Comparison of BrO observed by ground-based MAX-DOAS and satellite for Barrow, Alaska during ARCTAS, March and April 2008

Abstract

Bromine monoxide is episodically present at relatively high mixing ratio (tens of pptv) in the tropospheric boundary layer during “bromine explosion” events as well as having a more ubiquitous presence in the stratosphere. These tropospheric bromine events cause tropospheric ozone depletion events and are correlated to atmospheric mercury depletion episodes. Currently, satellite remote sensing (e.g. OMI) is employed to determine BrO vertical column densities, thus detecting bromine explosion events. However, it is critical to differentiate between high concentration of BrO in the boundary layer, which cause these dramatic chemical effects, and more diffuse layers of BrO above the boundary layer. Since the BrO abundance in the stratosphere and the rough vertical profile are typically less variable than the boundary layer component, we developed a proxy for non-boundary layer BrO using the column O3/column BrO relationship from a site in central Greenland (71.5°N, 40°W) at nearly the same latitude as Barrow, Alaska (71.4° N, 156.5° W). Implicit in this analysis is an assumption that central Greenland does not experience significant enhancements in boundary layer BrO. Applying this proxy at Barrow, using OMI-derived ozone column measurements, we derived a non-boundary layer BrO column density estimation, thus partitioning the BrO column density into a boundary layer and non-boundary layer components. We then compared the satellite-derived BrO column abundance to column abundances derived from boundary layer BrO observations (using MAXDOAS at Barrow, Alaska) plus the proxy non-boundary layer BrO column density. We find agreement within errors in this validation. However, an analysis of measurement errors indicates that only intense boundary layer events can be detected above the noise on a daily basis. Due to this noise, it is difficult to verify the accuracy of the non-boundary layer BrO removal method. By making improvements in radiation transfer models, increasing our understanding of the non-boundary layer BrO’s vertical profile and variability, and reducing the noise of the satellite retrieval, we will increase the accuracy of satellite-based BrO retrieval of boundary layer BrO event quantification.