Reactive uptake coefficients for loss of N2O5 to micron-size aerosols containing oxalic malonic, succinic, and glutaric acids, and mixtures with ammonium hydrogen sulfate and ammonium sulfate, are presented. The uptake measurements were made using two different systems: atmospheric pressure laminar flow tube reactor (Cambridge) and the Large Indoor Aerosol Chamber at Forschungszentrum Juelich. Generally good agreement is observed for the data recorded using the two techniques. Measured uptake coefficients lie in the range 5 x 10(-4)-3 x 10(-2), dependent on relative humidity, on particle phase, and on particle composition. Uptake to solid particles is generally slow, with observed uptake coefficients less than 1 x 10(-3), while uptake to liquid particles is around an order of magnitude more efficient. These results are rationalized using a numerical model employing explicit treatment of both transport and chemistry. Our results indicate a modest effect of the dicarboxylic acids on uptake and confirm the strong effect of particle phase, liquid water content, and particulate nitrate concentrations.