There was a time when people first searched for weather updates when they logged on to the internet. Today, across several cities, people first search for smog- and pollution-related updates before beginning their day.

And, this is reflected in the trends data from Google. Compared to other health issues, such as heart attacks and flu, Indians seem far more concerned about air pollution. Search interest in terms related to air pollution exceeds both heart attacks and flu, and peak in October-November, driven by increased interest from Delhi-National Capital Region. This is the period when a combination of crop burning, industrial activity, higher traffic and winds envelope much of north India in a visibly toxic smog.

Though interest in air pollution peaks at this time of the year, it is in fact a year-long, nationwide phenomenon. There are many ways to measure air pollution and, on almost all of these measures, India’s air is more dangerous than the global average. On PM2.5 levels, which measures the concentration of the smallest and most dangerous pollutants in the air, the country’s air is especially toxic. For instance, in 2016, the last year for which there is globally comparable PM2.5 data, the average population-weighted exposure to PM2.5 in India was 76 micrograms per cubic metre (mg/m3), which is around 50% higher than the global figure of 50, eight times higher than the World Health Organization’s (WHO’s) recommendation of 10 mg/m3, and nearly double the less stringent Indian government recommendation of 40 mg/m3.

PM2.5 is especially dangerous because it can travel far from its source, making it a nationwide problem affecting both cities and villages. India’s air monitoring stations, though, only capture air quality in cities. This risks making air pollution an urban problem, when it is equally a rural one. According to one estimate, PM2.5 levels were actually 2% higher in rural India compared to urban areas in 2015.

Even among cities, much of the discourse has focused on the air quality in major cities—and notably Delhi—when almost all Indian cities are breathing bad air. Between 2017 and 2018, PM2.5 levels increased in 21 of the 26 cities for which data was available. In 2018, Delhi, Agra and Lucknow were cities with the foulest air. And, only six cities had air that met the Indian benchmark of 40 mg/m3.

Breathing in dirty air not just hurts the lungs, but can have other, equally damaging effects. PM2.5 particles, for instance, are associated with a range of other deadly diseases including strokes and heart attacks. These threats are prematurely curtailing lives around the world and in India.

According to the Air Quality Life Index, an index converting air pollution concentrations into their impact on life expectancy, calculated by researchers from the University of Chicago, the average Indian’s life expectancy would increase by around four years if PM2.5 levels were brought down to WHO standards. In the polluted northern belt of the country, the rewards would be even larger with life expectancy potentially increasing by seven years.

Beyond health costs, air pollution can also hurt the economy in other ways. In a 2018 study, Jamie Hansen-Lewis of Brown University finds that air pollution hurts productivity in India’s labour-intensive industries. She estimates that bringing the country’s air to global standards would lead to a small increase in profits of 0.3% across manufacturing companies with more pronounced effects in labour-intensive firms. Similarly, pollution is also hurting agriculture by stifling crop productivity. One 2014 study estimated that air pollutants were responsible for 19% of the loss in yields in wheat production in India in 2010.

Finally, air pollution is also linked inextricably to climate change. Some of the same particles that clog up the lungs can clog up the atmosphere and contribute to the changing weather patterns.

If the effects of air pollution are manifold, so are the causes. Globally, air pollution is largely a product of five factors: Vehicles, industry, household burning (wood/coal), natural sources (for example, dust or sea salt) and other human activity (for example, crop burning). In India, too, all these factors matter, but their relative importance changes with geography. In many parts of India, for instance, the biggest source of PM2.5 in outdoor air actually comes from indoors. Millions of Indians still use traditional cooking methods that generate fumes laden with PM2.5.

In larger metros, where clean cooking fuels are more prevalent, pollution sources vary more. For instance, according to UrbanEmissions.info, an air pollution data portal, Delhi’s pollution, especially in the October-December period, is a combination of vehicles (around 30% of PM2.5 emissions), industry (20%) and crop burning (15%). In Chennai, air pollution is driven more by industrial activity (around 70% of emissions).

Different sources of air pollution require different policies that address these sources. And, given that air pollution has no boundaries, policies cannot be city-centric and should instead focus on regions, according to Santosh Harish, a fellow at the Delhi-based Centre for Policy Research.

“India’s air pollution policy needs to be more systematic," said Harish. “This means tackling each of the big sources of air pollution, actively prioritising solutions, and moving away from the reactive, urban-centric approach in place currently."

This is the fourth of a five-part data journalism series on India’s environmental crisis

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