5:15 PM - 6:30 PM
[HTT16-P03] Seasonal variation of δ34S and δ18O in sulfate in rain water and aerosols on the outskirts of Gifu City
Keywords:sulfate ion, sulfur isotope, atmospheric aerosol, rain water
1. Introduction
Reportedly, Lake Ijira, which is located on the outskirts of Gifu City, has the highest deposition of non-sea-salt sulfate ion (nss-SO4²-) and the hydrogen ion (H+) in Japan (Ministry of the Environment, 2004). It has also been demonstrated that its outflow of SO42- is about twice its inflow (Ministry of the Environment, 2004). Based on these results, we sampled atmospheric aerosols and rainwater before deposition from November 2018 until the present (2021) to measure the contained sulfate ion, its sulfur isotope ratio (δ34S) and oxygen isotope ratio (δ18O) for this study. Thereafter, we examined the source of sulfur derived from the atmosphere and accumulated on the soil surface around Lake Ijira.
2. Methods for Observations and Analyses
Rainwater was sampled using a simple rainwater collector: a PET bottle equipped with polypropylene 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 sulfur isotope ratio and the oxygen isotope ratio were precipitate SO4²- in the sample as BaSO4. 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.
3. Results
3-1. Changes in SO4²- and NO3- concentrations during the lockdown period in China
In early 2020, China adopted a lockdown policy because of the outbreak of COVID-19. Itabashi et al. (2020) reported that the concentrations of PM2.5, SO4²-, and NO3- were measured for three years of 2018–2020 at four sites (Goto Islands, Oki Islands, Maki, and Nonodake), the mean concentrations of PM2.5, SO4²-, and NO3- during January–March were lower than the prior year at all observation sites in the lockdown period of China during January–March. For Lake Ijira, comparison of SO4²- and NO3- concentrations of January–March between 2019 and 2020 indicated a remarkable decrease, suggesting a decrease in concentrations of atmospheric aerosols because of decreased economic activities resulting from lockdowns.
3-2. δ34S
δ34S in the sulfate ions in rainwater during December 2018 – December 2020 was 4–12‰ in winter and 2–4‰ in summer, exhibiting clear seasonal changes to decrease in winter and increase in summer. δ34S in sulfate aerosols was 5–6‰ in winter and 2–6‰ in summer, reflecting seasonal changes, although there were variations.
3-3. Analysis by back-trajectory analysis
Back-trajectory analysis was applied using NOAA HYSPLIT data every day during the observation period, to be classified into eight categories (Figure 1). Figure 2 shows nss-SO4²- and NO3- concentrations and the δ34S value of each category from December 2019 through December 2020. The most frequently classified category was CE (route that passes the eastern side of the Korean Peninsula) followed by the second-most frequent, CN (route that passes the western side of the Korean Peninsula). Air masses from the Eurasian continent accounted for 80% of air masses that arrived at the observation points. It is therefore considered that most of the atmosphere comes from the Eurasian continent.
Reportedly, Lake Ijira, which is located on the outskirts of Gifu City, has the highest deposition of non-sea-salt sulfate ion (nss-SO4²-) and the hydrogen ion (H+) in Japan (Ministry of the Environment, 2004). It has also been demonstrated that its outflow of SO42- is about twice its inflow (Ministry of the Environment, 2004). Based on these results, we sampled atmospheric aerosols and rainwater before deposition from November 2018 until the present (2021) to measure the contained sulfate ion, its sulfur isotope ratio (δ34S) and oxygen isotope ratio (δ18O) for this study. Thereafter, we examined the source of sulfur derived from the atmosphere and accumulated on the soil surface around Lake Ijira.
2. Methods for Observations and Analyses
Rainwater was sampled using a simple rainwater collector: a PET bottle equipped with polypropylene 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 sulfur isotope ratio and the oxygen isotope ratio were precipitate SO4²- in the sample as BaSO4. 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.
3. Results
3-1. Changes in SO4²- and NO3- concentrations during the lockdown period in China
In early 2020, China adopted a lockdown policy because of the outbreak of COVID-19. Itabashi et al. (2020) reported that the concentrations of PM2.5, SO4²-, and NO3- were measured for three years of 2018–2020 at four sites (Goto Islands, Oki Islands, Maki, and Nonodake), the mean concentrations of PM2.5, SO4²-, and NO3- during January–March were lower than the prior year at all observation sites in the lockdown period of China during January–March. For Lake Ijira, comparison of SO4²- and NO3- concentrations of January–March between 2019 and 2020 indicated a remarkable decrease, suggesting a decrease in concentrations of atmospheric aerosols because of decreased economic activities resulting from lockdowns.
3-2. δ34S
δ34S in the sulfate ions in rainwater during December 2018 – December 2020 was 4–12‰ in winter and 2–4‰ in summer, exhibiting clear seasonal changes to decrease in winter and increase in summer. δ34S in sulfate aerosols was 5–6‰ in winter and 2–6‰ in summer, reflecting seasonal changes, although there were variations.
3-3. Analysis by back-trajectory analysis
Back-trajectory analysis was applied using NOAA HYSPLIT data every day during the observation period, to be classified into eight categories (Figure 1). Figure 2 shows nss-SO4²- and NO3- concentrations and the δ34S value of each category from December 2019 through December 2020. The most frequently classified category was CE (route that passes the eastern side of the Korean Peninsula) followed by the second-most frequent, CN (route that passes the western side of the Korean Peninsula). Air masses from the Eurasian continent accounted for 80% of air masses that arrived at the observation points. It is therefore considered that most of the atmosphere comes from the Eurasian continent.