Collaborative Research: VOCALS--Interaction of Aerosols with Marine Boundary Layer Clouds

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This study will focus on physical and chemical analysis of ambient aerosol and residual cloud droplet nuclei obtained from the NSF C-130 aircraft over the southeast Pacific (SEP) during the 2008 VOCALS-REx (VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment) project. This work addresses the following VOCALS hypotheses: 1) Variability in aerosol properties impacts the formation of drizzle in stratocumulus clouds over the SEP, 2) The small aerosol radii over the SEP are primarily controlled by anthropogenic, rather than natural, aerosol production, and entrainment of polluted air from the lower free troposphere is an important source of cloud condensation nuclei (CCN), and 3) Ocean upwelling affects aerosol precursor gases and the aerosol size distribution in the atmospheric boundary layer over the SEP. To explore these hypotheses, the size and chemical composition of residual nuclei in cloud droplets will be measured following sampling with a counterflow virtual impactor (CVI), which separates droplets from interstitial aerosol and evaporates them. Aerosols outside of clouds will be sampled with an impactor. Filter and impactor samples of residual nuclei and ambient aerosol will be analyzed by electron microscopy with X-ray analysis. These data will be combined with cloud microphysical measurements to determine aerosol effects on cloud optical properties and lifetimes and the characteristics of aerosol particles that nucleate cloud droplets. Nuclei of larger droplets, which initiate drizzle production, will also be explored. These measurements will complement observations being made by other investigators in VOCALS. This work will lead to insight into how aerosol production due to human activity influences precipitation and the radiative impact of clouds on Earth's climate. The educational plans include an undergraduate student and postdoctoral scholar who will work with the investigators to analyze and interpret the data collected.