Increased pollution fuels smog crisis across north India, study finds

A study reveals that rising pollution levels are aggravating winter smog in northern India, with aerosols intensifying the temperature inversion effect, worsening air quality in Delhi

Seasonal weather patterns, such as calm winds and cooler temperatures, exacerbate air pollution across northern India, particularly during this time of the year. However, studies suggest that rising pollution levels are intensifying these natural weather phenomena, potentially worsening the smog crisis.

Pollution-weather feedback loop

According to a report by The Times of India, experts suggest that the current severe haze in Delhi and other regions of the Indo-Gangetic plain is partly due to a pollution-weather feedback loop. A recent study revealed that pollutants like soot, black carbon, and other aerosols are enhancing the natural ‘temperature inversion’ effect. 

In winter, warm air traps cooler air near the ground, preventing the dispersion of pollutants. Aerosols contribute to this phenomenon by warming the lower troposphere, the lowest part of the atmosphere, while cooling the air at the surface.

 

The report quoted Ritesh Gautam, a senior researcher at Environmental Defence Fund (EDF) in the US, that the rise in aerosol pollution has increased the stability of the lower troposphere, amplifying the effects of temperature inversion. 

His study found a significant increase in days with poor visibility — up to nine times more in November since 1980, and five times more during December and January, including in Delhi.

Surge in aerosol pollution

Over the past four decades, researchers analysed how pollution interacts with atmospheric conditions in the Indo-Gangetic plain. They discovered a 90 per cent rise in aerosol pollution during November between 2002 and 2019, likely driven by increased crop burning. This pollution spike was the same in December and January, with a 40 per cent rise in aerosol levels, the report said.

As a result, the lower troposphere warmed, and the height of the planetary boundary layer — which traps pollution near the surface — dropped. This means that the pollution is confined to the ground, worsening smog conditions.

Role of humidity and irrigation

Another key factor contributing to the smog is the rise in relative humidity, possibly linked to increased irrigation practices. More moisture in the air leads to the formation of more fog and smog droplets. The study found a 20 per cent increase in surface humidity since 1980, which further enhances the smog formation process, the report mentioned.

Long-term effects and climate variability

The feedback cycle between pollution and atmospheric stability is well-understood, and the study provides evidence of its growing impact over time. However, the increase in lower tropospheric stability and relative humidity is also tied to broader climate variability, according to Chandra Venkatraman, an aerosol specialist at IIT Bombay, as quoted by The Times of India.

While the exact contribution of these meteorological changes to extreme smog remains uncertain, emissions are still the primary driver of pollution.