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Gas Analyzer Theory of Operation

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									             Gas Analyzer Theory of
                   Operation



Gaseous Pollutants mini-course
TAMS Center
February 2009
Course materials can be found at:

http://itep68.itep.nau.edu/itep_downloads/

in the gaseouspollutants folder
Ozone Analyzer Theory of
       Operation
The ozone layer in the stratosphere absorbs
the vast majority of ultraviolet light entering
Earth’s atmosphere. We definitely need
ozone in the stratosphere.
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.
Ozone analyzers are photometers. They use
the fact that ozone absorbs UV light to
measure ozone.




By the way, don’t smoke around any gas analyzer
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.
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.




             Illustration is from Teledyne API 400E Operator’s manual
The above text is from Teledyne API 400E Operator’s manual
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
        A very important chemical reaction:




Notes:
NOx = NO + NO2
NOy = NOx + all other reactive oxides of nitrogen
NO reacts with ozone driving ozone concentrations down
NO2 reacts with VOCs in sunlight and produces ozone
Ozone, NOx, NO2 and NO data, Quapaw Nation
Cherokee Nation Tahlequah Site 7/19/06 through 7/21/06
The 5th and 6th is Saturday, Sunday
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).
          Wind Direction




Power Plant
                           Over 2 miles
                                          Monitoring Site
   Wind Direction




                    Ozone titration downwind of NO source



                                      Ozone Concentrations
                                                             NO2 + VOC
                                                             ozone produced




Power Plant
NOx Analyzer Theory of Operation:
      Chemiluminescence
                            Sample
                O3          gas w/NO



                                                           Light leaks can
                                                           impact measurement

                                                           PMTs are sensitive
                                                           and can be damaged
                                                           by light
Illustration is from Teledyne API 200E Operator’s manual
Illustration is from Teledyne API 200E Operator’s manual
Illustration is from Teledyne API 200E Operator’s manual
Illustration is from Teledyne API 200E Operator’s manual
Dark Cycle
                       NOx Cycle goes through converter
                                                                Only NO reacts
bypasses RX Cell
                                                                with ozone
                   NO                                         NO
                                                                                P
                                    MolyCon
                                                                                M
Sample Air       NOx          Molybdenum Converter                    Rx Cell
NOx = NO + NO2                                                                  T
                                  NO2 Converter
                   NO2         NO2 converted to NO            NO

     NO                                                      Valves
                                                                                E
                                                                                    O
                                                                                x
                                                                                    z
                                      NO Cycle                                  c
                                                                                    o
                                                                                e
                                                                                    n
                                                                                s
   NO Cycle passes sample air to reaction chamber                               s
                                                                                    e


   Ozone reacts with NO                                  Ozone generator
   Only NO reacts – NO2 isn’t measured
   NO2 is calculated: NOx – NO = NO2         Dry filtered air
                                   hv in reaction cell is measured by PMT
SO2 Analyzer Theory of Operation:
          Fluorescence
(UV Light)

                                                           Dark period every
                                                           30 minutes for
                                                           PMT offset (API)




       Illustration is from Teledyne API 200E Operator’s manual
Illustration is from Teledyne API 200E Operator’s manual
CO Analyzer Theory of Operation:
        Gas Correlation
Illustration is from Teledyne API 360U Operator’s manual

								
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