5:15 PM - 6:45 PM
[HTT16-P03] Seasonal variation of δ34S and δ18O in sulfate in rain water and aerosols on the outskirts of Gifu City
Keywords:sulfate aerosol, rain water, sulfur isotope ratio, oxygen isotope ratio, seasonal variation
1. Introduction
The stable sulfur/oxygen isotope (δ34S/δ18O) of sulfate aerosol and sulfate (SO42-) in precipitation is an important chemical component for understanding the sulfur cycle in the atmospheric environment. We studied to infer the sources of SO42- in the atmosphere in central Japan, by collecting rainwater and aerosol and measuring the δ34S and δ18O since November 2018 to the present.
In this study, we report on seasonal variation in SO42-, major ions, δ34S, nss-δ34S, and δ18O, in rainwater and aerosol during May 2019 to December 2022.
2. Methods for Observations and Analyses
Rainwater was sampled using a simple rainwater collector: a polyethylene bottle equipped with polyethylene funnel. For ion analyses, atmospheric aerosols were sampled onto a 0.2-µm PTFE filter at an 8–10 L/min flow rate with a vacuum pump. For isotope analyses, atmospheric aerosols were sampled onto a quartz filter (QR-100; Advantec) at a suction flow rate of 1000 L/min once a week using a high-volume air sampler (HV-RW; Sibata Scientific Technology Ltd.).
After the samples filtered through membrane filter, they were subjected to quantitative analysis for concentrations using ion chromatography (ICS-1100; Thermo Fisher Scientific Inc.) for anions and inductively coupled plasma atomic emission spectrometry (ICP-AES) (ULTIMA2; Horiba Ltd.) for cations.
For the δ34S and the δ18O were precipitate SO4²- in the sample as BaSO4. NO3- was removed from BaSO4 for δ18O using the DTPA method (Bao, 2006). It was analyzed using S-IRMS (Flash EA 2000 + ConFlo IV + delta V plus; Thermo Fisher Scientific Inc.) and OH-IRMS (TC/EA+ConFlo III+Delta plus XP; Thermo Fisher Scientific Inc.) installed in the Research Institute for Humanity and Nature. The data for PM2.5 and Ox were obtain from Atmospheric Environmental Regional Observation System (AEROS).
3. Results
3-1. rain water
The concentration of nss-SO42- in rainwater during December 2018 – December 2022 was 0.1 –8.7 mg L-1 (Ave 1.2 mg L-1). It showed high concentrations in February and March.
Nss-δ34S in the SO42- in rainwater was -3.1–12.4‰ (Ave 4.0‰). It was 4–12‰ in winter and 2–4‰ in summer, exhibiting clear seasonal changes to increase in winter and decrease in summer, similar to previous studies (e.g. Inomata et al. 2019; Sase et al. 2019).
δ18O ranged from 3.9 to 17.7‰ (Ave 10.7‰), with particularly high values observed in March.
3-2. aerosols
The concentration of SO42- in aerosols during December 2018 – December 2022 was 0.01 –9.4 µg m-3 (Ave 1.4µg m-3), exhibiting clear seasonal changes to decrease in winter and increase in summer, similar to PM2.5. δ34S in in the SO42- in rainwater was 1.3–11.3‰ (Ave 4.5‰), and nss-δ34S in the aerosols were ∼7.4‰ (Ave 3.4‰). Although no clear seasonal variations were observed like δ34S in rainwater. The low values were often observed in summer. Motoyama et al.(2000) observed δ34S in aerosol in Tsuruoka City on the Sea of Japan side of Yamagata Prefecture and Yamagata City in the inland area. They reported that he lowest value was observed in summer, and the highest value was observed sometime between autumn and spring in Tsuruoka City and there are no clear seasonal variations in Yamagata City. Since the results in this study were similar to those in inland city. It was inferred that aerosols are transported from Asian Continent to the site facing the Sea of Japan in winter, but these are little transported to inland areas. δ18O ranged from 5.3 to 13.0‰ (Ave 9.9‰), and observed high value in spring. As also reported by Yamamoto and Chiba (2016), there was a tendency to be higher in spring (March to May) and lower in summer to winter (August to February). Since Ox concentration also increases in spring, it is possible that the cause is a reaction with oxidants produced by Ox (OH radicals, H2O2, etc.).
