Chemical speciation and source apportionment of fine particulate matter in Santiago, Chile, 2013

Abstract

Santiago is one of the largest cities in South America and has experienced high fine particulate matter (PM2.5)concentrations in fall and winter months for decades. To better understand the sources of fall and wintertimepollution in Santiago, PM2.5 samples were collected for 24 h every weekday from March to October 2013 forchemical analysis. Samples were analyzed for mass, elemental carbon (EC), organic carbon (OC), water solubleorganic carbon (WSOC), water soluble nitrogen (WSTN), secondary inorganic ions, and particle-phase organictracers for source apportionment. Selected samples were analyzed as monthly composites for organic tracers.PM2.5 concentrations were considerably higher in the coldest months (June–July), averaging (mean ± standarddeviation) 62±15 μg/m3 in these two months. Average fine particle mass concentration during the study periodwas 40 ± 20 μg/m3. Organic matter during the peak winter months was the major component of fine particlescomprising around 70% of the particle mass. Source contributions to OCwere calculated using organic molecularmarkers and a chemical mass balance (CMB) receptor model. The four combustion sources identified were woodsmoke, diesel engine emission, gasoline vehicles, and natural gas. Wood smoke was the predominant source ofOC, accounting for 58 ± 42% of OC in fall and winter. Wood smoke and nitrate were the major contributors toPM2.5. In fall and winter, wood smoke accounted for 9.8 ± 7.1 μg/m3 (21 ± 15%) and nitrate accounted for9.1 ± 4.8 μg/m3 (20 ± 10%) of fine PM. The sum of secondary inorganic ions (sulfate, nitrate, and ammonium)represented about 30% of PM2.5 mass. Secondary organic aerosols contributed only in warm months, accountingfor about 30% of fine PM during this time.