O-3 AND OH SENSITIVITY TO HETEROGENEOUS SINKS OF HOX AND CH3O2 ON AEROSOL-PARTICLES

A new modification of matrix-isolation EPR has been developed for the measurement of uptake coefficients of polyatomic radicals. The techniq ue is combined either with a cylinder reactor having a movable source of radicals or a coaxial reactor having a movable rod and a fixed sour ce of radicals. The walls of the cylinder reactor or the rod surface a re covered with the aerosol material. A simple way to treat the experi mental data on the basis of the kinetic resistance additivity formula is proved. The results of HO2 and CH3O2 uptake coefficient measurement s are given and the possible implications for atmospheric chemistry ar e discussed. The measured value of the HO2 diffusion coefficient was c loser to D-H2O2 than to D-O2. The HO2 uptake coefficient on the concen trated 80 and 96% w/w H2SO4 was > 0.2 at 243 K. For NaCl, KCl, NH4NO3 and (NH4)(2)SO4, the gamma(HO2) values were in the range(1-2) x 10(-2) and gamma(CH3O2) = 0.3 x 10(-2) at 295 K for NaCl. No changes were fo und at [HO2] = 4 x 10(9)-3 x 10(11) cm(-3). The results are discussed from the viewpoint of stratospheric ozone in volcanic clouds and tropo spheric hydroxyl abundance in urban regions.