Satellite-Based Emission Estimates of Arctic Bromine and Application
within GEOS-Chem
Abstract
During polar spring, periods of elevated tropospheric bromine known as
“bromine explosion events” are associated with near complete removal
of surface ozone. The satellite-based Ozone Monitoring Instrument (OMI)
provides total column measurements of bromine monoxide (BrO) with daily
global coverage. In this study, we estimate springtime bromine emissions
over the Arctic using OMI retrievals of BrO in combination with the
GEOS-Chem (version 12.0.1) chemical mechanism, run online within the
GEOS Earth System Model. Tropospheric hotspots of BrO are identified
over the Arctic where the difference between OMI and modeled columns of
BrO exceeds the bias observed over regions not impacted by bromine
explosion emissions. The resulting hotspot columns are a lower-limit
estimate for the portion of the OMI BrO signal attributable to bromine
explosion events and are well correlated with BrO measured in the lower
troposphere by buoy-based instruments. Daily flux of molecular bromine
is calculated from hotspot columns of BrO based on the modeled
atmospheric lifetime of inorganic bromine in the lower troposphere and
partitioning of bromine species into BrO at OMI overpass time. Following
the application of Arctic emissions in GEOS-Chem, OMI-based tropospheric
hotspots of BrO are successfully modeled for 2008 – 2012 and periods of
isolated, large (> 50%) decreases in surface ozone are
captured during April and May. While this technique does not fully
capture the low ozone observed at coastal stations, if a lower threshold
is used to identify tropospheric hotspots of BrO, the representation of
surface ozone in late spring is improved.