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MEMORANDUM 

TO: Brian Shrager, US EPA\OAQPS\SPPD 

FROM: Eastern Research Group, Inc. 

DATE: November 2011 

SUBJECT: Incorporating Measurement Error in Reported Carbon Monoxide (CO) Data – 

Updated for Reconsideration Proposal 

1.0 INTRODUCTION

This memorandum describes the methods used to incorporate measurement error into the 

reported emission values of carbon monoxide (CO) where the reported measured emission values 

are uncharacteristically low. This analysis involved identifying calibration spans from the test 

reports of top performers and low reported CO levels in each subcategory, calculating a 

maximum calibration error based on the spans, and assigning the calibration error to emission 

testing data. Subsequent analyses for CO were based on the adjusted emissions data for those 

pollutants, which incorporated measurement error, where applicable. This memorandum 

includes revisions to the CO measurement error analysis that was previously conducted for the 

promulgated rule. After promulgation of the NESHAP for Industrial, Commercial, and 

Institutional Boilers and Process Heaters (Boiler MACT) in March 2011 additional test reports 

from best performing boilers in each subcategory were collected and reviewed to refine the 

analysis. 

Since no further reviews of the THC test reports were conducted, this memorandum does 

not discuss THC. The THC measurement error analysis calculated for the March 2011 Boiler 

MACT is applied to the baseline emissions and emission reductions analyses for this proposal.1

 
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This memorandum is divided into the following sections: 

1.0 Introduction 

2.0 Sources of Measurement Error From Instrumental Methods 

3.0 Identifying Span Values 

4.0 Calculation of Maximum Measurement Error 

5.0 Application of Measurement Error to Analysis 

6.0 References 

2.0 SOURCES OF MEASUREMENT ERROR FROM INSTRUMENTAL METHODS 

EPA Method 10 is structured such that we can assess measurement data quality relative 

to the calibration span of the instrument. For example, the allowable calibration error, system 

bias, and drift requirements are directly proportional to the site-specific instrument calibration 

span (i.e., ± 2.0 percent of the calibration span value). For instrument calibration span values of 

25 ppmv and less, the allowable calibration error, bias, or drift values are each ± 0.5 ppmv. We 

can estimate the equivalent of the method detection level for a measurement with an instrumental 

test method (e.g., EPA Methods 3A, 6C, 7E, 10, and 25A) using a square root formula, the 

reported calibration span value, and these allowable data quality criteria. The equation used to 

estimate the measurement error is shown in Equations 1 and 2. 

 (1 Equation (ሻଶሻሻܽ݊݌ݏ݊ ݋݅ݐܽݎ݈ܾܿܽ݅ .ݔ݉ܽ כ 0.02ሺ כ 3ሺ√ሺ כ 3 = Error Measurement

Where: Calibration span is greater than 25 ppmvd 

Measurement Error = 3 כ ሺ√ሺ3 כ ሺ0.5ሻଶሻሻ ൌ 3 (Equation 2) 

Where: Calibration span is 25 ppmvd or less 

A discussion of the derivation of this equation used to estimate the measurement error is 

discussed in another memorandum.2

3.0 IDENTIFYING SPAN VALUES 

In order to develop a basis for measurement error, the test reports of the top performers 

and low emitting units along with other units which submitted test reports that had previously 
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been reviewed for CO from each subcategory were investigated for reported instrument 

calibration data. Whereas the maximum value between the calibration span and the protocol gas 

certificate from each test report was used in the initial CO measurement error analysis2

, a 

hierarchy was established for the current analysis. The hierarchy for CO calibration data values 

is as follows: 

1. Analyzer response for the high-level calibration gas 

2. Value corresponding to 90% of the instrument range 

3. Analyzer response for the mid-level calibration gas (this often corresponds to the 

CO value used for drift calculations) 

4. CO protocol gas certificate maximum concentration 

This hierarchy was chosen to select a high, yet practical CO calibration value as it relates 

to the data. In most cases, the high-level calibration gas value was specified in the report. 

