title: Characterization of sulfurous acid, sulfite, and bisulfite aerosol systems.
abstract: Acidic tropospheric aerosols contain inorganic species such as sulfurous acid (H(2)SO(3)). As the main alkaline species, ammonia (NH(3)) plays an important role in the heterogeneous neutralization of these acidic aerosols. An aerosol flow-tube apparatus was used to obtain simultaneous optical and size distribution measurements using FTIR and SMPS measurements, respectively, as a function of relative humidity and aerosol chemical composition. A novel chemiluminescence apparatus was also used to measure ammonium ion concentration [NH(4)(+)]. The interactions between ammonia and hydrated sulfur dioxide (SO(2)·H(2)O) were studied at different humidities and concentrations. SO(2)·H(2)O is an important species as it represents the first intermediate in the overall atmospheric oxidation process of sulfur dioxide to sulfuric acid (H(2)SO(4)). This complex was produced within gaseous, aqueous, and aerosol SO(2) systems. The addition of ammonia gave mainly hydrogen sulfite (SHO(3)(-)) tautomers and disulfite ions (S(2)O(5)(2-)). These species were prevalent at high humidities enhancing the aqueous nature of sulfur(IV) species. Their weak acidity is evident due to the low [NH(4)(+)] produced. Size distributions obtained correlated well with the various stages of particulate compositional development.
authors.affiliation: Centre for Research into Atmospheric Chemistry, Department of Chemistry, University College Cork, and Environmental Research Institute, Cork, Ireland. thomasmtownsend@gmail.com
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Townsend
authors.forename: Arnaud
authors.initials: A
authors.lastname: Allanic
authors.forename: Colette
authors.initials: C
authors.lastname: Noonan
authors.forename: John R
authors.initials: JR
authors.lastname: Sodeau