Aerosol-cloud interactions of secondary organic aerosols formed from the oxidation of linear, branched, and cyclic alkanes and alkenes

Secondary organic aerosols (SOA) formed from the oxidation of anthropogenic and biogenic precursors comprise a significant fraction of the atmospheric aerosol burden and play an important role in the Earth's radiation budget. We conducted measurements of the cloud condensation nuclei (CCN) and ice nuclei activity of SOA formed from the oxidation of linear, branched, and cyclic alkanes and alkenes. Aerosol forming reactions were carried out in a PTFE environmental chamber, including oxidation of the precursors with O3, NO3, and OH in the presence and absence of NOx. Ice nucleation experiments were performed only for the O3 reactions and ice nuclei were not observed in detectable quantities for this subset of systems. Cloud condensation nuclei ability varied with the chain length of the expected products and the number of functional groups expected per carbon molecule in the condensed phase. From our experiments we found that CCN activity generally decreases with the precursor carbon number and depends on the quality of the functional groups and/or the oxidant that was used to form the condensed phase products. When expressed in terms of a hygroscopicity parameter, kappa, CCN activity ranged from kappa = 0.15 to kappa = 0, spanning the range from moderately CCN active to CCN inactive, respectively, at atmospherically relevant sizes and supersaturations.