1. AT737
Aerosols

2. Importance of Aerosols
Aerosols directly change the radiation budget
Aerosols modify cloud properties (and clouds modify aerosol properties)
Aerosols affect atmospheric chemistry
Aerosols affect biological systems, including human health
AT737 Aerosols

3. Characteristics of Aerosols
Sizes range from 0.01 to 10 or more micrometers
Chemical composition: NOTE: VERY CHEMICALLY HETEROGENEOUS ”PHYSICS OF DIRT”
o      Sulfate (SO4)
o      Nitrate
o      Soil and mineral dust (silicates, clays)
o      Carbonaceous compounds (elemental and organic carbon)
o      Sea-salt (NaCl)
SOURCE (of this and next four slides): Dr. Bill Collins, NCAR
AT737 Aerosols

4. Sources Sulfate: Nitrate: Soil and mineral dust:
Oxidation of sulfur dioxide from fossil fuel burning
Oxidation of DMS released from ocean micro-organisms
Volcanic emissions
Manmade now 4 times natural (IPCC time series)
Nitrate:
Combustion
Soil and mineral dust:
Dry lake beds from prehistoric lakes
Desertification
Carbonaceous compounds
Organic compounds released from forests
Natural biomass burning
Anthropogenic biomass burning
Fossil fuel combustion
Sea-salt: oceans, of course
AT737 Aerosols

5. Sinks Lifetime in the atmosphere: about 5-7 days. Stratosphere: x100
Removal mechanisms:
Sedimentation (settling) – about 10-20% by mass
V = 50 cm/s for large silicates (50 microns)
V =0.03 cm/s for small particles (1 micron)
“Scavenging” by precipitation – about 80-90% by mass
Consequence: aerosol is very uniformly mixed
AT737 Aerosols

6. Properties of Atmospheric Aerosols
Type
Altitude (km)
Horiz scale (km)
Freq.
Compo-sition
Mass loading (mg m−3)
Optical depth
Mean particle
Size
Trop. Aerosols
0-10 1
Sulfate, nitrate,
minerals
0.01 to 1
~0.1
0.1-1
Dust storms
0-3
Sporadic
Silicates, clays
<1 to 100
1-10
Volcanic
5-35
Mineral ash, sulfates
<1 to 1000
0.1 to 10
Smoke
1-100
Soot, ash,
tars
0.1 t 1
0.1 to 1
AT737 Aerosols

7. Types of Aerosol Continental: sulfate, nitrate, carbonaceous, mineral
Marine: sea salt
Stratospheric: e.g., sulfate formed from volcanic eruptions
AT737 Aerosols

8. Aerosol Variablility Size spectrum Composition Number density
Makes remote sensing difficult, perhaps more difficult than sensing clouds
AT737 Aerosols

9. Stratospheric Aerosols
Stratospheric aerosols are few in number
The long path length of limb sounding is useful
AT737 Aerosols

10. Solar Occultation
Measures transmittance of solar radiation as a function of tangent height
Self calibrating
AT737 Aerosols

11. Very peaky weighing functions
Abel’s Equation
Very peaky weighing functions
AT737 Aerosols

12. Corrections
Need to correct for Rayleigh scattering and atmospheric gas absorption
AT737 Aerosols

13. Results
AT737 Aerosols

14. Tropospheric Aerosols
If you can see them you can measure them, right?
MODIS truecolor 12/17/04 05:20 UTC
AT737 Aerosols

15. Note land/ocean differences!
Another Example
Note land/ocean differences!
MODIS truecolor 3/10/07
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16. Processes Aerosols scatter solar radiation toward satellite
Depends on aerosol properties as well as optical depth
AT737 Aerosols

17. NOAA POES AOD
SOURCE:
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18. NOAA GOES AOD
SOURCE:
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19. Good Paper
King et al., 1999: Remote sensing of tropospheric aerosols from space: Past, present, and future. BAMS, 80,
“Reflectance Function”
AT737 Aerosols

20. Aerosols Over Land
AT737 Aerosols

21. Color
Color Ratio
Angstrom exponent
AT737 Aerosols

22. Forecasts of Aerosols
AT737 Aerosols

23. National Park Service http://www.cira.colostate.edu/nps.html
AT737 Aerosols

24. CALIPSO
Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation
Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)
532 nm Backscatter
AT737 Aerosols