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April 7: QA Systems, EPA definitions, PQAOs and common sense – Mike Papp
April 14: Routine Quality Control and Data Management (1-pt QC, flow rate, and instrument stability checks) – Travis Maki
April 21: Audits Overview (NPAP, PEP, Annual PE, Flow Rate Audits) – Jeremy Howe
April 28: Calculating Bias and Precision and AQS reports – Bill Frietsche
May 5: 40 CFR 58 App. A- Gaseous Pollutants – Glenn Gehring
May 12: 40 CFR 58 App. A- Ozone – Chris Ellis, Southern Ute
May 19: 40 CFR 58 App. A- PM filter and continuous methods –Brandy Toft
Overall Course Overview:
O3 Dependence on Meteorology
Example of ozone dependence on meteorological conditions(Ute 1 monitoring site - 8/13/02)
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14:24 14:52 15:21 15:50 16:19 16:48 17:16 17:45 18:14
Time
O3
(pp
b),
RH
(%
)
O3
RH
NO + VOCs NO2 + O2
NO2 + hv (sunlight) O + NO O + O2 O3
Ozone Formation Chemistry
Ute 3 June 1st '02 ozone vs. precursor conditions
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Time of day
O3 &
NO
x [
pp
b],
pre
cu
rso
rs
Ozone [ppb]
Temperature [ o C]
Sunlight [AU]
NO X [ppb]NO 2 [ppb]NO [ppb]
Ozone is most efficient at absorbing light near the 254 nm wavelength. (We see about 400-800 nm, green being in the middle, 254 nm shorter than violet.) Sample gas fills the absorption tube (measurement cell) and ultraviolet light at near 254 nm is sent through the sample gas; how much gets absorbed by the ozone is measured to calculate ozone conc.
Illustration is from Teledyne API 400E Operator’s manual
One problem – other gases absorb at 254 nm– therefore scrubbers used
Think of the measurement as being divided into two
steps…….•Each measurement cycle is completed
within 10 to 20 seconds.•Each measurement contains two half
cycles
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Step 1: Measuring the “clean” air
Thermo Electron/Thermo Environmental Instruments Models 49, 49C, 49i
Automated Equivalent Method: EQOA-0880-047
Zero (reference) gas with the ozone “scrubbed”
Sample
The First Measurement Half Cycle
Solenoid
Scrubber
Absorption Tubes
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Summary: First Measurement Half-Cycle
Ambient (outside) air is sent thru the analyzer’s solenoid valve to the scrubber where any ozone present is converted to oxygen.
This ozone-free air is sent through the absorption tubes.
The UV source lamp shines on the air and the transmitted intensity (number of photons) is measured by the detector.
The analyzer stores this intensity value.I0
Scrubber Cartridge
copper screens coated with manganese dioxide
The MnO2 catalyzes the reaction of ozone to diatomic oxygen.
The air entering the absorption cell after passing through the filter is the same except for the ozone.
Sample without the ozone “scrubbed”
Sample
The Second Measurement Half CycleSolenoid
Absorption Tubes
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Summary: The Second Measurement Half-Cycle
air is directed to the absorption tubes. The UV source lamp illuminates the air. Any ozone in the airabsorbs some UV light
resulting in a lower intensity value as measured by the detector.
The detector measures the transmitted intensity.
This value is subtracted from the previously stored value and the resulting difference is the amount of ozone in the ambient sample.
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Primary Standards Located at a central laboratory where it can
remain stationary, protected from the physical shocks of transportation, operated by an experienced analyst under optimum conditions.
Serves as a common standard for all analyzers in a network.
Compared against other primary standards US EPA regions have primary standards,
called SRPs, or standard reference photometers.
The Ozone Transfer Standard Think of as two instruments: half makes
ozone, the other half measures the sample. Capable of generating and measuring
accurate ozone concentrations. Can be transportable but usually not Critical Components of an Ozone Transfer
Standard: Zero air source Pump Flow controller Ozone generator Manifold
Ozone Scrubber
Pump
Flow Controller
Ozone Generator
Manifold
To analyzer part of
transfer standard
capped
Analyzer
The Ozone Generator
The Ozone Generator ultraviolet radiation (light) from a mercury
vapor lamp shines on the incoming air. The oxygen absorbs the UV light. To dissipate the resulting gain in energy, the
irradiated O2 molecules split into two negatively charged oxygen atoms.
These atoms combine with unsplit oxygen to form O3.
5 LPM
2 LPM for analyzer part of transfer standard
2 LPM + excess to analyzer
Capped
The Manifold (connector)
QC: Patience is a Virtue Allow yourself enough time. How fast you can do it means nothing. If you rush you are bound to make mistakes. Mistakes usually cost lost data, time and
money. The best operators take their time, are
methodical and thorough.
indicated - actual
actualX 100 = Percent Difference
All checks use the same statistic: Percent Difference ( di )
1-pt QC (precision) checks:
Audit results:
d i
The .5 micron teflon® filter holder
Remember to change filter when dirty
Installed in sampling “train” before the analyzer. Will not degrade the ozone concentration. QC before changing filters regularly-audits find
dirty filters
0.5-micronTeflon® Filter
Measurement Quality Objectives (MQOs)
EPA has ozone MQOs for NAAQS meas’s Use these in element 7 of your QAPP MQOs are in validation templates
◦ Critical (any hour must be invalidated)◦ Operational (investigate, might still be okay)◦ Systematic (subsets might be invalid for
NAAQS, but data might be valid for other purposes)
MQOs (validation template)◦ Critical:
◦ 1-point QC check (used to be called precision) at least every 2 weeks conducted manually <= +7% (percent difference) Zero drift <= 2% of full scale (10 ppb away
from zero if full scale is 500 ppb) Span drift <= 7 % (e.g. near upper range of
ambient levels should show analyzer value that “drifts,” or changes less than 7% from the last span output)
Hourly values before such checks fail should be invalidated (not deleted) back to the previous passing check
Shelter temp between 20 and 30 C Annual audits should be within 15% of each
audit concentration NPAP audits should be within 10% for no
warning per conc. Verifications after moving, earthquakes
should have all points within 2% of best-fit straight line
The local ozone standard that you compare against must be certified annually
Operational criteria (investigate):
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Completeness Siting Residence time Probe material
Systematic criteria (some set of data maybe not comparable against NAAQS, but data may be usable for other purposes):
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NPAP auditing necessary for NAAQS data Your instrument may be able to do “better”
than validation criteria, see your spec sheets
Course website: http://itep68.itep.nau.edu/itep_downloads/QA101_Resources/
Our emails:◦ Chris Ellis [email protected]◦ [email protected]◦ [email protected]
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Ozone Monitoring Conclusions: