Delhi air pollution alert: How vehicular pollution is quietly damaging your lungs, raising PM2.5

NO₂ is harmful to the lungs. It also leads to the formation of more PM2.5 in the air, says report.

NO₂ is harmful on its own but it also leads to the formation of more PM2.5 in the air. (File Photo)

Elevated NO₂ readings worsen the overall AQI and make precautions such as wearing masks or limiting time outdoors advisable. (File Photo)

While Delhi’s pollution debates often centre around PM2.5, a more immediate and overlooked threat is rising in the city’s air: nitrogen dioxide (NO₂). Yes, it comes from rush hour traffic. It remains a major air quality challenge, regularly surpassing WHO limits and impacting the respiratory system through inflammation, coughing, wheezing, reduced lung function and higher infection risk.

The city’s dense traffic, particularly around major roads, intersections and the airport, is the primary source, pushing concentrations to two or three times recommended levels. These elevated NO₂ readings worsen the overall AQI and make precautions such as wearing masks or limiting time outdoors advisable, even during periods when other pollutants like PM2.5 fluctuate.

A Centre for Science and Environment (CSE) report released on Monday highlighted a recurring trend: PM2.5 levels rise and fall in step with nitrogen dioxide during the morning and evening rush hours, underscoring traffic’s central role in daily pollution spikes. While nitrogen dioxide surges sharply and immediately due to tailpipe emissions, PM2.5 builds up more gradually and becomes trapped beneath the shallow boundary layers typical of winter. Carbon monoxide — another hazardous pollutant for which vehicles are the primary source — has also shown a marked increase across the city.

According to Dr Arunesh Kumar, Director and HOD, Pulmonology at Paras Hospital, Gurugram, NO₂ is harmful on its own but it also leads to the formation of more PM2.5 in the air. Instead of asking which is worse, it’s important to recognise that exposure to both, which is common in cities like Delhi — significantly amplifies the health risk.

How does vehicular congestion increase pollution and impact health?

Traffic congestion doesn’t just slow us down; it poisons the air around us. Idling and slow-moving engines emit far more toxic pollutants, including nitrogen dioxide, carbon monoxide, benzene and ultrafine particles that stay right at the level we breathe. These fumes irritate the airways, trigger inflammation and worsen asthma or bronchitis almost immediately. Over time, such exposure increases the risk of COPD (chronic obstructive pulmonary disease), heart disease, stroke and even lung cancer. In winter, when pollution gets trapped close to the ground, the health impact becomes even more severe.

What is the impact of nitrogen dioxide (NO₂) on the human body?

To put it simply, nitrogen dioxide is a highly irritating gas produced mainly by vehicle exhaust. Once inhaled, it travels deep into the lungs and causes oxidative stress and inflammation. Even short-term exposure can lead to coughing, wheezing, tightness in the chest, and breathlessness.

Long-term exposure weakens the lungs’ natural defence system, making people more prone to chronic bronchitis, pneumonia, and respiratory infections. In children, consistent NO₂ exposure can slow lung development and increase the risk of lifelong asthma. For asthma and COPD patients, a spike in NO₂ often triggers severe flare-ups.

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How does nitrogen dioxide differ from PM2.5, and is it more harmful?

Nitrogen dioxide and PM2.5 are two very different types of pollutants. NO₂ is a gas while PM2.5 consists of tiny solid particles smaller than 2.5 microns. NO₂ mainly irritates the airways and causes inflammation. PM2.5 goes deeper; it can enter lung tissue and even the bloodstream, affecting the heart, brain and other organs.

NO₂ is harmful on its own but it also leads to the formation of more PM2.5 in the air. Instead of asking which is worse, it’s important to recognise that exposure to both, which is common in cities like Delhi, significantly amplifies the health risk.

Can an air purifier help when nitrogen dioxide levels are high?

Only to an extent. Typical home air purifiers are designed to remove particles like PM2.5 and dust, not gases. To reduce nitrogen dioxide, you need a purifier with high-quality activated carbon or advanced sorbent filters and even then, the effect is partial.

During high NO₂ periods, simple steps like keeping windows closed during peak traffic, avoiding indoor combustion sources and maintaining clean ventilation become important. Still, personal measures have limitations. The long-term solution lies in reducing emissions and improving outdoor air quality.