Cloud Condensation Nucleus Activity of Secondary Organic Aerosol Particles Mixed with Sulfate
Martin, Harvard University, email@example.com
Cloud condensation nuclei (CCN) activity of mixed organic-sulfate particles was investigated using a steady-state environmental chamber. The organic component consisted of secondary organic aerosol (SOA) generated in the dark from 22 ppb α-pinene at conditions of 300 ppb ozone and 40% relative humidity at 20°C. CCN analysis was performed for 80- to 150-nm particles having variable SOA-sulfate volume fractions. AMS measurements also determined an effective SOA density of 1.4 ± 0.1 g cm-3. Critical supersaturation, which increased for greater SOA volume fraction and smaller particle diameter, was well predicted by a two-component Köhler model that used ammonium sulfate and SOA as the two components and an effective molecular weight of 230 g mol-1 for the SOA component. Results from this study further imply that, for the range of conditions studied, the particles may not reach a non-liquid state even at very low water activities, which suggests that the effect of limited solubility may not be a necessary consideration in the parameterization of cloud droplet formation in global climate models.