Carbonaceous aerosols in PM2.5 (Particulate matter less than 2.5 ㎛ in aerodynamic diameter) plays an important role in the atmosphere relating to regional and global climate change, visibility reductions and adverse health effects. Carbon fractions can classified as organic carbon (OC) and elemental carbon (EC) by thermal-optical definition.
Two major protocols for thermal-optical methods to classify OC and EC have been applied to atmospheric PM2.5, one is the IMPROVE protocol and the other is the NIOSH protocol. In the NIOSH protocol, OC can divided by four OC fractions (OC1, OC2, OC3, and OC4 in a helium atmosphere at 310 °C, 475 °C, 615 °C, and 870 °C, respectively) and organic pyrolysis carbon (OP) was determined when transmitted laser light attained its original intensity after oxygen was added to the combustion atmosphere. And EC can divided by six EC fractions (EC1, EC2, EC3, EC4, EC5 and EC6 in a 2% oxygen/98% helium atmosphere at 550°C, 625°C, 700°C, 775°C, 850°C and 870°C, respectively). The NIOSH protocol defined OC as OC1 + OC2 + OC3 + OC4 + OP and EC as EC1 + EC2 + EC3 + EC4 + EC5 + EC6 ? OP, respectively.
In this study, routine measurements of OC and EC with other carbon fractions and organic speciations during two years were carried out at Anmyeon Island which is a background area in Korea to understand the characteristics of carbon fractions in PM2.5, especially, the temperature-resolved OC and EC concentrations. Sampling was performed on every sixth day and a total of 117 samples were obtained during June 2015 and May 2017 using high volume air sampler with pre-baked quartz fiber filter. OC and EC were analysed using the TOT (Thermal optical transmittance) method of NIOSH protocol. Among temperature-resolved OC and EC fractions, we found that OP had distinct seasonal characteristics. OP concentrations decreased in summer, while, increased in fall. The split points by the transmission correction between OC and EC had four different characteristics during the sampling period. Aomg four split point, the case of split in OC4 fraction were frequently occurred in the summer samples. .It can be explained by the high oxidation a conditions in the atmosphere during summer. OP has strong correlation with HULIS-C (r=0.72, P<.01), while weak correlation Levoglucosan (r=0.33, P<.01) in summer. But in the other season (fall, winter and spring), OP has strong correlation with HULIS-C (r=0.92, P<.01) and Levoglucosan (r=0.68, P<.01). When principle component analysis was applied to OP and other carbonaceous fractions, OP was extracted in the factor-1 with 28% of total variance (83%) HULIS-C and Levoglucosan which are indicators of biomass burning were also loaded with OP in factor-1. It suggests that OP might be related to the biomass burning.