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The Most Polluted Cities In The World


  • According to the United States-based Health Effects Institute’s recent report titled Air Quality and Health in Cities, Delhi and Kolkata are the top two most polluted cities in terms of exposure to harmful fine particulate matter (PM2.5).
  • The report looks at pollution and its effects on global health in over 7,000 cities around the world, focusing on two of the most dangerous pollutants: fine particulate matter (PM2.5) and nitrogen dioxide (NO2).


GS Paper – 3: Environmental Pollution & Degradation

Mains Question

Describe the key points of the World Health Organization’s recently released revised Global Air Quality Guidelines (AQGs) (WHO). What makes these updates different from the last one in 2005? What changes are needed in India’s National Clean Air Programme to meet revised standards? (250 Words)

Findings of the Air Quality and Health in Cities report:

  • Using data from 2010 to 2019, the report discovered that global patterns of exposure to the two key air pollutants (PM 2.5 and NO2) were strikingly different.
  • Particulate Matter (PM) (PM) 2.5 denotes a category of particulate pollutant with a size of 2.5 microns or less.
    • PM 2.5 is particularly hazardous to human health because it can bypass many of our body’s defences (nose hair, mucus) and enter our lungs, where it can eventually enter the bloodstream.
    • Nitrogen dioxide (NO2) is a gaseous air pollutant produced when high-temperature fossil fuels such as coal, oil, gas, or diesel are burned.
    • Because city dwellers are more likely to live near busy roads with heavy traffic, they are frequently exposed to higher levels of NO2 pollution than residents of rural areas.
  • While exposure to PM2.5 pollution is higher in cities in low- and middle-income countries, exposure to NO2 pollution is high in cities in both high- and low-income countries, according to the report.
  • According to the report, most global cities far exceed WHO air pollution guidelines, posing a serious health risk.
    • In 2019, 86% of the cities studied exceeded the WHO’s NO2 guideline of 10 g/m3 (microgram per cubic metre), affecting approximately 2.6 billion people.
  • India has 41 of the 50 cities with the highest increase in PM2.5, with Indonesia having nine.
  • On the other hand, China has all 20 cities with the greatest reduction in PM2.5 pollution from 2010 to 2019.

Findings specific to India:

  • When PM2.5 levels were compared, Delhi and Kolkata were ranked first and second in the top ten most polluted cities.
    • In terms of impact, Delhi and Kolkata ranked sixth and eighth in terms of PM2.5-related disease burden, with 106 and 99 deaths per lakh of population, respectively, due to PM2.5 exposure in 2019.
  • However, when N02 levels were compared, no Indian city appeared in the top 20 polluted cities (Shanghai was at the top with an average annual exposure of 41 g/m3).

Why is there such a schism in India?

  • According to the report, ground monitoring of air quality continues to be insufficient in many parts of the world, particularly in low and middle-income countries, masking the true extent of NO2 pollution in places like India.
    • For example, according to the 2022 WHO Air Quality Database, only two of the 20 cities with the steepest increases in PM2.5 exposures in the report (Satna and Varanasi in India) have an official ground-level monitoring station.
  • Experts believe that the paradoxical situation (difference in PM2.5 and NO2) in India was caused by the relatively low adoption of high-efficiency engine vehicles.
    • Complete combustion of fuel produces more NOx (nitrogen oxides), whereas incomplete combustion produces other types of emissions.
    • Because of their highly reactive nature, nitrogen oxides aided in the formation of other pollutants such as ozone and particulate matter.
  • NO2 has a shorter lifetime than PM2.5 and other air pollutants.
  • As a result, NO2 levels vary greatly in space and time, and levels can vary significantly even within a few kilometres of the city.
    • In comparison, at the fine scale, PM2.5 levels exhibit less spatial variation.

Ideas for Improving Air Quality and Health?

  • Adopt or revise national air quality standards in accordance with the most recent WHO Air Quality Guidelines.
  • Monitor air quality and look for sources of pollution.
  • Encourage the use of clean household energy exclusively for cooking, heating, and lighting.
  • Create safe and affordable public transportation systems, as well as pedestrian and bicycle networks.
  • Implement stricter vehicle emissions and efficiency standards, as well as mandatory vehicle inspection and maintenance.
  • Invest in energy-efficient housing and renewable energy generation.
  • Improve waste management in industry and municipalities
  • Reduce the incineration of agricultural waste, forest fires, and certain agroforestry activities (e.g. charcoal production)
  • Include air pollution in health professional curricula and provide tools for the health sector to engage.

Indian cities: Way Forward

  • More developed cities with PM2 control
  • The NO2 problem has now gripped 5 exposures.
  • As a result, according to the Centre for Science and Environment (CSE), Delhi and Kolkata require the most stringent time-bound multi-sector action to meet the clean air benchmark.
  • Indian cities must also learn from Beijing, which, despite significantly lowering its PM2.5 exposures, still has the highest PM2.5-related disease burden due to expanding and ageing populations.

The Way Forward

  • Following the WHO’s Four Pillar Strategy: The World Health Organization (WHO) passed a resolution (2015) to address the negative health effects of air pollution. There is a requirement to follow the roadmap outlined in this section.
    • This four-pillar strategy calls for a more aggressive global response to the negative health effects of air pollution. These four pillars are as follows:
    • Increasing one’s knowledge base
    • Reporting and monitoring
    • Global coordination and leadership
    • Institutional capacity building
  • Addressing Inequity: There are huge injustices at the heart of the air pollution problem, as poor people are also the ones who are most affected by it.
  • As a result, the Polluter Pays principle must be enforced, and an environment tax must be levied on polluting industries.


December 2023