Several schools in Delhi close during winter for at least two weeks because of high air pollution levels. Every winter, widespread crop burning in north India and weather conditions add to the already high air pollution levels from traffic, industry and waste burning, which build a thick smog, block sunlight, and make the air heavier to breathe.
Hospitals are hard-pressed to receive a large influx of patients with respiratory and cardiovascular illnesses. But is this problem restricted to exposures over short periods in winter or is it a year-around phenomenon? And how many people die from such high air pollution exposure?
Research in other parts of the world has consistently found microscopic particles suspended in the air to be harmful to health. These fine particles, known as PM2.5, measure less than 2.5 micrometres in diameter, 30 times smaller than human hair.
While individually invisible, in high air concentrations such as in India, the air becomes clouded and perceived as smog.
As PM2.5 are breathed in, they enter the lungs and the bloodstream to cause a cascade of reactions in the body such as inflammation. This increases the risk causing or worsening several chronic diseases such as heart disease, lung disease, cancer and dementia, as well as affecting maternal and child health. The consequences can ultimately be fatal.
My colleagues and I wanted to examine how exposure to air pollution may lead to deaths in the world’s most populated and highly polluted country – India. What we saw was alarming.
In a study published in The Lancet: Planetary Health journal earlier this year, we found that daily levels of air pollution exposure were indeed associated with a higher risk of death in ten Indian cities. We showed that local sources of air pollution were most toxic to human health.
Now, in a new publication in the same journal, we analysed instead yearly exposure to air pollution in all of India in relation to mortality.
We linked mortality counts between 2009 and 2019 from 655 Indian districts to national PM2.5 levels using a type of artificial intelligence called machine learning to combine data from air pollution monitoring, satellite products and information on land use.
We found that yearly PM2.5 levels, measured in micrograms per cubic meter of air (µg/m3), were very high across India with the lowest 5% of districts having almost 20µg/m3 and the highest 95% of districts 72µg/m3. Importantly, our findings indicated that every ten unit increase in annual PM2.5 was linked to an 8.6% increased risk of death across India.
Over a million deaths annually
The World Health Organization’s (WHO) Air Quality Guidelines based on scientific evidence recommend that the annual average PM2.5 levels should not exceed 5 µg/m3. In comparison to this benchmark, our new results indicate that air pollution was linked to 16 million deaths over a decade (or 1.5 million annually).
This is considerably higher than the 3.8 million related deaths if we instead compare to the Indian National Air Quality Standards, which allow for eight times higher levels than the WHO.
Our results also showed that all the districts we studied had higher annual levels than the WHO recommendations. Additionally, the mortality risk from air pollution exposure was high, even below the Indian National Air Quality Standards. As a result, the risk of death from air pollution exposure in India is a threat for all Indians and not limited to people living in cities.
Our findings clearly show that air pollution in India significantly increases the risk of mortality from daily and yearly exposures, leading to a very large number of deaths.
In comparison, the health effects of air pollution shown in studies from Europe and North America have contributed to stricter air quality regulations. As a result, people in these countries have benefited from improvements in air pollution exposure and health.
Our results point to a clear opportunity to clear up the skies in India, improving public health and, since most of the air pollution comes from fossil fuel emissions, contribute to mitigating climate change.
This project was funded by the Swedish Research Council for Sustainable Development (FORMAS).
Suganthi Jaganathan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
