Uniform particle-droplet partitioning of 18 organic and elemental components measured in and below DYCOMS-II stratocumulus clouds

TitleUniform particle-droplet partitioning of 18 organic and elemental components measured in and below DYCOMS-II stratocumulus clouds
Publication TypeJournal Article
Year of Publication2008
AuthorsHawkins, L. N., L. M. Russell, C. H. Twohy, and J. R. Anderson
JournalJournal of Geophysical Research-Atmospheres
Volume113
Abstract

Microphysical and chemical aerosol measurements collected during DYCOMS-II research flights in marine stratocumulus clouds near San Diego in 2001 were used to evaluate the partitioning of 18 organic and elemental components between droplet residuals and unactivated particles. Bulk submicron particle (between 0.2 and 1.3 mu m dry diameter) and droplet residual (above 9 mu m ambient diameter) filter samples analyzed by Fourier Transform Infrared (FTIR) spectroscopy and X-ray Fluorescence (XRF) were dominated by sea salt, ammonium, sulfate, and organic compounds. For the four nighttime and two daytime flights studied, the mass concentration of unactivated particles and droplet residuals were correlated (R-2 > 0.8) with consistent linear relationships for mass scavenging of all 18 components on each flight, meaning that the measured particle population partitions between droplet residuals and unactivated particles as if the particles contain internal mixtures of the measured components. Scanning electron microscopy (SEM) for flights 3, 5, and 7 support some degree of internal mixing since more than 90% of measured submicron particles larger than 0.26 mu m included sea salt-derived components. The observed range of 0.26 to 0.40 of mass scavenging coefficients for the four nighttime flights results from the small variations in temperature profile, updraft velocity, and mixed layer depth among the flights. The uniformity of scavenging coefficients for multiple chemical components is consistent with the aged or processed internal mixtures of sea salt, sulfate, and organic compounds expected at long distances downwind from major particle sources.