Impacts of dimethylamine emissions on particle number concentration and cloud condensation nuclei in Beijing

Abstract New particle formation (NPF) is a key source of atmospheric particles and cloud condensation nuclei (CCN). In polluted regions, the nucleation mechanism of sulfuric acid (H 2 SO 4 )-dimethylamine (DMA) is thought to play a crucial role in NPF. However, it still remains unclear about the sources of DMA and their contributions to regional particle number concentrations (PNC) and CCN. In this study, we incorporated the H 2 SO 4 -DMA nucleation mechanism into the aerosol module in the WRF-Chem model to improve the model’s simulation ability for NPF events. The default 8 size bins covering 39 nm to 10 μm were extended to 12 size bins ranging from 1 nm to 10 μm to better capture the formation and growth of the small particles. The modified model was applied to Beijing and its surrounding areas for an observation episode from March 1 to 18 in 2017. The results show that the revised model significantly improves its capability in simulating the particles number in the smaller size range (<20 nm), reducing the standardized bias from over 58% to 10%. The H 2 SO 4 -DMA nucleation mechanism contributes 46–78% of PNC in the surface layer (from the surface to ~300 m) and 22–36% of CCN at 0.5% supersaturation (CCN 0.5% ). The contributions to PNC and CCN 0.5% are notably higher on NPF days than those on non-NPF days. High PNC zones correspond to areas with elevated CCN 0.5% , suggesting that the nucleation process leads to increased CCN concentrations, and these regions also exhibit higher levels of H 2 SO 4 and DMA. Agricultural and residential activities were identified as the main sources of DMA in the study area. The contribution of residential DMA to PNC is particularly significant in urban Beijing, reaching up to 70%. This study enhances our understanding of how NPF events induced by H 2 SO 4 -DMA nucleation affect PNC and CCN in intensive anthropogenic emission regions.