PNNL

Abstract

The cloud condensation nuclei (CCN) properties of mixed particles composed of sulfate and organic material condensed during the hydroxyl-radical-initiated photooxidation of isoprene were investigated in the continuous-flow Harvard Environmental Chamber. CCN activation curves were measured for organic particle mass loadings of 0.3 to 7.2 µg m-3, NOx concentrations from below detection limit up to 38 ppbv, particle diameters from 70 to 150 nm, and thermodenuder temperatures from 25 to 100 °C. At 25 °C, a two-component Köhler model, based on a sulfate seed internally mixed with a condensed secondary organic component and using a single set of physicochemical parameters for the organic component, was successful in describing the observed CCN activation curves. Even though the CCN properties did not change, the particle mass spectra showed that element ratios of the organic component varied across 0.53