Data Lab: Delhi leads October pollution among major Indian cities. What awaits in the Diwali month?

In recent days, Delhi has been blanketed by a dense smog, as evidenced by images pouring in from various parts of the city. Thursday morning (Nov 2) saw the Air Quality Index (AQI) in the city at a dismal 352, placing it squarely in the "very poor category."

This was a slight improvement from the previous day's reading of 364 recorded at 4 pm on Wednesday (Nov 1).

Notably, Delhi has been mired in "very poor" air quality for six consecutive days.

Data from the Central Pollution Control Board (CPCB) indicates that at least five monitoring stations have reported AQI levels in the "severe" range (401 to 500) out of the 35 stations in total.

As Diwali festivities unfold, the annual air pollution menace returns. Amid this comes a comprehensive report analysing what the month of October looked like in terms of pollution from 2019 to 2023.

An analysis conducted by Respirer Reports has shown an increase in PM 2.5 air pollution levels in four major Indian cities when compared to the levels recorded one year ago. 

PM 2.5 describes fine inhalable particles, with diameters that are generally 2.5 micrometres and smaller. 

The study focused on PM 2.5 concentrations between 2019 and 2023 in eight significant state capitals facing air pollution challenges, including Delhi, Mumbai, Chennai, Kolkata, Bengaluru, Lucknow, Hyderabad, and Patna.

Here is the visualisation:

This is an interactive chart, please hover/click on the bars to get the data.

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City-wise trends

Delhi: The capital city had the highest PM 2.5 levels in October 2023 and has been experiencing a consistent upward trend since 2021.

This trend included a 32 per cent increase in PM 2.5 levels from 2019 to 2020, a 43.7 per cent decrease in 2021, and a steady rise in 2022 and 2023.

Notably, the air quality deteriorated by 4.4 per cent in the last year, significantly exceeding both the Central Pollution Control Board's 'safe' limit (30 μg/m3) and the World Health Organization's safe limit (15 μg/m3).

Mumbai: PM 2.5 levels in Mumbai also demonstrated a steady increase from 2019 to 2023, with a significant 42 per cent spike in pollution in October 2023 compared to the previous year.

Variability in PM 2.5 levels was observed in previous years, including substantial increases in 2019-2020 and slight decreases in 2021 and 2022.

Hyderabad and Kolkata: Both cities experienced an increase in PM 2.5 levels in October 2023 compared to 2022.

Hyderabad's PM 2.5 levels exhibited fluctuations in previous years, with a substantial 59 per cent increase in 2019-2020, followed by declines in 2021 and 2022, and another increase in 2023. Similarly, Kolkata witnessed fluctuations, including a significant increase in 2021, a decrease in 2022, and another rise in 2023.

Lucknow, Patna, Bengaluru, and Chennai: In contrast to the above-mentioned cities, Lucknow, Patna, Bengaluru, and Chennai saw declines in PM 2.5 levels between 2022 and 2023. Lucknow and Patna experienced improvements in air quality, with fluctuations over the years, including decreases and increases. Bengaluru and Chennai also observed reductions in PM 2.5 levels, with fluctuations in previous years, involving both increases and decreases.

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