Diverse mixing states of amine-containing single particles in Nanjing, China

Abstract. The mixing states of particulate amines with different chemical components are of great significance in studying the formation and evolution processes of amine-containing particles. In this work, the mixing states of single particles containing trimethylamine (TMA) and diethylamine (DEA) are investigated in order to study the formation and aging processes of the single particles using a high-performance single-particle aerosol mass spectrometer located in Nanjing, China, in September 2019. TMA- and DEA-containing particles accounted for 22.8 % and 5.5 % of the total detected single particles, respectively. The particle count and abundance of the TMA-containing particles in total particles notably increased with enhancement of ambient relative humidity (RH), while the DEA-containing particles showed no increase under a high RH. This result suggested the important role of RH in the formation of particulate TMA. Significant enrichments of secondary organic species, including 43C2H3O+, 26CN−, 42CNO−, 73C3H5O2−, and 89HC2O4−, were found in DEA-containing particles, indicating that DEA-containing particles were closely associated with the aging of secondary organics. The particle count and abundance of DEA-containing particles showed a prominent increase during the nighttime, but a sharp decrease during the afternoon. Furthermore, the differential mass spectra of the DEA-containing particles showed a much higher abundance of nitrate during the nighttime than during the daytime. In addition, the number fraction of organic nitrogen species in the DEA-containing particles and ambient NOx both showed consistent increasing trends, similar to the accumulation of DEA-containing particles during the nighttime. This suggested that the nighttime production of particulate DEA might be associated with reactions of gaseous DEA with HNO3 and/or particulate nitrate. Higher abundances of oxalate and glyoxylate were found in DEA-containing particles during the strong photochemistry period when the abundance of DEA-containing particles decreased to the lowest of the total particles. This result suggested a substantial impact of photochemistry on the aging process of DEA-containing particles. Further, greater than 80 % of TMA- and DEA-containing particles internally mixed with nitrate, while the abundance of sulfate was higher in the DEA-containing particles (79.3 %) than in the TMA-containing particles (55.3 %). In addition, a lesser amount of ammonium was found in the DEA-containing particles (13.2 %) compared with the TMA-containing particles (35 %). These observations suggested that particulate DEA existed both as nitrate and sulfate aminium salts, while the particulate TMA primarily presented as nitrate aminium salt. Overall, the different mixing states of the TMA- and DEA-containing particles suggested their different formation processes and various influencing factors, which are difficult to be investigated using bulk analysis. These results provide insights into the discriminated fates of organics during the evolution process in aerosols, which provides a better illustration of the behavior of secondary organic aerosols.