Delhi’s air pollution steadily worsening since 2021: Four key findings of a new air quality study

The analysis has been released at a time when Delhi’s air quality has plummeted to hit the ‘severe’ category for the first time this season. While on Thursday, the Air Quality Index (AQI) in the city breached the 400 mark, it reached 476 the next day

People walk enveloped by fog and smog in Kartavya Path in New Delhi, India, Friday, Nov. 3, 2023. Authorities on Friday shut primary schools and banned polluting vehicles and construction activity to control the worst haze and smog this season, causing respiratory infections among people and enveloping monuments and high-rise buildings in and around New Delhi. (AP Photo/Piyush Nagpal)

Written by: Alind Chauhan

4 min readNew DelhiNov 4, 2023 07:44 AM IST First published on: Nov 3, 2023 at 07:26 PM IST

Out of the eight of India’s major state capitals that face air pollution crisis, Delhi had the highest Particulate Matter (PM) 2.5 level in October for the past five years, according to a new study. Since 2021, the city has witnessed a consistent rise in PM 2.5 levels — they increased by 4.4% in October 2023 as compared to last year, the analysis added.

The study, ‘Respirer Reports’ Analysis of Air Quality in October for the past five years’, which came out on Thursday (November 2), has been conducted by Respirer Reports, an initiative of Respirer Living Sciences, a climate sciences IoT startup based out of Mumbai and Pune. It involved an examination of PM 2.5 levels in cities like Delhi, Mumbai, Hyderabad, Kolkata, Lucknow, Patna, Bengaluru and Chennai.

A GIF from @nasa Worldview, an interactive earth observation satellite imagery interface, shows the situation over North India from October 26 to November 3. The the last day, the image shows a thick haze over Delhi and surrounding areas, which are attributed mainly to the sudden spurt in agriculture burning in Punjab. The October 28 image is relatively clear, though cloudy.

The analysis has been released at a time when Delhi’s air quality has plummeted to hit the ‘severe’ category for the first time this season. While on Thursday, the Air Quality Index (AQI) in the city breached the 400 mark, it reached 476 the next day. Before Delhi, Mumbai in October witnessed ‘very poor’ or ‘severe’ air quality. Areas like Vile Parle — a suburb in western Mumbai where the airport is located — were among the worst affected spots.

Credit: Respirer Reports

PM 2.5 is one of the most harmful atmospheric pollutants. Sized at just 2.5 micrometres, which is around 3% of the diameter of a human hair, it can easily enter the circulatory system of humans through the nose and throat. PM 2.5 particles can cause chronic diseases such as asthma, heart attack, bronchitis and other respiratory problems.

Here are four key findings of the study:

1. Delhi’s air pollution worsening for the past two years

While the PM 2.5 level in the national capital in October 2021 was at 74.0 μg/m3, it rose to 113.9 μg/m3 in the next two years — an increase of about 54%. Notably, the October 2023 level was 3.7 times the Central Pollution Control Board’s ‘safe’ limit of 30 μg/m3 and 7.5 times the World Health Organisation’s safe limit of 15 μg/m3.

Credit: Respirer Reports

2. Mumbai’s air quality steadily deteriorates from 2019 to 2023

The PM 2.5 levels in Mumbai increased by 110% in the past four years — in October 2019, the level stood at 27.7 μg/m3, and two years later it jumped to 58.3 μg/m3.

Credit: Respirer Reports

3. Hyderabad and Kolkata also experience a rise in PM 2.5 levels

After a dip in the PM 2.5 level during October 2022 in comparison to the previous year, Hyderabad’s air quality worsened this year — the October 2023 level witnessed a spike of 18.6%.

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Meanwhile, Kolkata also saw an increase in pollution this October. The city’s level rose by 40.2% when compared to last year’s October.

4. Air pollution dips in Lucknow, Patna, Bengaluru and Chennai

The four state capitals saw a drop in PM 2.5 levels during October 2023 in comparison to 2022. Chennai was the least polluted as the level fell by more than 23% this year compared to a year ago.

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