Abstract
Horizontal gradients in atmospheric aerosol strong acidity have been interpreted in terms of the rate of neutralisation of aerosol H+ by gaseous ammonia. The results indicate a pseudo-first-order rate constant for this reaction within the range 4 x 10(-6) s-1 to 4.1 x 10(-4) s-1 consistent with model results and experimental data derived by other methods. The rate constant is reduced as the aerosol becomes less acidic, which is reflected in a positive correlation between rate constant and aerosol H+/NH4+ ratio.