Santiago's air is the most polluted air in Chile. In the 1990s air pollution fell by about one-third, but there has been little progress since 2000. A study by a Chilean university found in 2010 that pollution in Santiago had doubled since 2002. Particulate matter air pollution is a serious public health concern in Santiago, with atmospheric concentrations of PM2.5 and PM10 regularly exceeding standards established by the US Environmental Protection Agency and World Health Organization.