# Presentation: 457266

## Solomon Ricks, U. S. EPAOffice of Air Quality Planning and Standards Ambient Air Monitoring Group 

- CO Precursor Gas Monitoring Training Overview

## Outline

- Introduction
- Methodology
- Burdens Creek Operation
- Cautions
- Instrument Operation
- Interferences and Operational Issues
- Summary

## 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.

## 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 detector
- I	= light intensity after absorption by CO
- Io	= light intensity at zero CO concentration
- a	= specific CO molar absorption coefficient
- x	= path length, and
- C	= CO concentration

## 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

## 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   NafionTM Dryer
- Analyzer baseline determined and corrected using heated or other catalytic converter
- Frequent auto-zero
- The instrument has an ultra-sensitive or “hot” detector

## Methodology

**Diagram of a Precursor Gas CO instrument**

## Burdens Creek Operations

-              T-API 300 EU	                                         TEI 48C-TLE

## Responses to Daily Checks10-25-2006 thru 05-22-2007

| Point | Source
Value | TEI 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 |

## Slide 10

## Slide 11

## Slide 12

## Slide 13

## Slide 14

## 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!

## Instrument Operation

** **
- 	**Item**			**Schedule**
-  Replace particle filter			Bi-weekly
- 	Diagnostics Checks			Bi-weekly
- 	Perform Level I check			Daily
- 	Replace IR source			As needed
- 	Leak Check and Pump Check Out		Annually
- 	Inspect Pneumatic Lines			Semi-annually
- 	Clean inside of Chassis			As needed
- 	Rebuild or replace pump			As needed
- 	Clean optic bench			As needed
- 	Replace wheel motor 			As needed

## 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

## 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

##  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

##  Interferences and Operational Issues

**Auto-Reference Cycle**
**API 300EU**
**Instrument goes into “Aref” cycle (**_**<**_**15 minutes)**
**3-minute dwell period before and after auto-ref measurements**
**Auto-ref measurement lasts 9 minutes **
**Sample air re-routed to pass through converter - all CO is converted to CO****2**
**Analyzer examines the M/R Ratio**
**Since CO is scrubbed out,  any change in this ratio from last Aref cycle must mean that CO****2**** or H****2****0 are interfering **
**Analyzer CPU adjusts the M/R ratio to compensate and the offset is changed **
_**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**_
_** **_

## Interferences and Operational Issues

**Auto-Zero Cycle, TEI 48C-TLE**
- Sample stream re-routed through internal scrubber
- 10-minute duration
- Adjusts the zero background
- Not intended to replace routine calibration
- Front panel display does not freeze

## 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