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Temporal decrease in upper atmospheric chlorine
Author(s) -
Froidevaux L.,
Livesey N. J.,
Read W. G.,
Salawitch R. J.,
Waters J. W.,
Drouin B.,
MacKenzie I. A.,
Pumphrey H. C.,
Bernath P.,
Boone C.,
Nassar R.,
Montzka S.,
Elkins J.,
Cunnold D.,
Waugh D.
Publication year - 2006
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 - 10.1029/2006gl027600
Subject(s) - microwave limb sounder , chlorine , environmental science , hydrogen chloride , atmospheric sciences , ozone , context (archaeology) , stratosphere , ozone layer , satellite , atmosphere (unit) , atmospheric chemistry , climatology , meteorology , chemistry , geology , physics , organic chemistry , paleontology , astronomy
We report a steady decrease in the upper stratospheric and lower mesospheric abundances of hydrogen chloride (HCl) from August 2004 through January 2006, as measured by the Microwave Limb Sounder (MLS) aboard the Aura satellite. For 60°S to 60°N zonal means, the average yearly change in the 0.7 to 0.1 hPa (∼50 to 65 km) region is −27 ± 3 pptv/year, or −0.78 ± 0.08 percent/year. This is consistent with surface abundance decrease rates (about 6 to 7 years earlier) in chlorine source gases. The MLS data confirm that international agreements to reduce global emissions of ozone‐depleting industrial gases are leading to global decreases in the total gaseous chlorine burden. Tracking stratospheric HCl variations on a seasonal basis is now possible with MLS data. Inferred stratospheric total chlorine (Cl TOT ) has a value of 3.60 ppbv at the beginning of 2006, with a (2‐sigma) accuracy estimate of 7%; the stratospheric chlorine loading has decreased by about 43 pptv in the 18‐month period studied here. We discuss the MLS HCl measurements in the context of other satellite‐based HCl data, as well as expectations from surface chlorine data. A mean age of air of ∼ 5.5 years and an age spectrum width of 2 years or less provide a fairly good fit to the ensemble of measurements.