In one year, India's ozone pollution damaged millions of tonnes of the country's main field crops, causing losses of almost a billion pounds and destroying enough food to feed tens of millions of people living below the poverty line.

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New research backed by the American Geophysical Union (AGU) looked at the agricultural effects of high concentrations of ground-level ozone in 2005 (the year was chosen to be representative of the first decade of the 21^st Century). Although Ozone is best known for its presence in a layer of the stratosphere which prevents harmful ultraviolet radiation from reaching the Earth's surface, at higher concentrations nearer to the ground it can cause massive damage to plants.

Ozone emissions come primarily from vehicles, cooking stoves and industrial emissions. Ground-level ozone is formed when nitrogen oxides, carbon monoxide and volatile organic compounds react with sunlight after they are released into the atmosphere.

Rising emissions are causing severe ozone pollution in some of India's most populated regions. Capital city Delhi is now one of the most polluted cities in the world, according to India's Air Monitoring Centre, with pollution levels comparable to Beijing.

Ozone at ground level – the main component of polluting smog – can cause leaf damage that stifles plant growth, injuring and killing vegetation. There are currently no air quality standards in India designed to protect agriculture from the effects of ground-level ozone pollution.

Earlier this year, researchers in the United States warned that the combinatory effects of heat and pollution will affect yields of different crops in different ways. They warned that, as climate change and pollution worsen, wheat yields may be affected as the crop is very sensitive to ozone exposure, while maize is much more adversely affected by heat. Atmospheric pollution could cause temperatures to rise, which will then amplify the effects of pollution, the researchers said.

The AGU authors used computer modelling to calculate the damage to crops in India, based on emissions estimates, crop data and information on levels of ozone different crops can tolerate.

They estimate that in 2005, surface ozone pollution damaged 6 million metric tonnes of India's wheat, rice, soybean and cotton crops. Sachin Ghude, an atmospheric scientist at the Indian Institute of Tropical Meteorology (IITM) in Pune, India and lead author of the American Geophysical Union study said that 94 million people could have been fed with the lost yield – or about a third of the country's poor.  

Wheat – one of India's major food sources – saw the largest loss by weight of the four crops studied in Ghude's paper. Ozone pollution damaged 3.5 million metric tonnes of wheat in 2005. Rice losses amounted to 2.1 Mt. The total losses from ozone pollution are thought to be worth almost £800m.

Warmer temperatures, one of the anticipated results of ongoing climate change for India, could increase ground-level ozone, according to previous research. Ghude said his paper is the first to quantify damage India's ozone pollution has caused the country's major crops. Whilst most studies look at future scenarios, the AGU study examined how ozone emissions are already affecting crops.

Satellite data has shown that ozone has increased over the country in the last two decades, Ghude said.

The aim of the research was to convince policy makers of the need to introduce ozone pollution standards. It could also help India, a country with a high rate of poverty, as the country implements a new law that subsidises grain for two-thirds of the country’s residents, he said.

The new food security bill will require authorities to provide 61.2 Mt of cereal grains – including wheat and rice – to India’s poor each year at a subsidized rate.