Observation of Chlorine Activation near the Midlatitude Tropopause
Abstract
It has been proposed that heterogeneous chlorine activation on cirrus cloud particles near the tropopause could provide a chemical explanation for ozone trends in the midlatitude tropopause region. During the 1998 WAM (WB-57 Aerosol Mission) campaign, an in situ ClO instrument was deployed on the NASA WB-57 aircraft in the midlatitudes. On the 11 April 1998 flight, clear examples of enhancements to reactive chlorine in sunlit, wet, particle laden air near the tropopause were observed over eastern Wyoming (approximately 42\deg N, 105\deg E) at 11-12 km. The air being sampled appeared to contain evaporating cirrus, and the observed chlorine enhancements (up to 20% activation) were strongly correlated with both particle surface area and total water. Ozone values in this enhanced ClO region ranged from 80-300 ppbv, consistent with both tropospheric and lowermost stratospheric air. These observations suggest that near tropopause reactive chlorine enhancements likely occur in regions of recent stratospheric-tropospheric exchange providing water and increased particle surface area to otherwise relatively dry stratospheric air. Due to greater insolation, ozone loss rates in this region may be higher than those previously reported for similar active chlorine abundances at similar altitudes in the Arctic.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.A14C..06T
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0305 Aerosols and particles (0345;
- 4801);
- 0317 Chemical kinetic and photochemical properties;
- 0320 Cloud physics and chemistry