HETEROGENEOUS INTERACTIONS OF HOBR, HNO3, O-3, AND NO2 WITH DELIQUESCENT NACL AEROSOLS AT ROOM-TEMPERATURE

To better quantify the rates at which key trace gases interact with se a-salt aerosols, the kinetics of uptake of HOBr, HNO3, O-3, and NO2 by deliquescent NaCl aerosols at 75% relative humidity (RH) and room tem perature have been studied using an aerosol kinetics flow tube techniq ue. Results for HOBr indicate that the uptake coefficient (gamma) is l arger than 0.2 for highly acidic aerosols at pH 0.3 and for aerosols t hat 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 rea ction is less than 1.5 x 10(-3). For HNO3, the uptake coefficient on u nbuffered, 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 s how low reactivity on pH neutral aerosols with upper limits to the upt ake coefficients of 10(-4) With acidic aerosols, slight O-3 loss occur s 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 i mply that gas-phase diffusion, and not reaction kinetics, determines t he mass-transfer rates of gas-phase HNO3 and HOBr to marine aerosols i n the boundary layer. Also, the HOBr results support modeling studies which have proposed that HOBr uptake initiates autocatalytic release o f bromide from sea-salt aerosols.