An improved OClO retrieval from TROPOMI observations

Abstract

Understanding stratospheric ozone depletion and recovery is crucial for atmospheric science. Ozone shields Earth from harmful UV radiation and influences atmospheric chemistry and global warming. Depletion rates are influenced by chlorine, bromine, nitrogen, and hydrogen oxides, particularly in Polar Regions with low temperatures favoring chlorine activation. Chlorine oxide (OClO) serves as a valuable indicator for chlorine activation, although it does not directly contribute to ozone destruction. The ClO-BrO cycle catalyzes ozone destruction, leading to the formation of the ozone hole over polar regions. While OClO is primarily found within the Polar Vortex during winter and spring, current models often underestimate its levels under certain conditions. This highlights the need for improved measurement and modeling accuracy. OClO columns can be determined through remote sensing by the Differential Optical Absorption Spectroscopy (DOAS) method. This sensitive technique has been utilized from ground and satellite platforms. Global OClO has been retrieved from various satellite instruments, including SCIAMACHY, GOME-2, OMI, and TROPOMI measurements. Despite recent efforts to improve OClO retrievals, challenges remain, particularly regarding possible spectral interferences with other species. This study focuses on a new OClO TROPOMI product, which involves preliminary tests to optimize DOAS retrieval parameters. These parameters include the fit window, polynomial degree, and treatment of interfering species included in the fit. The optimized retrieval methodology developed in this study will serve as the basis for future missions, such as Sentinel-5, aimed at enhancing our ability to accurately monitor atmospheric composition.