Air pollution from dirty fuel sources and congested roadways is taking a huge toll on human life, a new study has found. According to a report from the Washington Post, nearly 5.5 million people die each year due to complications related to breathing polluted air.

Air pollution is worse in some places than in others. While the air in the United States is relatively clean in many areas, the study found that some of the most polluted air comes from the coal-fired power plants and factories of China and India.

The study’s authors ranked diseases caused by air pollution against other leading global causes of death. It came in right behind smoking, which the World Health Organization says is responsible for the death of more than 6 million people each year. The study’s findings were presented at the recent annual conference of the American Association for the Advancement of Science in Washington, DC.

There are many different types of air pollution that can contribute to a wide range of negative health outcomes, but fine particulates from the burning of coal, wood, and other heavy fuels are some of the most dangerous. Burning wood in indoor cooking stoves is also responsible for a huge amount of health issues – breathing dirty air can lead to heart attacks and strokes.

The study showed that almost 1 million people in China died from heart attacks or strokes related to air pollution, as well as more than 500,000 people in India, and almost 300,000 in the U.S. and European Union in 2013. While the data is now 3 years old, researchers said that air pollution levels around the world haven’t changed a whole lot since then.

China’s constantly growing economy is largely to blame for the massive amounts of particulate matter in the air. The government is taking measures to equip cars and trucks with clean technologies that reduce their contribution to air pollution, the country’s massive manufacturing sector continues to dump more pollution into the air each year.

The picture in the United States and Europe is a little more rosy, with U.S. death rates from air pollution dropping from 119,000 to 79,000 between 1990 and 2013. Europe’s deaths dropped from 350,000 to 218,000 over the same time period.

While coal’s contribution to air pollution is a tougher problem to solve, both India and China are working to provide households with clean-burning stoves. This could massively reduce deaths due to air pollution, and the biggest issue remains making people aware of the risks.

A press release from the University of British Columbia describing the details of the study can be found here.