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| Method | Principle | Typical Operation | Known Issues | Compounds |
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| ------ | ----------| ----------------- | ------------ | --------- |
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| 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) ) | <ul><li>Ambient air is continuously drawn through the analyser by a vacuum pump.</li><li><li>Sample is split into two flow paths. One path incorporates a scrubber which selectively removes ozone, while the other path does not.</li>
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| 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) ) | <ul><li>Ambient air is continuously drawn through the analyser by a vacuum pump.</li>
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<li>Sample is split into two flow paths. One path incorporates a scrubber which selectively removes ozone, while the other path does not.</li>
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<li>Both flow paths are connected to a solenoid valve, which switches at a fixed interval to allow either the sample gas stream (I), or the scrubbed, reference gas stream (Io), to flow through a quartz tube (cell) of accurately known length.</li>
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<li>Typically a mercury vapour lamp at one end of the quartz cell produces a monochromatic beam of ultraviolet light at 254 nm. A vacuum diode at the opposite end of the cell measures the intensity of transmitted light (I/Io).</li>
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<li>The intensities of 254 nm UV light transmitted through the sample (I) and ozone-free reference gas streams (Io) are related to the concentration (C) of ozone in the sample gas stream according to the Beer-Lambert Law.</li>
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