1. Gas Analyzer Theory of Operation
Gaseous Pollutants mini-course
TAMS Center
February 2009

2. Course materials can be found at:
in the gaseouspollutants folder

3. Ozone Analyzer Theory of Operation

4. 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

5. 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.

6. Ozone analyzers are photometers
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

7. One problem – other gases absorb at 254 nm.
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.

8. 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

9. The above text is from Teledyne API 400E Operator’s manual

10. Ozone conditioning Nitrogen oxide titration
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

11. 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

12. Ozone, NOx, NO2 and NO data, Quapaw Nation

13. Cherokee Nation Tahlequah Site 7/19/06 through 7/21/06

14. The 5th and 6th is Saturday, Sunday

15. 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).

16. Wind Direction
Power Plant
Over 2 miles
Monitoring Site

17. Wind Direction
Ozone titration downwind of NO source
Ozone Concentrations
NO2 + VOC ozone produced
Power Plant

18. NOx Analyzer Theory of Operation: Chemiluminescence

19. Light leaks can impact measurement
Sample gas w/NO O3
Light leaks can impact measurement
PMTs are sensitive and can be damaged by light
Illustration is from Teledyne API 200E Operator’s manual

20. Illustration is from Teledyne API 200E Operator’s manual

21. Illustration is from Teledyne API 200E Operator’s manual

22. Illustration is from Teledyne API 200E Operator’s manual

23. MolyCon Molybdenum Converter
NOx Cycle goes through converter
Dark Cycle
bypasses RX Cell
Only NO reacts with ozone
MolyCon Molybdenum Converter
NO2 Converter
Sample Air
NOx = NO + NO2 NO NO
Rx Cell
PMT
NOx
NO2
NO2 converted to NO NO NO
Valves
Excess Ozone
NO Cycle
NO Cycle passes sample air to reaction chamber
Ozone reacts with NO
Only NO reacts – NO2 isn’t measured NO2 is calculated: NOx – NO = NO2
Ozone generator
Dry filtered air
hv in reaction cell is measured by PMT

25. SO2 Analyzer Theory of Operation: Fluorescence

26. Dark period every 30 minutes for PMT offset (API)
(UV Light)
Dark period every 30 minutes for PMT offset (API)
Illustration is from Teledyne API 200E Operator’s manual

27. Illustration is from Teledyne API 200E Operator’s manual

28. CO Analyzer Theory of Operation: Gas Correlation

29. Illustration is from Teledyne API 360U Operator’s manual