Characteristics and gas-particle partitioning of amine-containing particles from firework emissions: New insights from machine learning and single-particle mass spectrometry.

Firework displays during the Spring Festival (SF) trigger intense short-term emissions and severe air quality deterioration, yet their effects on particulate amines remain poorly understood. This study conducted field observations during the 2023 SF using single-particle aerosol mass spectrometry combined with source sample analysis to investigate the emission characteristics and transformation mechanisms of amine-containing particles. Results show that amine-containing particles increased by 96.2% during the firework period, accompanied by a peak size shift from 0.42 µm to 0.44 µm and enhanced internal mixing with sulfate. Firework emissions altered mixing states by elevating metals and mixed elemental-organic carbon particles but reducing biomass burning and secondary components. Source sample analysis confirmed fireworks as the primary contributor, with N‑methylaniline emerging as a potential tracer distinguishing fireworks from firecrackers. Fireworks increased modified aerosol acidity (Rra') and altered the atmospheric acid-base balance. The multi-model comparative framework identified Rra' as the dominant driver governing gas‑particle partitioning of amines during the FW period, where aerosol liquid water content (ALWC) and O3 exerted secondary influences, and ALWC showed notable potential nonlinear threshold effects under certain humidity conditions. These findings establish fireworks as a crucial amine source and provide insights into modeling secondary aerosol formation under extreme pollution events.