[AAS13-P01] Formation of sulfuric acid clusters governed by a combined effect of dimethylamine and condensation sink in polluted northern China
Keywords:new particle formation, sulfuric acid, dimethylamine
Formation of sulfuric acid (H2SO4, SA) clusters is considered to be responsible for atmospheric sulfuric acid - dimethylamine (C2H7N, DMA) nucleation in atmospheric new particle formation (NPF) processes, where the critical roles of both amines and condensation sink (CS) have been demonstrated. However, their combined effect is still not quantitively discussed in ambient observation. In this study, a comprehensive field campaign of NPF was carried out in Wangdu, Hebei province, which represents a typical polluted site in northern China. A number of key precursors and atmospheric parameters were recorded concurrently including the concentrations of sulfuric acid monomers and dimers, DMA, and aerosol particle number size distributions. H2SO4-DMA-H2O ternary nucleation mechanism was responsible for the observed NPF events through the correlation analysis of sulfuric acid monomers, sulfuric acid dimers, CSs, and nucleation rates, and the comparisons with the results from atmospheric cluster dynamics code (ACDC) and CLOUD experiments. The CS and [DMA] varied significantly on NPF event days: CS ranged from 0.01 to 0.04 whereas the 25-75% percentiles of [DMA] covered 1.1-8.2 pptv (part per trillion by volume), which indicates that the formation of clusters should be govern by the two factors. Based on the well-accepted formation pathway of sulfuric acid dimers in the literature, we quantitatively described the combined effect of [DMA] and CS in the formation of sulfuric acid dimers. The ratio of sulfuric acid dimer to the square of sulfuric monomer, a parameter that describes the likelihood of NPF events, could be written as a function of [DMA] and CS. Our ambient observation in four strong NPF events validates this combined effect.