[1] We report here results of an experimental study of the OH-initiated oxidation of solid organics in the presence of O 2 , NO x and H 2 O, using two kinds of self-assembled organic monolayers (alkane and aromatic), paraffin and pyrene films as proxies for organic aerosol. We show that the OH-initiated oxidation of the alkane surfaces leads to rapid volatilization. The gas-phase products detected include HO 2 , H 2 O 2 , CO, CO 2 , HCO, CH 2 O, CH 3 CHO, CH 3 OH, and HCOOH. We conclude that volatilization is at least as efficient as wet deposition as a removal process for aliphatic particulates, whereas aromatic particulates show higher stability towards volatilization.

The interaction between water and organic substances is of extreme importance in physical, biological, and geological chemistries. Understanding the interactions between water and organic interfaces is one of the earliest chemical quandaries. In this research, self-assembled monolayers (SAMs) were used as a tool to investigate the interaction between water molecules and hydrophobic surfaces. Real-time adsorption and desorption kinetics of water on hydrophobic SAM surfaces was monitored using a new type of field effect transistor (FET)-like device called MOCSER (molecular controlled semiconductor resistor) coated with SAMs. A quartz crystal microbalance (QCM) was used as a complementary technique to give an estimate of total water mass adsorbed. It is shown that water adsorption depends on relative humidity and is reversible. The amount of adsorbed water increased with surface corrugation. The measurements suggest that adsorption takes place as small water clusters, originating on irregularities on the surface organic layer. Molecular dynamics simulations were carried out to study the interactions of water and hydrophobic surfaces as well. These simulations also suggest the formation of water microdroplets on hydrophobic surfaces, and indicate a strong correlation between increased surface corrugation and adsorption. This paper examines the possible consequences of these interactions on the properties of organic aerosols in the troposphere.

The diffusion of OH, HO2, and O3 in He, and of OH in air, has been investigated using a coated-wall flow tube reactor coupled to a chemical ionization mass spectrometry. The diffusion coefficients were determined from measurements of the loss of the reactive species to the flow tube wall as a function of pressure. On the basis of the experimental results, D(OH-He) = 662 +/- 33 Torr cm2 s-1, D(OH-air) = 165 +/- 20 Torr cm2 s-1, D(HO2-He) = 430 +/- 30 Torr cm2 s-1, and D(O3-He) = 410 +/- 25 Torr cm2 s-1 at 296 K. We show that the measured values for OH and HO2 are in better agreement with measured values of their polar analogues (H2O and H2O2) compared with measured values of their nonpolar analogues (O and O2). The measured value for OH in air is 25% smaller than that for O (the nonpolar analogue). The difference between the measured value for HO2 and O2 (the nonpolar analogue) in air is expected to be even larger. Also we show that calculations of the diffusion coefficients based on Lennard-Jones potentials are in excellent agreement with the measurements. This gives further confidence that these calculations can be used to estimate accurate diffusion coefficients for conditions where laboratory data currently do not exist.

The reaction of an atomic beam of O(3P) with organized organic thin films (OOTFs) of amphiphilic molecules was investigated applying in-situ IR, X P S , and wettability measurements. Both kinetics and surface temperature effects were monitored. The reaction probability was much larger for the OOTF relative to the gas phase process. The reaction rate was found to depend on the organization of the thin films. Structural phase transition was observed by monitoring the changes in reactivity. A curve-crossing model explains the observations and rationalizes the lack of activation energy and the dependence of the reactivity on the penetrability in between the chains.