Abstract
Abstract. The stratospheric inorganic bromine (Bry) burden arising from the degradation of brominated very short-lived organic substances (VSLorg) and its partitioning between reactive and reservoir species is needed for a comprehensive assessment of the ozone depletion potential of brominated trace gases. Here we present modeled inorganic bromine abundances over the Pacific tropical tropopause based on aircraft observations of VSLorg from two campaigns of the Airborne Tropical TRopopause EXperiment (ATTREX 2013, carried out over the eastern Pacific, and ATTREX 2014, carried out over the western Pacific) and chemistry-climate simulations (along ATTREX flight tracks) using the specific meteorology prevailing. Using the Community Atmosphere Model with Chemistry (CAM-Chem) we model that BrO and Br are the daytime dominant species. Integrated across all ATTREX flights, BrO represents ∼ 43 and 48 % of daytime Bry abundance at 17 km over the western and eastern Pacific, respectively. The results also show zones where Br / BrO > 1 depending on the solar zenith angle (SZA), ozone concentration, and temperature. On the other hand, BrCl and BrONO2 were found to be the dominant nighttime species with ∼ 61 and 56 % of abundance at 17 km over the western and eastern Pacific, respectively. The western-to-eastern differences in the partitioning of inorganic bromine are explained by different abundances of ozone (O3), nitrogen dioxide (NO2), total inorganic chlorine (Cly), and the efficiency of heterogeneous reactions of bromine reservoirs (mostly BrONO2 and HBr) occurring on ice crystals.
Highlights
The role of bromine in stratospheric ozone depletion has been discussed in several studies (Brinckmann et al, 2012; Daniel et al, 1999; Fernandez et al, 2017; Hossaini et al, 2015; Prather and Watson, 1990; Salawitch et al, 2005; Sinnhuber et al, 2009; Wofsy et al, 1975)
The reaction mechanisms of very short-lived organic substances (VSLorg) that lead to the formation of inorganic bromine (Bry) involve complex sets of reactions that have been described in previous modeling studies (Krysztofiak et al, 2012; Ordóñez et al, 2012; Hossaini et al, 2010)
Once the model performance during the Airborne Tropical TRopopause EXperiment (ATTREX) campaign is evaluated in Sect. 3.1, we proceed to the Community Atmospheric Model with Chemistry (CAMChem) modeling case study to determine the Bry partitioning (Sect. 3.2) and efficiency of heterogeneous recycling reactions (Sect. 3.3) on the mostly unexplored eastern and western Pacific tropical tropopause layer (TTL)
Summary
The role of bromine in stratospheric ozone depletion has been discussed in several studies (Brinckmann et al, 2012; Daniel et al, 1999; Fernandez et al, 2017; Hossaini et al, 2015; Prather and Watson, 1990; Salawitch et al, 2005; Sinnhuber et al, 2009; Wofsy et al, 1975) Many of these discuss the contribution of brominated very short-lived organic substances (VSLorg) like bromoform (CHBr3), dibromomethane (CH2Br2), bromochloromethane (CH2BrCl), dibromochloromethane (CHBr2Cl), and bromodichloromethane (CHBrCl2), in addition to long-lived halons and methyl bromide, as an important source of stratospheric bromine. Navarro et al.: Modeling the inorganic bromine partitioning in the tropical tropopause layer cals The fate of these radicals, and their mechanisms of reaction, is controlled by NOx conditions and OH levels. In “clean” environments (low-NOx regime), the radicals undergo a series of cross reactions (including reaction with HO2) leading to the formation of several different products that can continue reacting with OH (or Cl), washout, or photodissociate to form Bry species as the end product (Krysztofiak et al, 2012)
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