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Coupled evolution of BrOx-ClOx-HOx-NOx chemistry during bromine-catalyzed ozone depletion events in the arctic boundary layer

  • Author(s): Evans, MJ
  • Jacob, DJ
  • Atlas, E
  • Cantrell, CA
  • Eisele, F
  • Flocke, F
  • Fried, A
  • Mauldin, RL
  • Ridley, BA
  • Wert, B
  • Talbot, R
  • Blake, D
  • Heikes, B
  • Snow, J
  • Walega, J
  • Weinheimer, AJ
  • Dibb, J
  • et al.
Abstract

Extensive chemical characterization of ozone (O ) depletion events in the Arctic boundary layer during the TOPSE aircraft mission in March-May 2000 enables analysis of the coupled chemical evolution of bromine (BrO ), chlorine (ClO ), hydrogen oxide (HO ) and nitrogen oxide (NO ) radicals during these events. We project the TOPSE observations onto an O chemical coordinate to construct a chronology of radical chemistry during O depletion events, and we compare this chronology to results from a photochemical model simulation. Comparison of observed trends in ethyne (oxidized by Br) and ethane (oxidized by Cl) indicates that ClO chemistry is only active during the early stage Of O depletion (O > 10 ppbv). We attribute this result to the suppression of BrCl regeneration as O decreases. Formaldehyde and peroxy radical concentrations decline by factors of 4 and 2 respectively during O depletion and we explain both trends on the basis of the reaction of CH O with Br. Observed NO concentrations decline abruptly in the early stages Of O depletion and recover as O drops below 10 ppbv. We attribute the initial decline to BrNO hydrolysis in aerosol, and the subsequent recovery to suppression of BrNO formation as O drops. Under halogen-free conditions we find that HNO heterogeneous chemistry could provide a major NO sink not included in standard models. Halogen radical chemistry in the model can produce under realistic conditions an oscillatory system with a period of 3 days, which we believe is the fastest oscillation ever reported for a chemical system in the atmosphere. 3 x x x x 3 3 x 3 3 3 3 2 x 3 3 3 3 3 4 x

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