BrO retrievals from the Geostationary Environment Monitoring Spectrometer: Early results

Abstract

The Geostationary Environment Monitoring Spectrometer (GEMS), launched in February 2020, is a spaceborne spectrometer providing hourly measurements of hyperspectral ultraviolet-visible radiances for the first time from space. This study presents early results of retrieving bromine monoxide (BrO) columns from GEMS measurements. The retrieval algorithm is based on the direct fitting method developed in the Smithsonian Astrophysical Observatory (SAO). We optimize the spectral fit by examining biases in slant column densities (SCDs), SCD uncertainties, fitting residuals, and correlations between fitting parameters obtained by different fitting windows. The optimized retrievals represent the diurnal variability of BrO columns over Asia, which has not been observed from space so far. Considering the role of halogens in the tropospheric ozone chemistry, we expect the GEMS BrO retrievals will contribute to a better understanding of ozone pollution in Asia. Besides, we demonstrate that GEMS observed enhancement of BrO columns over the Nishinoshima volcano in Japan during its eruption in August 2020. These results imply that the GEMS BrO product will also contribute to the investigation of volcanic activities in Asia, especially through the synergistic use with the GEMS SO2 product.