17:15 〜 18:45
[ACC27-P02] グリーンランド南東ドームアイスコアに含まれる硫酸エアロゾルの粒径分級装置の開発
キーワード：アイスコア、硫酸エアロゾル、グリーンランド
Sulfate aerosols can serve as cloud condensation nuclei (CCN) that can affect the climate. Because CCN activity is characterized by the diameter and chemical composition of aerosols, it is important to understand the diameter, chemical composition, and origin of sulfate aerosols. However, there are few past observational data on the sulfate aerosols in the Arctic region. For ice core study, the size-fractioned data for past sulfate aerosols only exist for two periods: the 1970s, when the anthropogenic sulfate maximum, and the 2010s, which represents the period after widespread regulation of sulfur emissions1). Due to high accumulation rates with an annual average accumulation rate of 1.0 m w.e. yr-1 2), the southeastern dome of the Greenland ice sheet (SE-Dome) has the advantage of high temporal resolution and low alteration of atmospheric aerosols after deposition. A 250 m-long ice core drilled from SE-Dome (SE-Dome II ice core) covers from 1799 to 2020 with a precise time scale with a half-year uncertainty2) and enables to reconstruct the paleoenvironment from pre-industrial era to the present. In this study, we aim to establish a method to classify size-fractioned sulfate aerosol concentrations in SE-Dome II ice core.
We established an analytical equipment of classify size-fractioned sulfate aerosol concentrations as below. The equipment is from clean air dryer (IAC, P6-QD20), regulator, mass flow meter (YAMATAKE, azbil), stainless sample chamber, cascade impactor (Tokyo Dylec, MAIS-9), and vacuum pump. A polycarbonate filter with a pore size of 8 μm in the clean chamber, which placed in an ultra-low temperature freezer at −50℃. The cascade impactor can collect particles with diameters from 0.33 µm to 8.8 µm in nine different size fractions. We used a clean polycarbonate filter with a pore size of 0.2 μm as a particle collection filter. To test contamination of the equipment, clean and dry air with a dew point of −65 °C and atmospheric pressure flowed through at a rate of about 8 L min−1 for 48 hours. After then, nine filters are taken away from cascade impactor and put in the Teflon bottle. The Teflon bottle was filled with 3 ml of ultrapure water and sonicated for 30 minutes. Then, we measured the sulfate ion concentration by an ion chromatography (Thermo Scientific, Integrion). The column was AS19 column (Thermo Scientific) with 23 mM KOH eluent. The analytical precision was 10%.
As a result, the average sulfate concentration is less than 1ppb. The average sulfate concentration of SE-Dome II ice core is about 36 ppb. Because the sulfate contamination in this sublimation and classification method is about 3% of that in the ice core, this method is enough to collect size-fractioned sulfate aerosols in the SE-Dome II ice core with very little contamination.
1) Iizuka et al., 2022: J. Geophys. Res. Atmos., 127(17), e2022JD036880.
2) Kawakami et al., 2023: J. Geophys. Res. Atmos., 128, e2023JD038874.
We established an analytical equipment of classify size-fractioned sulfate aerosol concentrations as below. The equipment is from clean air dryer (IAC, P6-QD20), regulator, mass flow meter (YAMATAKE, azbil), stainless sample chamber, cascade impactor (Tokyo Dylec, MAIS-9), and vacuum pump. A polycarbonate filter with a pore size of 8 μm in the clean chamber, which placed in an ultra-low temperature freezer at −50℃. The cascade impactor can collect particles with diameters from 0.33 µm to 8.8 µm in nine different size fractions. We used a clean polycarbonate filter with a pore size of 0.2 μm as a particle collection filter. To test contamination of the equipment, clean and dry air with a dew point of −65 °C and atmospheric pressure flowed through at a rate of about 8 L min−1 for 48 hours. After then, nine filters are taken away from cascade impactor and put in the Teflon bottle. The Teflon bottle was filled with 3 ml of ultrapure water and sonicated for 30 minutes. Then, we measured the sulfate ion concentration by an ion chromatography (Thermo Scientific, Integrion). The column was AS19 column (Thermo Scientific) with 23 mM KOH eluent. The analytical precision was 10%.
As a result, the average sulfate concentration is less than 1ppb. The average sulfate concentration of SE-Dome II ice core is about 36 ppb. Because the sulfate contamination in this sublimation and classification method is about 3% of that in the ice core, this method is enough to collect size-fractioned sulfate aerosols in the SE-Dome II ice core with very little contamination.
1) Iizuka et al., 2022: J. Geophys. Res. Atmos., 127(17), e2022JD036880.
2) Kawakami et al., 2023: J. Geophys. Res. Atmos., 128, e2023JD038874.