A new study in The Lancet Planetary Health says that even levels of air pollution below current Indian air quality standards lead to increased daily mortality rates in India – pointing to the need to address the problem on a war footing and go beyond the traditionally believed polluted zones in the northern belt and Delhi-NCR.
The study, seen by HealthTekPak, finds that across 10 cities in the country – Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla and Varanasi – approximately 33,000 deaths per year can be attributed to air pollution levels that are above the WHO permissible safe limit.
A significant number of deaths were seen even in cities generally not considered to have poor air quality, such as Mumbai, Bengaluru, Kolkata and Chennai. Off late, however, Mumbai’s deteriorating air quality, triggered by rampant construction and meteorological factors, has caused concern.
Conducted between 2008 and 2019, this is said to be a first-of-its-kind multi-city study that assesses the relationship between short-term air pollution exposure and death in India. To come to these conclusions, the authors used data on PM2.5 exposure in the 10 cities as well as daily counts of mortality between 2008 and 2019.
Particulate Matter (PM) 2.5 describes fine inhalable particles with diameters that are generally 2.5 micrometers and smaller. These can penetrate deep into the lungs and even enter the bloodstream, causing a wide range of health issues.
The authors include researchers from academic institutions such as Sustainable Futures Collaborative, Ashoka University, and Centre for Chronic Disease Control from in India, Karolinska Institutet of Sweden, Harvard University and Boston University from the US and others.
During the study period, 7.2% of all deaths (~33,000 each year) across all 10 of these cities could be linked to short-term PM2.5 exposure higher than the WHO guideline value of 15 μg/m3. Each 10 μg/m3 increase in short-term PM2.5 exposure was associated with a 1.42% increase in daily deaths, the study said.
This estimate nearly doubled to 3.57% when the researchers used a causal modeling approach that isolates the impact of local sources of air pollution. Increases in risk of death were steep at lower concentrations of PM2.5 and tapering off at higher concentrations, with significant effects observed below the current National Ambient Air Quality Standard of 60 μg/m3 for 24-hour exposure, the study said. India’s Central Pollution Control Board’s annual average permissible limits for PM 2.5 is 40 ug/m3 for the annual average and 60 ug/m3 for 24 hours – much lower than WHO’s limits.
City-wise data: Delhi tops list
In Delhi, one of the most polluted cities in the world, during the study period, 11.5% of all deaths (~12,000 each year; the highest across all cities studied) were attributable to short-term PM2.5 exposure higher than the WHO limit. Each 10 μg/m3 increase in short-term PM2.5 exposure was associated with a 0.31% increase in daily deaths. This estimate increased to 0.78% a causal modeling approach was used, indicating the need for greater attention to local air pollution sources.
In Chennai, which is believed to be better off than Delhi in terms of air quality, during the study period, 4.9% of all deaths (~2,900 each year) were attributable to short-term PM2.5 exposure higher than the WHO guideline value of 15 μg/m3 . Each 10 μg/m3 increase in short-term PM2.5 exposure was associated with a 0.97% increase in daily deaths. It increased to 5.31% when a causal modeling approach was used, indicating the strong effect of local air pollution in the city, the study said.
Shimla, way up in the hills, had the lowest air pollution levels recorded across all the cities in the study. However, air pollution was still a risk here with 3.7% of all deaths (59 per year) attributable to short-term PM2.5 exposure higher than the WHO guideline value of 15 μg/m3. The results from Shimla add credence to global evidence that there is no safe level of air pollution exposure.
Among other cities, in Ahmedabad 5.6% of all deaths were attributable to short-term PM2.5 exposure, Bengaluru 4.8%, Hyderabad 5.6%, Kolkata 7.3%, Mumbai 5.6%, Vanarasi was high at 10.2% and Pune reported 5.9% deaths during the study period.
Remedial action needed
The findings underscored the need for India’s air quality standards to be made more stringent and for remedial action to be expanded beyond current ‘non-attainment cities’.
