Chennai: A new international study led by Indian Institute of Technology Madras has uncovered strong evidence linking heavy particulate pollution to the rising frequency and persistence of dense winter fog across North India.
The findings, published in the journals Science Advances and Geophysical Research Letters, reveal that high concentrations of airborne particles, especially during nighttime play a critical role in intensifying fog events.
The research team, led by N. Arun and Professor Chandan Sarangi from IIT Madras, found that calm winter nights allow pollutants to accumulate close to the ground. As temperatures drop, water vapor condenses rapidly onto these particles, forming millions of tiny droplets that reduce visibility.
The study highlights that the calm winter nights over the region favor the accumulation of pollutants near the ground. As the air temperature drops, water vapor quickly condenses on these particles, resulting in the formation of water droplets that are typically a few micrometers in size. This large number of droplets (typically, for fog, between 1 and 50 million droplets per cubic meter) obstructs light and reduces visibility.
It said as these droplets form, they release “latent heat” (hidden energy). This heat causes the fog to grow vertically, reaching nearly 600-800 meters-much higher than previously expected.
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.
Traditionally, scientists attributed increasing fog events in North India to large-scale wind circulation changes linked to global warming. However, this new research suggests that regional air pollution is just as influential.
“If the fog layer persists, solar heating is further reduced, creating conditions that favor even more condensation the next night,” explained N. Arun, a doctoral researcher at IIT Madras. “We are now realizing that pollution can play an equally important role in prolonging fog events.”
Professor Sarangi added that the findings could significantly improve fog forecasting, helping airports and transportation systems make better-informed decisions during winter months.
The study also offers a hopeful takeaway: reducing particulate pollution could directly decrease the frequency and severity of winter fog.
With contributions from researchers affiliated with the Cyprus Institute, Environmental Defense Fund, Bennett University, and Pacific Northwest National Laboratory, the research underscores the global importance of addressing air pollution, not just for health, but also for climate and visibility-related challenges.
As North India continues to grapple with hazardous winter air quality, the study reinforces a clear message: cleaner air could mean clearer skies.
