Air pollution has become the world’s largest single environmental health risk, killing more people worldwide than AIDS, malaria, breast cancer or tuberculosis each year. China’s problems with smog and harmful emissions have been well documented, but a recent study has apparently managed to calculate its cost on the nation’s health. According to the study, to be published in PLoS One, air pollution in China is killing a staggering 4,400 people per day.

The researchers, from the non-profit organization Berkeley Earth, estimate that around 1.6 million people in China die per year from conditions related to air pollution, including heart problems, lung cancer and stroke. This pollution mainly comes from burning coal, which is still used as the country's major source of fuel, and was reflected in data that showed that pollution levels increased during winter when more coal was being burnt to heat homes.

The study used data collected over a period of four months from over 1,500 ground stations, which gathered information every hour on the fine airborne particles present in the air. These minuscule particulates, less than 2.5 microns in diameter, cause health problems when inhaled as they can subsequently enter the bloodstream and circulate throughout the body.

They found that pollution was worse in the north-east of the country, around the city of Beijing. This is despite government promises to cut levels of pollution in the city in the lead up to the 2022 Winter Olympics. Interestingly, the researchers found that while the city itself might be implementing measures to try and cut emissions within the city, such as limiting car use, most of the pollution actually originates in the major industrial zone of Shijiazhuang, 320 kilometers (200 miles) southwest of the capital.

It was also shown that a shocking 38% of Chinese people live in areas where the air they breathe would be classed as “unhealthy” by United States standards. But the country is trying to mitigate the causes, especially in tackling its reliance on coal. In recent years, the use of coal in China has started to drop, with the first four months of 2015 showing an 8% decrease when compared to the same period last year. The country is also one of the world’s major investors in renewable energy.

The data used by Berkeley Earth is to be made available to the public so that other researchers can wade through the figures and do their own studies. It’s hoped that with more studies such as this, Chinese authorities might make bigger commitments to cut their emissions.