REACTION PROBABILITIES FOR N2O5 HYDROLYSIS ON SULFURIC-ACID AND AMMONIUM-SULFATE AEROSOLS AT ROOM-TEMPERATURE

The uptake coefficients for N2O5 hydrolysis have been measured at room temperature on micron-sized aerosols composed of both sulfuric acid a queous solutions and ammonium sulfate solutions. The measurements have been performed in a laminar flow tube which is coupled to a chemical ionization mass spectrometer for monitoring the concentration of N2O5 in the gas phase and an optical particle counter which sizes the aeros ols and determines their number density. The aerosols are generated wi th an ultrasonic nebulizer from aqueous solutions of either sulfuric a cid or ammonium sulfate, and their liquid-phase concentration is deter mined by the relative humidity (RH) set within the flow tube. For both the sulfuric acid and ammonium sulfate aerosols, the reaction probabi lity (gamma) is largest for the lowest relative humidities studied: fo r sulfuric acid aerosols, gamma = 0.05-0.06 for RH = 9-20%, gamma = 0. 02 for RH = 90%; for ammonium sulfate aerosols, gamma = 0.04-0.05 for RH = 50-69%, gamma = 0.02 for RH = 83-94%. In the case of ammonium sul fate aerosols, significant reactivity with N2O5 is found at relative h umidities below the deliquescence point of 80%, consistent with the ob servation that ammonium sulfate aerosols are readily formed in supersa turated, liquid states.