Air pollution killed 7 million people worldwide in 2012, about one-in-eight of all deaths, according to new estimates released Tuesday by the World Health Organization.

That figure more than doubles previous estimates, making air pollution the single greatest environmental health risk today. WHO, the United Nations’ public health agency, linked outdoor air pollution to 3.7 million premature deaths in 2012. Indoor air pollution accounted for 4.3 million deaths that year.

The death toll falls disproportionately on low- and middle-income countries, particularly in WHO’s South-East Asia and Western Pacific Regions, where more than 70 percent of all air pollution deaths occurred. China, where clouds of smog envelop entire cities, accounts for a sizable chunk of global air pollution deaths. A separate study, published in the Lancet, linked outdoor air pollution to 1.2 million premature deaths in China in 2010.

Scientists have linked air pollution exposure to heart disease, stroke, chronic obstructive pulmonary disease, lung cancer and acute lower respiratory infections in children.

Indoor air pollution primarily affects households that still use solid fuels for cooking and heating. The smoke produced from burning coal, wood or dung can lead to respiratory and cardiovascular diseases.

“Poor women and children pay a heavy price from indoor air pollution since they spend more time at home breathing in smoke and soot from leaky coal and wood cook stoves,” said WHO Assistant Director Dr. Flavia Bustreo in a statement.

WHO linked deaths caused by outdoor air pollution to “unsustainable policies in sectors such as transport, waste management and industry.” The report urged policymakers to look towards cleaner options.

“In most cases, healthier strategies will also be more economical in the long term due to health-care cost savings as well as climate gains,” said WHO Coordinator for Public Health Dr Carlos Dora in a statement. “WHO and health sectors have a unique role in translating scientific evidence on air pollution into policies that can deliver impact and improvements that will save lives.”