Carbonaceous aerosols observed at Ieodo Ocean Research Station and implication for the role of secondary aerosols in fog formation
Abstract:Carbonaceous components and soluble ions of PM2.5 were measured at Ieodo Ocean Research Station (IORS) from December 2004 to June 2008. IORS is a 40-m research tower and located in the East China Sea (32.07°N, 125.10°E). As IORS is distanced equally from South Korea, China, and Japan, it is an ideal place to monitor Asian outflows with the least influence of local emissions. The mean concentration of PM2.5 mass was 21.8 ± 14.9 μg/m3 with the maximum of 35.3 μg/m3 (March) and the minimum of 11.2 μg/m3 (September). The monthly variation of PM2.5 mass was similar to that of O3 due to meteorological conditions, which determines the degree of influence from nearby lands. Chinese outflows were mostly responsible for the enhancement of mass and major constituents of PM2.5 such as sulfate, OC, and EC. Their concentrations were the lowest in summer when aged marine air masses were dominant. It is noteworthy that sulfate was also enhanced when air mass passed through Japan, even though its concentration was not as high as that of Chinese outflows. In June, OC concentration was distinctively high with high OC/EC ratio of ~9.5. At IORS, June is characterized by the most frequent occurrence of fog and the lowest visibility with the highest relative humidity. In China, the clearing fire of agricultural residues is the major source of fine aerosols in June, leading to severe haze (e.g., Cheng et al., 2014). In addition, the aerosol optical depth was also observed to be the maximum over northeast Asia in June (Kim et al., 2007). Consequently, our results suggest that organic aerosol played a critical role in fog formation in the study region.
Cheng, Z., et al. (2014) Impact of biomass burning on haze pollution in the Yangtze River delta, China: a case study in summer 2011, Atmos. Chem. Phys., 14, 4573-4585, doi:10.5194/acp-14-4573-2014.
Kim, S.–W., et al. (2007) Seasonal and monthly variations of columnar aerosol optical properties over east Asia determined from multi-year MODIS, LIDAR, and AERONET Sun/sky radiometer measurements, Atmos. Environ., 41, 1634-1651.