Optimization of temperature protocol for carbonaceous aerosol thermal-optical analysis using the TLLP approach

Thermal-optical analysis (TOA) is a widely used method for assessing the organic carbon (OC) and elemental carbon (EC) collected on atmospheric aerosol filters. Currently, there is no uniform or standardized temperature protocol for determining the carbon components. Different temperature protocols can cause significant discrepancies of up to 35.8 % in OC and EC measurements for the same filter, resulting in short of expected comparability among different laboratories. In order to evaluate the two main factors (He -mode highest temperature and residence time at each temperature plateau that affects TOA measurements), this study proposed a novel approach for investigating the temperature change that occurred when the laser reached its lowest point (TLLP). The measurements were based on a total of 682 ambient aerosol filter samples collected from ten cities/ areas of China. An optimized new temperature protocol referred to as COTP had been obtained. As a primary characteristic, the He -mode highest temperature was set to 650 degrees C. The COTP protocol can minimize the measurement deviations caused by the TOA method itself. It can apply to the ambient aerosol samples with TC loading less than 100 mu g/cm2. Compared to the base temperature protocols, the measurement results of the COTP protocol demonstrated better relative accuracy, and the consistency and comparability among laboratories were significantly improved.