Understanding Aerosol Measurements

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Understanding AerosolMeasurements
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Purpose Looking for Relationships

• Between Aerosols and
• Temperature
• Cloud cover
• Humidity
• Precipitation
• Seasonal change

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Solar Elevation and Airmass

• Airmass - a term meaning how much atmosphere in
  the path of the light
• The Sun should be more than 30 deg (mlt2) for the
  aerosol measurement to be accurate.

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Aerosols Scatter Light

• Fewer particles
• Less scattering
• Smaller AOT
• More transmission

• More particles
• More scattering
• Larger AOT
• Less transmission

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The Sun Photometer has 2 channels

• For green light 505 nm
• Human eyes are most sensitive at this wavelength
• For red light 625 nm
• Sensitive to larger aerosol particles
• Together the two wavelengths tell us about how
  much aerosol is present AND what size particles.

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The Sun Photometer measures VOLTS

• Based on a photocell - light causes electricity
  to flow.
• A voltmeter measures the flow.
• Must be converted to AOT.
• Requires pre-calc
• We can use a web page instead!

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AOT or Transmission?
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When to take measurements?

• When you have Sun!
• When the Sun is more than 30 deg high
• Airmass gt2
• Morning - air is less turbulent
• In winter - closer to noon
• Its important to report your latitude

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Are you getting good data?

• Volts will vary - depends on the electronics
  inside each instrument.
• Wires, photocell detectors, battery etc
• Dark voltage - small current in the wires
• Red AOT tends to be less than green AOT
• Aerosols tend to scatter green light better than
  red light.

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What do scientists look for in the data?

• Compare the two channels
• Green is usually higher than red
• Are the 3 measurements similar?
• If your careful, then any changes are due to
  atmospheric changes.
• Look for relationships with cloud cover, etc.
• Compare with satellite measurements.

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Comparing with Satellites

• NASA's Terra and Aqua spacecraft
• Measure as the satellites goes overhead
• 40,000 km in one orbit
• 90 minutes for one orbit
• Speed 40,000km/90 min 450 km/min!
• Highest peak time is best
• Predict the satellite http//earthobservatory.nas
  a.gov/MissionControl/overpass.html

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Satellites that monitor Aerosols

• TERRA

• AQUA

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Aqua monitors Katrina

• http//aqua.nasa.gov/highlight.php?id30

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• http//www.spaceref.com/news/viewsr.html?pid17926