11:45 AM - 12:00 PM
[AAS09-11] Factors Controlling the Concentration of Water-Soluble Pyrogenic Carbon in Atmospheric Aerosols in Sapporo
Keywords:pyrogenic carbon, carbonaceous aerosols, Sapporo
Pyrogenic carbon (PyC) is a mixture of various compounds produced mainly by the incomplete combustion of biomass and fossil fuels. However, the behavior of PyC in the global carbon cycle is not well understood. A part of PyC becomes soluble in water after partial oxidation. The water soluble PyC, defined as dissolved pyrogenic carbon (DPyC), is transported from land to the ocean via rivers and the atmosphere, and is a relatively large pool in the ocean that accounts for 2% of the dissolved organic carbon (DOC) pool. Although atmospheric deposition has been suggested to be an important source of marine DPyC, only three studies have evaluated water-soluble PyC (WSPyC) concentrations in atmospheric aerosols, and further observations are needed to elucidate factors controlling WSPyC concentrations in atmospheric aerosols. In this study, we investigated the relationship between WSPyC concentration and various carbon parameters to elucidate the controlling factors of WSPyC concentration in atmospheric aerosols.
Atmospheric aerosols were collected in the central area of Sapporo, Japan from September 19, 2022 to September 28, 2023 using a high volume aerosol sampler. Elemental carbon (EC) and organic carbon (OC) concentrations in the aerosol samples were determined by an thermal-optical-transmittance carbon analyzer, and water-soluble organic carbon (WSOC) concentrations were measured by a total organic carbon analyzer with high temperature catalytic oxidation. The concentration of WSPyC was determined using the benzene polycarboxylic acid (BPCA) method with a high-performance liquid chromatography. In addition, the UV-visible absorption fraction of WSOC (water-soluble brown carbon; WSBrC) were determined by a spectrophotometer.
The WSPyC concentrations observed in this study (average 0.013 ± 0.01 µgC/m³) were comparable to those observed in the open western North Pacific Ocean (Bao et al., 2019) and in Malaysia under influence of fossil fuel combustion (Geng et al., 2021). This result suggests that the atmospheric aerosols in Sapporo were not strongly influenced by biomass burning. The highest average concentrations of carbon parameters (i.e., OC, EC, WSBrC, WSPyC) in atmospheric aerosols were observed in spring (March to May). The average concentrations of parameters derived from combustions and biological activities (OC and WSOC) were relatively high in summer (June to August) (OC : 2.2±0.4 µgC/m³, WSOC : 1.1±0.3 µgC/m³), whereas the average concentrations of parameters derived from combustions (EC, WSBrC, WSPyC) were relatively high in winter (EC :0.5±0.2 µgC/m³, WSBrC: 0.05±0.01 Mm-¹, WSPyC : 0.018±0.007 µgC/m³).
The seasonal difference in the origin of WSPyC was determined by correlation between WSPyC and other parameters together with the results of local wind direction and velocity data and backward trajectory analysis. A strong correlation was observed between WSPyC and EC in spring (r=0.88, p<0.001), suggesting a contribution of fossil fuel conbustion-derived WSPyC from local and continental sources. In autumn, the correlation of WSPyC with WSBrC (r=0.96, p<0.001) was stronger than that with EC (r=0.58, p=0.03), suggesting a greater contribution of WSPyC from biomass burning from local and continental sources than in other seasons. In winter, the correlation between WSPyC and WSBrC (r=0.69, p=0.01) as well as EC (r=0.69, p=0.008) was comparable, but the high WSPyC/WSOC and WSPyC/EC suggested a contribution of burning-derived WSPyC, including biomass burning from continental sources. On the other hand, no significant linear correlation was found between WSPyC and any of the parameters in summer, suggesting that WSPyC was diluted by mixing with air masses unaffected by combustion. These results suggest that the WSPyC concentration in atmospheric aerosols in central Sapporo is controlled by the origin of the air mass, including differences in combustion sources.
Atmospheric aerosols were collected in the central area of Sapporo, Japan from September 19, 2022 to September 28, 2023 using a high volume aerosol sampler. Elemental carbon (EC) and organic carbon (OC) concentrations in the aerosol samples were determined by an thermal-optical-transmittance carbon analyzer, and water-soluble organic carbon (WSOC) concentrations were measured by a total organic carbon analyzer with high temperature catalytic oxidation. The concentration of WSPyC was determined using the benzene polycarboxylic acid (BPCA) method with a high-performance liquid chromatography. In addition, the UV-visible absorption fraction of WSOC (water-soluble brown carbon; WSBrC) were determined by a spectrophotometer.
The WSPyC concentrations observed in this study (average 0.013 ± 0.01 µgC/m³) were comparable to those observed in the open western North Pacific Ocean (Bao et al., 2019) and in Malaysia under influence of fossil fuel combustion (Geng et al., 2021). This result suggests that the atmospheric aerosols in Sapporo were not strongly influenced by biomass burning. The highest average concentrations of carbon parameters (i.e., OC, EC, WSBrC, WSPyC) in atmospheric aerosols were observed in spring (March to May). The average concentrations of parameters derived from combustions and biological activities (OC and WSOC) were relatively high in summer (June to August) (OC : 2.2±0.4 µgC/m³, WSOC : 1.1±0.3 µgC/m³), whereas the average concentrations of parameters derived from combustions (EC, WSBrC, WSPyC) were relatively high in winter (EC :0.5±0.2 µgC/m³, WSBrC: 0.05±0.01 Mm-¹, WSPyC : 0.018±0.007 µgC/m³).
The seasonal difference in the origin of WSPyC was determined by correlation between WSPyC and other parameters together with the results of local wind direction and velocity data and backward trajectory analysis. A strong correlation was observed between WSPyC and EC in spring (r=0.88, p<0.001), suggesting a contribution of fossil fuel conbustion-derived WSPyC from local and continental sources. In autumn, the correlation of WSPyC with WSBrC (r=0.96, p<0.001) was stronger than that with EC (r=0.58, p=0.03), suggesting a greater contribution of WSPyC from biomass burning from local and continental sources than in other seasons. In winter, the correlation between WSPyC and WSBrC (r=0.69, p=0.01) as well as EC (r=0.69, p=0.008) was comparable, but the high WSPyC/WSOC and WSPyC/EC suggested a contribution of burning-derived WSPyC, including biomass burning from continental sources. On the other hand, no significant linear correlation was found between WSPyC and any of the parameters in summer, suggesting that WSPyC was diluted by mixing with air masses unaffected by combustion. These results suggest that the WSPyC concentration in atmospheric aerosols in central Sapporo is controlled by the origin of the air mass, including differences in combustion sources.