BrO Retrievals Using TROPOMI on Sentinel-5 Precursor and Comparison with Independent Satellites and Ground-based Measurements

Bromine compounds play an important role in atmospheric chemistry in particular as a catalytic element in destroying ozone with high efficiency. Due to their effect on the oxidizing capacity of the atmosphere, global distributions of bromine monoxide (BrO) have been monitored by satellites since the launch in 1995 of the GOME. Satellite BrO observations have shown huge areas of elevated BrO covering several thousand km² over the Arctic and Antarctic sea ice region in polar spring. The Sentinel-5 Precursor satellite which was launched in October 2017 provides daily global coverage as the predecessor instruments, but with its unprecedented high spatial resolution (3.5x7 km²), this instrument enables to detect spatial variations and small-scale emission sources in more detail.

In this study, we present the total and tropospheric BrO columns retrieved from TROPOMI data and comparisons with data from other satellites and ground-based measurements. DOAS settings optimized for TROPOMI BrO retrieval were determined based on sensitivity tests for various measurement scenarios. Also, approaches for the stratospheric correction to separate the tropospheric partial columns from total BrO columns are tested using several different methods. The TROPOMI BrO retrieval algorithm is verified by comparing satellite BrO columns with ground-based MAX-DOAS measurements at the NDSC station in Ny-Ålesund, Svalbard. Comparisons of TROPOMI BrO columns with other satellites (i.e. OMI and GOME-2B/C) and ground-based measurements for the Arctic BrO explosion event show a good consistency and accuracy, and moreover, capabilities of TROPOMI to investigate small-scale halogen chemistry.