Seasonal characteristics of atmospheric water-soluble organic nitrogen in PM2.5 in Seoul, Korea: Source and atmospheric processes of free amino acids and aliphatic amines

The seasonal characteristics of atmospheric water-soluble organic nitrogen (WSON) in particulate matter with a diameter of 2.5 μm or smaller (PM2.5) were analyzed focusing on sources and atmospheric processing. Daily collected samples over 23 h (10:00–9:00) from 7 August 2018 to 31 December 2019 on quartz filters with a high-volume sampler at the Korea Institute of Science and Technology (KIST) in Seoul were considered. The most common species in the Seoul atmosphere included Glycine (5.45 ± 9.81 ng/m3) among free amino acids (FAAs) and trimethylamine (TMA) (5.35 ± 3.80 ng/m3) among aliphatic amines (AAs). The top 10 WSON species (93.6% of all WSON species) were categorized into three groups based on correlation analysis considering meteorological data, (e.g., temperature, rainfall, relative humidity (RH), wind speed) gaseous pollutants (e.g., SO2, CO, NO2) and mass concentration of PM10 and PM2.5. Those three groups are G1 (Glycine, Alanine, and Threonine), G2 (Gln Glutamine, Lys Lysine, and Glutamic acid) and G3 (Trimethylamine (TMA), dimethylamine (DMA), and methylamine (MA)), where G1, G2 and G3 accounted for 31.1%, 8.8% and 51.1%, respectively, of the total species. Among these three groups, G1 and G3 are from combustion sources, and G2 shows secondary features generated by photochemical reactions involving ozone. Although both G1 and G3 exhibited features influenced by combustion sources, the AA species (TMA, DMA, and MA) in G3 demonstrated typical features enhanced under high-humidity conditions, suggesting not only primary sources but also secondary formation at the local scale influence to the AA in G3 group. Based on long-term measurements more than a year, our findings suggest that complex and diverse sources of atmospheric WSON are in Seoul, Korea both from primary and secondary, which may affect its environmental, climate and health.