Half of world’s cities had PM2.5 levels above least-stringent WHO standards last decade: Report

A new report has found that particulate matter (PM) 2.5 decreased in some cities of the world between 2010 and 2019 but almost half of all cities analysed still had PM2.5 levels above even the least-stringent World Health Organization (WHO) standards.

India and Indonesia recorded the most severe increase in PM2.5 pollution while China saw the greatest improvements. Some 7,239 cities were analysed in the study. India was found to be home to 18 of the 20 cities with the most severe increase in PM2.5 pollution from 2010 to 2019.

Some 41 of the 50 cities with the most severe increase in PM2.5 were found to be in India and nine in Indonesia.

On the other hand, all 20 cities with the greatest decrease in PM2.5 pollution from 2010 to 2019 were found to be located in China. However, China was also home to 15 of the top 20 cities with the highest PM2.5-linked deaths.

Factors such as an aging population and change in disease rates due to increasing population are also important factors that drive the changes in death rates related to PM2.5, in addition to PM2.5 exposure.

Thus, even if PM2.5 levels are falling, other factors like an aging population which is more vulnerable to aerial pollutants and a fast-growing populace can lead to a higher burden of disease.

Overall, the top 20 cities with highest PM2.5-related exposure showed an increase of more than 10 micrograms per cubic metre (µg/m3) in PM2.5 exposure from 2010 to 2019.

 Source: Air Quality and Health in Cities

The report also showed that cities with higher nitrous dioxide (NO2) pollution were located in large cities of countries across all income levels. PM 2.5 pollution was highest in low- and middle-income countries.

Eighteen among the 20 cities that showed the largest decrease in NO2 exposure from 2010 to 2019 were located in China. The other two were in the United States (Los Angeles) and Japan (Tokyo).

Cities showing the largest increase in NO2 exposure during this period include those in low- and middle-income countries in North Africa and the Middle East, south Asia, southeast Asia and Latin America.

Globally, progress has been made with regard to NO2 mitigation as 211 more cities met the WHO guideline in 2019 as compared with 2010. Eighty-six per cent of 7,239 cities still exceeded the WHO guideline for healthy air in terms of NO2 (10 µg/m3) in 2019.

Cities in developed countries in North America (Winnipeg, Canada and Fargo, United States), Asia-Pacific (Seoul, South Korea and Asahikawa, Japan), and western Europe (Paris, France and Albacete, Spain), as well as in middle- to high-income countries in eastern Europe (Moscow, Russia and Minsk, Belarus) also show high NO2 exposures.

There are no Indian cities in the top 20 cities most afflicted with NO2 pollution and the most NO2 pollution-afflicted cities are located in high- to middle-income and industrialised countries.

The report, Air Quality and Health in Cities, was released by US-based research organisation Health Effects Institute’s (HEI) State of Global Air Initiative August 17, 2022.

Traffic-related pollution and industrialisation is an accurate indicator of NO2-related pollution. Since NO2 is a result of combustion from various sources, higher urbanisation and industrial density lead to more nitrous oxide release.

Thus, more preventive measures and pollution-mitigating actions need to be taken in Indian cities as India moves towards more industrialisation, urbanisation and development.

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