The reaction probability of OH on organic surfaces of tropospheric interest

Using a flow-tube reactor coupled to a chemical ionization mass spectromete r, we investigated the heterogeneous loss of OH on Halocarbon wax, two type s of organized organic monolayers, and several solid organic surfaces (para ffin wax, stearic acid-palmitic acid mixture, pyrene, and soot) that are re presentative of surfaces found in the troposphere. The heterogeneous reacti on is very efficient: the reaction probability is greater than 0.1 for all the organic surfaces investigated, except for Halocarbon wax. These results indicate that OH-organic heterogeneous reactions will significantly modify the hygroscopic properties and cloud condensation nuclei (CCN) ability of organic surfaces in the troposphere, and thus may play an important role in the Earth's radiative balance by affecting the properties of clouds. We al so determined the diffusion coefficient of OH in helium to be 665 +/- 35 To rr cm(2) s(-1). This value is close to that of its polar analogue, H2O, sug gesting that the diffusion coefficient of OH can be calculated accurately w ith H2O transport properties.