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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) ) | Gaseous hydrocarbons with strong absorption at 254 nm, such as aromatic hydrocarbons (i.e., benzene and substituted benzene rings)| O3 |
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| 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) | |
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| Ethylene Chemiluminescence | Chemiluminescence is the emission of light (luminescence), as the result of a chemical reaction. Chemiluminescence occurs as a result of the reaction of ozone with ethylene, leading to an excited molecule. The return to a fundamental electronic state of the excited molecules is made by luminous radiation in a specific spectrum, which can be measured. The concentration of sample ozone is directly proportional to the intensity of light emitted. The broadband emission is detected using a photomultiplier tube (at 440 nm for ethylene + ozone). | Water vapour | |
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| Eosin-Y Chemiluminescence | Chemiluminescence is the emission of light (luminescence), as the result of a chemical reaction. Chemiluminescence occurs as a result of the reaction of ozone with eosin-Y, leading to an excited molecule. The return to a fundamental electronic state of the excited molecules is made by luminous radiation in a specific spectrum, which can be measured. The concentration of sample ozone is directly proportional to the intensity of light emitted. The broadband emission is detected using a photomultiplier tube (at ~560 nm for eosin-Y + ozone). | Water vapour | |
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| rhodamine B chemiluminescence | Chemiluminescence is the emission of light (luminescence), as the result of a chemical reaction. Chemiluminescence occurs as a result of the reaction of ozone with rhodamine B, leading to an excited molecule. The return to a fundamental electronic state of the excited molecules is made by luminous radiation in a specific spectrum, which can be measured. The concentration of sample ozone is directly proportional to the intensity of light emitted. The broadband emission is detected using a photomultiplier tube (at ~580 nm for rhodamine B + ozone). | Water vapour | |
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| chemiluminescence (internal molybdenum converter) | Chemiluminescence is the emission of light (luminescence), as the result of a chemical reaction. Chemiluminescence occurs as a result of the reaction of NO with ozone (NO+O3 --> NO2*+O2). The return to a fundamental electronic state of the excited NO2* molecules is made by luminous radiation in a 600-3000 nm spectrum (NO2* --> NO2 + hv), which can be measured. This method is designed specifically to directly measure NO directly (and NOx/NO2 indirectly). O3 can also be measured by inverting the measurement technique (using canister of NO for reaction). | Water vapour (above 20 ppmv), 3rd body quenching (CO2, SOx), other NOy species converted to NO by molybdenum converter (PAN, ethyl nitrate, ethyl nitrite, HONO, HNO3, methyl nitrate, n-propyl nitrate, n-butyl nitrate, nitrocresol, NH3), other species undergoing chemiluminescence with O3 (SOx). | |
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