Unexpected large uptake of O-3 on sea salts and the observed Br-2 formation

Uptake coefficients of O-3 On various model compounds of sea salts at ambie nt temperature were measured using a Knudsen cell reactor coupled to a diff erentially pumped quadrupole mass spectrometer. Uptake of O-3 was below the detection limit (< 1x10(-5)) for pure alkali metal bromides, whereas react ive uptake with Br-2 formation was observed on two types of synthetic sea s alts (Aqua Ocean and Instant Ocean) and commercial natural sea salt. Measur ed uptake coefficients were 10(-2)-10(-3), (1.4 +/- 1.1) x 10(-3) and (9.7 +/- 4.6) x 10(-4) for Aqua Ocean, Instant Ocean and natural sea salt, respe ctively. These uptake coefficients were about three orders of magnitude lar ger than that on bulk bromide solution estimated from known liquid phase re actions. The results imply that minor components enhance reactivity of O-3 On synthetic and natural sea salts. This heterogeneous reaction is potentia lly an important Br source in the marine boundary layer on a global scale a s well as in the polar troposphere.