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MEMORANDUM

TO: Jim Eddinger, U.S. Environmental Protection Agency, OAQPS

FROM: Eastern Research Group, Inc.

DATE: August 2012

SUBJECT:   Incorporating Measurement Error in Reported Carbon Monoxide (CO) and Total

Hydrocarbon (THC) Data (Revised August 2012)

1.0 INTRODUCTION

This memorandum describes the methods used to incorporate measurement error into

the reported emissions values of carbon monoxide (CO) and total hydrocarbons (THC) where

the reported measured emission values are uncharacteristically low.  This memorandum

focuses only on the methodology that has changed since the analysis conducted for the

December 21, 2011 proposed reconsideration of the rule (76 FR 80598).  The methods used for

the previous analysis are described in another memorandum.1 This analysis involved identifying

calibration spans from the emissions testing reports of top performers and low reported CO

and THC levels in each subcategory, calculating a maximum calibration error based on the

calibration spans, and assigning a calibration error to emissions testing data in the EPA ICR

Databases.

This memorandum is organized as follows:

1.0 Introduction

2.0 Sources of Measurement Error from Instrumental Methods for CO

3.0 Identifying CO Span Values

4.0 Calculation of Maximum Measurement Error for CO

5.0 Application of CO Measurement Error to Analysis

6.0 Measurement Error for THC
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7.0 References

Appendix A:  Summary of Test Reports Reviewed for Measurement Error
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2.0 SOURCES OF MEASUREMENT ERROR FROM INSTRUMENTAL METHODS FOR CO

The sources of measurement error are provided in another memorandum.2 This

memorandum also provides the equations that are used calculate the error for a measurement

made using an instrumental test method.  Equations 1 and 2 below were used to calculate the

method detection limit (MDL) for each test run.  In the equations, “S” represents 90 percent of

the test‐specific calibration span value.

ܮܦܯௌ ൌ ඥሾሺ0.02 ∗ ܵሻଶ ൅ ሺ0.025 ∗ ܵሻଶ ൅ ሺ0.015 ∗ ܵሻଶ ൅ ሺ0.02 ∗ ܵሻଶሿ    (Equation 1)

Where:  S is greater than 19 ppm.

ܮܦܯௌ ൌ ඥሾሺ0.5 ∗ ܵሻଶ ൅ ሺ0.5 ∗ ܵሻଶ ൅ ሺ0.25 ∗ ܵሻଶ ൅ ሺ0.1 ∗ ܵሻଶሿ     (Equation 2)

Where:  S is less than or equal to 19 ppm.

3.0 IDENTIFYING CO SPAN VALUES

Top performer test reports were reviewed for CO calibration span information using the

same methods as used in the previous analysis.  These methods are detailed in another

memorandum.1 Appendix A provides a list of the top performers for which test reports were

reviewed for CO span information.  Additional reports were reviewed from best performers

since the December 2011 proposal. Table 1 below shows the maximum calibration span or

protocol gas concentration determined from the test reports reviewed for each fuel category.

Table 1 – Summary of Maximum CO Span Values from Top Performer Test Reports 

Fuel Category

Maximum CO Span

(for tests conducted on or

before May, 2008)

(ppmvd)

Maximum CO Span

(for tests conducted after

May, 2008)

(ppmvd)

Coal 900 506.1

Biomass (non‐Bagasse) 2,280 1,720.56

Biomass (Bagasse) 9,085 9,070

Liquid 435.6 435.6

Process Gas 17 17.2
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4.0 CALCULATION OF MAXIMUM MEASUREMENT ERROR FOR CO

Using the equations provided in section 2.0 and the maximum calibration spans

identified in Table 1 above, we estimated he maximum measurement errors for each

subcategory.  The resultant maximum measurement errors for each fuel category were

rounded to two significant figures, and are provided in Table 2 below.

Table 2 – Summary of Maximum Measurement Errors by Subcategory 

Fuel Category

Maximum CO Measurement

Error

(for tests conducted on or

before May, 2008)

(ppmvd)

Maximum CO Measurement

Error

(for tests conducted after

May, 2008)

(ppmvd)

Coal 37 21

Biomass (non‐Bagasse) 93 70

Biomass (Bagasse) 370 370

Liquid 18 18

Process Gas 0.76 0.76

5.0 APPLICATION OF CO MEASUREMENT ERROR TO ANALYSIS

EPA received several public comments on the methods used to assign measurement

error to the emissions test data in the EPA ICR Databases.  Commenters voiced concern that the

measurement error calculated for each fuel category was not corrected to any oxygen

concentration (i.e., they are at stack conditions), whereas the emissions data in the EPA ICR

Databases are corrected to 3 percent oxygen.  To account for this, changes were made to the

methodology used to implement measurement error into the CO emissions data.

