Estimation of tropospheric column BrO and free tropospheric BrO concentrations using satellite measurements of total column BrO and cloud pressure from the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite

Bromine monoxide (BrO) is an intermediate chemical in a catalytic ozone loss cycle that occurs in the polar boundary layer during early spring. In addition, BrO alters oxidation pathways in the troposphere and removal processes of atmospheric trace species including mercury, dimethyl sulfide (DMS), and hydrocarbons at polar and lower latitudes. In the stratosphere, bromine species can cause ozone destruction. Atmospheric BrO can be observed with nadir-viewing space-based UV sensors. Recent studies suggest that regions of highly enhanced total column BrO retrieved by satellite instruments during Arctic spring can be caused by compression of stratospheric air to high pressure, as well as the traditional interpretation of surface release of bromine. We derive estimates of tropospheric BrO column amounts during April 2008 using total column BrO measurements from Ozone Monitoring Instrument (OMI) and the second Global Ozone Monitoring Experiment (GOME-2) and a stratospheric column BrO from a model simulation using assimilated winds and meteorlogical conditions. We conduct a comprehensive analysis of satellite-derived tropospheric columns BrO including a detailed comparison with aircraft in-situ observations of BrO and related species. Our result show reasonable agreement between tropospheric columns BrO derived from the satellite observations and columns calculated from aircraft in-situ BrO measurements. After accounting for stratospheric contribution to total column BrO, several events of rapid BrO activation due to surface processes in the Arctic are apparent in both of the OMI and GOME-2 based tropospheric columns. Previous ground-based and space-based studies also suggest the existence of ubiquitous free tropospheric BrO, although the estimated amounts vary. We derive free tropospheric BrO concentrations as well as stratospheric column amounts using cloud slicing, which referrs to quantification of the relationship between total column BrO and cloud pressure.