LAUSR

Abstract In Chile, at least 60% of the country's urban population live in cities at which ambient PM2.5 exceeds the annual ambient air quality standard (AAQS) of 20 μg/m3. We assess the effectiveness of ambient PM2.5 regulations in Chile by estimating meteorologically adjusted trends in ambient PM2.5. This analysis includes 9 geographical regions, 33 monitoring sites in 23 cities, comprising 61% of Chile's urban population. We find a significant downward trend in ambient PM2.5 in most cities that have an Air Quality Management Plan (AQMP, PDA in Spanish); these include the case of Santiago and southern cities at which ambient PM2.5 is dominated by residential wood burning (RWB). However, in cities without AQMP our results are mixed: in some cities there is no significant trend at all and in others there is a downward, significant trend, ascribed to nationwide regulations upon mobile sources. Overall, we estimate a significant downward trend in ambient PM2.5 for 56% of Chile's urban population. Hence, ongoing regulations have been efficient in reducing ambient PM2.5. The significant downward trends are higher in magnitude (up to 4.4 μg/m3 per year) for smaller, more polluted cities than for cleaner or larger urban zones (down to 0.3 μg/m3 per year).