The role of NH3 and DMA in new particle formation from ambient measurements, bias exchange metadynamics and reactive MD simulations

Ammonia (NH3) and organic amines (dimethyl amine, DMA) play an important role in the heteromolecular nucleation of sulfuric acid (H2SO4) and water. Nucleation rates depend on their concentrations. Extremely low amine concentrations can increase nucleation rates drastically, giving a significant contribution to the uncertainty related to the aerosol indirect effect. We investigate the differences between the nucleation mechanism with NH3 and DMA using a novel multiscale approach combining bias exchange metadynamics to determine kinetic basins of the nucleation process and reactive MD to analyse them. Results show stepwise formation mechanism and higher affinity of H2SO4 to DMA than to NH3.