To assess the extent to which BB particles affect OSIA and OP, an evaluation was conducted of OSIA, OP and chemical components in PM2.5 environmental samples collected during periods of high BB activity, that is, the burning of agricultural residue in Japan. Not only were PM2.5 concentrations higher, but also OSIA and OP per unit air volume and per unit PM mass in periods of high open burning activity than in other seasons. The results indicate that management of BB activity is important toward maintaining good air quality and protecting public health. This study received financial support from the National Institute for Environmental Studies (2015–2017), JSPS KAKENHI (Grant Number 17K00590), and the Environment Research and Technology Development Fund (Grant Number JPMEERF20165005) administered by the Ministry of the Environment, Japan. The authors gratefully acknowledge the technical assistance provided by Dr. Y. Kondo, Ms. M. Ihara, Ms. E. Shimaya, Mr. Y. Sugaya, and Ms. M. Chiba, Mr. A. Togashi, Ms. S. Takahashi, Ms. K. Higo, and Ms. M. Kobayashi (NIES), Mr. T. Fujii and Mr. H. Konno (Horiba Techno Service), and Mr. M. Oikawa and Mr. M. Nakamura (Green Blue Corp.). Meteorological data was obtained from the Air Quality Research Station at NIES. Bates, J.T., Fang, T., Verma, V., Zeng, L., Weber, R.J., Tolbert, P.E., Abrams, J.Y., Sarnat, S.E., Klein, M., Mulholland, J.A. and Russell, A. G. (2019) Review of acellular assays of ambient particulate matter oxidative potential: methods and relationships with composition, sources, and health effects. Environmental Science & Technology, 53(8): 4003−4019. 4. Conclusions Acknowledgments References the main causative component. We focused on October 2015 samples in detail. As in Section 3.1, ID 09Oct.2015 and ID described 26Oct.2015 were samples collected during especially active open burning, while ID 07Oct.2015 and ID 26Oct.2015 were samples collected during windy (> 1.9 m s-1) days when it was largely soil particles that tended to aerosolize. Accordingly, the contribution of soil and BB to OSIA and OP increased in ID 07Oct.2015 and ID 09Oct.2015, respectively. For ID 26Oct.2015, both emissions exhibited likely resulting in the highest OSIA and OP per unit air volume and per unit PM mass (Fig. 1). simultaneous Figure 3 also shows the predicted values of total OSIA and OP. For aged BBOA, no unit values of OSIA or OP were available. Therefore, we determined the predicted values of total OSIA and OP for the case in which the unit values of OSIA and OP for aged BBOA were assumed to be the identical to those of fresh BBOA, or for the case in which they were ignored (i.e., unit values of OSIA and OP assumed zero). The predicted values generally followed the inter-sample variability trend of the measured values in October 2015, and most of the samples were predicted to be close to the measured values, except for ID 26Oct.2015 for OSIA and ID 09Oct.2015 for OP. This result indicates that OSIA and OP values can be estimated retrospectively for most samples using chemical components such as metals and sub-organic aerosol classes, and unit values of OSIA and OP for those chemical components. concentration data By comparing these two cases in which unit values of OSIA and OP for aged BBOA are either identical to values for fresh BBOA or zero, it is possible to estimate whether unit values of OSIA and OP in aged BBOA are greater or lesser relative to their values in fresh BBOA. Namely, the unit values of OSIA and OP of aged BBOA for water-soluble samples are expected to be lower than those of fresh BBOA, since the total predicted values of water-soluble OSIA and water-soluble OP for most samples exceed the measured values. On the other hand, the unit values of OSIA and OP for aged BBOA of water-insoluble samples are expected to be higher than those for fresh BBOA, since the total predicted values of water-insoluble OSIA and water-insoluble OP for most samples are lower than the measured values. Accordingly, the results indicate that oxidative stress induction changes with aging, but the amount of substances that induce oxidative stress or their unit values may have decreased in the water-soluble the water-insoluble samples as a result of aging. For example, although not an oxidative stress inducer, water-soluble components such as levoglucosan have also been suggested to decrease with aging (Fujitani et al., 2020). This hypothesis should be validated laboratory experiments in future challenges. samples and Oxidative Stress Induction Ability of Particles Emitting from Agricultural Open Burning in Japan influence, for increased in Underestimation of the predicted value of OSIA compared to the measured value (ID 26Oct.2015) is similar to the tendency seen in a previous study (Fujitani et al., 2023): underestimation OSIA when it is high. This can be explained by the following hypotheses. 1) The high actual value is due to the presence of substances such as endotoxins, rather than of chemical components; 2) The HO-1 gene is expressed by the oxidation and degradation of Kelch-like ECH-associated protein 1 (Keap1). In addition, several other antioxidants such as glutathione coordinate metals in the cell. In samples with high OSIA, antioxidants such as glutathione alone may not be able to counteract oxidatively active substances, resulting in these greater quantity of oxidatively active substances reacting with Keap1, leading to higher HO-1 expression. in 33

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