Properties of Arctic Aerosol Particles and Residuals of Warm and Ice Clouds: Cloud Activation Efficiency and the Aerosol Indirect Effect

Alla Zelenyuk-Imre Pacific Northwest National Laboratory
Dan Imre Imre Consulting
Warren Leaitch Imre Consulting - Climate Chem. Meas. and Research Section
Mikhail Ovchinnikov Pacific Northwest National Laboratory
Peter Liu Environment Canada
Ann Marie Macdonald Environment Canada
J. Walter Strapp Environment Canada
Alexei Korolev Environment Canada
Steven Ghan Pacific Northwest National Laboratory

Category: Field Campaigns

The single-particle mass spectrometer, SPLAT II, was deployed onboard research aircraft to characterize the properties of Arctic aerosol particles, including those that serve as cloud condensation nuclei and ice nuclei. Here we present a detailed comparison between properties of aerosols characterized during clean and highly polluted days. We used the data to: (1) develop a clear picture of what the properties of atmospheric aerosol particles in the Arctic spring are, which includes particle number concentrations, size distributions, and compositions; (2) establish the relationship between particle properties and CCN activity; and (3) establish the relationships between particle properties and IN activity to provide information about the mechanisms responsible for the ice formation. On clean and polluted days we find the Arctic spring atmosphere to be highly stratified, with particle number concentrations exhibiting high variability. On clean days, particle number concentrations were below 250 cm-3, and they were composed of organics and organics mixed with sulfates, biomass-burning (BB) particles, fresh and processed sea salt, and a small number of soot and mineral dust particles. On polluted days, aerosol plumes with number concentrations as high as 2500 cm-3 were dominated by BB particles, organics associated with BB, and their internal mixtures with sulfate. Under clean conditions more than 90% of particles activated to form cloud droplets, while during polluted days fewer than 50% of particles were activated. In both cases, the compositions of cloud-activated particles were virtually the same as those of interstitial particles, but the activated particles were somewhat larger. Data analysis for all ISDAC flights points to a simple relationship between particle number concentrations and activation fraction, indicating a kinetically controlled process. Characterization of ice crystal residuals presents at concentrations that are 3–4 orders of magnitude lower than background aerosol, represent a significant challenge. Nevertheless, using data collected on five flights, we established that these ice clouds were formed by heterogeneous nucleation on mineral dust particles.

This poster will be displayed at ASR Science Team Meeting.