Characterization of SulfurousAcid, Sulfite, and BisulfiteAerosol Systems.

Acidic tropospheric aerosols contain inorganic speciessuch assulfurous acid (H2SO3). As the main alkalinespecies, ammonia (NH3) plays an important role in the heterogeneousneutralization of these acidic aerosols. An aerosol flow-tube apparatuswas used to obtain simultaneous optical and size distribution measurementsusing FTIR and SMPS measurements, respectively, as a function of relativehumidity and aerosol chemical composition. A novel chemiluminescenceapparatus was also used to measure ammonium ion concentration [NH4+]. The interactions between ammonia and hydratedsulfur dioxide (SO2·H2O) were studied atdifferent humidities and concentrations. SO2·H2O is an important species as it represents the first intermediatein the overall atmospheric oxidation process of sulfur dioxide tosulfuric acid (H2SO4). This complex was producedwithin gaseous, aqueous, and aerosol SO2systems. The additionof ammonia gave mainly hydrogen sulfite (SHO3–) tautomers and disulfite ions (S2O52–). These species were prevalent at high humidities enhancing theaqueous nature of sulfur(IV) species. Their weak acidity is evidentdue to the low [NH4+] produced. Size distributionsobtained correlated well with the various stages of particulate compositionaldevelopment. [ABSTRACT FROM AUTHOR]