CHENNAI: Heavy particulate pollution, particularly during calm winter nights, is a key driver behind the increasing frequency and persistence of dense fog across North India, finds a new international research led by the Indian Institute of Technology Madras (IIT-M).
The findings, published in leading peer-reviewed journals, challenge the long-held view that large-scale wind circulation changes linked to global warming are the primary cause of worsening fog episodes.
The study, led by N Arun and Prof Chandan Sarangi of IIT-M, found that high concentrations of fine particles near the ground during winter nights accelerate fog formation and intensification. As temperatures drop, water vapour condenses rapidly on these particles, producing millions of microscopic droplets that severely reduce visibility.
The process triggers a feedback loop. The formation of droplets releases latent heat, allowing the fog layer to grow vertically up to 600–800 metres, far higher than earlier estimates. By morning, this dense layer acts as a barrier to sunlight, limiting surface heating and slowing the natural dissipation of fog.
"If the fog layer persists, solar heating is dampened further, creating conditions for more condensation the following night," said Arun, a doctoral scholar at IIT-M. "We are now understanding that regional pollution can play an equally important role in prolonging fog events," he added.
The prolonged fog leads to dull sky conditions, often disrupting flights and delaying trains across the region during peak winter. Sarangi said the findings could significantly improve fog forecasting. "A clearer understanding of pollution–fog interactions can help airports and pilots make more informed operational decisions," he said.
The study also offers a policy insight: reducing particulate pollution could directly curb the intensity and duration of winter fog. Researchers from institutions in Cyprus, the United States and India contributed to the study.