Deep stratospheric intrusion and Russian wildfire induce enhanced tropospheric ozone pollution over the northern Tibetan Plateau

Abstract

By using ozonesonde measurements during July–August in 2016, 2019, and 2020 at Golmud and Qaidam, European Centre for Medium-Range Weather Forecasts (ECMWF) next-generation reanalysis ERA5 data, satellite-borne Moderate Resolution Imaging Spectrometer data products, and backward trajectory calculations from the chemical Lagrangian model of the stratosphere (CLaMS) model, this study analyzes vertical ozone distributions and explores the influence of deep stratospheric intrusions and wildfires on ozone variation in the northern Tibetan Plateau (TP) during the Asian summer monsoon period. Large ozone partial pressures were observed between 20 and 30 km, with a maximum of ~16 mPa at approximately 27 km latitude. The comparisons between the vertical ozone profiles with and without the occurrence of stratospheric intrusions showed that their relative ozone difference was up to 72.4% in the tropopause layer (15.8 km), and a secondary maximum of 66.7% existed in the middle troposphere (10.1 km). The stratospheric intrusions dried the atmosphere by 52.9% and enhanced the ozone columns by 26.1% below the upper troposphere and lower stratosphere. A case study of deep stratospheric intrusion exhibited the occurrence of large ozone partial pressure in the middle troposphere in detail, with an ozone peak of ~6 mPa at 10 km, which was caused by a tropopause fold associated with the westerly wind jet at the north flank of the Asian summer monsoon anticyclone. The stratospheric intrusion processes effectively transported the cold and dry air mass with high ozone in the stratosphere downward to the middle troposphere over the northern TP. This study also confirmed that by long-range transport processes, large wildfire smoke occurred around central and eastern Russia on 19–26 July 2016 greatly caused ozone pollution in the troposphere (6 km depth from the surface) over the northern TP.