Fig. 4: Ice nucleation properties and modelled regional contribution of upper tropospheric particles formed from HNO3–H2SO4–NH3 nucleation.
From: Synergistic HNO3–H2SO4–NH3 upper tropospheric particle formation
a, Active surface site density versus ice saturation ratio, measured by the mINKA instrument at CLOUD, at 233 K and 25% relative humidity. Pure ammonium nitrate particles (purple points) show homogeneous freezing. However, addition of only small amounts of sulfate creates highly ice-nucleation-active particles. At around 1.7% sulfate fraction (red points), the ice nucleating efficiency is comparable with desert dust particles24. b, Simulation of particle formation in a global model (EMAC) with efficient vertical transport of ammonia into the upper troposphere during the Asian monsoon. Including multi-acid HNO3–H2SO4–NH3 nucleation (on the basis of the blue dashed curve in Fig. 2) enhances particle number concentrations (nucleation mode) over the Asian monsoon region by a factor of 3–5 compared with the same model with only H2SO4–NH3 nucleation (from Dunne et al.8, similar to the red solid curve in Fig. 2).
