Nine out of ten people around the world are exposed to polluted air... and about seven million people died due to air pollution last year.<br /> The World Health Organization says air pollution is worse in under-developed countries, while big cities in rich countries improved their air quality between 2010 and 2016.<br />It says South Asia and South East Asia suffer the most from poor air quality.<br />The head of the WHO warned that sustainable development won't be possible if the world does not tackle the problem. <br />
