Effects of environmental alerts and pre-emergencies on pollutant concentrations in Santiago, Chile

► Santiago's air quality policy significantly reduced pollutant's concentrations. ► Reductions in PM10 and PM2.5 were 5%-7% in alerts and 12% in pre-emergencies. ► The average decline in CO and NOx was 10% in alerts and 20% in pre-emergencies. ► Restrictions led to significant reductions in CO, NOx, PM10 and PM25 in weekdays.