Additional OClO formation due to major forest fires and volcanic eruptions: comparison between TROPOMI measurements and EMAC model simulations

Chlorine dioxide (OClO) is a by-product of the ozone depleting halogen chemistry in the stratosphere and serves as an indicator of the chlorine activation in polar regions during polar winter and spring at twilight conditions because of the nearly linear dependence of its formation on chlorine oxide (ClO) and its detectability by UV-VIS spectral instruments.

The TROPOspheric Monitoring Instrument (TROPOMI) is an UV-VIS-NIR-SWIR instrument on board the Sentinel-5P satellite developed for monitoring the composition of the Earth’s atmosphere. Launched on 13 October 2017 in a near polar orbit, it provides    continuous monitoring of many constituents including the observation of OClO at an unprecedented spatial resolution.

The EMAC (ECHAM5-MESSy Atmospheric Chemistry) model is a chemistry climate model based on a general circulation model including interactive gasphase and aerosol atmospheric chemistry simulation and is nudged to the meteorology (in particular ERA5).

In this study we analyse the time series of slant column densities (SCDs) of chlorine dioxide (OClO) at polar regions and compare them with EMAC simulations in particular for the periods of the 2019/2020 Australian megafires and the Hunga volcanic eruption (January 2022).

While in the aftermath of the Australian megafires an increased, anomalous pattern of OClO is found for a period of two years no such an anomaly can be seen with respect to the Hunga eruption, both being well in agreement between the model and the measurements.