Heterogeneous reactivity of chlorine atoms with ammonium sulfate and ammonium nitrate particles

Abstract

In this laboratory study, model particles of ammonium sulfate (AS) and ammonium nitrate (AN) were exposed to chlorine atoms and uptake experiments were performed in a coated wall flow tube reactor coupled to a molecular beam mass spectrometer. The reactive surfaces were prepared by coating the inner surface of the reactor using two different methods: either by depositing size-selected particles on the halocarbon wax or by spray depositing thin films using a constant output atomizer. The observed uptake coefficients vary for (NH₄)₂SO₄, ranging from γ_Cl^AS ≈ 1 × 10⁻³ for size-selected particles to γ_Cl^AS ≈ 6 × 10⁻² for thin films prepared by spray. An uptake coefficient of γ_Cl^AN ≈ 2.5 × 10⁻³ of Cl˙ on size-selected NH₄NO₃ particles was measured. A heterogeneous recombination of Cl atoms to from Cl₂ molecules was observed for the two surfaces. Furthermore, an ageing process was observed for AS particles, this phenomenon leading to the formation of new chlorine species on the solid substrate.