Heterogeneous Chemistry

Multiphase processes in aerosols are known to affect the chemical composition of the atmosphere, its refractive ability, the process of cloud formation, and ultimately the climate. Models trying to reproduce and predict the chemical composition of the atmosphere are still limited by large uncertainties about chemical reactions occurring in the gas phase and in condensed aerosols. In particular, there is an urgent need to increase our understanding of reactions occurring at or near the gas–liquid interface. 

We investigate the OH-initiated heterogeneous oxidation of mixed aqueous aerosols containing surface active and non-surface- active components. The experiments are performed in an atmospheric-pressure flow tube at room temperature. The relative concentrations of the aerosol reactants and primary products are monitored by off-line analysis as a function of the time-integrated total concentration of OH radical. In the case of particle containing saccharide molecules,  the kinetic traces of monosaccharide and disaccharide reactants are significantly different. 

To gain more detailed insights into this mechanism, MD simulations are carried out, allowing for prediction of reactant concentration profiles near the air–water interface. Stochastic simulations using a simplified chemical model are also performed to support the interpretation of the data. 

The experimental results are consistent with the formation of an  exclusion layer of disaccharides at the particle surface resulting in a more probable reaction of the monosaccharide with the OH radical. The experimental and modeling studies provide clear evidence that partitioning at the interface will affect the chemical evolution of aqueous organic aerosols.