The stable sulfur/oxygen isotope (δ34S/δ18O) of sulfate aerosol and sulfate (SO42-) in precipitation is an important chemical component for understanding the sulfur cycle in the atmospheric environment. We studied to infer the sources of SO42- in the atmosphere in central Japan, by collecting rainwater and aerosol and measuring the δ34S and δ18O since November 2018 to the present.
In this study, we report on seasonal variation in SO42-, major ions, δ34S, nss-δ34S, and δ18O, in rainwater and aerosol during May 2019 to December 2022.
2. Methods for Observations and Analyses
Rainwater was sampled using a simple rainwater collector: a polyethylene bottle equipped with polyethylene funnel. For ion analyses, atmospheric aerosols were sampled onto a 0.2-µm PTFE filter at an 8–10 L/min flow rate with a vacuum pump. For isotope analyses, atmospheric aerosols were sampled onto a quartz filter (QR-100; Advantec) at a suction flow rate of 1000 L/min once a week using a high-volume air sampler (HV-RW; Sibata Scientific Technology Ltd.).
After the samples filtered through membrane filter, they were subjected to quantitative analysis for concentrations using ion chromatography (ICS-1100; Thermo Fisher Scientific Inc.) for anions and inductively coupled plasma atomic emission spectrometry (ICP-AES) (ULTIMA2; Horiba Ltd.) for cations.
For the δ34S and the δ18O were precipitate SO4²- in the sample as BaSO4. NO3- was removed from BaSO4 for δ18O using the DTPA method (Bao, 2006). It was analyzed using S-IRMS (Flash EA 2000 + ConFlo IV + delta V plus; Thermo Fisher Scientific Inc.) and OH-IRMS (TC/EA+ConFlo III+Delta plus XP; Thermo Fisher Scientific Inc.) installed in the Research Institute for Humanity and Nature. The data for PM2.5 and Ox were obtain from Atmospheric Environmental Regional Observation System (AEROS).
3. Results
3-1. rain water
The concentration of nss-SO42- in rainwater during December 2018 – December 2022 was 0.1 –8.7 mg L-1 (Ave 1.2 mg L-1). It showed high concentrations in February and March.
Nss-δ34S in the SO42- in rainwater was -3.1–12.4‰ (Ave 4.0‰). It was 4–12‰ in winter and 2–4‰ in summer, exhibiting clear seasonal changes to increase in winter and decrease in summer, similar to previous studies (e.g. Inomata et al. 2019; Sase et al. 2019).
δ18O ranged from 3.9 to 17.7‰ (Ave 10.7‰), with particularly high values observed in March.
3-2. aerosols
The concentration of SO42- in aerosols during December 2018 – December 2022 was 0.01 –9.4 µg m-3 (Ave 1.4µg m-3), exhibiting clear seasonal changes to decrease in winter and increase in summer, similar to PM2.5. δ34S in in the SO42- in rainwater was 1.3–11.3‰ (Ave 4.5‰), and nss-δ34S in the aerosols were ∼7.4‰ (Ave 3.4‰). Although no clear seasonal variations were observed like δ34S in rainwater. The low values were often observed in summer. Motoyama et al.(2000) observed δ34S in aerosol in Tsuruoka City on the Sea of Japan side of Yamagata Prefecture and Yamagata City in the inland area. They reported that he lowest value was observed in summer, and the highest value was observed sometime between autumn and spring in Tsuruoka City and there are no clear seasonal variations in Yamagata City. Since the results in this study were similar to those in inland city. It was inferred that aerosols are transported from Asian Continent to the site facing the Sea of Japan in winter, but these are little transported to inland areas. δ18O ranged from 5.3 to 13.0‰ (Ave 9.9‰), and observed high value in spring. As also reported by Yamamoto and Chiba (2016), there was a tendency to be higher in spring (March to May) and lower in summer to winter (August to February). Since Ox concentration also increases in spring, it is possible that the cause is a reaction with oxidants produced by Ox (OH radicals, H2O2, etc.).