Electrospray Mass Spectrometric Detection of Products and Short-Lived Intermediates in Aqueous Aerosol Microdroplets Exposed to a Reactive Gas

The intermediates ISO3 - (m/z = 207) and IS2O3 - (m/z = 239) generated in aqueous (NaI/Na2S2O3) microdroplets traversing dilute O3 gas plumes are detected via online electrospray mass spectrometry within ∼1 ms, and their stabilities gauged by collisionally induced dissociation. The simultaneous detection of anionic reactants and the S2O6 2-, HSO4 -, IO3 -, and I3 - products as a function of experimental conditions provides evidence of genuinely interfacial reaction kinetics. Although O3(aq) reacts about 3 times faster with I- than with S2O3 2- in bulk solution, only S2O3 2- is significantly depleted in the interfacial layers of [I-]/[S2O3 2-] = 10 microdroplets below [O3(g)] ∼ 50 ppm.