Measurement-Procedure-Standardisations.md

@@ -65,6 +65,7 @@ Now the
 | Method | Principle | Known Issues | Measured Compounds |                                                      
 | ------ | ----------| ------------ | ------------------ |
 | Ultraviolet Photometry | Operates on the principle that a specific species efficiently absorbs light at a known wavelength in the UV range. This is the case for ozone, at 253.65nm. The degree to which the UV light is absorbed by a specific species is directly related to the species concentration as described by the Beer-Lambert Law (I/Io = e−KLC; K = molecular absorption coefficient at STP (308 cm-1 atm-1 for O3), L = optical path length of cell, C = species concentration , I = light intensity of sample gas, Io = light intensity of sample without measured species (reference gas) ) | Gaseous hydrocarbons with strong absorption at 254 nm, such as aromatic hydrocarbons (i.e., benzene and substituted benzene rings)| O3 |
+| Visible Photometry | Operates on the principle that a specific species efficiently absorbs light at a known wavelength in the visible range. This is the case for NO2, at 405nm. The degree to which the visible light is absorbed by a specific species is directly related to the species concentration as described by the Beer-Lambert Law (C = 1/Lσ * ln(Io/I) ; σ = absorption cross section (6.06×10-19 cm2 molec-1 for NO2 at 405nm), L = optical path length of cell, C = species concentration , I = light intensity of sample gas, Io = light intensity of sample without measured species (reference gas) ). | Water vapour, small particles (< 5 um) | |