Impact of Arctic boundary layer BrOx chemistry on NOx concentrations

The figure shows the observed (in Red) relationship between NOx and O3 during Br catalysed O3 depeletions events in the Arctic.  The measurements were made during the TOPSE program and show a marked depletion in NOx at moderate concentrations of O3 and a subsequent recovery at lower concentration.  Box model simulations (in Black) reproduce this feature and attribute the initial loss of NOx to uptake of BrNO3 by aerosols.  As O3 concentrations drop further the concentration of BrNO3 also drops resulting in a reduction of the magnitude of the NOx sink.  A surface NOx emission leads to NOx concentrations recovering at very low O3 concentration.  More information about this work can be found in [Evans et al., 2002]