Last year it was reported that over three million people a year die prematurely due to air pollution. But new research has found that this is in fact an underestimate, and that the real figure is somewhere in the region of 5.5 million. From this, they found that more than half of these premature deaths occurred in just two countries: India and China. As both nations continue to develop, the number of deaths from air pollution in these countries is expected to climb.

“One of the surprises to us is that air pollution is one of the leading risk factors for death and disease around the world,” explains Michael Brauer, who presented the research at the meeting of the American Association for the Advancement of Science. “Estimates are that five and a half million people every year are dying as a result of air pollution. One of the unique things about air pollution is that you can’t run [and] you can’t hide from it, but we know that if you improve air quality, everybody benefits.”

There are two main types of air pollution: outdoor, and household. The first is caused mainly by things such as power plants, vehicle exhaust, and land clearing for agriculture, while the second comes from people using open fires or inefficient stoves within their homes. While outdoor air pollution is common to almost every city worldwide, household air pollution is primarily a problem in rural areas of developing countries.

As part of the Global Burden of Disease project, the study looked into how as pollution is inhaled, the risk of heart disease, stroke, and even cancer is increased. Pollution is generally defined as tiny liquid or solid particles typically 0.0025 millimeters in diameter. Combining pollution data with health statistics, they estimate that in China there are 1.6 million deaths a year, and in India 1.3 million, which are attributed to air pollution. In China, many of these deaths are due to the country's heavy reliance on coal, while in India it is more likely to be due to the burning of wood and dung as a fuel source.

“One of the reasons that we focus particularly on China and India is that the sources that contribute to air pollution are also major sources contributing to climate change,” says Brauer. “And by highlighting the health impacts of air pollution we’re hoping to catalyze a faster shift away from these dirtier sources to cleaner energy sources for these countries.”