Spatiotemporal Trends in Air Pollution and the Built Environment in Urban Areas in Chile 2002-2015

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Chile has undergone rapid urbanization during a three-decade period of sustained development, resulting in increased air pollution in urban areas. In developed countries, health effects of air pollution have been shown to be modified by the built environment, but few studies have been conducted in South American cities due to lack of data. Remote sensing is an underused global resource that can be used to characterize air pollution and the built environment in countries such as Chile. We performed a spatiotemporal analysis of PM2.5, greenness, nighttime lights (NTL) trends in 493 urban areas in Chile from 2002 to 2015. We used annual mean PM2.5 estimates developed for the Global Burden of Disease at 1 km2 resolution. Greenness was assessed using Moderate Resolution Imaging Spectroradiometer derived Normalized Difference Vegetation Index (NDVI) at 250 m2 and 16-day resolution. Visible Infrared Imaging Radiometer Suite derived NTL at 500 m2 and 30-day resolution was used to measure urbanization density. We compared changes in PM2.5, NDVI and NTL across the 13-year period in urban areas of Chile. We also stratified by geographical region into north, central and south zones. Annual average PM2.5 and NTL increased by 10.8% (1.23 µg/m3) and 24%, respectively over the study period, while NDVI decreased by 4.2%. PM2.5 and NTL were positively correlated (r =0.66; p<0.001); while NDVI was inversely correlated with PM2.5 (r =-0.44; p<0.001) and NTL (r =-0.58; p<0.01). We found differential change rates over time by geographical region, with urban areas in the central zone having the most pronounced increases in PM2.5 and NTL and fastest decrease in NDVI compared to north and south zones. We generated built environment data for urban areas in Chile using public satellite data, applying methods that can be replicated in any country. The PM2.5, greenness, and NTL databases generated are a valuable resource that can be used in urbanization studies and air pollution epidemiology.