IIT Madras Study Shows Particulate Pollution Linked To Dense Winter Fog Over North India
Offering new insights beyond the earlier climate change-only explanation, research shows nighttime polluted air traps moisture, accelerates condensation and prolongs dense fog.
Published : March 23, 2026 at 4:13 PM IST
Chennai: A recent study led by the Indian Institute of Technology, Madras, has provided compelling new evidence that heavy particulate pollution is a key driver behind the increasing frequency and persistence of dense winter fog over North India.
The findings published in Science Advances and Geophysical Research Letters reveal that high amounts of particulate pollution at nighttime are the primary reason for the intensification of fog.
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The study led by N Arun and Prof. Chandan Sarangi of the Civil Engineering Department, IIT Madras, in collaboration with international experts, explains that a cocktail of nighttime particles favours the intensification and duration of fog events over North India.
The study reveals that calm winter nights over the region favour the accumulation of pollutants near the ground.
As the air temperature drops, water vapour quickly condenses on these particles, resulting in the formation of water droplets that are typically a few micrometres in size. This large number of droplets (typically, for fog, between 1 and 50 million droplets per cubic meter) obstructs light and reduces visibility," IIT Madras said in its statement on Monday.
As these droplets form, they release latent heat (hidden energy), which causes the fog to grow vertically, reaching nearly 600-800 meters, much higher than previously expected, it said.
"The next morning, this thick layer acts as a massive shield, blocking the sun. Because solar energy does not reach the surface, natural heating of the ground is reduced, slowing down the evaporation of fog from the surface, which leads to “dull sky” conditions that ground flights and delay trains," it said.
N. Arun, doctoral scholar at the Department of Civil Engineering, said, “If the fog layer persists, then the solar heating of the surface is further dampened, leading to more favourable conditions for condensation to occur the next night. Previously, scientists believed that the root cause behind the increasing fog frequency was wind circulation changes over North India associated with global warming; however, we understand now that the regional pollution can also play an equally important role in prolonging fog events.”
Arun said the findings provide a better understanding of how pollution can impact fog intensity and duration.
Sarangi, Associate Professor at the Civil Engineering department, said this understanding can be critical for improving fog forecasting, and can help pilots and airports to make better and informed decisions.
The research offers a glimmer of hope: fog is closely tied to particulate pollution levels over North India. Improving air quality can directly reduce the frequency and severity of fog events during winter days.
Apart from Arun and Prof. Sarangi as lead authors, the study was co-authored by Vijay P. Kanawade from Cyprus Institute, Cyprus; Ritesh Gautam from Environmental Defence Fund, US; Manoj K Singh from Bennett University, India and Yun Qian from Pacific Northwest National Laboratory, US.
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