HETEROGENEOUS CHEMICAL-PROCESSING OF (NO2)-N-13 BY MONODISPERSE CARBON AEROSOLS AT VERY-LOW CONCENTRATIONS

The heterogeneous reaction of NO2 with different carbon aerosol partic les was investigated in situ. The NO2 was labeled with the beta(+)-emi tter N-13 (half-life 10.0 min) which allowed application of NO2, at ve ry low concentrations. The carbon aerosol was either produced by a spa rk discharge generator using graphite electrodes or by a brush generat or resuspending commercial soot material. Monodisperse size cuts betwe en 50- and 490-nm diameter were selected and mixed with the (NO2)-N-13 . After a defined reaction time, the different reaction products were separated by means of selective traps and detected on-line by gamma-sp ectrometry. A sticking coefficient for chemisorption of NO2 between 0. 3 x 10(-4) and 4.0 x 10(-4) and a rate constant for the reduction of a dsorbed NO2 to NO(g) between 4.0 x 10(-4) and 9.4 x 10(-4) s(-1) were determined for both aerosols. The sticking coefficient obtained in thi s study in situ with aerosol particles is 2 orders of magnitudes small er than the uptake coefficient recently reported with bulk carbon mate rial.