Understanding Aerosol Measurements

Purpose: Looking for Relationships  Between Aerosols and –Temperature –Cloud cover –Humidity –Precipitation –Seasonal change  Between Aerosols and –Temperature –Cloud cover –Humidity –Precipitation –Seasonal change

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 (m<2) for the aerosol measurement to be accurate.  Airmass - a term meaning how much atmosphere in the path of the light  The Sun should be more than 30 deg (m<2) for the aerosol measurement to be accurate.

Aerosols Scatter Light  Fewer particles  Less scattering  Smaller AOT  More transmission  Fewer particles  Less scattering  Smaller AOT  More transmission  More particles  More scattering  Larger AOT  Less transmission  More particles  More scattering  Larger AOT  Less transmission

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.  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.

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!  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!

AOT or % Transmission? Optical Thickness % TransmissionSky Appearance %Very clear %Clear day %Very Hazy %Extreme haze

When to take measurements?  When you have Sun!  When the Sun is more than 30 deg high –Airmass >2  Morning - air is less turbulent  In winter - closer to noon –It’s important to report your latitude  When you have Sun!  When the Sun is more than 30 deg high –Airmass >2  Morning - air is less turbulent  In winter - closer to noon –It’s important to report your latitude

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.  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.

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.  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.

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: verpass.html verpass.html  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: verpass.html verpass.html

Satellites that monitor Aerosols  TERRA  AQUA

Aqua monitors Katrina  

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