Recently, a first-of-its kind multi-city analysis in India that studied the health effects of short-term exposure to air pollution published in the peer-reviewed Lancet Planet Health.

• The scientists analyzed pollution and death registry data from Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla, and Varanasi.

Spike In Death Rates From Air Pollution, Crucial Insights on Findings of the Lancet Study

The researchers looked at 3.6 million deaths between 2008 and 2019 across the sample areas, and overlapped them with a detailed map of the distribution of PM 2.5, a compound of cancer-causing pollutants so small they can penetrate the bloodstream. 

Enroll now for UPSC Online Classes

• Rise in Death Trolls: The death toll from India’s air pollution is elevated even in cities previously thought to have relatively clean air, underscoring how the problem extends beyond megacities such as Delhi.
  • • It reinforces the message that there is no safe level of exposure to air pollution, even in highly polluted regions.
  • Even in the Himalayan town of Shimla, which had the cleanest air among the cities studied, 3.7% of all deaths were pollution related.
  • 11.5% of Delhi’s annual deaths are attributable to air pollution, and 4.8% in Bengaluru and had 30% more exposure to daily air pollution than the average Delhi resident.
• Threatening Particles Exposure: An exposure as short as 48 hours to high levels of the particles could worsen life expectancy at a collective level, with 7.2% of all fatalities linked to PM 2.5 concentrations above the World Health Organization standard of 15 micrograms per cubic meter.
  • Daily deaths totalled across the 10 cities rose by 1.42% for every 10 μg/m3 increase in the average PM2.5 exposure over a two-day period.
• Risk of Mortality: It found a “much stronger link” between air pollution and mortality than the traditional approach of correlating annual air pollution readings with mortality.
  • The risk of mortality rose more quickly at lower PM2.5 levels but became constant as levels increased. 
  • The mortality risk is very high (2.65%) even when analyzing days with PM2.5 levels below the current Indian national air quality standard of 60 μg/m3.
• Comparison with Global Level: The variation in mortality in different cities in India mirrors findings from similar studies in other countries. 
  • Example: A 272-city study in China reporting a 0·22% increase, per 10 μg/m³ increase in PM2·5. However, death rates were higher in Greece (2·54%), Japan (1·42%), and Spain (1·96%), which had lower base pollution levels.
• Use of Instrumental Variable Approach: Through this approach, researchers isolate the effect of locally generated air pollution since the used instruments are linked to dispersal and transport of air pollution.
  • Instrumental Variable Approach: Researchers identified three weather-related parameters — planetary boundary layer height or mixing height; wind speed; and atmospheric pressure that are directly related to variations in daily air pollution, but are unrelated to daily deaths except through air pollution changes. 

Check Out UPSC NCERT Textbooks From PW Store

Conclusion

The sharper mortality spike in cities with lower pollution loads than more polluted cities as an example of the ‘harvesting effect’, in epidemiology. This does not mean that risk is low at higher levels, it is just that the increase in risk slows down. There is a need to address dispersed local sources of air pollution in addition to traditional fixed and line sources.