Deciphering Natural and Human Impacts on Atmosphere Through Sophisticated Modeling

The Earth’s atmosphere is influenced by diverse natural and anthropogenic processes, including emissions, photochemistry, and dynamics. Due to such complexities, it is extremely challenging to design policies for mitigation of air pollution and climate change. The relative contributions of human activities versus natural processes are particularly poorly understood in developing regions, such as South Asia. The uncertainty stems from sparse observations, uncertain emissions, and limited ability of models to resolve complex topography. To address these gaps, we incorporated recent observations from multiple platforms—ground-based stations, balloons, ships, aircraft, and satellites—alongside comprehensive modeling. Our simulations successfully replicated the secondary ozone peaks over the Himalayas and the widespread winter haze across the Indo-Gangetic Plain. The observed peaks over the Himalayas are found to be inter-continental transport of natural stratospheric ozone. While biomass-burning emissions worsen air quality during post-monsoon, these have limited effect in winter, when haze problem is most severe. These findings unravel a larger role of atmospheric dynamics in enhancing climate-forcing pollution over South Asia, than previously thought.