Have the increasing reports of air pollution prompted you to look for a cleaner city? If Bengaluru or Pune are on your list, you may want to reconsider.

Last week, a peer-reviewed report in Lancet Planetary Health revealed something surprising. It found that a spike in air pollution in cities that otherwise have cleaner air may lead to more pollution-related mortalities compared to highly polluted cities. So, the effects of short bursts of polluted air in Bengaluru or Pune could, in fact, be more damaging compared to, let’s say, Delhi, where polluted air is a constant.

The study, the first to look at multiple Indian cities, examines the relationship between short-term exposure to fine particulate matter suspended in the air and mortality. The correlation was established by analysing data on pollution and deaths in 10 cities—Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla and Varanasi—for over a decade.

Interestingly, pollution-related deaths in Bengaluru, Chennai, Kolkata and Mumbai accounted for a significant share of the 33,000 annual fatalities linked to air pollution. These cities are considered moderately polluted, at best.

So, then would a short trip to Himachal's Shimla offer cleaner air? That may be unlikely too. Between 2008 and 2019, Shimla, on average, saw 59 pollution-related deaths annually.

Worse, the study found that short-term exposure to a high level of PM 2.5—fine particulate matter in the air that is 2.5 microns or less in diameter—even for as little as 48 hours could drastically worsen life expectancy. Long-term exposure can increase the risk of lung cancer. That’s because these particles are so small that they can travel deep into the respiratory tract and penetrate the bloodstream.

But that still leaves us with the question: Why is short-term exposure worse?

How does short-term pollution worsen mortality? Short-term exposure to pollution in cities that are not characterized by it may be triggering a phenomenon called the “harvesting effect”. This means that the increase in risk from air pollution slows down in highly polluted cities, perhaps because exposure to poor air is constant. In effect, this means that cities such as Bengaluru or Pune, where pollution levels are relatively lower than Delhi, pose a bigger danger to public health.

“The study observes that at lower pollution concentration levels till 60 micrograms per cubic metre (µg/m3) or 100 µg/m3, the health impacts are very high, implying that even populations breathing in geographies where PM2.5 levels are within the limits of the National Ambient Air Quality Standards (NAAQS) are subject to huge health impacts and mortality,” says Sunil Dahiya, an analyst at the Centre for Research on Energy and Clean Air. In essence, this means that with every 10 µg/m3 rise in the concentration of PM2.5, the impact to health nearly doubles, he adds. However, he says that “as the concentration increases, mortalities too increase but not with the same steep slope”.

This means that it is of utmost importance to reduce levels of fine pollutants in these cities. But many of them are already compliant with NAAQS. Bengaluru, for instance, has a PM2.5 level of 33 µg/m3 while Chennai has a PM2.5 level of 33.7 µg/m3, below the NAAQS permissible limit of 40 µg/m3. So, where’s the issue?

Standards too lenient? Despite conforming to the Indian air quality standards, Bengaluru reported 2,102 pollution-related deaths per year between 2008 and 2019 while Chennai saw 2,870. So then, are the standards to blame?

“Given that we have never generated any data for these cities (which were considered clean for so long) before finding thousands of deaths related to air pollution is a matter of deep concern,” the study’s co-author Bhargav Krishna tells The Morning Context. “These are all cities that, on an annual basis, at least, meet the air quality standards,” he adds.

In these cities perhaps some months may report poor air quality. However, this is made up for in other months, which results in their annual overall pollution levels still abiding by the NAAQS.

Remember that the NAAQS standards were set by the Central Pollution Control Board in 2009 and haven’t been revised since. Also, the PM2.5 level of 40 micrograms per cubic metre of air is way above the World Health Organization’s limit of 5 µg/m3.

Krishna believes that India’s air quality standards may indeed be too lenient.

“We have seen the WHO, the US Environmental Protection Agency and other agencies around the world update their air quality standards based on newer information and studies that come out every year. The rate at which new studies have been published has ramped up substantially over the last 10 years, and our standards haven't been revised since 2009,” he says.

A national committee was constituted in late-2021 to revise these standards, but they still haven't come up with a report, he adds.

The study’s findings also highlight the need for better air quality monitoring systems in the country. Under the National Air Quality Monitoring Programme (NAMP), 804 air monitoring systems have been set up covering 344 cities, towns, villages in 28 states and 6 union territories as of December 2019. But just relying on monitors may not be enough.

“Monitoring data only tells us so much, ultimately, because you have a limited number of fixed monitors. Each one of these costs in crores and you have to train folks to maintain them,” says Krishna.

Also, a set of monitors across a city can only give a general understanding of the overall air quality. To understand the effects of local air quality in particular parts of the city, perhaps a different approach may be needed.

Bottom line: All cities would do well if treated with the same seriousness as heavily polluted ones. Also, India needs to revise its air quality measuring standards and look beyond just its monitoring system.

“To be able to reduce the health burden across cities we need to acknowledge the impact of air pollution on populations living in geographies throughout the country, come up with stratified NAAQS standards for different regions in India and try to move closer to WHO guideline levels and interim targets,” says Dahiya.

“Setting of ambitious targets for cities below the existing NAAQS can direct them to formulate clean air action plans similar to the action plans formulated by existing non-attainment cities under National Clean Air Programme and implementation of stringent measures can help reduce pollution levels systematically, which will help reduce the health burden and mortality due to hazardous air pollution,” he adds.

In the meantime, there's a need for urgent measures in cities that are reporting higher impact owing to such short-term exposure to pollutants.