5:15 PM - 6:30 PM
[ACG44-P03] Seasonal Variation of Phosphate in Atmospheric Aerosols in Higashi-Hiroshima
Keywords:Atmospheric aerosol, Phosphorus, Pollen, Dry deposition flux
Phosphorus is an essential element for the life support of all living organisms, but it can be depleted in the surface layer of the ocean and may control the primary productivity. The supply of phosphorus into the oceans is primarily from rivers, with atmospheric deposition accounting for about 5% of the supply. Atmospheric deposition can be an important source of phosphorus in the Seto Inland Sea, where the amount of phosphorus flowing into rivers has decreased in recent years and the primary productivity has decreased. However, reports on the source and behavior of phosphorus in the atmosphere are limited. In this study, we focused on phosphate (PO43-), which is most easily utilized by organisms, and investigated the concentration range, seasonal variation, and source of phosphate in atmospheric aerosols in Higashi-Hiroshima, Japan.
Atmospheric aerosol samples were collected on cellulose fiber filters using a high-volume air sampler from December 2017 to June 2020 at the campus of Hiroshima University in Higashi-Hiroshima, Japan. The molybdenum blue method was used to determine the concentration of phosphate in the samples. Water-soluble inorganic ions were also measured by ion chromatography. In order to estimate the source of phosphate, backward trajectory analysis, comparison with meteorological data, and principal component analysis were conducted.
Concentrations of phosphate in atmospheric aerosols during the observation period ranged from 1.7 to 49.0 ng m-3 and tended to be high in spring and low in winter. Principal component analysis showed that phosphate had the same factor as non seasalt- (nss-) Ca2+ and K+. Because the concentration of phosphate is high in spring and mineral dust is a source of phosphorus in the atmosphere, the peaks of phosphate in spring was considered to originate from Kosa. However, the peak of nss-Ca2+, which is an indicator of mineral dust, coincided with the Kosa periods, but slightly deviated from the peaks of phosphate. Furthermore, backward trajectory analysis showed that the air mass during the period of phosphate peaks did not pass through the arid regions of the Asian continent. On the other hand, the variation of phosphate concentration was similar to that of nss-K+, an indicator of plant origin, suggesting that the source of phosphate is plant in addition to mineral particles. Specifically, the high concentration of phosphate in spring, a positive correlation with solar radiation, and the presence of phosphorus as a major component of pollen suggested that pollen contributed to the origin of phosphate. Although the calculated dry deposition flux of phosphate was as small as 0.21 to 0.54 mg m-2 month-1, phosphate from the atmosphere is suggested to be used for phytoplankton production in the Seto Inland Sea, where phosphorus is depleted particularly in spring.
Atmospheric aerosol samples were collected on cellulose fiber filters using a high-volume air sampler from December 2017 to June 2020 at the campus of Hiroshima University in Higashi-Hiroshima, Japan. The molybdenum blue method was used to determine the concentration of phosphate in the samples. Water-soluble inorganic ions were also measured by ion chromatography. In order to estimate the source of phosphate, backward trajectory analysis, comparison with meteorological data, and principal component analysis were conducted.
Concentrations of phosphate in atmospheric aerosols during the observation period ranged from 1.7 to 49.0 ng m-3 and tended to be high in spring and low in winter. Principal component analysis showed that phosphate had the same factor as non seasalt- (nss-) Ca2+ and K+. Because the concentration of phosphate is high in spring and mineral dust is a source of phosphorus in the atmosphere, the peaks of phosphate in spring was considered to originate from Kosa. However, the peak of nss-Ca2+, which is an indicator of mineral dust, coincided with the Kosa periods, but slightly deviated from the peaks of phosphate. Furthermore, backward trajectory analysis showed that the air mass during the period of phosphate peaks did not pass through the arid regions of the Asian continent. On the other hand, the variation of phosphate concentration was similar to that of nss-K+, an indicator of plant origin, suggesting that the source of phosphate is plant in addition to mineral particles. Specifically, the high concentration of phosphate in spring, a positive correlation with solar radiation, and the presence of phosphorus as a major component of pollen suggested that pollen contributed to the origin of phosphate. Although the calculated dry deposition flux of phosphate was as small as 0.21 to 0.54 mg m-2 month-1, phosphate from the atmosphere is suggested to be used for phytoplankton production in the Seto Inland Sea, where phosphorus is depleted particularly in spring.