Decoded: Why Delhi suffocates every winter – role of traffic, regional pollution, firecrackers and stubble burning | Today’s news

Winter air pollution in Delhi-NCR is once again drawing attention and the region remains under the blanket of smog even days after Diwali. Although firecrackers are a significant contributor to pollution during the festive season, they are only one part of a larger problem involving vehicle emissions, industrial activity, construction dust, regional pollution and weather conditions.

An assessment by the Indian Institute of Tropical Meteorology (IITM), Pune, found that firecrackers contributed 71.1% to the concentration of PM2.5 in the air in Delhi between 1 am and 9 am on November 9, immediately after Diwali celebrations. The contribution was 43.4% in the same hours on November 8 and 5.6% on November 7, The Indian Express reported.

The figures highlight the immediate impact of firecrackers during the analyzed period. However, Delhi’s recurring winter pollution cannot be attributed to just one activity. The accumulation of pollutants from multiple sources, combined with weather conditions that limit their dispersion, makes this problem particularly acute during the colder months.

Quick answers to key questions

•5 QUESTIONS

Delhi’s winter smog comes from several sources, including vehicle exhaust, industrial emissions, construction and road dust, waste and biomass burning, and pollution from neighboring states. Firecrackers and burning of crop residues can increase the pollution load at certain times.

Low wind speeds and reduced atmospheric mixing make it difficult for pollutants to disperse. Temperature inversions can also trap polluted air close to the ground, while Delhi’s location in the Indo-Gangetic plain exposes it to regional pollution.

Firecrackers can cause a sharp, short-term spike in pollution, but they are not the only cause of Delhi’s recurring winter smog. IITM Pune found that they contributed 71.1% of PM2.5 between 1 am and 9 am on November 9, the specific period after Diwali.

Pollution from vehicles, industry, dust and other sources continues even after the emissions from firecrackers subside. Low winds and temperature inversions can keep pollutants trapped near the ground, allowing smog to persist for days.

Fog consists of tiny water droplets that form when moist air cools. Smog is polluted air containing particles and gases; can reduce visibility and pose health risks and can occur simultaneously with fog.

So what causes winter smog in Delhi, how is it different from fog and why does it persist?

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What is smog and how does it differ from fog?

The word smog combines “smoke” and “mist”. It refers to polluted air containing a mixture of solid particles and gases, which often results in reduced visibility.

These pollutants include fine particles such as PM2.5 and PM10, along with gases emitted by vehicles, industries and other sources. Nitrogen oxides and volatile organic compounds can also react in sunlight to form ground-level ozone, which is known as photochemical smog.

However, Delhi’s winter smog is mainly associated with the accumulation of fine particles under weather conditions that prevent the spread of pollutants.

PM10 refers to particles with a diameter of 10 micrometers or less, while PM2.5 refers to finer particles with a diameter of 2.5 micrometers or less. These particles can include dust, soot and smoke, as well as substances created by chemical reactions involving gases in the atmosphere.

In contrast, fog is made up of tiny water droplets suspended close to the ground. It occurs when moist air cools and water vapor condenses into droplets, reducing visibility.

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The key difference is that fog is a natural weather phenomenon, while smog contains air pollutants that can pose health risks. Both can also occur simultaneously.

Why does Delhi’s air pollution worsen in winter?

Delhi’s winter pollution is the result of a combination of emissions, geographical and meteorological conditions. As temperatures drop and wind speeds decrease, pollutants become less dispersed and can accumulate closer to the ground.

During warmer months, rising air and stronger winds help carry pollutants away and disperse them. In winter, this movement can be limited by weaker winds and reduced atmospheric mixing, allowing pollution to accumulate.

Another important factor is temperature inversion. Under normal conditions, warmer air near the surface rises and helps carry pollutants up. During a temperature inversion, a layer of warmer air lies above cooler air closer to the ground. It acts as a lid, limiting vertical movement and trapping pollutants near the surface.

Delhi’s location in the Indo-Gangetic Plain also adds to the challenge. Pollution from neighboring states can contribute to regional pollution loads, while adverse weather conditions can allow pollutants to accumulate over several days.

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Together, these factors help explain why winter smog can persist even as emissions from a particular source decline.

Where does air pollution in Delhi come from?

Pollution in Delhi comes from several sources, including vehicle exhaust, industrial emissions, construction activities, road dust, waste burning and biomass burning. Their relative contributions vary depending on the season, location and prevailing weather conditions.

In the post-monsoon period, smoke from the burning of agricultural residues in neighboring states may add to Delhi’s existing pollution. However, local sources such as traffic, industrial activity and dust also contribute to air pollution in the city.

The contribution of individual sources can change significantly in short periods. Before Diwali, sources such as biomass and waste burning, vehicular emissions and secondary organic aerosols were major contributors to Delhi’s PM2.5 pollution.

During the hours immediately following Diwali, firecrackers became the dominant contributor. According to an analysis by IITM Pune, 71.1% of the PM2.5 concentration in the air in Delhi was between 1 am and 9 am on November 9. The corresponding contribution was 43.4% in the same period on 8 November and 5.6% on 7 November.

These figures refer to specific time windows and should not be interpreted as the share of firecrackers in the total pollution of Delhi during the winter season.

Why does Delhi’s smog persist after Diwali?

The end of a temporary source of pollution will not clear the air immediately. Even after firecracker emissions subside, pollutants from vehicles, industry, dust and other sources continue to enter the atmosphere.

When wind speeds remain low and a temperature inversion restricts air movement, these pollutants can remain trapped close to the ground. This allows pollution levels to remain elevated for several days.

The persistence of smog is therefore not just a matter of how much pollution is emitted on a particular day. Weather conditions and accumulated pollution also determine how quickly air quality improves.

How dangerous is PM2.5 pollution?

Fine particles, especially PM2.5, are a major health concern due to their small size. These particles, 2.5 micrometers or less in diameter, can penetrate deep into the lungs. Some may also enter the bloodstream and affect other parts of the body, the Indian Express reported.

Exposure to polluted air can cause eye and throat irritation, coughing and breathing difficulties. It can also make asthma and other breathing problems worse.

Long-term exposure to fine particle pollution is associated with a higher risk of cardiovascular disease, stroke, lung cancer and chronic respiratory disease.

Children, the elderly, pregnant women and individuals with pre-existing heart or lung disease are particularly vulnerable. However, long-term exposure to high levels of air pollution can affect otherwise healthy people.