A laboratory study of the properties of tropospheric aerosol particles

This thesis describes studies of the kinetics of N2O5 hydrolysis using proxies for tropospheric aerosols, measured using an atmospheric pressure aerosol flow tube. The rate of N2O5 hydrolysis has been shown previously to depend on particle phase and water content so these physical properties were characterised in detail for some aerosols. The N2O5 hydrolysis reaction was initially studied on sulphate aerosols, specifically sulphuric acid, ammonium sulphate and ammonium bisulphate. Good agreement was found between this work and previous studies in the literature. The effect of the organic component of tropospheric aerosol on the N2O5 hydrolysis reaction was then considered. Two classes of atmospherically relevant organic species were investigated: dicarboxylic acids and polycarboxylic acids (represented by humic acid). For single-component dicarboxylic acid aerosols, uptake was found to depend on aerosol liquid water content. It was shown that the reactivity of mixed dicarboxylic acid/sulphate aerosols can be predicted based on a knowledge of the liquid water content of the single-component aerosols. The phase transitions of aerosols containing humic acid and mixtures of humic acid and ammonium sulphate were studied prior to an investigation of their chemical reactivity. Ammonium sulphate phase transitions were modified when humic acid was present. The growth of these mixed aerosols could be predicted assuming that the organic and inorganic components take up water independently. The reactivity of ammonium sulphate aerosol was significantly lowered in the presence of humic acid. The results from these experimental measurements are considered within the context of NOx chemistry in the troposphere.EThOS - Electronic Theses Online ServiceGBUnited Kingdo