Since the inception of the World Health Organization’s (WHO) Air Quality Guidelines in 1987, scientific understanding of the health risks of polluted air has expanded. Evidence has mounted that even low-level exposure to air pollution is harmful to humans, especially with chronic exposure. It is increasingly evident that there is no safe level of air pollution. The WHO renews its guidelines to reflect developments in our understanding of the threats and risks from air pollution. The last update was in 2005.
