Observational Evidence Characterizing Aerosol-Cloud Interactions (Invited Presentation)

Aerosol particles in the marine boundary layer include primary organic and salt particles from sea spray and combustion-derived particles from ships and coastal cities. These particle types serve as nuclei for marine cloud droplet activation, although the particles that activate depend on the particle size and composition as well as the supersaturation that results from cloud updraft velocities. Two recent studies, the Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) 2011 and the Stratocumulus Observations of Los-Angeles Emissions Derived Aerosol-Droplets (SOLEDAD) 2012 studied the role of sea spray particles and fossil fuel combustion emissions as cloud droplet nuclei. The collaborative E-PEACE results include: (1) the size and chemical composition of the emitted smoke particles compared to ship-track-forming cargo ship emissions as well as background marine particles, with particular attention to the role of organic particles, (2) the characteristics of cloud track formation for generated smoke and cargo ships, and (3) the implications of these findings for quantifying aerosol indirect effects. The SOLEDAD campaign provided evidence of the cloud-nucleating roles of both marine organic particles and coastal urban pollution, with simultaneous measurements of the effective supersaturations of the clouds in the California coastal region. In this talk, we compare the composition of droplets measured in cloud during E-PEACE and SOLEDAD with the effective supersaturations, which are measured by the cloud condensation nuclei (CCN) spectra of the droplet residuals sampled with a counterflow virtual impactor (CVI). The composition and supersaturation of the droplet residuals are also used to provide constraints on aerosol cloud parcel modeling simulations.