Integrating Cloud Condensation Nuclei Predictions with Fast Time Resolved Aerosol Instrumentation to Determine the Hygroscopic Properties of Emissions Over Transient Drive Cycles

The physical and chemical properties of aerosols emitted from vehicles can vary in composition under different driving conditions. Thus, characterizing ephemeral changes in aerosol cloud condensation nuclei (CCN) activity and apparent hygroscopicity for vehicle-testing procedures conducted over transient drive cycles can be challenging. To evaluate CCN activity of these emitted aerosols, a closure method integrating traditional CCN measurements with fast time resolved aerosol instrumentation typically used to measure engine exhaust was utilized. Calibration of the method predicted activation diameters, D-d, within 10% and 15% of D-d derived from Kohler theory for two stable sources, aerosolized ammonium sulfate and -pinene secondary organic aerosol, respectively. It was then applied to a transient source to estimate the effect of six different ethanol and iso-butanol gasoline blends on the hygroscopic properties of emissions downstream a gasoline direct injection light duty passenger vehicle over transient drive cycles. To describe the CCN activity, a single hygroscopicity parameter, kappa, was used. Results indicate low CCN activity with kappa ranging between similar to 0.002 and 0.06.Copyright 2015 American Association for Aerosol Research