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Characterization of particulate matter (PM 1 and PM 2.5 ) from 1 incense burning activities in temples in Vietnam and Taiwan 2

Particulate matter (PM) emitted from incense burning is a serious problem because of its effects on 18 human health and the environment, especially on the air quality of Southeast Asia. This study 19 investigated the PM 1 and PM 2.5 concentrations in two temples in Vietnam and Taiwan, focusing on 20 events (i.e., new moon and full moon day) and non-event days using PM sensors. Moreover, PM 2.5 21 samples were collected to determine organic carbon (OC) and elemental carbon (EC) 22 concentrations. The PM 1 and PM 2.5 concentrations in Vietnam (22.7±18.7 and 36.5 ± 33.9 µg m -3 , 23 respectively) were lower than those at the Taiwan temple (74.5±53.4 and 97.0±65.4 µg m -3 , 24 respectively). The incense burning activity in the Taiwan temple occurred inside the temple while 25 the incense burner at Vietnam’s temple was located outdoors. During the event days, PM 1 and 26 PM 2.5 concentrations were about two times greater than on non-event days, highlighting the impact 27 of incense burning on the PM concentrations. By breaking the study area into control and exposure 28 sites, we found that the people inside the temple experienced 2–5 times higher PM concentrations 29 as compared to those in the ambient air. The PM 1 /PM 2.5 ratio was 0.6±0.1 for the Vietnam temple, 30 which was lower than the Taiwan value (0.7±0.1). The OC and EC concentrations in the Taiwan 31 temple were 129.40±97.68 and 1.16±2.31 µg m -3 , respectively, significantly greater than those 32 found in the Vietnam temple (OC = 27.70±7.66 µg m -3 , EC = 1.63±0.93 µg m -3 ). Furthermore, the 33 OC/EC ratio in the Vietnam temple (20.24) was similar to those reported from incense and biomass 34 in previous research. The increase in religious activities was the major factor leading to the 35 levels surrounding the study areas. This study provides valuable information on PM and carbonaceous aerosols emitted from incense burning in Southeast Asia megacities.

of PM2.5 measured inside a temple could reach 184 -625 µg m -3 during special occasions (Bootdee 48 et al., 2016). Previous studies have indicated that low quality incense could be the source of the 49 high emission rate of particles in the temple (Zhang et al., 2015). However, Lee and Wang (2004) 50 found that using high quality and environmentally friendly incense did not reduce the pollution 51 emission. A review study by Alfano indicated that incense burning was a major factor influencing 52 indoor PM2.5 concentrations (Alfano et al., 2020). A study in Vietnam found a 61.6% elevation of 53 indoor PM2.5 concentrations at houses that burned incense compared to those without incense 54 burning (Tran et al., 2021). In Taiwan, it was found that incense burning resulted in 40.3 ± 35.5 µg 55 m -3 of PM2.5, which was 1.53 ± 1.79 times the concurrent outdoor levels, when the subjects burned   121 According to the tradition in Southeast Asia, people usually go to the temple on the full 122 moon day (15 th ) and the new moon day (1 st ) to pray for good luck. In this study, PM1 and PM2.5 123 concentrations were measured in these two periods. Each monitoring period (either new moon or 124 full moon day) included the events 2 days before and 2 days after the day.

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measurement was conducted in the morning (from 7:30 to 11:30) and in the afternoon (from 13:45 128 to 17:45). The PM low-cost sensors (i.e., ASLUNG-P) provided by Academia Sinica, Taiwan, were 129 employed to monitor the PM1 and PM2.5 concentrations. The researcher carried the instrument near 130 the chest and covered each area in the temple (A1, A2, A3), called the exposure site (Fig. S1). The 131 total time for one measurement round in the exposure site was about 30 minutes. Simultaneously, 132 for comparison purposes, another ASLUNG-P was set at the entrance to the temple, called the 133 control site. The control site was 50 m away from a three-lane road in front of the temple (Fig. S1).

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The number of worshippers was counted every 30 minutes. Moreover, PM2.5 was also sampled 135 using the SKC Sampler to analyze OC and EC. This device was fixed in the A2 area (Fig. S1), 1 -136 1.5 m from the large censer and placed at a height of 1.5 m from the ground.

