Tropospheric ozone as an atmospheric pollutant and short-lived climate forcer in the Third Pole

The Third Pole (TP) consists of cold, dry and ecologically fragile regions of 12 countries in Asia, encompassing an area of 7.1 million km². The enormous ice mass of TP is the source of fresh water for about 2 billion people in the surrounding regions. The environmental condition of TP has been gradually decreasing due to the increase in anthropogenic activities in and around the region for the past two decades. Ozone is an important oxidant and a greenhouse gas in the troposphere. It has positive feedback on temperature, and harms human health and ecosystems at higher concentrations. We investigate the spatiotemporal characteristics, long-term trends, and the climatic impact in terms of radiative forcing (RF) of tropospheric column ozone (TPO) in TP derived from the satellite measurements of Microwave Limb Sounder (MLS) and Ozone Monitoring Instrument (OMI) in 2005-2020. The analysis shows a high annual average TPO (35-40 DU) in the south and east, but lower values (20-30 DU) in the inner TP. There is a significant increase in TPO in TP, with higher values of about 0.3 DU yr^-1 in the north TP and are highest in the southeast TP during summer (up to 0.35 DU yr^-1) and the north TP in winter. This increase in tropospheric ozone alone contributes to a radiative forcing up to 0.3 Wm^-2 near the tropopause (125 hPa) and triggers a warming up to 0.4 °C within the troposphere of TP. The ozone-induced temperature change is stronger during 2014-2019 compared to that in 2005-2014, suggesting the impact of high anthropogenic activities and associated pollution on the TP climate in recent decades. Therefore, the increasing tropospheric ozone could affect the public health, ecosystems and climate of the region.