Air quality status and trends over large cities in South America

Air pollution is one of the most persistent environmental issues in South America, with exposure to air pollutants being associated with increased mortality and morbidity. According to estimates of the World Health Organi-zation (WHO), in 2016, 91 % of the global population lived in cities that exceeded the WHO PM2.5 annual guideline (10 mu g/m(3)). In Latin America and the Caribbean, other studies affirm that approximately 100 million people are exposed to poor air quality, exceeding WHO guidelines. This study presents a review of long-term (annual) and short-term (daily) concentrations of nitrogen dioxide (NO2), sulfur dioxide (SO2), particulate matter (PM10 and PM2.5), carbon monoxide (CO), and ozone (O-3), collected between 2010 and 2017 by the automatic monitoring networks of 11 metropolitan areas of South America, including three of global 33 megacities (Rio de Janeiro, Sao Paulo, and Buenos Aires), and three from all 34 largest cities in the world (Bogot ' a, Lima, and Santiago). Despite efforts to monitor air quality, in some cities, the information on air quality provided by environmental authorities still has poor publicity and presentation, making it difficult to take action for critical air pollution episodes. Annual particulate matter (PM2.5 and PM10) monitored in all cities (2010-2017) exceeded the World Health Organization Air Quality Guidelines (WHO-AQG). The annual NO2 guideline was exceeded at least in one city between 2010 and 2017, except in 2014. Most average daily concentrations of SO2 in South America were below the WHO-AQG. Still, Vit ' oria, Rio de Janeiro, and Belo Horizonte Metropolitan Areas presented values over WHO guidelines, and for the two last cities, over intermediate standards of Brazilian national legislation. Most of the ozone concentration (8-h running average) was below WHO-AQG, but Rio de Janeiro, Sao Paulo, and Belo Horizonte presented exceedances of this limit between 2010 and 2017. Although some cities in South America have their pollutant concentrations reduced since 2010 (PM2.5, for example), such as Sao Paulo, Vit ' oria, and Bogot ' a, the region does not report a trend in the same direction, with the WHO guidelines and national or local standards being continuously exceeded.