1Chemical Sciences Division, Lawrence Berkeley National Lab., Berkeley, CA 94720, USA
2Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, MA 01821, USA
3Dept. of Civil and Environmental Engineering, Univ. of California, Davis, CA 95616, USA
4Dept. of Chemistry, Univ. of California, Berkeley, CA 94720, USA
5Dept. of Physics, Univ. of California, Berkeley, CA 94720, USA
Abstract. The heterogeneous reaction of OH radicals with sub-micron squalane particles, in the presence of O2, is used as a model system to explore the fundamental chemical mechanisms that control the oxidative aging of organic aerosols in the atmosphere. Detailed kinetic measurements combined with elemental mass spectrometric analysis reveal that the reaction proceeds sequentially by adding an average of one oxygenated functional group per reactive loss of squalane. The reactive uptake coefficient of OH with squalane particles is determined to be 0.3±0.07 at an average OH concentration of ~1×1010 molecules·cm−3. Based on a comparison between the measured particle mass and model predictions it appears that significant volatilization of a reduced organic particle would be extremely slow in the real atmosphere. However, as the aerosols become more oxygenated, volatilization becomes a significant loss channel for organic material in the particle phase. Together these results provide a chemical framework in which to understand how heterogeneous chemistry transforms the physiochemical properties of particle phase organic matter in the troposphere.