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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

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


Characterization of aerosols and clouds by ace fts measurements

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


Characterization of aerosols and clouds by ace fts measurements

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.


Characterization of aerosols and clouds by ace fts measurements

Waterloo Centre forAtmospheric Sciences

University of Waterloo

Flow Tube Technique + Fourier Transform Spectrometer = Optical Constants


Characterization of aerosols and clouds by ace fts measurements

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


Characterization of aerosols and clouds by ace fts measurements

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


Characterization of aerosols and clouds by ace fts measurements

Waterloo Centre forAtmospheric Sciences

Applications to ACE FTS Observations Polar Mesospheric Clouds Polar Stratospheric Clouds Tropical Cirrus Clouds

University of Waterloo


Characterization of aerosols and clouds by ace fts measurements

High altitude (sub-visual) Cirrus clouds

Waterloo Centre forAtmospheric Sciences

University of Waterloo

Typical cirrus observation

Vertical density profiles


Characterization of aerosols and clouds by ace fts measurements

Size distribution

Waterloo Centre forAtmospheric Sciences

University of Waterloo

Number density size distribution

centred at 3 - 7 microns


Characterization of aerosols and clouds by ace fts measurements

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


Characterization of aerosols and clouds by ace fts measurements

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.

CloudCloud-free


Characterization of aerosols and clouds by ace fts measurements

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


Sts clouds

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


Ice clouds

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


Characterization of aerosols and clouds by ace fts measurements

Volume versus Number Density

Waterloo Centre forAtmospheric Sciences

University of Waterloo


Characterization of aerosols and clouds by ace fts measurements

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


Characterization of aerosols and clouds by ace fts measurements

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


Characterization of aerosols and clouds by ace fts measurements

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,…


Characterization of aerosols and clouds by ace fts measurements

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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