Climate-driven atmospheric circulation fuels dangerous heat-PM2.5 extremes over India
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Conceptual diagram of the formation mechanism of compound heatwave–PM2.5 extreme events.
view moreCredit: Huibin Dai
As global warming intensifies, extreme heat events are becoming more frequent and severe worldwide, and are increasingly occurring alongside air pollution to form compound heatwave–air pollution events. Because simultaneous exposure to extreme heat and polluted air poses substantially greater health risks than either hazard alone, these compound events have emerged as a growing global environmental concern.
India has been at the forefront of this challenge. In the pre-monsoon season of 2026, temperatures exceeded 46°C across many parts of the country, with northern and central India experiencing prolonged and intense heatwaves. At the same time, compound heatwave–PM2.5 pollution events during the pre-monsoon season have become increasingly frequent, drawing renewed attention to their impacts on public health and air quality. But why are these compound extreme events becoming more common, and what are the key mechanisms driving their formation?
A research team from Hong Kong Baptist University investigated pre-monsoon heat-PM2.5 compound extreme events across India between 2017 and 2024 by combining ground observations, satellite measurements, and atmospheric chemistry simulations. The team found that the frequency of compound extreme events increased markedly after 2020. During April 2022, more than 70% of severe PM2.5 pollution episodes across northern India occurred simultaneously with heat waves, highlighting the increasing overlap between the two environmental hazards.
The research team reported its findings in Advances in Atmospheric Sciences .
Further analyses revealed that large-scale atmospheric circulation played a central role in shaping these compound extremes. An anomalous anticyclonic circulation over northern India strengthened heat conditions while generating anomalous southeasterly winds that transported additional pollution precursors into the region. These meteorological conditions accelerated atmospheric chemical processes, substantially enhancing the formation of secondary organic aerosols (SOA), a major component of PM2.5. Atmospheric chemistry simulations showed that SOA production increased by approximately 2.3 times during compound events, contributing significantly to elevated particle concentrations under extreme heat.
“Most studies have focused on heat waves and air pollution separately,” said Huibin Dai, lead author of the study. “This study shows that large-scale atmospheric circulation can simultaneously intensify heat and promote secondary aerosol formation, creating favorable conditions for compound heat-PM2.5 extremes. It highlights an important pathway through which climate variability can influence both weather extremes and air quality.”
The findings suggest that understanding future air quality requires considering not only emissions but also climate-driven changes in atmospheric circulation and atmospheric chemistry. As climate warming is expected to increase the occurrence of extreme heat, these coupled meteorological and chemical processes may further increase the risk of compound environmental extremes in densely populated regions.
“The next step is to investigate how compound heat-PM2.5 extremes will evolve under future climate change and to quantify their impacts on human health,” Dai said. “Ultimately, this work aims to better understand the mechanisms behind compound heat-PM2.5 extremes and provide scientific evidence to support early prevention, risk reduction, and climate adaptation.”
The research was conducted by a team from the Department of Geography, Hong Kong Baptist University, led by Prof. Meng Gao. This work was supported by grants from the National Natural Science Foundation of China and the Research Grants Council of the Hong Kong Special Administrative Region, China.
Article Title
Revival of Compound Heat–PM2.5 Extremes in Pre-Monsoon India: Meteorological Shifts and Fueled Secondary Aerosol Production (2017–24)
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