The researchers found that air pollution policy currently focuses on ‘non-attainment cities’, which fail to meet the current Indian standard. Since these standards are 4X the current WHO guideline value of 15 μg/m3, people in many more regions beyond these cities are also vulnerable. This study shows the need to expand remedial action beyond current ‘non-attainment cities’
It says there is a need to increase focus on action year-round and not just on seasonal extremes. A large proportion of mortality risk is concentrated at low to moderate PM2.5 levels with risk tapering off at higher levels. The current policy instruments such as the Graded Response Action Plan (GRAP) largely focus on pollution extremes and must be recalibrated to focus on year-round action, the study says.
Policy instruments need to be developed to better address dispersed local sources of air pollution. These are the sources most people are exposed to regularly but are also the most complex to address. Doing so, however, would bring with it substantial health gains. This would require focusing not just on ambient concentrations but also on polluting sources, the study says.
Bhargav Krishna, fellow at the Sustainable Futures Collaborative and a lead author on the study, said, “The results of this multi-city study show us that reducing air pollution is a nationwide challenge. Our analyses highlight air pollution’s substantial effects on death even in cities previously considered less polluted such as Mumbai, Bengaluru, Kolkata and Chennai. The significant effects observed below the current Indian standards have implications for what we consider acceptable air quality, and emphasize the need for stringent year-round action across the whole country.”
Jeroen de Bont, a postdoctoral researcher at Karolinska Institutet and a lead author, emphasized the significance of India’s first multi-city 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,” he said.
The study accounted for a diverse air quality profile across 10 Indian cities and demonstrates for the first time that the risk of mortality is significant even at lower levels of air pollution, said Poornima Prabhakaran, director of the Centre for Health Analytics Research and Trends (CHART) at the Trivedi School of Biosciences, Ashoka University and India lead of the CHAIR-India consortium.
“The insights signal an urgent need to revisit our air quality management strategies that currently focus only on ‘non-attainment cities’, rethink current air quality standards accounting for the lower risk thresholds and shift from addressing regional to local sources to effectively protect human health,” Prabhakaran said.
Professor Joel Schwartz of Harvard University, a co-author of the study, said lowering and enforcing Indian air quality standards will save tens of thousands of lives per year. Methods for controlling pollution exist and are used elsewhere. They urgently need to be applied in India, Schwartz said.
The levels of air pollution in India are extremely high and this study shows how day-to-day variations in these levels lead to considerable mortality, said Petter Ljungman, associate professor at the Karolinska Institutet, and one of the researchers involved in the study. Local pollution sources are likely to be more toxic than more distant sources which have implications for policymakers addressing this highly relevant threat to human health, Ljungman said.
Air pollution is a major problem in India, with the average number of deaths caused by air pollution in India estimated at over two million in 2021, according to Satista. The number of deaths caused by air pollution in India has increased by almost 60% since 1990. Another report by The Lancet said pollution led to more than 2.3 million premature deaths in India in 2019. According to a modeling study published in The BMJ last year, outdoor air pollution from all sources accounted for 2.18 million deaths per year in India in 2019, second only to China.
Initially believed to be a pain point in Delhi-NCR and the surrounding northern belt, various studies have shown that air pollution is a pan-India problem, ranging from the fragile reaches of Kashmir to the green zones of Northeast India to the coastal belts of Southern India – calling for concerted efforts and year-long efforts to address the problem.
The Lancet study says focus cannot only remain on seasonal high exposure events such as during winter, and requires action on all sources year-round. The Graded Response Action plans focused solely on these extremes and hence would only yield marginal benefits concerning daily mortality, with negative health effects continuing to accrue all year round even at much lower exposure levels.
Casual analyses highlight the need for greater attention to the numerous dispersed sources of local air pollution across cities, including from transport and waste burning among others. These are more challenging to address, but could yield substantial health benefits, the study says.
