Particle Generation and Chemical Composition of Particles from Low Concentration SO₂ Using a Flow-Type Reactor

Abstract

Aerosol formation via a reaction from low concentration SO₂ (sub-ppm level) was carried out using a flow-type reactor and the change in gaseous species was simulated by a numerical calculation. Particle generation was observed when 248 nm laser beam was irradiated to the gas mixture containing SO₂, O₃ and H₂O vapor. The amount of SO₂ was reduced by 21 % at initial concentrations of SO₂ = 179 ppb and OH = 183 ppb, and the number concentration of generated particles ranged from 6 × 10⁶ to 9 × 10⁶ cm ^-3. The generated particles were less than 100 nm in diameter and SO₄^2- concentration was 70 wt% at the first stage of nucleation, which decreased rapidly to less than 10 wt%. Sulfuric acid molecules were detected as a precursor of nucleation by a mass spectrometer. It was suggested that sulfuric acid molecules efficiently attracted not only water molecules but also water clusters and small water droplets during the gas-to-particle nucleation process.