Air pollution exposure leading to deaths even when meeting Indian norms: Study

Air pollution exposure can cause deaths even at levels much lower than what is considered the Indian national standard, according to a new study published in Lancet Planetary Health.

The report found that across 10 major cities in India — Delhi, Ahmedabad, Bangalore, Chennai, Hyderabad, Kolkata, Mumbai, Pune, Shimla, and Varanasi – around 33,000 deaths every year are attributable to PM 2.5 pollution levels that breach the WHO guideline of only 15 micrograms per cubic metres. The national standard for fine, particulate matter or PM 2.5 (24 hours) is 60 micrograms per cubic metres.

In terms of proportion, Delhi recorded the highest deaths attributable to air pollution across all cities studied – 11.5% of all deaths – amounting to 12,000 each year. Varanasi is estimated to have recorded 10.2% of all deaths (830 each year) during the study period, which were attributable to short-term PM2.5 exposure higher than the WHO guideline value of 15 micrograms per cubic metres.

While in these cases, the numbers may not be as surprising due to the generally high air pollution, the study also surprisingly revealed that cities such as Chennai, Bengaluru and Shimla, which largely meet the nation standard, are estimated to have recorded 4.8% of all deaths (2,100 each year); 4.9% of all deaths (2,900 each year) and 3.7% of all deaths (59 per year).

The deaths are higher in Delhi, Varanasi, Kolkata etc because of higher average exposure, possibly the nature of sources and population according to authors who said the purpose of the study was not to compare the number of deaths but to stress that cities that are understood to have relatively low pollution are also seeing high impact on health.

“7·2% of all deaths were attributable to PM2·5 concentrations higher than the WHO recommended 15 μg/m³, corresponding to 33627 annual deaths across our ten cities (table). Delhi had the largest attributable fraction and highest attributable yearly deaths,” the paper said.

The authors used data on PM 2.5 exposure in the 10 cities and correlated it with daily counts of mortality between 2008 and 2019 to arrive at their conclusions. It is the first multi-city study according to the authors, to assess the relationship between short-term air pollution exposure and death in India, with the cities recording a wide range of air pollution concentrations including those that largely meet the national standards.

During the study period, 7.2% of all deaths (33,000 each year) across all cities could be linked to short-term PM2.5 exposure higher than the WHO guideline value of 15 micrograms per cubic metres, it found.

Each 10 micrograms per cubic metre increase in short-term PM2.5 exposure was associated with a 1.42% increase in daily deaths. Further, this estimate nearly doubled to 3.57% when authors isolated the impact of local sources of air pollution especially combustion sources such as vehicles, diesel generators etc.

Interestingly, increases in risk of death is found to be steep at lower concentrations of PM2.5 and tapering off or moderating at higher concentrations. This indicates why significant health effects are observed even below the current National Ambient Air Quality Standard of 60 micrograms per cubic metres for 24-hour exposure.

Conclusions from the study have led the authors to recommend upgrading the national standard; a recalibration of the Graded Response Action Plan which largely focuses on pollution extremes to focus on year-round action; covering more cities for air pollution control because most cities in India do not meet the WHO guideline.

“Short-term PM2.5 exposure was associated with a high risk of death in India, even at concentrations well below the current Indian PM2.5 standard. These associations were stronger for locally generated air pollutants quantified through causal modelling methods than conventional time-series analysis, further supporting a plausible causal link,” the study concluded.

“India needs to tighten its national standards. But the results also show that we cannot remain too fixated on curbing dust. Local combustion sources such as vehicles, dg sets, waste burning need to be curbed to see improvements in health impacts and we need to move away from taking action only in non-attainment cities, many more areas with lower levels of air pollution also require interventions,” said Bhargav Krishna, Fellow at the Sustainable Futures Collaborative and a lead author on the study.

“Spanning data from 2008 to 2019 across India’s largest cities, our findings support the evidence that approximately 7.2% of all deaths in India are attributable to daily PM2.5 exposure. As efforts to combat air pollution intensify, addressing dispersed local sources becomes crucial alongside existing strategies,” said Jeroen de Bont, Postdoctoral researcher at Karolinska Institutet and a lead author said in a statement.

“This is very important evidence in India that shows the high impact of short term changes in local air pollution on the daily number of air pollution related deaths. Even more worrying is the confirmation of the global evidence that PM2.5 (and what the WHO has been saying for a long time), - does not have any safe threshold and can be very harmful and cause an increase in daily deaths even at low concentration – lower than the current national ambient air quality standard. This requires accelerated action for significant reduction in pollution levels across all regions,” said Anumita Roychowdhury, Executive Director of Research and Advocacy at the Centre for Science and Environment (CSE).

Nearly 170,000 children under the age of 5 years are estimated to have died in India due to air pollution in 2021, according to the State of Global Air report released in June.

Despite some progress, air pollution-related deaths among children under five years of age has remained high in several regions, particularly in South Asia and East, West, Central, and Southern Africa, according to the State of Global Air report, based on data from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD 2021) by the Institute for Health Metrics and Evaluation.

But the Lancet study doesn’t depend on modelling alone. It uses national spatiotemporal exposure model and daily mortality data from ten cities.

HT sought a response from Ministry of Environment, Forests and Climate Change (MoEFCC) on findings of the study but did not receive a response immediately.