Ambient particulate matter in Santiago, Chile: 1989–2018: A tale of two size fractions

Abstract

We have analyzed trends in ambient fine (PM2.5) and coarse (PM2.5-10) particulate matter in Santiago, Chile, forthe last 30 years. PM2.5 has monotonously decreased between 67% and 72% at those sites. Trends varied between􀀀 2.0 and 􀀀 2.7 (μg/m3/year) between 1989 and late 90’s, and between 􀀀 0.7 and 􀀀 1.1 (μg/m3/year) afterwards.This slowing down is likely a consequence of fast increase of motor vehicles in the city, which have become adominant source of ambient PM2.5. Annual ambient PM2.5 concentrations are still above 20 (μg/m3), so moreregulation is needed to bring them down.Coarse particles have changed little in 30 years, decreasing between 0% and 12%; particle concentrations haveevolved in a non-linear way: first increasing in 1989–1995, then decreasing until 2003, and with a flat trendafterwards. We ascribe these trends to a combination of a) public works implemented throughout the city, b)fugitive dust controls like street sweeping programs and emission offsets for PM10 and c) increasing numbers ofmotor vehicles in the city. Further initiatives are needed to curb down coarse particles as well.By considering interaction between trend and seasonality, we have found that ambient PM2.5 has monotonouslydecreased all year long at all monitoring sites with similar patterns; this is characteristic of a regionalscalepollution. For ambient PM2.5-10 trend and season have a more complex, site-specific interaction, suggestinglocal sources and site location in the basin are relevant in determining ambient concentrations of coarseparticles.A limitation of this study is that no quantitative link between ambient concentrations trends and atmosphericemissions could be established with the analyses carried out. A strength of the study is the long period analyzedwith measurements conducted with the same gravimetric methodology.