EDUCATION: URBANMAAP

Aerosols Study: Sunphotometer Basics

Sunphotometers employ a Light Emitting Device (LED) to measure the intensity of sunlight transmitted through the atmosphere.

Sunlight is an ideal probe for measuring aerosols. The intensity of sunlight at the top of the earth's atmosphere is constant. While the sunlight travels through the atmosphere, though, aerosols can dissipate the energy by scattering and absorbing the light. More aerosols in the atmosphere cause more scattering and less energy transmitted to the surface. Therefore, knowing the sunlight's energy at the top of the atmosphere, the thickness of the atmosphere, and the amount of sunlight transmitted to the earth's surface and can allows us to determine the amount of scattering, and thus, the amount of aerosols.

Different wavelengths of light transmit different amounts of energy, so accurate measurements require detecting sunlight over a small range of wavelengths. Using a reversed LED meets this narrow-band requirement because it absorbs almost monochromatic light.

Sunphotometers absorb sunlight energy with the LED and convert the intensity into a quantified voltage. Taking measurements with the sunphotometer simply requires aligning the sunlight on the LED, using the external guides, and measuring the corresponding voltage with a voltmeter. See diagram.

Student Questions

1. Using your school instruments, identify each instrument part labeled in the diagrams above and discuss the purpose of each part
2. The sunphotometer uses a scientific technique called remote sensing to measure aerosol in the atmosphere. Learn more about this by reading and discussing the Earth Observatory article "Remote Sensing"

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