A new study shedding light on the high mortality associated with air pollution in India points to the need for more stringent air quality standards, say experts. The study, published in the Lancet journal, found a “clear association” between short-term exposure to air pollution and mortality, which “could serve as a strong addition” to emerging research suggesting India’s air quality standards be more health-focussed.

The current National Ambient Air Quality Standards (NAAQS) set the safe limit of 24-hour exposure to Particulate Matter 2.5 (PM_2.5) at 60 µg/m³, which is significantly higher than the World Health Organisation’s safe limit of 15 µg/m³. The Lancet study, which studied the association between air pollution related mortality in India for the first time, finds that short term exposure can increase risk of mortality by a higher margin than previously thought. The study estimates at least 33,000 people die from exposure to air pollution in 10 cities on an annual basis.

India’s NAAQS, which were last revised in 2009, are being reviewed by a committee led by the Indian Institute of Technology Kanpur, the government had said. Dr. Harshal Salve, additional professor in the Centre for Community Medicine at the ​All India Institute Of Medical Sciences Delhi and a member of the revision committee, told Mongabay-India that discussions on the committee’s work is ongoing with the Central Pollution Control Board (CPCB), but did not share further details. The revision process has been underway since at least 2022.

“When the review of the standard happens, health evidence that exists should be taken note of. There are several global studies and standards that exist which take health impacts into account and can help inform our own standard making process, but more needs to be done to understand local contexts and vulnerabilities.” said Anumita Roychowdhury, executive director of research and advocacy at the Centre for Science and Environment.

Higher mortality than previously thought

The Lancet study conducted two time series analyses from 2008 and 2019, looking at whether 48-hour variations in air pollution affected the daily number of deaths across 10 cities in India – Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla, and Varanasi.

The study’s main analysis used a more conventional approach of evaluating changes in PM_2.5 had on mortality, using aggregated, all-cause mortality from each city. This approach included using variables like satellite-based observations, meteorology, land-use patterns, emissions inventories, and reanalysis-based data to observe effects of PM_2.5 on deaths. A second “instrumental” analysis sought to isolate the effect of locally generated air pollution on deaths, by including more particular variables like wind speed, atmospheric pressure and the height at which air mixes (planetary boundary layer height PBLH). “For the instrumental analysis, we specifically call it air pollution because it could be a cocktail effect of both PM_2.5 and nitrogen oxide, from combustion sources like transport emissions and waste burning,” said Bhargav Krishna, author of the study and fellow at the Sustainable Futures Collaborative.

On average, the study’s main analysis observed a 1.42% increase in daily mortality per 10 μg/m3 increase of PM_2.5 levels. The instrumental analysis, which isolated the effects of local air pollution generation, found the rate of daily mortality to be even higher for every 10 μg/m3 increase – at 3.57%. The difference in rate indicates that past analyses “probably underestimated the effect of short-term exposure to air pollution on daily mortality.” Previous studies using global data sets estimated a 0. 68% increase in daily mortality per 10 μg/ m3 increase in PM_2.5.

The study also finds that the risk of mortality sharply increased at lower concentrations of PM_2.5, indicating “ambient PM_2.5 must be reduced substantially from current concentrations to garner concomitant health benefits.” The causal effects of air pollution at lower concentrations were seen in relatively cleaner cities like Shimla and Bengaluru. “People dying from air pollution are probably dying at lower to moderate levels of exposure, because they are already at risk. This includes people who have pre-existing health conditions, young children, and the elderly,” Krishna explained.

Collectively, the 10 cities recorded 3.6 million all-cause deaths from 2008 to 2019. The study estimates 7.2% of all deaths were attributable to PM_2.5 concentrations higher than WHO recommended limits, corresponding to 33,627 air pollution deaths annually. “Delhi had the largest attributable fraction and highest attributable yearly deaths,” says the study.

Setting health-based standards

The WHO’s guidelines on air pollution are devised through a five step process: formulating the scope and key questions of the guidelines, systematic review of the relevant evidence, assessing the certainty level of evidence resulting from systematic reviews, formulation of the air quality guidelines and formulation of other supporting guidance. While the guideline recommends a limit of 15 µg/m3 for safe 24-hour exposure to PM_2.5 levels, it also provides four interim targets for countries with high pollution levels to follow as they bring levels down.

India’s NAAQS have taken six components into consideration: land use patterns, pollutants, average time of exposure (annual, daily, eight hourly and hourly), levels of pollution, monitoring methods, and conditions (for example, the 24-hour or 8 hours averaged values should meet the NAAQS guideline levels 98% of the time in a year. However, the NAAQS don’t have a health component. India has lacked evidence-based research linking impacts of air pollution on morbidity and mortality.

In 2023, the Centre for Policy Research published a framework to include health indicators into the NAAQS, which was also co-authored by Krishna. It suggested a scientific review committee guide the standard making process, with help from working groups in charge of reviewing literature, ecological and health impacts, and advancements in monitoring methods, among other aspects.

According to Roychowdhury, the main challenge lies in enforcing standards. “We can tighten the benchmark of regulation, but in reality, we also have to meet the standard. That’s turning out to be a challenge in the Indo-Gangetic Plain and other parts of the country because it requires changes in how we carry out air quality management,” she said. Researchers and civil society groups have advocated an airshed level approach, which prioritises management of air quality beyond administrative and political boundaries.

Policies aimed at reducing air pollution levels, like the the National Clean Air Programme and the Graded Response Action Plan, kick in at high concentrations which would “only yield marginal benefits with respect to daily mortality, and negative health effects could continue to accrue even at lower pollution concentration,” says the Lancet study.

“Background levels of air pollution are also influenced by anthropogenic activity. Setting the air pollution standard low forces you to be much more stringent about how we approach some of the sources of air pollution and set more stringent metrics of progress. The point is to be ambitious, and work backwards to try and meet the standard,” said Krishna.

Banner image: Air pollution in India. Image by Yiğit KARAALİOĞLU via Pexels.

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