## 1 Introduction  
Particulate matter (PM) which is composed of carbonaceous aerosols, ions, and elemental components affects not only human health but also climate change [1; 2; 3; 4; 5; 6]. Carbonaceous aerosols such as organic carbon (OC) and elemental carbon (EC) have been measured and quantified by an evolved gas analysis (EGA) among various analytic methods [7; 8; 9; 10; 11]. Thermal-optical analysis, one of the EGA methods, uses different responses of light-absorbing carbonaceous aerosols to the temperatures of collected samples. The sample is analyzed in a helium (He) phase and a helium-oxygen (He-Ox) phase. In the He phase, the OC components collected on the filter are volatilized by increasing the temperature step by step under a helium atmosphere. In the next phase (He-Ox phase), the EC on the filter is oxidized at various temperatures with helium-oxygen mixture. The OC and EC components volatized from the filter are oxidized to carbon dioxide and then reduced to methane. Eventually, the reduced methane concentration is measured to quantify the amount of OC and EC. OC is mostly measured by volatilization from the filter at the He phase, but some of the OC is carbonized or pyrolyzed. Then, they remain volatile on the filter. This is called as the pyrolyzed carbon or pyrolytic carbon (PyC), which absorbs light as EC does. Usually, PyC is oxidized in the He-Ox phase and is recognized as if it were EC. Therefore, it is important to carefully calculate PyC for better quantification of OC and EC. The optical attenuation measurement is commonly used to determine PyC. The intensity of transmitted or reflected light is continuously monitored during analysis, in which the intensity decreases by the PyC and then increases by the oxidation of PyC again. The point at which the intensity of transmitted or reflected light becomes equal to the intensity at the start of analysis is defined as the split time. PyC is artificially calculated from the EC fractions from the beginning of the He-Ox phase to the split point. The measurement of OC and EC depends on analysis protocols in which the temperature profiles and the thermal decomposition correction methods are defined in different ways from each other. The analysis protocols include Interagency Monitoring of Protected Visual Environment (IMPROVE), National Institute for Occupational Safety and Health (NIOSH 5040), European Supersites for Atmospheric Aerosol Research (EUSAAR) and Specification Trans Network (STN), a modification of NIOSH temperature protocols [10; 11; 12; 13]. Each protocol has a different operating temperature profile as shown in Table 1.  
Equivalent black carbon (eBC) concentration is usually measured by filter-based optical transmittance instruments such as an aethalometer, and its limitation has been updated [14]. A multi-angle absorption photometer (MAAP), another filter-based instrument, was successfully applied to the continuous monitoring of local eBC concentrations for more than three months [16; 17]. Thus, we employed the MAAP in order to verify EC concentrations with the help of eBC concentrations. PyC complicates the quantification of EC. The split time is associated with the determination of PyC quantity. This study aims to find not only a relationship between EC and various EC fractions but also the role of PyC in quantifying EC. Uncertainties have been reported on the analysis of OC and EC. For example, PyC depended on how to define the split time and on data processing in the analyzer [18]. Another example is that metal salts might affect the quantification of OC and EC in the case of diesel exhaust particles [19]. However, efforts are underway to quantify OC and EC using a thermal-optical transmittance or a thermal-optical-reflectance despite such uncertainties. In order to better understand EC quantification, we have just initiated the investigation of PyC, the split time, EC concentration and their relationships.