Wood burning pollution in Chile: A tale of two mid-size cities

Cities in southern Chile are facing high levels of PM2.5 because of wood burning pollution. We quantify the contribution of wood smoke to fine particles in two mid-size cities: Molina and Valdivia, located in different climate zones. The sampling campaigns were carried out during austral winter (July to September) in 2018 (Molina) and 2019 (Valdivia). 24-h filter samples were analyzed for carbonaceous compounds, secondary ions, metals, and particle-phase organic molecular markers. Average winter concentrations of PM2.5 were 53 ± 32 μg/m3 (average ± standard deviation) in Molina and 89 ± 55 μg/m3 in Valdivia. The major component of fine particles was organic matter, representing more than 70% of PM2.5. Concentrations of organic molecular markers were used in a receptor model (US EPA CMB8.2) to identify and quantify primary sources of PM2.5. The major source of PM2.5 was wood smoke, which accounted for 41.55 ± 9.77 μg/m3 (62.9 ± 15.3%) in Molina and 43.65 ± 24.06 μg/m3 (51.7 ± 21.1%) in Valdivia. Secondary organic aerosols (SOA) generated from inefficient wood burning, contributed 20.4 ± 17.7% in Molina and 28.9 ± 27.6% in Valdivia. Secondary inorganic ions and dust are minor sources of PM2.5. The total contribution of wood smoke (adding primary wood smoke and SOA) could be as much as 83% in Molina and 81% in Valdivia, during the winter season.