solomon ricks, u. s. epa office of air quality planning and standards ambient air monitoring group
DESCRIPTION
CO Precursor Gas Monitoring Training Overview. Solomon Ricks, U. S. EPA Office of Air Quality Planning and Standards Ambient Air Monitoring Group. Outline. Introduction Methodology Burdens Creek Operation Cautions Instrument Operation Interferences and Operational Issues Summary. - PowerPoint PPT PresentationTRANSCRIPT
EPA Precursor Gas Training Workshop
Solomon Ricks, U. S. EPAOffice of Air Quality Planning and Standards
Ambient Air Monitoring Group
CO Precursor Gas Monitoring Training Overview
EPA Precursor Gas Training Workshop
Outline
• Introduction
• Methodology
• Burdens Creek Operation
• Cautions
• Instrument Operation
• Interferences and Operational Issues
• Summary
EPA Precursor Gas Training Workshop
Introduction
Why analyze for Carbon Monoxide (CO) as a precursor gas?
• CO is formed from incomplete combustion• Values across the nation are falling below the
sensitivity of current CO methods• Characterize typical urban/rural concentrations
for long-term trends analysis.
EPA Precursor Gas Training Workshop
Methodology Measurement Principles – Non-Dispersive Infrared (NDIR) based on Beers Law
T = I/Io = e(-axC)
where:
T = Transmittance of light through the gas to the detectorI = light intensity after absorption by COIo = light intensity at zero CO concentrationa = specific CO molar absorption coefficientx = path length, andC = CO concentration
EPA Precursor Gas Training Workshop
Methodology Measurement Principles – Non-Dispersive Infrared (NDIR)
based on Beers Law
I/Io = e(-axC) Rearranging this equation:
ln I/Io = axC Rearranging this equation:
C = (ln I/Io)/(a*x)
I and Io are measured by detector (i.e. The M/R or S/R ratios of the instruments readout)
“a” is a constant CO molar absorption coefficient at a wavelength of 4.6 micrometers
“x” is the path length of the detection cell
EPA Precursor Gas Training Workshop
Methodology
What makes a precursor gas CO instrument?
The Precursor CO instrument is identical to a non-precursor CO analyzer with the following exceptions:
• Required sample stream dried using permeation or Nafion™ Dryer
• Analyzer baseline determined and corrected using heated or other catalytic converter
• Frequent auto-zero• The instrument has an ultra-sensitive or “hot” detector
EPA Precursor Gas Training Workshop
MethodologyDiagram of a Precursor Gas CO instrument
EPA Precursor Gas Training Workshop
Burdens Creek Operations
T-API 300 EU TEI 48C-TLE
EPA Precursor Gas Training Workshop
Responses to Daily Checks10-25-2006 thru 05-22-2007
PointSource
ValueTEI Avg T_API Avg
TEI
Std Dev.
T_API
Std Dev.
Span 4500 ppb 4614 ppb 4612 ppb 81 ppb 155 ppb
Precision 500 ppb 514 ppb 550 ppb 17 ppb 30 ppb
Zero 0 ppb 1 ppb -8 ppb 17 ppb 33 ppb
EPA Precursor Gas Training Workshop
CO Span Values10-25-2006 thru 05-22-2007
3500
3700
3900
4100
4300
4500
4700
4900
5100
Con
cent
ratio
n, p
pb
API 300EU
TEI 48C
EPA Precursor Gas Training Workshop
CO Precision Values10-25-2006 thru 05-22-2007
400
450
500
550
600
650
700
Con
cent
ratio
n, p
pb
API 300EU
TEI 48C
EPA Precursor Gas Training Workshop
CO Zero Values10-25-2006 thru 05-22-2007
-100
-80
-60
-40
-20
0
20
40
60
80
100
Con
cent
ratio
n, p
pb
API 300EU
TEI 48C
EPA Precursor Gas Training Workshop
Ambient Data 03-05-2007 thru 03-07-2007
100
150
200
250
300
350
0:00
:00
4:00
:00
8:00
:00
12:0
0:00
17:0
0:00
21:0
0:00
1:00
:00
5:00
:00
9:00
:00
13:0
0:00
18:0
0:00
22:0
0:00
2:00
:00
6:00
:00
10:0
0:00
14:0
0:00
19:0
0:00
23:0
0:00
Co
nce
ntr
atio
n, p
pb
TEI 48C
API 300EU
EPA Precursor Gas Training Workshop
Ambient Data05-20-2007 thru 05-22-2007
100
150
200
250
300
350
0:00
:00
4:00
:00
8:00
:00
12:0
0:00
17:0
0:00
21:0
0:00
1:00
:00
5:00
:00
9:00
:00
13:0
0:00
18:0
0:00
22:0
0:00
2:00
:00
6:00
:00
10:0
0:00
14:0
0:00
19:0
0:00
23:0
0:00
3:00
:00
Co
nce
ntr
atio
n, p
pb
TEI 48C
API 300EU
EPA Precursor Gas Training Workshop
Cautions
•Bench Cleaning
•Inspections
•Cylinders, handling, shipping, storage
•CO is poisonous!!!
