<p>An urgent examination of one of the biggest global crises facing us today, air pollution, looking at the rise of the problem, how we understand it and what needs to change.<br>More than 90% of the world's population is exposed to air pollutant concentrations exceeding World Health Organisation guideline levels. Having air that is healthy to breathe is one of the greatest challenges of the 21st Century. Some of this is unfinished business from ...