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-, SO4analyzed -, NO3+) was 28 2.1 Site Descriptions and Sampling Methods 2. Experimental Methodology particles contribute greatly to the OP of PM (Verma, et al., 2015; Daellenbach, et al., 2016; Weber, et al., 2018; Fushimi, et al., 2021) among various emission sources. In addition, BB organic aerosol (BBOA) has been shown to have higher OP per unit concentration (Verma, et al., 2015) as well as higher OSIA per unit concentration than other sub-classes of organic aerosol such as secondary organic aerosols (Fujitani, et al., 2023). While chemical composition data have been accumulated historically with wide spatiality, in contrast, data on oxidative stress assessment are scarce. Fujitani, et al. (2023) showed that estimation of cellular OSIA and OP can be obtained from the chemical components of PM using concentration data of metals and subclasses of organic aerosol including BBOA. This would be useful in assessing oxidative stress from chemical composition data in areas where data on oxidative stress are not available and for comparison with previous epidemiological findings retrospectively. However, the predictability of OSIA or OP from chemical composition needs to be further validated with different seasonal data sets. In this study, to assess the extent to which BB particle emissions affect OSIA and OP, evaluations were performed for PM2.5 collected during periods of high activity in open burning of agricultural residue in Tsukuba, Japan. The results were compared with those of samples collected during other seasons with different magnitudes of BB activity at the same sampling site. Furthermore, OSIA and OP were estimated from concentrations of chemical components such as metals and sub-classes of organic aerosol and compared to actual measurements. The observation site was located at the National Institute of Environmental Studies (NIES) center in Tsukuba (36.05°N, 140.12°E; population, about 200,000), Japan, about 50 km northeast of Tokyo. The main harvest season for rice tends to span September and October, and open burning of rice husks and rice straw are often conducted in these two months. During the year of observation, 2015, rice harvesting and the burning of rice husks peaked in the middle of September and the burning of rice straw peaked in October (Tomiyama, et al., 2017). Atmospheric observations were conducted between 7 October and 30 October 2015. Observations were intermittent from 16 to 20 Oct because of power outages. PM2.5 was concurrently collected both on 20.32 cm × 25.4 cm Teflon filters (TFH-R, Horiba, Kyoto, Japan) and on quartz fiber filters (2500QAT-UP, Pall, New York, USA) by means of a high-volume air samplers (HV-1000R, Sibata Scientific Technology, Soka, Japan) with PM2.5 impactor (Kaneyasu, 2010). All sampling was conducted from around 10 a.m. on weekdays to 10 a.m. two days later (i.e., 48 hours of sampling) and on Y. FUJITANI et al. 2.2 Chemical Analysis of PM2.5 Samples weekends from around 10 a.m. on Friday to 10 a.m. on Monday (i.e., 72 hours of sampling), with a sampling flow rate of 740 l min-1. During sampling, the aerosol species in PM1.0 were a high-resolution time-of-flight particle aerosol mass spectrometer (AMS, Aerodyne Research Inc., Billerica, USA) and the sub-classes of organic aerosol were determined by positive matrix factorization (PMF) analysis. In PMF analysis, the measured mass spectrum is decomposed for several factors, and the concentration and mass spectrum is obtained for each factor by determining the residual matrix become minimum. Each PMF factor can be assigned an emission source and particle type (sub-class of organic aerosol) by its diurnal pattern, mass spectrum comparison of PMF factors obtained in previous studies, and correlation of time variation with external tracers. Atmospheric pollutants (i.e., PM2.5, NO, NO2, etc.) and meteorological data were obtained continuously from the NIES Air Quality Research Station. These PM1.0 and atmospheric pollutant data are discussed in detail by Fujitani, et al. (2020). The Teflon filter samples were analyzed for particle mass, water soluble ions and elements. Particle mass was obtained by incrementing the mass of the collection media after sampling. Before weighing the Teflon filter samples, the Teflon filters were placed in the chamber at 25°C and 50% humidity for at least 24 hours. An electronic balance (minimum reading 0.1 mg, LA130S-F, Sartorius AG, Göttingen, Germany) was used for weighing. Each sample was weighed at least twice, and the results were averaged if the difference was within 1 mg; the mean value was adopted as the weight of the sample. The water-soluble 2-, oxalate ion ion component (F-, Cl-, NO2(C2O4ion chromatography (IC850, Metrohm, Herisau, Switzerland). For the analysis, one-third of the Teflon filter was placed in a 15 ml polypropylene container, 10 ml of ultrapure water was added, and ultrasonic extraction using an ultrasonic bath (US-5A, ASONE, Osaka, Japan) was performed for 10 min two times. The extract was filtered through a disposable membrane filter (hydrophilic PTFE) with a pore size of 0.45 μm. Elements (Be, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Ag, Cd, Sb, Ba, Tl, Pb, Th, U) were analyzed by inductively coupled plasma–mass spectrometry (7700x, Agilent Technologies, Santa Clara, USA). For the analysis, samples were prepared using 1/32 of the Teflon filter, and pretreatment was performed by the ultrasonic-heat block method. Carbon components (elemental carbon, organic carbon and total carbon) were analyzed using quartz fiber filter samples. For the analysis, 8 mmΦ of the filter was punched out from two locations and analyzed using a thermal optical carbon analyzer (Model 2001 Carbon Analyzer, Desert Research Institute, Reno, USA) by 2-), Na+, NH4concurrently measured with by

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