[HTT18-P09] Development of the analytical method for sulfur isotope in SO2 gas
キーワード：硫黄同位体比、SO2ガス
1. Introduction
Sulfur is a major source of acid deposition. Usually sulfur is emitted as SO2 and it is oxidized to SO42- in atmosphere. S isotopic analysis of water and particulate samples were conducted in many studies. But gaseous SO2 was rarely used for isotopic study. Isotopic ratio of SO2 is strongly influenced by emission source near the sampling point. Because most of SO2 emitted far from sampling point is oxidized to SO42- during transportation. It is possible to distinguish domestic emission from transboundary emission. Moreover, dry deposition processes of SO2 and particulate SO42- and their interactions with tree canopy could be discussed more precisely. Isotopic analysis of SO2 is considered as a powerful method to investigate the behavior of S in the atmosphere and ecosystems. We studied about the analytical method for S isotope in SO2.
2. Method
(1) Equipment
SO2 concentration in Japan is very low (e.g. annual 0.02ppb at Sado). We need to collect air sample at least 1m3 that is the amount we can obtain 1.2mg of BaSO4 precipitation enough for isotopic analysis. High volume air sampler is generally used to collect around 1m3 of air sample. It uses filter, so we examined filter collection of SO2 by K2CO3 filter generally used to collect SO2 in filter-pack method.
(2) Filters
We used quarts filter for particulate SO42- and K2CO3 filter for gaseous SO2 next to it. K2CO3 filter is made on the basis of EANET manual. But to get enough flow rate for high volume air sampler, the size of K2CO3 filter is larger (20×26 cm, same size with quarts filter) than the manual and already dried before sampling.
(3) Flow rate/leak test
Under flow rate 100~400 L/min in this system, we confirmed weather sampling can be carried out stably. And we checked leak using two K2CO3 filters.
(4) Sample treatment
On the basis of EANET manual, the sample was extracted with 0.05% H2O2aq and filtered. Then 2N HCl was added and concentrated to remove CO32-. Next 1%(w/w)BaCl2 was added. We filtered forming BaSO4 precipitation. We examined the method to get BaSO4 precipitation and to remove the components from K2CO3 filter.
3. Results
(1) Sampling and sample treatment
Sampling could be conducted under flow rate 100~400 L/min. Sampling efficiency was about 80%..
Several conditions to get BaSO4 precipitation ware examined, it could be gotten by the method as below.
Filter was cut and ultrasonic extracted with 0.05% H2O2aq 30 minutes and filtered. 2.5 ml of 2N HCl was added and concentrated to around 10 ml. Then 1 ml of heated 1 %(w/w) BaCl2 was added under pH 4~6. Next evaporated all solvent and added 10 ml of water. BaSO4 precipitation was observed. After put for one night, the precipitation was separated by centrifuge 3,600 rpm for 10 minutes and we removed the solvent. The precipitation was washed twice by 10 ml of water and filtered. At last the filter was ashed for four hours in muffle furnace in 800 ℃ .
(2) Actual analysis
We used two K2CO3 filters and collected 2160.2 m3 of air sample under flow rate 300 L/min. 3.80 mg of particular SO42- and 0.89 mg (first) and 0.14 mg (second) of SO42- from SO2 were obtained. δ34S of particular SO42- was 8.64 ‰ and that of SO2 from the first filter was -1.54 ‰. The amount of precipitation from second filter was not enough for isotopic analysis. This difference was caused by effect of sea salt mainly. But nss-δ34S of particular SO42- was 4.78 ‰. It was still higher than SO2. It suggested that nss- SO42- contains both transboundary SO42- and domestic SO42-. According to the relevant literature, domestic SO2 may have negative isotopic values because of imported oil from Middle East. Considering that this sampling was carried out in January, possible effect of transboundary SO2 with higher isotopic values should also be taken into account for source identification of the collected SO2.
We would like to discuss at the conference with the latest data.
Sulfur is a major source of acid deposition. Usually sulfur is emitted as SO2 and it is oxidized to SO42- in atmosphere. S isotopic analysis of water and particulate samples were conducted in many studies. But gaseous SO2 was rarely used for isotopic study. Isotopic ratio of SO2 is strongly influenced by emission source near the sampling point. Because most of SO2 emitted far from sampling point is oxidized to SO42- during transportation. It is possible to distinguish domestic emission from transboundary emission. Moreover, dry deposition processes of SO2 and particulate SO42- and their interactions with tree canopy could be discussed more precisely. Isotopic analysis of SO2 is considered as a powerful method to investigate the behavior of S in the atmosphere and ecosystems. We studied about the analytical method for S isotope in SO2.
2. Method
(1) Equipment
SO2 concentration in Japan is very low (e.g. annual 0.02ppb at Sado). We need to collect air sample at least 1m3 that is the amount we can obtain 1.2mg of BaSO4 precipitation enough for isotopic analysis. High volume air sampler is generally used to collect around 1m3 of air sample. It uses filter, so we examined filter collection of SO2 by K2CO3 filter generally used to collect SO2 in filter-pack method.
(2) Filters
We used quarts filter for particulate SO42- and K2CO3 filter for gaseous SO2 next to it. K2CO3 filter is made on the basis of EANET manual. But to get enough flow rate for high volume air sampler, the size of K2CO3 filter is larger (20×26 cm, same size with quarts filter) than the manual and already dried before sampling.
(3) Flow rate/leak test
Under flow rate 100~400 L/min in this system, we confirmed weather sampling can be carried out stably. And we checked leak using two K2CO3 filters.
(4) Sample treatment
On the basis of EANET manual, the sample was extracted with 0.05% H2O2aq and filtered. Then 2N HCl was added and concentrated to remove CO32-. Next 1%(w/w)BaCl2 was added. We filtered forming BaSO4 precipitation. We examined the method to get BaSO4 precipitation and to remove the components from K2CO3 filter.
3. Results
(1) Sampling and sample treatment
Sampling could be conducted under flow rate 100~400 L/min. Sampling efficiency was about 80%..
Several conditions to get BaSO4 precipitation ware examined, it could be gotten by the method as below.
Filter was cut and ultrasonic extracted with 0.05% H2O2aq 30 minutes and filtered. 2.5 ml of 2N HCl was added and concentrated to around 10 ml. Then 1 ml of heated 1 %(w/w) BaCl2 was added under pH 4~6. Next evaporated all solvent and added 10 ml of water. BaSO4 precipitation was observed. After put for one night, the precipitation was separated by centrifuge 3,600 rpm for 10 minutes and we removed the solvent. The precipitation was washed twice by 10 ml of water and filtered. At last the filter was ashed for four hours in muffle furnace in 800 ℃ .
(2) Actual analysis
We used two K2CO3 filters and collected 2160.2 m3 of air sample under flow rate 300 L/min. 3.80 mg of particular SO42- and 0.89 mg (first) and 0.14 mg (second) of SO42- from SO2 were obtained. δ34S of particular SO42- was 8.64 ‰ and that of SO2 from the first filter was -1.54 ‰. The amount of precipitation from second filter was not enough for isotopic analysis. This difference was caused by effect of sea salt mainly. But nss-δ34S of particular SO42- was 4.78 ‰. It was still higher than SO2. It suggested that nss- SO42- contains both transboundary SO42- and domestic SO42-. According to the relevant literature, domestic SO2 may have negative isotopic values because of imported oil from Middle East. Considering that this sampling was carried out in January, possible effect of transboundary SO2 with higher isotopic values should also be taken into account for source identification of the collected SO2.
We would like to discuss at the conference with the latest data.