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In Taiwan, the monitoring campaign was carried out during 2 periods: lunar 2021, 29 138 September to 3 October (lunar October 1 st , new moon day), and lunar 13-17 October (lunar October 139 15 th , full moon day). According to the traditional belief, worshipping is preferred in the morning.

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Therefore, all the monitoring was performed from 8:00-12:00 in the morning. In the control site, 141 one ASLUNG-P sensor was fixed on a shelf at a height of at least 120 cm. This site was located on 142 a pavement 10 m from the entrance and away from a four-lane road running in front of the temple. 143 To sample PM in the exposure site, one ASLUNG-P sensor and a personal environmental 144 monitoring (PEM) system were loaded on a backpack and carried by the researcher. The sampling 145 inlets of all instruments were located above the chest of the researcher to resemble the actual 146 breathing exposure. To simulate the actual worshipping pathway, every hour the researcher 147 followed the worshipping path and spent 2-3 minutes at each censer (within a distance of 2 m) 148 before moving to the next one. In total, the researchers approached 10 censers, which took roughly

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8 40 minutes for each round. After finishing the worshipping path, the researcher returned to the 150 main hall to wait for the next round. In addition to the censers for incense burning, joss paper 151 burners were also located inside the two temples.

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Four ASLUNG-P sensors were used in this study. In Taiwan on pre-treated quartz filters (Advantec, Japan) at a flow rate of 10 L min -1 for OC and EC analysis.

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Prior to sampling, all samplers were calibrated to achieve a recommended flow rate of 10 L min -1 . 160 Before use, quartz filters were heated at 400°C to remove impurities for 8 hours, cooled, stabilized 161 in a plastic Petri dish and placed in a desiccator at 25°C with an RH of 30-40%. After sampling, 162 the filters were put into a plastic Petri dish, then wrapped with a layer of aluminum foil to avoid 163 photochemical reactions and determine the mass after stabilizing, and stored at -20°C. 164 In Taiwan, the PM2.5 samples were collected onto filters using a personal environmental 165 monitoring (PEM) system. The PEM sampling head was equipped with 17 mm quartz filters. 166 Before sampling, all the quartz filters were treated at 900°C to avoid contamination. The samples 167 were collected with a BGI-400 pump at the flow rate of 10 L min -1 for 4 hours or until the filters 168 were saturated. The filter was then collected and brought back to the laboratory for OC/EC analysis. respectively, in a non-oxidizing helium atmosphere) and six EC fractions (EC1, EC2, EC3, EC4, 175 EC5 and EC6 at 550, 625, 700, 775, 850 and 870°C, respectively, in an oxidizing helium 176 atmosphere of 2% O2 and 98% helium). The pyrolysis of OC (OP) was continuously monitored by 177 the reflectance or transmittance of laser signals. OC was operationally defined as OC1 + OC2 + 178 OC3 + OC4 + OC5 + POC, and EC was defined as EC1 + EC2 + EC3 + EC5 + EC6 -OP.

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In Taiwan, the quartz filters were not weighted. Particulate OC and EC were measured on   Table S2. This difference could be due to the design of  Moreover, the instrument and sampling design might have caused the difference between this study 214 and the abovementioned Thailand and India studies. In those studies, PM2.5 was collected using a 215 filter-based sampling method in which the samplers were in a fixed position in the temple, whereas 216 in our study, PM2.5 was measured using a real-time monitoring system that was carried by 217 researcher around the temple. Therefore, our study might have better represented the PM2.5 study. Another result in Taiwan showed that PM1 values were slightly higher than the result in 223 Vietnam, averaging about 33.7 µg m -3 , which were measured by GRIMM (Lung et al., 2014). 224 Nevertheless, PM1 in the Taiwan temple in this study was greater than in the previous study in 2014.

