India is on the verge of overtaking China as the country with the most deaths caused by air pollution, the world's biggest environmental killer, according to research published on Tuesday. From a report: The State of Global Air 2017 report states that extensive, long-term exposure to fine particulate matter contributed to more than four million premature deaths in 2015. The report is a joint effort between the Health Effects Institute and the Institute for Health Metrics and Evalution's Global Burden of Disease Project. "We are seeing increasing air pollution problems worldwide," Dan Greenbaum, president of the Health Effects Institute, said in a statement. "The trends we report show that we have seen progress in some parts of the world -- but serious challenges remain," Greenbaum went on to add. The report's analysis showed that India -- with extra exposure and its aging population -- now competes with China in terms of air pollution health burdens. Both countries saw around 1.1 million early deaths due to air pollution in 2015.