Where available, the reported oxygen concentration for the test run was used to

convert the standardized CO emissions back to stack conditions, via Equation 3 below. Due to

the format of many emission data points, which were reported to the ICR as oxygen adjusted

CO emission values without the stack O2 values, this adjustment could not always be made.
5 

݌݌݉௦௧௔௖௞ ൌ ݌݌݉ଷ%	ைమ ∗ ቀଶ଴.ଽସ଺ିைమ,ೞ೟ೌ೎ೖ

ଶ଴.ଽସ଺ିଷ ቁ           (Equation 3)

Where:

ppmstack = CO emissions, ppm @ stack O2

ppm3% O2 = Standardized CO emission, ppm @ 3% O2

20.946 = Approximate percentage of oxygen in ambient air

O2,stack = Reported stack oxygen concentration, percentage

For the top performers, the test‐specific CO measurement error identified by the test

report review was compared to the CO emissions at the reported stack oxygen concentration.  

For the remaining units for which test reports were not reviewed, the CO measurement error

for the subcategory shown in Table 2 was compared to the CO emissions at the reported stack

oxygen concentration.  If the reported CO emission concentration was lower than the

corresponding measurement error, the measurement error was used in lieu of the reported CO

emission concentration.  The chosen value was then standardized back to 3 percent oxygen

using Equation 4 below in order to compute the MACT floor.

݌݌݉ଷ%	ைమ ൌ ݌݌݉௦௧௔௖௞ ∗ ൬ ଶ଴.ଽସ଺ିଷ

ଶ଴.ଽସ଺ିைమ,ೞ೟ೌ೎ೖ൰           (Equation 4)

For the top performers presented in Appendix A, the specific measurement error for

that test run was used to compare with the reported emissions in lieu of the default

measurement error for the subcategory in Table 2.

Stack oxygen concentrations were not reported with all CO emissions data.  In these

cases, the reported oxygen‐adjusted values were compared to the measurement error from a

specific test report or the default CO span values in Table 2 of this memorandum. Although this

comparison introduces some error because the numbers are not both on an ‘at‐stack’ condition

basis, the analysis represents the most accurate comparison available given the data available

to EPA at the time of this rulemaking.  

6.0 MEASUREMENT ERROR FOR THC
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Due to differing performance criteria in the instrumental method used to measure THC,

a different equation was used to calculate the MDL for THC than those used for CO.  This

reasoning is explained in more detail in another memorandum.2 Equation 5 below was used to

calculate the MDL for each test run.

ܮܦܯௌ ൌ ඥሾሺ0.030 ∗ ܵሻଶ ൅ ሺ0.050 ∗ ܵሻଶ ൅ ሺ0.020 ∗ ܵሻଶሿ       (Equation 5)

Equation 5 applies to all test‐specific calibration span values; similarly to Equations 1

and 2, “S” represents 90 percent of the test‐specific calibration span.  Test reports were

reviewed for THC span information for an analysis conducted for the March 21, 2011 final rule

notice (76 FR 15608).  The analysis conducted for the March 2011 rule notice is detailed in

another memorandum.3 The span data that were identified during the test report review for

the previous analysis were also used for this revised analysis.  Table 3 below shows the

maximum calibration span or protocol gas concentration and the corresponding measurement

error (calculated using Equation 5, rounded to two significant figures) determined from the test

reports reviewed for each fuel category.  Since EPA Testing Method 25A did not undergo

significant revisions in May of 2008, maximum span values were not generated before and after

this date; instead, there is only one maximum span value for each fuel category.

Table 3 – Summary of Maximum THC Span Values and Measurement Error from Reviewed Test Reports 

Fuel Category Maximum THC Span

(ppmvd)

Maximum THC

Measurement Error

(ppmvd)

Coal 100 5.5

Biomass (non‐Bagasse) 113.4 6.3

Biomass (Bagasse) 2,500 140

Liquid 100.5 5.6

Process Gas 13 0.72
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The methods used to apply the THC measurement error to reported THC emissions data

were identical to those used to implement the CO measurement error data.  For test reports

that were reviewed for THC span information, the test‐specific MDL was used as the basis of

the comparison to reported emissions data.  For all other test data where a test report was not

reviewed, the maximum calibration span from Table 3 was used as the basis of comparison.

The maximum THC span for the liquid fuel subcategory is based on the test with the

second highest span value.  As noted in a previous memorandum, the November 2009 test

from facility ID “VANewportNewsShipbuildingDryDock” was excluded due to an

uncharacteristically high calibration span.3 Although this facility’s data were excluded from the

determination of the default MDL for the liquid subcategory, the data were used to establish

the test‐specific MDL for the facility.

   
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7.0 REFERENCES

1. Eastern Research Group, Inc.  Incorporating Measurement Error in Reported Carbon

Monoxide (CO) Data – Updated for Reconsideration Proposal.  November 2011.

2. Westlin, Peter.  U.S. EPA OAQPS/SPPD.  Measurement Detection Capabilities for EPA for

Instrumental Test Methods.  April 10, 2012.

3. Eastern Research Group, Inc.  Incorporating Measurement Error in Reported Carbon

Monoxide (CO) and Total Hydrocarbon (THC) Data.  January 2011.

   
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Appendix A

Summary of Test Reports Reviewed for Measurement Error