Characteristics and sources of amine-containing particles in the urban atmosphere of Liaocheng, a seriously polluted city in North China during the COVID-19 outbreak()

The Chinese government issued an unprecedentedly strict lockdown policy to control the spread of the novel coronavirus disease 2019 (COVID-19), significantly mitigating air pollution because of the dramatic reduction of industrial and traffic emissions. To explore the impact of COVID-19 lockdown (LCD) on organic aerosols, the mixing states and evolution processes of amine-containing particles were studied using a single particle aerosol mass spectrometer from January to March 2020 in Liaocheng, which is a seriously polluted city in North China. The counts and percentages of amine-containing particles in total obtained particles during the pre-LCD (547832, 29.8 %) were higher than those during the LCD (283983, 20.7 %) and post-LCD (102026, 18.4 %), mainly due to the reduced emission strength of amines and suppressed gas-to-particle partitioning of amines during the LCD and post-LCD. (74)(C(2)H(5))(2)NH(2)(+) was the most abundant amine marker, which accounted for 98.2 %, 98.4 %, and 96.7 % of all amine-containing particles during the pre-LCD, LCD, and post-LCD, respectively. Correlation analysis and temporal variations indicated that the gas-to-particle partitioning of amines was facilitated by the stronger acidic environment and lower temperature, while the effect of RH and aerosol liquid water content was minor. The A-OC particles were the most abundant type (accounting for ~40 %) throughout the observation period. The temporal profiles and correlation analysis suggested that the impact of the increased O(3) on the amines and their oxidation products (e.g., trimethylamine oxide) was minor. The identified particle types, correlation analysis, and the potential source contribution function results implied that the amine-containing particles were mainly derived from local and surrounding sources during the LCD, while those were mainly affected by long-range transport during the pre-LCD and post-LCD. Our results could deepen the comprehension of the sources and atmospheric processing of amines in the urban area of North China during the COVID-19 outbreak.