HR: 1340h
AN: A13D-0960    [Abstracts]
TI: Chlorine Recovery and the Role of Bromine: New Lessons
AU: * Wilmouth, D M
EM: wilmouth@huarp.harvard.edu
AF: Harvard University, Department of Chemistry and Chemical Biology, Cambridge, MA 02138 United States
AU: Stimpfle, R M
EM: stimpfle@huarp.harvard.edu
AF: Harvard University, Department of Chemistry and Chemical Biology, Cambridge, MA 02138 United States
AU: Anderson, J G
EM: anderson@huarp.harvard.edu
AF: Harvard University, Department of Chemistry and Chemical Biology, Cambridge, MA 02138 United States
AB: The first simultaneous, in situ atmospheric measurements of ClO, ClOOCl, ClONO₂, and HCl, which together nearly comprise total inorganic chlorine, Cl_y, were obtained using the NASA ER-2 aircraft, deployed from Kiruna, Sweden, during the SOLVE/THESEO mission. These chlorine measurements, along with Cl_y inferred from in situ measurements of organic chlorine source gases, enable an examination of chlorine activation and recovery during a polar winter to an extent not previously possible. Moreover, this suite of measurements enables the first evaluation of the inorganic chlorine budget in the polar winter stratosphere, i.e., a test of the quantitative agreement between the sum of ClO_x (ClO + 2×ClOOCl), ClONO₂, and HCl with inferred Cl_y. Analysis of the late winter inorganic chlorine budget indicates that the budget does not agree for the majority of the data. This discrepancy is likely the result of an error in the ClONO₂ and/or HCl measurement. Whenever the reservoir species comprise a more significant fraction of Cl_y, e.g., outside the Arctic vortex versus inside, the budget agreement is worse. Calculations of ClONO₂ from a photochemical steady-state expression agree well with the measured values, implying that the budget discrepancy is due to the HCl measurements being biased low. A diurnal box model constructed to analyze chlorine recovery rates supports this result. For any realistic photochemical mechanism of HCl production, significant HCl formation necessarily accompanies net ClONO₂ production. This is in stark contrast to the historic paradigm of the vortex recovering preferentially into ClONO₂ before significant HCl production [e.g., Figure 3.1, WMO, 1995]. Moreover, recent results from the SOLVE/THESEO mission indicate that inorganic bromine levels are 3-4 ppt higher than Br_y inferred from organic bromine measurements. This suggests that the inorganic bromine values used in ozone trend assessments may not be valid, consistent with the recent work of Salawitch et al. [ GRL, 2005].
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0340 Middle atmosphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005