Diverse mixing states and atmospheric processes of urban amine-containing particles in the North China Plain

Abstract

Amine-containing particles play a critical role in atmospheric chemistry, new particle formation, and haze episodes, but their mixing states and atmospheric processes remain poorly understood, resulting in significant uncertainties in accurately assessing their global budget by models. Here we investigated the seasonal differences in the mixing states and evolution processes of particulate amines in Liaocheng, a heavily polluted city in the North China Plain (NCP), during winter and summer. The dominant amine markers were diethylamine (DEA), trimethylamine (TMA), and triethylamine (TEA) particles, with DEA particles constituting over 70% of total amines. Winter amine-containing particles exhibited higher abundances (winter: 23.0% vs. summer: 17.5%) and elevated biomass–burning indicators (e.g., ⁴⁵CHO₂⁻, ⁵⁹C₂H₃O₂⁻, ⁷³C₃H₅O₂⁻, and ¹¹⁵K₂Cl⁺), along with broader size distributions (0.6–0.9 μm), attributed to anthropogenic sources and particle aging. Conversely, summer amine particles showed fresher signatures (unimodal 0.42 μm peak) with dominant carbonaceous fragments and weaker secondary inorganic signals, reflecting less aging. The gas-to-particle partitioning of amines was significantly influenced by temperature, particle acidity (R_ra), and acid-base reactions, with lower temperatures and higher acidity promoting the amine uptake. DEA particles presented stronger associations with sulfate (r² = 0.87) and nitrate (r² = 0.69) compared to TMA particles. Winter haze events significantly enhanced particulate amines, driven by elevated humidity, lower temperatures, and enhanced R_ra, with random forest and multiple linear regression analyses identifying temperature, R_ra, and O₃ (≥ 15%) as dominant controls. Photochemical processes and sulfate interactions also played critical roles in amine transformations. These findings highlight the complex interplay of environmental and chemical factors governing amine behavior in atmospheric particles, providing essential insights for urban air quality management and climate modeling in the NCP.

Graphical abstract

Keywords

Amine-containing particles / Diethylamine (DEA) particles / Mixing states / Gas-to-particle partitioning / Seasonal characteristics

Highlight

	● Higher winter amines are due to lower temperatures ( T ) and higher relative humidity.
	● T , acidity, and acid-base reactions affected gas-to-particle partitioning of amines.
	● Haze events with higher acidity and relative humidity favor amine particle formation.

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