Characteristics of aerosol aminiums over a coastal city in North China: Insights from the divergent impacts of marine and terrestrial influences

Aminium ions, as crucial alkaline components within fine atmospheric particles, have a notable influence on new particle formation and haze occurrence. Their concentrations within coastal atmosphere depict considerable variation due to the interplay of distinctive marine and terrestrial sources, further complicated by dynamic meteorological conditions. This study conducted a comprehensive examination of aminiums ions concentrations, with a particular focus on methylaminium (MMAH⁺), dimethylaminium (DMAH⁺), trimethylaminium (TMAH⁺), and triethylaminium (TEAH⁺) within PM_2.5, over varying seasons (summer, autumn, and winter of 2019 and summer of 2021), at an urban site in the coastal megacity of Qingdao, Northern China. The investigations revealed that the total concentration of particulate aminium ions (∑Aminium) was 21.6 ± 23.6 ng/m³, exhibiting higher values in the autumn and winter compared to the two summer periods. Considering diurnal variations during autumn and winter, concentrations of particulate aminium ions (excluding TEAH⁺) exhibited a slight increase during the day compared to night, with a notable peak during the morning hours. However, it was not the case for TEAH⁺, which was argued to be readily oxidized by ambient oxidants in the afternoon. Additionally, the ∑Aminium within the summer demonstrated markedly elevated levels during the day compared to night, potentially attributed to daytime sea fog associated with sea-land breeze interactions. Positive matrix factorization results indicate terrestrial anthropogenic emissions, including vehicle emission mixed with road dust and primary pollution, as the primary sources of MMAH⁺ and DMAH⁺. Conversely, TMAH⁺ was predominantly emitted from agricultural and marine sources. With the dominance of sea breeze in summer, TMAH⁺ was identified as a primary marine emission correlated with sea salt, while MMAH⁺, DMAH⁺, and TEAH⁺ were postulated to undergo secondary formation. Furthermore, a notable inverse correlation was observed between TMAH⁺ and methanesulfonate in PM_2.5, consistent with dynamic emissions of sulfur-content and nitrogen-content gases reported in the literature.