Organic amine weakens chloride depletion in coastal atmosphere

Abstract. Chloride depletion from sea salt aerosols (SSA) has frequently been observed in polluted coastal regions, severely impacting air quality and human health. However, the influencing mechanism of alkaline species in chloride depletion remains incompletely understood. Here, we report the first investigation 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 NO_x 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 organic amine on chloride depletion is more pronounced than that of NH₃, primarily because DMA has 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 NO_x. The detection of organic chlorinated products, which were formed via active chlorine-induced oxidation, is consistent with the role of alkaline species in weakening chloride depletion. The formation of organic chlorinated compounds was weakened by the addition of alkaline species, indicating the significant role of alkaline species in reducing active chlorine. These findings suggest that alkaline species, more specifically organic amines, are significant factors influencing chloride depletion in the coastal atmosphere. This further enhances our understanding of chloride depletion phenomena in coastal regions.