Disentangling fine particles (PM_2.5) composition in Hanoi, Vietnam: Emission sources and oxidative potential

A comprehensive chemical characterization of fine particulate matter (PM_2.5) was conducted at an urban site in one of the most densely populated cities of Vietnam, Hanoi. Chemical analysis of a series of 57 daily PM_2.5 samples obtained in 2019-2020 included the quantification of a detailed set of chemical tracers as well as the oxidative potential (OP), which estimates the ability of PM to catalyze reactive oxygen species (ROS) generation in vivo as an initial step of health effects due to oxidative stress. The PM_2.5 concentrations ranged from 8.3 to 148 μg m^-3, with an annual average of 40.2 ± 26.3 μg m^-3 (from September 2019 to December 2020). Our results obtained by applying the Positive Matrix Factorization (PMF) source-receptor apportionment model showed the contribution of nine PM_2.5 sources. The main anthropogenic sources contributing to the PM mass concentrations were heavy fuel oil (HFO) combustion (25.3 %), biomass burning (20 %), primary traffic (7.6 %) and long-range transport aerosols (10.6 %). The OP activities were evaluated for the first time in an urban site in Vietnam. The average OP_v levels obtained in our study were 3.9 ± 2.4 and 4.5 ± 3.2 nmol min^-1 m^-3 for OP^DTT and OP^AA, respectively. We assessed the contribution to OP^DTT and OP^AA of each PM_2.5 source by applying multilinear regression models. It shows that the sources associated with human activities (HFO combustion, biomass burning and primary traffic) are the sources driving OP exposure, suggesting that they should be the first sources to be controlled in future mitigation strategies. This study gives for the first time an extensive and long-term chemical characterization of PM_2.5, providing also a link between emission sources, ambient concentrations and exposure to air pollution at an urban site in Hanoi, Vietnam.