Uptake of Cl and Br by organic surfaces - A perspective on organic aerosols processing by tropospheric oxidants

Abstract

The reactive uptake of Cl and Br atoms by closely packed organic thin films was studied in a flow reactor. For Cl, the reactive uptake coefficient, γ, was near collision rate for alkane and alkene surfaces. For Br, γ =(3±1) × 10-2 for alkane and γ=(5±2) × 10-2 for alkene surfaces. The processing of the surface was monitored using FTIR, XPS and contact angle measurements. Oxidized surface-bound products and a concurrent increase in hydrophilicity were observed. The probability of a reactive collision between Br, Cl, O(3P), O3 and NO3 and surface-bound organics is compared with that of comparable gasphase reactions, showing that reactions with a high activation energy in the gas-phase have an enhanced surface reaction probability. The uptake coefficients for these tropospheric oxidants are used to estimate the processing time for an organic coated aerosol.