《Table 2–Summary of chemical constituents of PM2.5integrated filters (all concentrations are inμg/m3

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《Exposure to air pollutants in Vietnam:Assessing potential risk for tourists》

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Integrated PFTE filter samples were analysed for a suite of elements and ionic species，and a summary of results is presented in Table 2.Among ions，sodium，sulphate，nitrate and potassium were found to be the most abundant，while in case of elements，iron（Fe）and sulphur（S）were the most abundant species.Elements typically associated with crustal dust（i.e.，silicon，aluminium）were found to be below the detection limit in more than 50%of the samples and were not included in the final analysis.This is not entirely surprising since the sampling focused on personal exposure，and was conducted during the wet season when the contribution of dust to PM levels is limited.Zinc（Zn），and nickel（Ni）were moderately correlated with PM2.5（r=0.62 and 0.7），and a weaker correlation was observed between barium（Ba）Zn and Ni（r~0.40）.Previous source apportionment analyses in Vietnam have reported Ni and Zn as markers for vehicular emissions（Hang and Kim Oanh，2014），and research elsewhere also supports the use of these markers for road traffic（Pant and Harrison，2013）.Currently，Vietnam allows both diesel and gasoline with 500 ppm sulphur（Searle and Malins，2016），and this could be the reason for high sulphur（S）concentrations.Ba and titanium（Ti）were also moderately correlated（r=0.65），and this could be due to the influence of brake wear particles.Ba has been extensively used as a marker for brake wear emissions（Pant and Harrison，2013），and a recent review of brake wear emissions indicated that titanate compounds are an integral part of brake wear systems（Grigoratos and Martini，2014）.SO42-and NH4+were strongly correlated（r=0.83），NO3-was moderately correlated with Na+（r=0.53）and K+（r=0.56）.Na+and Cl-were strongly correlated indicating contribution from marine aerosols（r=0.96）.