Evaluation of Thermal Optical Analysis (TOA) using an aqueous binary mixture

Chemical composition and sources of amines in PM2.5 in an urban site of PRD, China

Atmospheric amines have attracted increasing attention due to their significant impact on new particle formation, particle hygroscopicity and particle optical properties. In this study, four low-molecule-weight amines were detected from PM_2.5 filter samples collected at an urban site of Pearl River Delta (PRD) region of China in 2018 autumn. During the campaign, the mass concentrations of ambient particulate methylamine (MA, CH₃NH₂), dimethylamine (DMA, (CH₃)₂NH), trimethylamine (TMA, (CH₃)₃N), and diethylamine (DEA, (C₂H₅)₂NH) were quantified at daily or 12-h resolution using an optimized Ion Chromatograph (IC) method. The total measured amine concentration was 297 ± 209 ng/m³, which can account for 0.76 ± 0.33% of PM_2.5 mass concentrations. The particulate amines in PRD urban area were dominated by MA (243 ± 179 ng/m³), accounting for over 80% of total amines, then followed by DMA (49 ± 30 ng/m³, 16.5%), TMA (4 ± 2 ng/m³) and DEA (1 ± 1 ng/m³). Based on the correlation analysis, MA and DMA mainly presented as nitrate and sulfate salts. We speculate the amines tend to react with gas-phase HNO₃ or particle-phase nitrate to form particulate amine salts via local process in Guangzhou. As the relative humidity (RH) increased, enhanced partitioning of amine towards the particle phase was observed. Using approach of multiple linear regression, 71% of the particulate amines in PRD urban site could be explained by acid-base process and the rest by primary emissions from combustion sources (29%).