Heterogeneous chemical processing of 13NO2 by monodisperse carbon aerosols at very low concentrations

Abstract

The heterogeneous reaction of NO2 with different carbon aerosol particles was investigated in situ. The NO2 was labeled with the β+-emitter 13N (half-life 10.0 min) which allowed application of NO2 at very low concentrations. The carbon aerosol was either produced by a spark discharge generator using graphite electrodes or by a brush generator resuspending commercial soot material. Monodisperse size cuts between 50- and 490-nm diameter were selected and mixed with the 13NO2. After a defined reaction time, the different reaction products were separated by means of selective traps and detected on-line by γ-spectrometry. A sticking coefficient for chemisorption of NO2 between 0.3 × 10ˉ⁴ and 4.0 × 10ˉ⁴ and a rate constant for the reduction of adsorbed NO2 to NO(g) between 4.0 × 10 ˉ⁴ and 9.4 × 10 ˉ⁴ /s were determined for both aerosols. The sticking coefficient obtained in this study in situ with aerosol particles is 2 orders of magnitudes smaller than the uptake coefficient recently reported with bulk carbon material.