Organic amine weakens chloride depletion in coastal atmosphere

Abstract. Chloride depletion from sea salt aerosols (SSA) is frequently observed in polluted coastal regions, and despite they severely impact air quality and human health, the influencing mechanism of alkaline species in this phenomenon remains incompletely understood. Here, we conducted laboratory experiments to investigate the effect of alkaline species including NH3 and an organic amine (dimethylamine, DMA) on chloride depletion and the subsequent formation of organic chlorinated compounds. Results showed that alkaline species could weaken chloride depletion caused by acidic gases, mainly due to acid-base neutralization. Specifically, chloride depletion in the presence of NOx decreased from 20.1 % to 15.8 % when NH3 concentration increased from 100 to 300 ppb. Chloride depletion also decreased from 18.6 % to 13.5 % with DMA concentration increasing from 50 to 150 ppb. The weakening effect of DMA on chloride depletion is more pronounced than that of NH3, primarily DMA stronger alkalinity and nucleation ability. These alkaline species exhibit a stronger reduction of chloride depletion in the presence of SO2 than in the presence of NOx. The detection of organic chlorinated products, formed via active chlorine-induced oxidation, is consistent with the role of alkaline species in weakening chloride depletion, which subsequently results in the reduction of active chlorine. These findings suggest that alkaline species, more specifically organic amines, are significant factors influencing chloride depletion in the coastal atmosphere, further improving our understanding of this phenomenon.