•The Catalytic Converter and Bench are operated at 48 – 50o C. It is Hot!
EPA Precursor Gas Training Workshop
Instrument Operation
Item Schedule
Replace particle filter Bi-weeklyDiagnostics Checks Bi-weeklyPerform Level I check DailyReplace IR source As neededLeak Check and Pump Check Out AnnuallyInspect Pneumatic Lines Semi-annuallyClean inside of Chassis As neededRebuild or replace pump As neededClean optic bench As neededReplace wheel motor As needed
EPA Precursor Gas Training Workshop
Interferences and Operational Issues
•Water Vapor•Water absorbs strongly in many IR spectra
•Water must be removed using permeation or Nafion dryer
•Carbon Dioxide
•CO2 absorbs in several of the same regions as CO
•Baseline adjustment via Auto-zero (Azero) or Auto-reference (Aref) Cycle
EPA Precursor Gas Training Workshop
Interferences and Operational Issues
• Why auto-reference or auto-zero?– Continuous measurements at low concentrations may
be limited by gradual changes in baseline
• What cause the changes?– Environmental changes, i.e., temperature– Drift related to the age of optical bench components
– Interferents, such as CO2
EPA Precursor Gas Training Workshop
Interferences and Operational Issues
Auto-reference or auto-zero cycle
TEI 48C-TLE • Performs an auto-zero, or “Azero”, cycle - 10 minutes
through the Carolite scrubber. • Length of test not adjustable• Frequency is adjustable• Adjusts the baseline of the instrument
T-API 300EU • Performs an auto-reference, or “Aref”, cycle - <15 minutes
through the heated palladium catalytic converter• Length of test not adjustable• Frequency is adjustable• Adjusts the measurement/reference (M/R) ratio
EPA Precursor Gas Training Workshop
Interferences and Operational IssuesAuto-Reference Cycle
API 300EU1. Instrument goes into “Aref” cycle
(<15 minutes)• 3-minute dwell period before
and after auto-ref measurements
• Auto-ref measurement lasts 9 minutes
2. Sample air re-routed to pass through converter - all CO is converted to CO2
3. Analyzer examines the M/R Ratio4. Since CO is scrubbed out, any
change in this ratio from last Aref cycle must mean that CO2 or H20 are interfering
5. Analyzer CPU adjusts the M/R ratio to compensate and the offset is changed
6. Note: API recommends that you set this to once every 24 hours for ambient conditions. For process control, more often. We have set it to once every 12 hours
EPA Precursor Gas Training Workshop
Interferences and Operational Issues
Auto-Zero Cycle, TEI 48C-TLE1. Sample stream re-routed through internal scrubber
2. 10-minute duration
3. Adjusts the zero background
4. Not intended to replace routine calibration
5. Front panel display does not freeze
EPA Precursor Gas Training Workshop
Summary
• Carbon Monoxide in rural and suburban settings can be an indicator for VOCs
• OAQPS continues operating instruments at its on-site monitoring station, Burdens Creek: TEI 48C-TLE and T-API 300EU
• Other instrument(s) are available: Ecotech• Auto-reference or auto-zero sequence is an operational
issue• Water vapor and CO2 can cause interference. The dryer
and CO scrubber must be plumbed and working properly or baseline shifts occur