New Delhi: Between 2008 and 2019, air pollution was linked to the deaths of 33,000 people every single year in ten Indian cities, a study published on Thursday (July 4) in the journal The Lancet Planetary Health has found.
The study, which examined the link between short-term exposure to fine particulate matter (or PM2.5, an air pollutant) and daily mortality, found that even cities where the levels of fine particulate matter were lower than the current Indian air quality standards witnessed increased daily mortality rates. These included Mumbai, Bengaluru, Kolkata and Chennai.
Meanwhile, Rohtak in Haryana had the most polluted air in June this year, when compared to around 250 cities in the country, as per a monthly ambient air quality report of cities published on July 3 by the Delhi-based Centre for Research on Energy and Clean Air, based on data from the Central Pollution Control Board.
Air pollution and permissible limits
Lung and heart-related illnesses, cancers and even death: these are some impacts that occur when fine particulate matter, which are tiny, inhalable particles less than 2.5 micrometers in diameter, lodge themselves in our bodies when we’re exposed to air pollution.
As per the recent State of Global Air 2024 report, the deaths of 8.1 million people worldwide in 2021 were linked to air pollution. This made air pollution the second leading risk factor (something that increases the possibility) of deaths that year, just after high blood pressure. Fine particulate matter or PM2.5 – produced when burning fossil fuels are burnt – is the main culprit.
The report found that PM2.5 (both ambient and household together) is the largest contributor to the air pollution disease burden worldwide, accounting for 7.8 million deaths, or more than 90% of the total air pollution disease burden. Disease burden refers to the intensity or severity of the disease and its possible impact on the daily lives of people exposed to air pollution. India alone accounted for 2.1 million of these deaths attributed to air pollution.
That’s why there are permissible limits to the levels of PM2.5 that people should be exposed to. Guidelines prescribed by the World Health Organisation specify that annual average concentrations of PM2.5 should not exceed 5 µg/m³, and 24-hour average exposures should not go beyond 15 µg/m³ for more than three to four days per year. The limits prescribed by the Indian government are less stringent: a limit of 60 µg/m³, under the National Ambient Air Quality Standards (NAAQS).
But how is short-term exposure to PM2.5 levels linked to deaths? To find out, a team of scientists including Bhargav Krishna, fellow at the Sustainable Futures Collaborative, obtained data on daily mortality (ranging from three-seven years per city, which qualifies as short-term exposure to PM2.5) from death registries in ten cities — Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla and Varanasi — for the time period from 2008 to 2019. Their final list contained 3.6 million deaths. The team then obtained data on fine particulate matter (PM2.5) in these cities, from several sources — regulatory monitors, satellite data and meteorology. They then combined these with machine-learning based models that they developed, to generate data on city dwellers’ exposures to PM2.5.
Need to revise existing air pollution standards
The results of this study show that that 7.2% of all daily deaths were attributable to PM2.5 concentrations that were higher than the WHO-specified guideline of 15 μg/m3. This amounted to an estimated 33,627 annual deaths across ten cities every year.
“Delhi had the largest attributable fraction and highest attributable yearly deaths,” the study noted. The national capital recorded around 12,000 deaths per year that could be attributed to air pollution.
The study, published on July 4 in The Lancet Planetary Health, also noted that “no safe threshold for air pollution exposure exists”. For every 10 μg/m³ of exposure to PM2.5, the team found an increase of 1.42 percent in daily mortality. This is more than double the increase specified in some global studies over the years. When the team used their modelling methods to identify the effect of locally generated air pollution, they found a far stronger effect on daily mortality — an increase of 3.57%.
What is alarming is that the study also found that even cities where levels of fine particulate matter were lower than the current Indian air quality standards witnessed increased daily mortality rates. These included the cities of Mumbai, Bengaluru, Kolkata and Chennai. In the case of Bengaluru, for instance, 4.8% of all deaths (~2,100 each year) from 2008 to 2019 were attributable to short-term PM2.5 exposure that was 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 3.06% increase in daily deaths. This estimate nearly tripled to 9.12% when the team used their modelling approach, suggesting that policymakers have to focus on regulating local air pollution sources in the city.
“The results of this first-of-its-kind, multi-city study show us that reducing air pollution is a nationwide challenge,” commented Krishna, one of the lead authors of the study, in a press release.
Also read: Air Pollution Linked to 8.1 Million Deaths in 2021; African, South Asian Countries Bear the Brunt
“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 emphasise the need for stringent year-round action across the whole country.”
India is currently in the process of reviewing its national ambient air quality standards (NAAQS), the study noted. “The NAAQS are substantially more relaxed than the WHO guidelines for acceptable exposure for all pollutants (eg 60 μg/m³ vs 15 μg/m³ for 24 h PM2·5 exposure). This study could serve as a strong addition to the growing local evidence base that the review could include in developing new standards for India,” it read. The study also recommended that it is vital to address dispersed local sources of air pollution – such as dust emitted from construction sites – along with the usual fixed sources of pollution (such as factories and thermal power plants), and linear sources (such as roads and rail routes).
Notably, a monthly ambient air quality report published by the Centre for Research on Energy and Clean Air (CREA) using data provided by the Central Pollution Control Board found that Rohtak was the city with the most polluted air in June this year. The city recorded a monthly average PM2.5 concentration of 116 µg/m³, surpassing India’s daily NAAQS. As per this standard, the safe limit of PM2.5 is 60 µg/m³ on every single day of the month.
As per the CREA report, only 14 out of the 60 cities featured in the daily top 10 most polluted cities list in June this year are part of India’s National Clean Air Programme (NCAP). The remaining 46 cities, per the report, do not have any action plan in place to reduce hazardous air pollution concentrations.
Out of 251 cities that had more than 80% of days of data from continuous ambient air quality monitoring stations, 228 recorded PM2.5 concentrations below India’s daily National Ambient Air Quality Standards (NAAQS) of 60 µg/m³. However, only 33 cities, including Bengaluru, Mumbai, Imphal, Puducherry, Bhopal and Bhubaneswar met the World Health Organisation’s (WHO’s) daily safe guideline concentration of 15 µg/m³.
