Gas Analyzer Theory of Operation
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Transcript of Gas Analyzer Theory of Operation
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Gas Analyzer Theory of Operation
Gaseous Pollutants mini-courseTAMS Center February 2009
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Course materials can be found at:
http://itep68.itep.nau.edu/itep_downloads/
in the gaseouspollutants folder
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Ozone Analyzer Theory of Operation
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The ozone layer in the stratosphere absorbs the vast majority of ultraviolet light entering Earth’s atmosphere. We definitely need ozone in the stratosphere.
UV
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Ground level ozone, however, is known to have significant adverse impacts on the health of humans and ecosystems. Ground level ozone is what we monitor.
Ozone isn’t typically emitted directly; it is formed by atmospheric chemical reactions in the presence of sunlight (photochemical reactions). Major precursors are reactive oxides of nitrogen and volatile organic compounds.
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By the way, don’t smoke around any gas analyzer
Ozone analyzers are photometers. They use the fact that ozone absorbs UV light to measure ozone.
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Ozone is most efficient absorbing UV light near the 254 nm wavelength. Sample gas fills the absorption tube (measurement cell) and ultraviolet light at near 254 nm is sent through the sample gas; absorbance is measured.
Illustration is from Teledyne API 400E Operator’s manual
One problem – other gases absorb at 254 nm.
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Illustration is from Teledyne API 400E Operator’s manual
Solution: Add a reference cycle to the sample cycle - use a manganese dioxide scrubber to selectively remove ozone from the sample gas, measure absorbance due to interferants, and subtract interferants from sample cycle.
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The above text is from Teledyne API 400E Operator’s manual
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The above text is from Teledyne API 400E Operator’s manual
Manganese dioxide scrubbers can adsorb interferants and rapid humidity changes can cause release of interferants impacting measurement .
Ozone conditioning Nitrogen oxide titration
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A very important chemical reaction:
Notes:NOx = NO + NO2NOy = NOx + all other reactive oxides of nitrogenNO reacts with ozone driving ozone concentrations downNO2 reacts with VOCs in sunlight and produces ozone
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Ozone, NOx, NO2 and NO data, Quapaw Nation
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Cherokee Nation Tahlequah Site 7/19/06 through 7/21/06
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The 5th and 6th is Saturday, Sunday
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Why does a remote location have higher 24-hour averages?It has few NO sources to titrate ozone down at night. Remote areas typically have a much less pronounced diurnal pattern (daytime and nighttime concentrations are much closer).
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Power Plant
Monitoring SiteOver 2 miles
Wind Direction
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Power Plant
Ozone Concentrations
Wind Direction
NO2 + VOCozone produced
Ozone titration downwind of NO source
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NOx Analyzer Theory of Operation: Chemiluminescence
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Illustration is from Teledyne API 200E Operator’s manual
Sample gas w/NOO3
Light leaks can impact measurement
PMTs are sensitive and can be damaged by light
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Illustration is from Teledyne API 200E Operator’s manual
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Illustration is from Teledyne API 200E Operator’s manual
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Illustration is from Teledyne API 200E Operator’s manual
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MolyConMolybdenum Converter
NO2 Converter
NO
NO2 NO2 converted to NO NO
NO
Rx Cell
NOx Cycle goes through converterOnly NO reacts with ozone
NO Cycle passes sample air to reaction chamberOzone reacts with NOOnly NO reacts – NO2 isn’t measuredNO2 is calculated: NOx – NO = NO2
Sample AirNOx = NO + NO2
NOx
NO
NO Cycle
Valves
Dark Cycle bypasses RX Cell
Ozone generator
Dry filtered air
hv in reaction cell is measured by PMT
PMT
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SO2 Analyzer Theory of Operation:Fluorescence
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(UV Light)
Illustration is from Teledyne API 200E Operator’s manual
Dark period every 30 minutes for PMT offset (API)
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Illustration is from Teledyne API 200E Operator’s manual
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CO Analyzer Theory of Operation:Gas Correlation
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Illustration is from Teledyne API 360U Operator’s manual