Global_Environmental_Research_Vol.27No.1
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32 results of agricultural residue combustion experiments (Fushimi et al., 2017). Soil-derived metals were calculated using Al as an indicator, and the soil profile of the average earth crust was used (Mason, 1966). The remaining concentrations of metals and elemental carbon that were not assigned to vehicle tailpipe and BB emissions and soil, were assumed to originate from sources other than those. As a result, it was estimated that most of the metal in terms of amount was from other sources not considered in this study and most of the elemental carbon by amount was attributable to vehicle tailpipe emissions (Fig. 3e). Averaged over the samples in each season, the OSIA for the water-soluble samples was dominated by BB (fresh and aged BBOA) in October 2015, which contributed nearly 80% (Fig. 3a). In other seasons, the contribution of OOA and other metals increased and the contribution of BB decreased slightly, to around 40%−50%. The contribution of BB to OSIA in the Fig. 3 a) Oxidative stress induction ability (OSIA) and contribution of water-soluble (WS) chemical components to OSIA of WS samples, b) OSIA and contribution of sub-classes of organic aerosols (OA) and elemental carbon (EC) in water-insoluble (WIS) samples, c) Oxidative potential (OP) and contribution of chemical components to OP of WS samples, d) OP and contribution of sub-classes of OA and EC of WIS samples, and e) Composition of chemical species that exhibit OSIA or OP. Predicted values of total OSIA or OP were determined by multiplying the concentration of each chemical component and the unit value of OSIA or OP (per unit of chemical component mass) and the sum of each OSIA or OP value. The predicted values for cases without aged BBOA were determined by assuming the unit value of OSIA or OP was zero for aged BBOA. The error bars indicate the standard deviation of the samples in each sampling campaign. VTE indicates vehicle tailpipe emission. Y. FUJITANI et al. water-insoluble samples was about 50% in October 2015 and about 20% in the other seasons (Fig. 3b). In the other seasons, vehicle tailpipe emissions (HOA, vehicle tailpipe emission-elemental carbon) was predominant (70%−80%). The trend of the OP contribution for each solution was generally consistent with the trend of OSIA (Fig. 3c, d). These results indicate that OSIA and OP significantly increased during the active open burning season, and the majority of the increase was attributable to BB aerosols. The contributions of components with larger contributions to OSIA and OP (Fig. 3a−d) differed from their mass-based contribution (Fig. 3e). In particular, the contribution of metals was greater in the water-soluble samples, because the unit values of OSIA and OP for metals are orders of magnitude higher than those of organic aerosol. However, BB had low metal content according to the source profiles, and the BB-derived metals present contributed little to OSIA or OP. Therefore, in BB, organic matter rather than metals was found to be

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