Heterogeneous interactions of HOBr, HNO3, O3, and NO2 with deliquescent NaCl aerosols at room temperature

To better quantify the rates at which key trace gases interact with sea-salt aerosols, the kinetics of uptake of HOBr, HNO3, O-3, and NO2 by deliquescent NaCl aerosols at 75% relative humidity (RH) and room temperature have been studied using an aerosol kinetics flow tube technique. Results for HOBr indicate that the uptake coefficient (gamma) is larger than 0.2 for highly acidic aerosols at pH 0.3 and for aerosols that have been buffered to pH 7.2 using a 0.25 M NaH2PO4/Na2HPO4 buffer. For unbuffered NaCl aerosols, the HOBr uptake coefficient due to reaction is less than 1.5 x 10(-3). For HNO3, the uptake coefficient on unbuffered, NaCl aerosols is greater than 0.2, being driven by the very high solubility of HNO3 in aqueous salt solutions. Both NO2 and O-3 show low reactivity on pH neutral aerosols with upper limits to the uptake coefficients of 10(-4) With acidic aerosols, slight O-3 loss occurs either an the walls of the flow tube or on the aerosols, giving rise to Cl-2. These experiments are the first reported kinetics studies of the loss of HOBr, HNO3, and O-3 On aqueous NaCl solutions, and they imply that gas-phase diffusion, and not reaction kinetics, determines the mass-transfer rates of gas-phase HNO3 and HOBr to marine aerosols in the boundary layer. Also, the HOBr results support modeling studies which have proposed that HOBr uptake initiates autocatalytic release of bromide from sea-salt aerosols.