Since revisions were made to EPA Method 103,4 in May, 2008, it was common that units 

with CO test data reported on or before May 2008 were using the prescriptive span guidance of 

1,000 ppmvd that was listed in the old method. The current version of EPA Method 10 does not 

include these older span requirements but instead requires the tester to choose calibration ranges 

that reflect the range of expected emissions concentrations at the unit. As a result, the extracted 

span values from the test reports were grouped according to the date of the test. Appendix A 

shows a detailed list of each of the test reports reviewed, along with a mention of whether a 

substitution was made to fill data gaps for CO. Table 1 represents the maximum calibration span 

or protocol gas concentration determined from the test report reviewed in each subcategory. 

Table 1 – Summary of Maximum Span Values from 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 1,000 506 

Biomass 

(non-Bagasse) 2280 1720 

Biomass 

(Bagasse) 8991 N/A (no tests from after May 2008) 

Liquid 897 484 
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Fuel Category 

Maximum CO Span 

(for tests conducted on 

or before May, 2008) 

(ppmvd) 

Maximum CO Span 

(for tests conducted 

after May, 2008) 

(ppmvd) 

Process Gas 17 86 

Based on the data available, there was a significant difference in reported calibration 

spans for bagasse and other types of biomass, which is consistent with comments received from 

the bagasse industry on wide CO emission swings at their boilers. As a result, we identified the 

maximum calibration span for each separate group of biomass. 

The reported CO calibration spans were also reviewed for outliers in order to avoid 

establishing a default span value that is not representative of other best performing units. 

Subcategories with identified outlier span values are listed below: 

 Liquid subcategory: 

 SCMilliken-Dewey, D30 (Test date: August 2009) shows a maximum 

span of 2,234 ppmvd, nearly 1,200 ppmvd higher than the next highest 

span. This was based on reported gas certificate only and no calibration 

spans were reported. 

 NENebraskaCityStation, Auxiliary Boiler 2 (Test date: June 2007) shows 

conflicting span values in the report, and the correct calibration value 

could not be determined. 

 Biomass group (non-bagasse): 

 MSIPVicksburg, Power Boiler-AA-006 (Test date: March 24, 2006) test 

report indicated that CO was monitored incidentally and instrument was 

not properly calibrated. 

 Bagasse group: 

 FLUSSugarCorp, Boiler No. 8 (Test date: September 2005) test report 

showed inconsistent and incorrect results for span calculations. 

 

Although these outliers were not factored into the maximum calibrations listed in Table 

1, these data were used to compare to the reported CO emissions data at the specific unit. 
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4.0 CALCULATION OF MAXIMUM MEASUREMENT ERROR 

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

in Table 1 above, we estimated the maximum measurement errors for each subcategory, as 

outlined in Table 2. 

Table 2 – Summary of Default 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 110 54 

Biomass 

(non-Bagasse) 240 180 

Biomass 

(Bagasse) 930 

N/A (no tests from after 

May 2008), used 930 as 

a placeholder. 

Liquid 93 51 

Process Gas 3 9 

5.0 APPLICATION OF MEASUREMENT ERROR TO ANALYSIS 

Each test run for CO was reviewed to determine if the maximum measurement error 

values needed to be incorporated in the data analysis for the MACT floor, estimate of baseline 

emissions, and estimated emission reductions. If the reported CO emission concentration was 

lower than the measurement error for that test run, the measurement errors were used in lieu of 

the reported concentration. For the units in Appendix A that had tests reports available to extract 

a test-specific calibration span, the specific measurement error for this test was compared to the 

reported test run concentrations. For all remaining test data, the reported test run concentrations 

were compared to the appropriate default measurement error from Table 2. 

 
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6.0 REFERENCES 

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

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

2. Westlin, Peter. Measurement Imprecision for Carbon Monoxide. s.l. : EPA Emissions 

Measurement Center, January 2011. 

3. USEPA, Emissions Measurement Center. Old Version of EPA Method 10. [Online] 

http://www.epa.gov/ttn/emc/promgate/m-10.pdf. 

4. USEPA, Emissions Measurement Center. US EPA Method 10 (Revised). [Online] 2008 

May. http://www.epa.gov/ttn/emc/promgate/method10r06.pdf.