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The PM1 and PM2.5 concentrations were significantly different at both events and non- which was 2 -4 times higher than the number on non-event days (Table S3). Similarly, during 235 these two days in Taiwan, the number of pilgrims significantly increased, leading to higher incense-236 burning activities (Table S3)  particulate matter was significant for both PM1 (r=0.47, p-value < 0.001) and PM2.5 (r=0.44, p-241 value < 0.001). For PM1, the concentration on event days was 120.3 ± 48.8 µg m -3 , which was 1.9 242 times higher than that on non-event days (62.8 ± 47.9 µg m -3 ). Similarly, the concentration of PM2.5 243 during event days (149.9 ± 59.6 µg m -3 ) was 1.80 times higher than that on non-event days (83.4 ± 244 59.6 µg m -3 ). It was also found that particulate matter (PM2.5) was higher during event days that those entering the temple were exposed to concentrations of particulate matter five times higher 277 than those exposed to ambient air. Moreover, for non-event days, we found that post-event days in 278 Taiwan and pre-15 th days in Vietnam showed higher particulate matter than other non-event days 279 because those were weekend days. People tend to go to the temple when they have the day off 280 rather than on weekdays. So, at the two temples on weekends, PM concentrations were higher than 281 on the weekdays.   Worshippers usually assemble at A1 to praise good fortune or burn incense instead of 285 gathering at A2 and A3 because of the large space at A1 in the Vietnam temple (Fig.3). Therefore,

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PM values at A1 were significantly different from the remaining areas (Wilcoxon test, p-value < 287 0.05) (Fig. 6). For A2 and A3, which are inside the temple, the air pollution hardly dispersed,

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16 PM1 and PM2.5 reached 91.1 ± 46.61 and 119.1 ± 55.9 µg m -3 , respectively (Fig. 7). Moreover, we 295 found that when the researcher walked around the temple, the concentrations of particulate matter 296 fluctuated greatly (high standard deviation). This fluctuation indicated that even when the people 297 were not at the worshipping distance, they could still be exposed to a high concentration, mostly 298 owing to walking close to people holding incense. In Vietnam, a high peak of PM 299 concentration was also observed (Fig. 3) when the researcher approached the incense burner. This 300 result implied that when the worshippers stayed close to the censers, they might be exposed to 301 much higher PM concentrations.   To investigate the emission characteristics of the particulate matter from incense burning, the mass 308 concentration ratio of PM1/PM2.5 should be considered (Cui et al., 2018). Therefore, we further 309 analyzed the PM1/PM2.5 ratios in the two temples. Fig. 8 shows that the ratios of PM1/PM2.5 at two  Taiwan. The OC concentration in the Vietnam temple was 4.7 times lower than that in Taiwan.

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However, the EC concentration in Vietnam was 1.4 times higher than Taiwan's EC concentration.

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In the Vietnam temple, the mass percentages of OC and EC in PM2.5 were quite high (Fig. 9), should be conducted 1-2 days before or after the full moon. Therefore, worshipping activities can 376 be more concentrated during the new moon day than during the full moon day, which in turn emits 377 higher pollution concentrations. Taiwan temples might be due to the type of incense used, incense burned at a Taiwan temple emits 392 more OC, which leads to a high OC/EC ratio. Moreover, the OC/EC ratios on the two event days 393 were significantly lower than on the days before and after the event. This can be explained by the

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22 lower rate of increase in OC compared with that in EC on the 1 st and 15 th (Fig. 10), resulting in a 395 marked decrease in the OC/EC ratio on these days. Overall, carbonaceous aerosol at temples tends 396 to increase sharply on major event days, significantly influenced by Buddhist and Taoist customs. This study contributed to our understanding of particulate matter emissions while also 419 providing preliminary information on the composition of carbonaceous aerosols emitted by incense 420 burning in Vietnam and Taiwan, a case study in Asia. The PM1 and PM2.5 concentrations in the 421 Vietnam temple were about 3.3 times (for PM1) and 2.6 times (for PM2.5) lower than the Taiwan 422 temple. In the two temples, the PM concentrations were associated with the number of worshippers 423 (r > 0.4, p-value < 0.05). It increased the PM on the event days. Furthermore, if worshippers stand 424 closer to censers, they might be exposed to a higher PM concentration. The concentration in the 425 Vietnam temple was 4.7 times lower than the average OC concentration and 1.4 times higher than 426 the EC concentration in the Taiwan temple. The average OC/EC ratio in the Vietnam temple was 427 20.24, while the ratio in the Taiwan temple was many times higher. Overall, carbonaceous aerosol 428 levels in temples tend to rise sharply on major event days, owing to Buddhist and Taoist customs.

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The OC and EC concentrations increased dramatically on event days, but the OC/EC ratio was 430 lower than on the days before and after the event. The authors declare that they have no known competing financial interests or personal 443 relationships that could have appeared to influence the work reported in this paper. Also, the views