Visibility Monitoring

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Visibility Monitoring


The Nephelometer is used as a standard part of Air quality monitoring networks in many parts of the world, including state EPA’s in Australia and the U.S.A.

The Nephelometer measures the scattering of light, thus it can detect the distance the naked eye can see (in km). This monitoring is extremely useful when reporting data to the general public who can relate bad air quality to visible distance more than traditional parts per billion or Mg/m3(pollution).

This factor has been demonstrated most evidently during the 2008 Beijing Olympics where the measure of improvement of air quality was that the people of Beijing could see the blue sky, as reported in many articles including the following:

True and accurate visibility measurement by a nephelometer must be performed by taking wet measurements. Wet measurements do not control humidity (by heating sample) and include the affects of humidity, fog and their interaction with aerosols in the visibility measurement.

National Parks

The degredation of pollution and visibility not only harms people's health, but it also has an economic effect on Tourism. Visibility is important for national parks as clear skies provide more spectacular views of nature. Monitoring this visibility is key to ensuring all visitors and tourists recieve the best experience possible, and eliminating any threats to this. One of the main programs designed to monitor visibility at national parks is the I.M.P.R.O.V.E. program (

Air port visibility

Visibility monitoring at airports is vital for aircraft landing and the safety of passengers. Nephelometers have been shown to provide an accurate, real-time measurement of visibility. The Nephelometer’s strength in this department is found in its wet mode of operation; this mode doesn’t heat the sample and combines both the effects of haze, smog and fog within its calculation.

Nephelometers use in airports has been cited in numerous publications for their use in Airport visibility, one of the most important ones is stated below:

"The planned transition from human to automated airport visibility monitoring has unfortunate implications for visibility monitoring. Most of the existing information about historical haze trends is from airport data. The new automated instruments are designed to measure the very poor visibility conditions that are of primary concern for aviation safety, but will provide little or no more information on haze under typical visibility conditions. We recommend that the proposed instrumentations be supplemented with integrating Nephelometer which would permit measurement of light scattering coefficients under visibility conditions. The addition of Nephelometers to airport instrumentation would ensure that haze levels are monitored over a broad and representative geographic scale, thereby providing important information on spatial & temporal trends of regional haze."

Page 140 "Protecting Visibility in National Parks and Wilderness Areas"

National Research Council Committee (U.S.)