Why you need an integrating nephelometer
Why you need a nephelometer
The Nephelometer is an important instrument in a variety of air monitoring applications. Many organisations throughout the world including EPA’s, Meteorological agencies, Universities, Airports, Federal, State and local governments use Nephelometers everyday in a variety of ways.
What is a Nephelometer?
An integrating nephelometer provides a real-time, direct measurement of the light scattered by dust pollution in the air.
What is light scattering?
is the measurement of particulates (dust/aerosol) in the air by shining
light through sample air and measuring the deflected light (scattering).
This light scattering allows us to measure the visibility of air (how
far we can see) along with how much light is scattering back.
Why measure visibility?
Visibility measurements are important as they indicate how much pollution is in the air. Visibility shows how much Haze, Smog or Fog is present, a therefore determine how much pollution is in the air.
A good indicator of PM2.5 mass measurement!
The Nephelometer is known through numerous studies to track closely with PM2.5 monitors. The Nephelometer can be correlated with a mass monitor and used accurately to measure masses of PM2.5 or lower.
Aerosols and Global warming
Investigations have provided much evidence that particles present in the air (aerosols) are affecting the radiation reaching the earth’s surface. This has direct implications on global warming and the increase of Global temperatures. Nephelometers measure light scattering and therefore is the perfect tool to study this aspect of global warming.
Wet V Dry sampling
Wet sampling is used for accurate Visibility monitoring, it does not heat sample air and thus all water vapour and fog components are included. Dry sampling heats the sample air removing water vapour and providing a more accurate assessment of Particulate mass.
- Dry Mode has a strong correlation with PM2.5
- Set point of R.H. between 40% and 70% used
- This lowers the relative humidity and decreases particle scattering. The effect is greatest at high humidity (RH >80%) and becomes negligible at low humidity (RH <50%)
- In wet mode the temperature rise in the measurement chamber is 0.5°C
- >60% RH, particles uptake of water and appear to grow this results in increase particle diameter
- Useful to detect fog and the affect of water in visibility.
- Provides more of a true visibility measurement
Sources of pollution
Pollution measured in the air is from 2 sources, Natural and Artificial.
- Natural Sources: forest fires, dust, pollen, chemicals emitted by plants/trees, sea salt, volcanic eruptions.
- Artificial (anthropogenic) Sources: automobile emissions, coal-burning power plants, intentional burning of forests and range lands, industrial and mining operations, dust from unpaved roads and agricultural fields.
This pollution directly affects human health with lower visibility meaning more airborne pollution.
Health impacts from Haze/Smog
- Reduces the visible distance
- Increases respiratory diseases
- makes breathing difficult
- Fine particulate matter (PM2.5 and smaller) are generally composed with chemical and can penetrate deeply into lungs, enter blood and cause many other sicknesses
What different measurements can Nephelometers perform?
There are 3 different wavelengths that nephelometers can measure at (green, red and blue) along with backscatter and polar measurements:
- Green: 525 nm – most sensitive for the human eye best measurement for smog, fog, haze
- Red: 635 nm - interacts strongly with large particulate matter (pollen, sea salt)
- Blue: 450 nm - interacts strongly with fine and ultrafine particulates (wood fires, automobiles)
- Backscatter: 90-170° - measures the light reflectied back towards light source
- Polar: 10-90°