The Toxic Soup of Pollutants | Delhi's air quality is a toxic soup of pollutants, with some of the main culprits being: SO2 (Sulfur Dioxide), NO2 (Nitrogen Dioxide), PM2.5 (Particulate Matter with a diameter of 2.5 micrometers), PM10 (Particulate Matter with a diameter of 10 micrometers), O3 (Ozone).

Contributors to this noxious mix include vehicles (25%), biomass burning (26%), solid waste burning (8%), ash (5%), dust (4%), and construction (2%). These figures are estimates and may vary depending on various factors.

Delhi's air pollution problem takes a dramatic turn for the worse during the winter months, primarily due to a combination of seasonal and atmospheric factors. Seasonal factors include farm fires, biomass burning for heating, and firecracker-related pollution. These activities release a substantial amount of pollutants into the air.

Atmospheric factors exacerbate the problem. In the colder months, pollutants are unable to disperse as they usually do due to winter inversion and the valley effect in the Indo-Gangetic plain. This phenomenon results in the formation of a toxic winter smog.

What is Winter Inversion? During the summer, the air in the lowest part of the atmosphere is warmer and lighter, causing it to rise upwards and carry pollutants away from the ground through vertical mixing. However, in the winter, the air near the Earth's surface is cooler and denser, which traps it under the warmer upper layer, creating an atmospheric "lid" known as winter inversion. This restricts vertical mixing to the lower layers, preventing pollutants from dispersing into the atmosphere and keeping them close to the ground.

Burning crop stubble in the surrounding regions of Punjab, Uttar Pradesh, Haryana, and Rajasthan significantly increases the concentration of pollutants in the air. The polluted air remains trapped, unable to disperse effectively during the colder months, leading to lingering pollution.

Cities closer to the coast, such as Mumbai and Chennai, benefit from sea breezes and moisture, which help disperse pollution. However, the Indo-Gangetic plain, where Delhi is located, is land-locked by the Himalayas and other mountain ranges. The low wind speeds in this region make it challenging for polluted air to escape, resulting in smog that blankets most of northern India.

It's important to note that the increase in pollution during the winter is not unique to Delhi but is a global phenomenon. This issue made headlines during the Great Smog of London, a lethal smog that covered the city of London for five days in 1952. An anticyclone settled over London, trapping emissions from factories and domestic fires near ground level due to inversion. This smog led to the loss of approximately 12,000 lives and prompted Britain to enforce stricter air quality norms in its aftermath.