The heterogeneous reaction of NO 2 with different carbon aerosol particles was investigated in situ. The NO 2 was labeled with the + -emitter 13 N (half-life 10.0 min) which allowed application of NO 2 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 13 NO 2 . 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 NO 2 between 0.3 × 10 -4 and 4.0 × 10 -4 and a rate constant for the reduction of adsorbed NO 2 to NO(g) between 4.0 × 10 -4 and 9.4 × 10 -4 s -1 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.

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