Atmospheric reactive chlorine and bromine at the Great Salt Lake, Utah

Abstract

The presence of chlorine radical species in the lower troposphere has been postulated, but only indirect evidence of its existence has been reported. We present the first direct spectroscopic observations of up to 15 ± 2 pmoles/mole‐air chlorine oxide (ClO) in the mid‐latitude boundary layer and confirm a previous discovery of the existence of bromine oxide (up to 6 ± 0.4 pmoles/mole‐air BrO). Our observations from October 2000 suggest that reactive halogens are mobilized from salt on the flats around the Great Salt Lake, Utah. The results imply levels of 105 Cl atoms per cm3, which doubles the atmospheric oxidation capacity. Ozone concentrations are anti‐correlated with the halogen oxide levels, particularly BrO, indicating that ozone depletion by catalytic reaction cycles may have occurred. If the mobilization of halogens from salt flats that was observed here is widespread, there are important implications for atmospheric chemistry and the biogeochemical cycling of mercury.

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…Large concentrations of bromine and iodine (up to 200 ppt of BrO -Tas et al, 2005, and up to 10 ppt of IO -Zingler and Platt, 2005) have been reported over the Dead Sea (Israel) causing O 3 as low as 2 ppb; however, observations in other locations have shown much lower values (e.g. 6 ppt of BrO and 15 ppt of ClO over the Great Salt Lake; Stutz et al, 2002). The database of observations is very sparse and shows large variability between different locations, suggesting that the local characteristics (e.g.…”

Gas-phase radical chemistry in the troposphere

“…24). 60 The authors speculate that the chlorine has been mobilised by heterogeneous reactions from the high molality salt solutions or crystalline salt on the flats, this likely to be the by-product of the bromine explosion mechanism (cf. reaction (67) b) The HO 2 to OH ratio can be changed via reactions 65 and 66.…”

“…The [X]/[XO] ratio is largely determined by a combination of the reactions (56), (57), (59), (60). At any given time ,0.1% for Cl, 0.1 to 1% for Br and several 10% for I will be present in the form of a halogen atom.…”

“…e) Bromine catalysed chlorine activation has the potential to enhance the tropospheric oxidation capacity. 60 f) Reactive bromine could be responsible for upper tropospheric ozone loss. 54 g) The deposition rate of Hg may be enhanced by the presence of bromine species.…”

Impact of reactive bromine chemistry in the troposphere

“…von Glasow and Crutzen (2003) for an overview). BrO has been found in the boundary layer during polar ozone depletion events (ODEs) (Hausmann and Platt, 1994), over salt lakes Stutz et al, 2002;Hönninger et al, 2004), and in the marine boundary layer (MBL) (Leser et al, 2003;Saiz-Lopez et al, 2004) and also in volcanic plumes (Bobrowski et al (2003), N. Bobrowski, pers. comm.).…”