Hydrochloric acid and the chlorine budget of the lower stratosphere
- Jet Propulsion Lab., Pasadena, CA (United States)
- California Institute of Technology, Pasadena, CA (United States)
- Harvard Univ., Cambridge, MA (United States)
- and others
Concentrations of HCl measured in the lower stratosphere in 1993 by the ALIAS instrument on the ER-2 aircraft reveal that only 40% of inorganic chlorine (Cl{sub y}, inferred from in situ measurements of organic chlorinated source gases) is present as HCl, significantly lower than model predictions. Although the sum of measured HCl, ClO, and ClONO{sub 2}, the latter inferred from measurements of ClO and NO{sub 2}, equals Cl{sub y} to within the uncertainty of measurement, it is systematically less than Cl{sub y} by 30-50%. This discrepancy suggests that concentrations of ClONO{sub 2} may exceed those of HCl near 20 km altitude, consistent with a slower photolysis rate for ClONO{sub 2} than calculated using recommended cross sections. Comparison of profiles of HCl measured during 1992 and 1993 at mid-latitudes by balloon (BLISS and MARKIV), space shuttle (ATMOS), and satellite (HALOE) instruments with the aircraft data reveal an apparent pressure dependence to the HCl to Cl{sub y} ratio, consistent with a factor of 3-10 reduction in the photolysis rate for ClONO{sub 2} at ER-2 altitudes. However, the diurnal variation of ClO is well-simulated by models using the recommended photolysis rate, and simultaneous measurements of ClONO{sub 2} and HCl at mid-latitudes by ATMOS and MARKIV report HCl/(HCl + ClONO{sub 2}) ratios {ge} 50%. Preliminary measurements by ALIAS in the southern hemisphere report HCl/Cl{sub y} values of about 75%. It is unclear to what extent elevated aerosol surface area, uncertainties in the estimation of Cl{sub y} or in the photolysis rates, or missing reactive pathways contribute to the inability to balance the budget of inorganic chlorine using the aircraft measurements. 20 refs., 3 figs., 1 tab.
- OSTI ID:
- 57039
- Journal Information:
- Geophysical Research Letters, Journal Name: Geophysical Research Letters Journal Issue: 23 Vol. 21; ISSN GPRLAJ; ISSN 0094-8276
- Country of Publication:
- United States
- Language:
- English
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