Trends in particle matter and its elemental composition in Santiago de Chile, 2011 - 2018

Daily fine (PM_2.5) and coarse (PM_10-2.5) particle matter (PM) samples collected at Parque O'Higgins station in downtown Santiago de Chile have been studied to find the trends in concentration from 1998 to 2018. Elemental concentration was obtained using X-ray fluorescence (XRF). Regression models from previous studies indicate that the PM_2.5 and PM_10-2.5 fractions have had a continuous decrease since 1988 mostly due to several policy control measures carried out over several decades. PM_2.5 has decreased from 68.3 in 1988 to 27.6 μg/m³ in 2018 (60.4%). However, if only the last 8 years are considered (2011-2018), a leveling off can be observed in PM_10-2.5 and PM_2.5, which points to a change in the tendency. Cluster analysis of the elements in the fine and coarse fractions were identified to evaluate trends in the contributing sources. In the fine fraction, the mass contribution of crustal elements (Si, Al, Ca, and Fe) has remained stable in the last 8 years, and mass contribution of elements (Pb, Br, and Cl) associated to anthropogenic sources (traffic, wood burning) has also remained stable in the same period. For the coarse fraction, the contribution of one group of elements associated to crustal or anthropogenic sources has remained stable, and another group has decreased in the last 8 years. The leveling off can be ascribed to decreased rainfall during the last 8 years that have promoted soil dryness and resuspension of dust facilitated by wind or vehicular traffic. Mean temperatures have increased in the last 30 years, but have not contributed directly to the leveling of the concentration.Implications: Regression models indicate that the PM_2.5 (fine) and PM_10-2.5 (coarse) fractions at Parque O'Higgins station in Santiago de Chile have had a continuous decrease since 1988 mostly due to several policy control measures carried out over several decades. However, in the last 8 years (2011-2018), a leveling off can be observed in PM_10-2.5 and PM_2.5. X-ray fluorescence (XRF) analysis was performed in the fine fractions indicating that the mass contribution of crustal elements (Ca, Al, Si, Fe) to the fine fraction has remained stable. This phenomenon can be ascribed to decreased rainfall during the last 8 years that have promoted soil dryness and resuspension of dust facilitated by wind or vehicular traffic. The crustal elements in the coarse fraction have also remained stable.