Why smog came early to Punjab, parts of north India this year

What is smog?

Smog is a type of air pollution that creates a hazy or foggy atmosphere, reducing visibility and affecting air quality. Originally used in the early 1900s to describe a blend of smoke and fog, the term “smog” referred to pollution from coal-burning, especially common in industrial areas. Today, smog is still prevalent in densely populated cities with high levels of industrial and vehicular emissions.

Smog forms when pollutants such as nitrogen oxides, volatile organic compounds (VOCs), and other harmful particles are released into the atmosphere from sources like factories, vehicles, and power plants. These pollutants react chemically in the presence of sunlight, creating a harmful mixture. When combined with fog or high humidity, this reaction produces a thick haze, further reducing visibility and posing risks to public health.

Does smog come every winter?

Yes, it comes every year, generally by the end of November or in December in the Northern plains. Winter brings lower temperatures and weaker sunlight, leading to atmospheric inversion—a phenomenon where a layer of warmer air traps cold air close to the ground. This inversion layer holds pollutants near the surface, preventing them from dispersing.

Is stubble burning responsible for smog?

Stubble burning is widely cited as a major contributor to smog in northern India, particularly in states like Punjab and Haryana.

Experts note that smoke from burning stubble releases high levels of particulate matter, carbon monoxide, sulfur dioxide, and nitrogen oxides. However, stubble burning isn’t the only cause of smog — it plays a part in intensifying pollution levels across the region.

What are the other pollutants that contribute to smog?

Beyond stubble burning, year-round sources, including vehicular emissions, industrial smoke, and construction dust, worsen during winter due to the trapped atmospheric conditions. Vehicle exhaust, in particular, releases nitrogen dioxide and fine particulate matter (PM2.5), which are significant contributors to smog. Thermal power plants and factories also emit a steady stream of pollutants, compounding the problem.

What led to the early smog this year?

Experts explain that specific meteorological conditions in northern India this year have created an environment more favourable for early smog. Prolonged slow wind speed — which is around one km per hour — at the onset of winters just after Diwali led to accumulation of the pollutants in the air, resulting in poor air quality which contributed to the early smog.

Surinder Kumar, Director of the IMD Chandigarh office, said that weak western disturbances (weather systems that bring rain to the western Himalayas), primarily active in the hills, have brought moisture into the plains, which is also responsible for the smog. Typically, this smog appears in the northern plains by late November or early December, he said. “Limited rainfall reduces the natural cleansing of the atmosphere, allowing pollutants to remain suspended for longer durations causing early smog,” Kumar said.

Another factor is that Diwali was 12 days earlier this year than the last, and celebrated for two days by many because of astrological factors. Widespread bursting of firecrackers releases large amounts of particulate matter into the air. Fireworks release toxic metals and gases that contribute to the haze, creating immediate and harmful effects on air quality.

Experts also said that climate change is increasingly altering weather patterns, contributing to unseasonable smog and prolonged pollution episodes. The smog crisis in northern India is a complex issue rooted in seasonal patterns, agricultural practices, industrial emissions, and changing climate dynamics, they said, adding that some solutions—such as incentivising alternative stubble management techniques and tightening emission standards—show promise.

The average temperature of Punjab on Wednesday was below normal by -2.9°C, and it was below normal by -2°C in Haryana, also shallow moderate fog is expected till November 15.