Mixing Primary and Secondary Organic Cloud Condensation Nuclei

Cloud condensation nuclei (CCN) are atmospheric particles that have the ability to uptake water and form cloud droplets. Understanding the chemical and thermodynamic properties that control CCN activity and droplet growth is necessary for constraining impacts on the hydrological cycle and uncertainties from the aerosol indirect effect. Quantifying anthropogenic effects are important for predicting CCN concentrations and understanding climate changes due to human influence. In our study we investigate changes in the CCN activity of biogenic secondary organic aerosol (SOA) modified by the presence of two anthropogenic two types of primary organic aerosol (POA) that are emitted by anthropogenic sources; POA from a flash vaporized mixture of motor-oil and fuel and POA emitted by a diesel engine. The aerosol are sampled from a 12 meter-cubed chamber and an Aerodyne quadrapole aerosol mass spectrometer (Q-AMS) measures changes in aerosol chemical composition and a continuous flow thermal gradient CCN counter measures CCN activity at different instrument supersaturations. We present the CCN activity of alpha-pinene SOA, motor-oil fuel and diesel exhaust POA and their subsequent mixtures. Alpha-pinene SOA is moderately CCN active and the POA that contain lubricating oil components are significantly less active. CCN measurements are compared with mass spectra to identify correlations in the data sets. CCN concentrations are predicted using Q-AMS chemical composition data; particle time of flight data is used to infer the aerosol mixing state and size-resolved CCN predictions are compared to measurements. The assumption that CCN properties are additive is tested by applying CCN properties of individual species to data from mixing experiments.