Globally, air pollution is a silent killer. The air pollution levels in India are among the highest in the world, posing a heavy threat to the country's health and economy. Almost all of India’s 1.4 billion people are exposed to unhealthy levels of ambient PM 2.5 – the most harmful pollutant - emanating from multiple sources. These small particulates with a diameter of less than 2.5 microns, is about one-thirtieth the width of a human hair. Exposure to PM 2.5 can cause such deadly illnesses as lung cancer, stroke, and heart disease. Ambient and indoor air pollution is estimated to have caused 1.7 million premature deaths in India in 2019. The health impacts of pollution also represent a heavy cost to the economy. Lost labor income due to fatal illness from PM 2.5 pollution in 2017 was in the range of $30-78 billion, equal in magnitude to about 0.3-0.9 percent of the country’s GDP.
PM 2.5 comes from a variety of sources. Some of the most common sources include emissions from burning fossil fuels such as coal or oil and biomass such as wood, charcoal, or crop residues. PM 2.5 can also come from windblown dust, including natural dust as well as dust from construction sites, roads, and industrial plants.
Over half of PM 2.5 emissions in India are formed in “secondary” way in the upper atmosphere when different types of gaseous pollutants from one area such as ammonia (NH3), mix with other gaseous pollutants like sulfur dioxide (SO2), and nitrogen oxides (NOx) from another place. Agriculture, industry, power plants, households, and transport all contribute significantly to the formation of secondary PM 2.5. This secondary form spreads farther and wider than primary PM2.5 and travels across states, cities, and crosses jurisdictional borders.
The air pollution challenge in India is therefore inherently multi-sectoral and multi-jurisdictional. The common geographic area where pollutants mix and create similar air quality for everyone is called an airshed. Cities need to look beyond their immediate jurisdiction for effective air pollution control strategies and apply a new set of tools for airshed-based management. Also, standardizing tools across India is important so control strategies and relevant data sets can be linked.