The Atmosphere Chemistry Studies in the Oceanic Environment (ACSOE) Aerosol Characterisation Experiment (ACE) Hill Cloud Experiment (HILLCLOUD) used a hill cap cloud which forms over a ridge on the NE of the island of Tenerife as a natural flow through reactor. An additional objective of this experiment was to characterise the size distribution, size dependent chemical composition and hygroscopic properties of the marine and modified continental aerosol arriving at the North coast of the island. The trace gas concentrations at the same site were similarly characterised.