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Characterization of Aerosols and Clouds by ACE-FTS measurements.

Waterloo Centre for Atmospheric Sciences. University of Waterloo. Characterization of Aerosols and Clouds by ACE-FTS measurements. Alex Zasetsky, Maxim Eremenko, Jim Sloan Waterloo Centre for Atmospheric Sciences Department of Chemistry, University of Waterloo. Method.

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Characterization of Aerosols and Clouds by ACE-FTS measurements.

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  1. Waterloo Centre forAtmospheric Sciences University of Waterloo Characterization of Aerosols and Clouds by ACE-FTS measurements. Alex Zasetsky, Maxim Eremenko, Jim Sloan Waterloo Centre for Atmospheric SciencesDepartment of Chemistry, University of Waterloo

  2. Method Waterloo Centre forAtmospheric Sciences assuming single scattering and homogeneous particles matrix notation and  minimization problem subject to University of Waterloo - solution vector P gives particle size distribution - sum (pi) give Number, Area, or Volume density of aerosol particles

  3. Method Waterloo Centre forAtmospheric Sciences k1,k2,k3,…,kN * P = I * = University of Waterloo Radius(i); i =1,96 0.05 to 12 mm • Extinction efficiency (scattering) calculations: • Mie – spherical particles (liquid water and aqueous solutions) • T-matrix - spheroids, cylinders (NAT and NAD) • Discrete Dipole – hexagonal prisms (Ice, NAT, NAD) Components Optical constants Liquid water & Ice Liquid (ternary) solution of H2SO4/HNO3/H2O Crystalline hydrates: nitric acid tri-hydrate (NAT) and di-hydrate (NAD), sulphuric acid mono-hydrate (SAM) etc.

  4. Waterloo Centre forAtmospheric Sciences University of Waterloo Flow Tube Technique + Fourier Transform Spectrometer = Optical Constants

  5. Optical Constants via extinction measurements Waterloo Centre forAtmospheric Sciences University of Waterloo Complex refractive indices of solid (NH4)2SO4 • Optimization Procedure • “small particle spectra” as a first guess • two loops 1) Inner loop - imaginary part, k(n), is scaled linearly 2) outer loop - k(n) values are corrected at each frequency according [ Dohm et al. J. Phys. Chem. A 2004, 108] Best fit

  6. Optical constants of metastable liquids Waterloo Centre forAtmospheric Sciences University of Waterloo Refractive indices of liquid water (between 234 and 273K) Best fits and corresponding size distributions

  7. Waterloo Centre forAtmospheric Sciences Applications to ACE FTS Observations Polar Mesospheric Clouds Polar Stratospheric Clouds Tropical Cirrus Clouds University of Waterloo

  8. High altitude (sub-visual) Cirrus clouds Waterloo Centre forAtmospheric Sciences University of Waterloo Typical cirrus observation Vertical density profiles

  9. Size distribution Waterloo Centre forAtmospheric Sciences University of Waterloo Number density size distribution centred at 3 - 7 microns

  10. Size distribution Waterloo Centre forAtmospheric Sciences University of Waterloo “Volume” size distribution Estimates of the total volume In the (simplest) case of spherical uniformly distributed particles A is absorption and Sc is scattering rc is cut-off radius The total volume as a function of cut-off radius

  11. Polar StratosphericClouds Waterloo Centre forAtmospheric Sciences University of Waterloo • 20 optically dense (in infrared) clouds from 26 January to 28 February • clustered in the region between 13E and 70E / 60N and 70N. Cloud Cloud-free

  12. Waterloo Centre forAtmospheric Sciences Liquid Solutions (STS) or Crystalline Hydrates? NAT STS University of Waterloo Spectral feature ~ 820 cm-1 (NAT) sharp ~ 810 cm-1 (NAD) sharp ~ 820 cm-1 (STS) broad ‘n’ weak

  13. Waterloo Centre forAtmospheric Sciences University of Waterloo STS clouds • Most common type of PSCs for January-February, 2005 • ~0.5-1.0 mm3/cm3 • Particles radius ~1-2 mm Volume density distribution Number density size distribution

  14. Waterloo Centre forAtmospheric Sciences University of Waterloo Ice clouds • Optically densest clouds • Close to the Scandinavian Mountains • Volume is dominated by Ice • Amount of NAT is substantial

  15. Volume versus Number Density Waterloo Centre forAtmospheric Sciences University of Waterloo

  16. Polar Mesospheric -NoctilucentClouds Waterloo Centre forAtmospheric Sciences No cloud 82 km University of Waterloo • 60% of all the ACE observations from July 5 to 14, 2004 between 65 and 70N • Signal/Noise ratio 2 to 10

  17. Number density Waterloo Centre forAtmospheric Sciences University of Waterloo Water vapour reduction (i.e. difference between cloud and cloud free events from ACE level 2 ) = 5 108 1/cm3. Radius = 60 nm (OSIRIS results) ACE  10 < r < 100 nm Optical path length  100 km  Number density 100-200 cm-3

  18. Shape of PMC particles Waterloo Centre forAtmospheric Sciences University of Waterloo • Surface modes  symmetric O-H band • O-H band in the ACE spectra is non-symmetrical • “Poly-dispersion” does not improve fit • Breaking symmetry  better fit Pro- and oblate spheroids, cylinders, hexagons,…

  19. Waterloo Centre forAtmospheric Sciences University of Waterloo • Remarks in conclusion • Desperate need for improved optical constants  NAT, >160K to 200K  STS (HNO3/H2SO4/H2O) solutions – data need to be revised  more accurate measurements below 1000 cm-1 (all existing data) • Imagers and MAESTRO Extinction  better description of small particles  sulfate aerosols Thank you

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