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Depolarization of Light by Single Particles: Identifying Dust Particles In and Out of Clouds

Depolarization of Light by Single Particles: Identifying Dust Particles In and Out of Clouds During PRADACS Darrel Baumgardner Centro de Ciencias de la Atmósfera Universidad Nacional Autónoma de México February 4, 2011 PRADACS Planning Meeting San Juan, Puerto Rico.

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Depolarization of Light by Single Particles: Identifying Dust Particles In and Out of Clouds

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  1. Depolarization of Light by Single Particles: Identifying Dust Particles In and Out of Clouds During PRADACS Darrel Baumgardner Centro de Ciencias de la Atmósfera Universidad Nacional Autónoma de México February 4, 2011 PRADACS Planning Meeting San Juan, Puerto Rico

  2. The Aerosol Particle Spectrometer with Depolarization (APSD) Will measure the size and state of depolarization of individual aerosol particles from 0.5 – 10 μm and derive their refractive index when they are spherical.

  3. Contribution of the APSD Measurements to PRADACS • Testing the PRADACS hypotheses: • Cloud properties in the TMCF are different during intense LRTAD periods. • LRTAD has unique chemical and physical properties which influence cloud properties and processes. • The APSD measurements of the optical properties of aerosol particles will help identify their sources: dust, bioaerosols and inorganic or organic spherical particles. • Comparison of the optical properties of cloud droplet residual aerosols with those of interstitial particles will help identify removal by cloud droplet through inertial or nucleation scavenging with respect to particle composition.

  4. Results from measurements in Paris fog show significant variation in aerosol size distributions during different fog events that seem linked to the source of the aerosols. 17 18 19 20 21 22 23

  5. There are also significant variations in the depolarization ratios over a one week time period. But there are no signficant local sources of dust in this region. 17 18 19 20 21 22 23

  6. Long range transport of north African dust or local sources of bioaerosols? Primary Biological Aerosol Particles? 17 18 19

  7. Research Objectives • Document the changes in aerosol properties (size, depolarization and concentration) before, during and after cloud events. • CVI and interstitial inlets, APSD, FM-100, PVM, ATOFMS, AMS. • Evaluate the evolution of cloud droplet distributions with respect to the aerosol properties before and after the formation of fog. • APSD, FM-100, CCN, IN, ATOFMS, AMS, Cloud water chemistry • Document the changes in aerosol properties as a function of air mass origin. • APSD, Back trajectory modeling, ATOFMS, AMS, CCN • Compare the APSD with other instruments. • ATOFMS, AMS, Cloud water chemistry, FM-100 (in clear air)

  8. Examination of six types of dusts, Icelandic volcanic dust and Colorado pine pollen show some distinct differences in their “fingerprints” and other subtle differences are evident when maps are compared by differencing.

  9. The “fingerprints” that we can create using the three detector signals are clearly different depending on the ambient conditions and the source of the aerosols.

  10. The UNAM APSD will be available with 99% certainty for the PRADACS research period following ICE-T. If the proposal to participate in ICE-T is not approved the UNAM APSD can be deployed also for the July period of PRADACS. If the proposal to participate in ICE-T is approved (and funded), the APSD will not be available for the July period; however – The University of Manchester also has an APSD that could possibly be borrowed either for PRADACS or ICE-T

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