This thesis describes the development and application of a laboratory system to investigate the loss of peroxy radicals to aerosol. The laboratory system consisted of an aerosol flow tube coupled to a custom-built PEroxy Radical Chemical Amplifier (PERCA). Aerosol was generated using an atomiser and their distribution measured using a SMPS. New values of the HO2 uptake coefficient, γ , were obtained for wet and dry sodium chloride aerosol and dry ammonium sulphate aerosol. The mass accommodation coefficient, α, was also determined for NaCl. A box model was used to determine the implications of the new uptake coefficient of HO2 loss to NaCl aerosol for tropospheric chemistry in the marine boundary layer.