Determination of Water Soluble Organic Carbon in Atmospheric Particulate Matter by Non-Dispersive Infrared Absorption Spectrometry with Combustion Oxidation

TSP (total suspended particulate matter with aerodynamic equivalent diameter not exceeding 100 μm) samples were collected using the high flow sampler (the TSP quartz film as the sampling membrane with the membrane area of 414 cm²)) at a flow rate of 1.05 m³·min^-1 for 24 h. PM_2.5 (particulate matter with aerodynamic equivalent diameter not exceeding 2.5 μm) samples were collected using the low flow sampler (the PM_2.5 quartz film as the sampling membrane with the membrane area of 12.56 cm²) at a flow rate of 16.67 L·min^-1 for 24 h. The TSP sampling membrane with usable area of 11.5 cm² or the whole PM_2.5 sampling membrane was taken, and deionized water was added to 50 mL. The mixture was shaken and sonicated for 80 min. After shaking, the mixture was passed through a 0.45 μm needle filter, and the first 5 mL of filtrate was discarded. The subsequent filtrate was collected, and placed into a total organic carbon (TOC) analysis sample bottle. After sealing with tin foil, total carbon (TC) and inorganic carbon (IC) were determined by the TOC analyzer, and water soluble organic carbon (WSOC) was determined by subtraction method. It was shown that linear relationships between values of the mass concentration and the absorbance of TC and IC were kept within 28.0 mg·L^-1 and 8.0 mg·L^-1, and detection limit (3.143 s) of WSOC obtained by subtraction method was 0.12 mg·L^-1. Test for recovery was conducted by the standard addition method, giving results in the range of 90.0% -118%, and RSD (n=7) of the determined values was 2.8%. The proposed method was applied to the analysis of 301 PM_2.5 samples from a certain city site in Beijing from January 2019 to December 2019, with detected mass concentrations in the range of 0.51-23.79 μg·m^-3 for WSOC.