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