In September 2019, 20 municipalities in Acre, Amazonas, Mato Grosso and Rondônia had critically poor air quality, according to government data (see Figure 4). On average, PM 2.5 concentrations were between 50 and 78.5 micrograms per cubic meter on any given day of the month, between two and three times the maximum threshold of 25 micrograms prescribed by the WHO to protect health. In another 148 municipalities across the region, average PM 2.5 levels exceeded the maximum value set by WHO guidelines, ranging above 25 and up to 50. A total of 4,499,582 people residing in these 168 municipalities were exposed to these harmful pollution levels. Source: System of Environmental Information Integrated to Health (SISAM)