CHENNAI: A study led by Indian Institute of Technology Madras (IIT Madras) has found high levels of pollution during winter nights play a major role in making fog more intense and long-lasting over north India.
The research, published in Science Advances and Geophysical Research Letters, challenges previous beliefs that climate change alone was responsible for increasing fog events, said a statement issued by the institute.
The study, led by N Arun and professor Chandan Sarangi from IIT Madras, reveals the pollutants in the air during calm winter nights create the perfect conditions for fog to form. On cold nights, pollutants like dust and soot collect close to the ground. When the temperature drops, water vapour in the air quickly condenses on to these particles, forming millions of tiny droplets that reduce visibility.
What makes this fog different is the release of “latent heat” as the water droplets form. This heat causes the fog to rise higher, up to 600-800 metres, much higher than scientists had previously thought. “The thick fog then acts like a blanket, blocking sunlight the next day. With less sunlight reaching the ground, the fog doesn’t evaporate as quickly, extending the foggy conditions for hours,”said the statement.
As the fog persists, it creates a cycle: reduced sunlight at the surface makes it easier for more fog to form the next night. This explains why fog can last for several days, disrupting transportation, including flights and trains.
The researchers stress the buildup of pollution at night is a key driver of this phenomenon, adding it can make fog events worse than expected. Their findings suggest reducing air pollution could directly decrease the severity and duration of winter fog. This discovery provides insights into managing fog and improving safety, especially for airports and transport systems in the region, added the statement.