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(C₂H₅)₂NH₂⁺ 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 O₃ 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.

Gas-particle partitioning of carbonyls and its influencing factors in the urban atmosphere of Zhengzhou, China

Despite their profound roles in atmospheric chemistry and health concerns, the gas-particle partitioning of carbonyl compounds and its influencing factors in the ambient atmosphere are poorly elucidated. In this work, a reliable method using a denuder/filter-pack system coated with the derivative reagent, O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) was developed for the simultaneous collection of gaseous and particulate carbonyls. Sampling campaigns were performed at an urban site in Zhengzhou, China. The average field-derived partitioning coefficients (K_p^f) of the six most abundant carbonyls (formaldehyde, acetaldehyde, acetone, propionaldehyde, glyoxal, and methylglyoxal) were in the range of 10^-5-10^-4 m³·μg^-1, and their effective Henry's law coefficients (eff. K_H) ranged from 10⁷ to 10⁹ M·atm^-1. Comparisons revealed that their K_p^f and eff. K_H were 10⁴-10⁶ times and 10²-10⁷ times higher than theoretically predicted, respectively. Given that the aerosol liquid water is a concentrated salt solution, these six carbonyls very clearly salted in to three atmospherically relevant aqueous salts, following the order of sulfate > ammonium > nitrate. However, even taking salting-in effects into account, the Pankow's absorptive partitioning theory and effective Henry's law both failed to explain the unexpected highly particulate carbonyls. In regard to the influencing factors, the negative correlations between K_p^f and temperature indicate that lower temperature is conducive to carbonyls partitioning. As for the strong relative humidity (RH) dependence of K_P^f, high partitioning coefficients were observed under low and high RH conditions. Partitioning is considered to be dominated by the carbonyl-oligomer formation when RH increases from <10% to 50%, and driven by the abundant aerosol liquid water content when RH exceeds 50%. The presence of particulate inorganic components and the transition of particle phase state may also impact the partitioning process, especially in the urban atmosphere.