Delhi tops list of world’s most polluted cities, Kolkata close 2nd

Delhi and Kolkata are the two most polluted cities in the world in terms of average annual population-weighted PM 2.5 exposure, according to a new report, Air Pollution and Health in Cities, released by the Health Effects Institute’s (HEI) State of Global Air Initiative.

Mumbai was ranked 14th. No other Indian city features in the top 20. In terms of the highest disease burden from a PM 2.5-related ailment, though, Beijing, with 124 attributable deaths per 100,000 people was the worst. Delhi came in at 6th, with 106 deaths per 100,000 and Kolkata at 8th with 99. Five Chinese cities were in the top 20.

A total of 7,000 cities were covered by the study, although only 103, the most populous across six regions were considered for the ranking.

In terms of NO2 exposure, Shanghai was the worst in terms of average exposure, and no Indian city was in the top 20.

A large number of global cities across the world exceeded the World Health Organization’s (WHO) norms for both PM 2.5 and NO2. The report found Delhi’s average PM 2.5 exposure to be 110 micrograms per cubic metre in 2019, which is 22 times the WHO benchmark of 5 micrograms per cubic metre. Kolkata had an average exposure of 84 micrograms per cubic metre.

Shanghai had average NO2 exposure of 41.6 micrograms per cubic metre, followed by Moscow in Russia (40.2 micrograms per cubic metre). The WHO standard for NO2 exposure is 10 micrograms per cubic metre. The report said in 2019, exposure to pollutants in 86% of the more than 7,000 cities included in the report exceeded WHO’s standard, therefore impacting around 2.6 billion people.

In terms of absolute numbers, the study attributed 29,900 deaths in Delhi in 2019 to be due to PM 2.5 exposure; 21,380 in Kolkata; and 16,020 in Mumbai. In comparison, Beijing saw 26,270 deaths in 2019 on account of PM 2.5 exposure.

The report, which used data from 2010 to 2019, also found that global patterns for exposures to the two key air pollutants , NO2 and PM 2.5 were strikingly different. While exposures to fine particulate matter was found to be higher in cities located in low and middle-income countries, exposure to nitrogen dioxide, or NO2 was high across cities in high-income as well as middle-income countries. NO2 is primarily released in the form of emissions from vehicles and through power plants.

“As cities around the world rapidly grow, the impacts of air pollution on residents’ health are also expected to increase, underscoring the importance of early interventions to reduce exposures and protect public health,” said Pallavi Pant, a Senior Scientist at HEI, involved in the study.

The analysis also highlighted data gaps in low and middle-income nations. Referring to the WHO’s Air Quality Database, it said only 117 nations currently have ground-level monitoring systems to track PM2.5, and only 74 nations are monitoring NO2 levels. “Strategic investments in ground-level air quality monitoring systems and expanded use of satellites and other emerging technologies in targeted regions can provide critical first steps toward cleaner air,” it said.

Anumita Roychowdhury, executive director, research and advocacy at the Centre for Science and Environment (CSE) says that Delhi continues to rank as the most polluted city in terms of PM 2.5, and that while it is making gradual improvements, much more is required.

“The study takes 2019 levels into consideration and we saw a drop in 2020 in all cities, but saw it increase once again in 2021. Another aspect is deaths linked to PM 2.5 and Delhi is actually ranked sixth in comparison to Beijing in first, which has actually seen a considerable drop in PM 2.5 concentration. This is largely down to Beijing’s aging population and for them, the disease burden is high. We need to ensure for Delhi and other Indian cities, the disease burden does not increase similarly,” she added.