Clusters are unique, isolated nanoreactors that enable the mimicking of small aerosol particles for the detailed investigation of chemical reactions. In this presentation, two topics will be discussed. In the first one, the doping of hydrated acid clusters with various molecules is investigated. Sticking efficiencies, including uptake cross sections, are determined using the combination of cluster mass spectrometry and velocity measurements. The combined experimental and computational approach provides insights into molecule-cluster collision dynamics, illustrated by a series of measurements involving diverse molecular interactions and steric effects. The second topic focuses on the dissociation of nitric acid on large water clusters. While dissociation is often reported for clusters containing as few as five water molecules, it is shown that on nanometer-sized ice nanoparticles, dissociation occurs only to a limited extent, with the majority of nitric acid remaining undissociated on the ice surface.