoichiometry of the heterogeneous reaction of hydrochloric acid with chlorine nitrate on polar stratospheric clouds (PSCs): HCl + ClONO 2 → Cl 2 + HNO 3 . To constrain the role of different heterogeneous reactions and PSC types, we have used a photochemical trajectory model which includes heterogeneous sulfate and PSC chemistry. Model calculations of the evolution of reactive gases are compared with the in situ observations. In addition, simultaneous measurements of OH and HO 2 are used as a diagnostic for the occurrence of the heterogeneous reaction HOCl + HCl → Cl 2 + H 2 O, which contributes to suppressed levels of HO x inside the vortex. It is shown that the amount of chlorine activation is not strongly dependent on the composition of PSCs. However, HO x levels exhibit different signatures depending on the type of heterogeneous surfaces that affected chlorine activation. Furthermore, this analysis implies that in the edge region of the Antarctic vortex, the observed near‐total removal of HCl can result from latitudinal excursions of air parcels in and out of sunlight during the winter, which photochemically resupply HOCl and ClONO 2 as oxidation partners for HCl.