DIRECT OBSERVATION OF HETEROGENEOUS CHEMISTRY IN THE ATMOSPHERE

The heterogeneous replacement of chloride by nitrate in individual sea -salt particles was monitored continuously over time in the tropospher e with the use of aerosol time-of-flight mass spectrometry. Modeling c alculations show that the observed chloride displacement process is co nsistent with a heterogeneous chemical reaction between sea-salt parti cles and gas-phase nitric acid, leading to sodium nitrate production i n the particle phase accompanied by liberation of gaseous HCl from the particles. Such single-particle measurements, combined with a single- particle model, make it possible to monitor and explain heterogeneous gas/particle chemistry as it occurs in the atmosphere.