Distinguishing Between Reactive and Non-reactive Condensation with a Fast-Switching Bipolar Mass Spectrometer

Here we present recent results from coupling the Filter Inlet for Gases and AEROsols (FIGAERO) to a Bipolar Time-of-Flight (BTOF) Chemical Ionization Mass Spectrometer. Fast switching-between positive and negative reagent ions addresses the need for instruments that can simultaneously characterize both precursors and oxidation products in ambient measurements. The FIGAERO inlet allows for measurements of gas and particle phase composition as well as thermal desorption profiles of particulate species. FIGAERO-BTOF measurements of laboratory standards and complex chamber mixtures are discussed. FIGAERO-BTOF thermal desorption profiles of inorganic and organic salts such as ammonium nitrate, ammonium sulfate and ammonium oxalate, show that the appearance of simultaneous high temperature desorption peaks in both acidic and basic moieties can be used to distinguish between reactive and non-reactive condensation processes. These observations indicate that previous unipolar (I^- only) FIGAERO desorption measurements that assigned high temperature desorptions of small organic acids to thermal decomposition may underestimate the formation of low volatility species from reactions of small organic acids and bases in the atmosphere. Ambient measurements with the FIGAERO-BTOF are also discussed and compared/contrasted with the laboratory observations. The temporal evolution of the particle phase composition and comparisons with the gas phase measurements obtained over the same time periods are investigated.