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MEMORANDUM 

TO: Brian Shrager, US EPA\OAQPS\SPPD 

FROM: Amanda Singleton and Graham Gibson, ERG 

DATE: January 2011 

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

Hydrocarbon (THC) Data 

1.0 INTRODUCTION

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

reported emission values of carbon monoxide (CO) and total hydrocarbons (THC) 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 and 

THC 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 and 

THC were based on the adjusted emissions data for those pollutants, which incorporated 

measurement error, where applicable. 

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 
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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. 

3 ൈ ሺ√ሺ3 ൈ ሺሺ0.02 כ ݉ܽݔ. ݈ܾܿܽ݅ݎܽݐ݅݋݊ ݌ݏܽ݊ሻଶሻሻ (Equation 1) 

Where: Calibration span is greater than 25 ppmvd 

3 ൈ ሺ√ሺ3 ൈ ሺሺ0.5ሻଶሻሻ = 0.9 (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.1

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 for CO and THC from each subcategory were investigated for reported 

instrument calibration spans. In most cases, a calibration span was specified in the report. If no 

span value was reported, the maximum concentration from a protocol gas certificate was used in 

lieu of the span. If both a calibration span and protocol gas certificates were in a test report, the 

maximum of the two values was used as the span for the emission test. In several cases a test 

report with the exact test date in question was not available to the Agency to extract the 

calibration span or protocol gas certificates. In order to fill data gaps test reports from the same 

units on alternate dates or test reports from similar units at the same facility were reviewed to 
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identify a likely calibration span for these low emitting units. If an alternate report was 

available, we used the report with the date closest to the test date associated with the low CO or 

THC levels. 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. 

Since revisions were made to EPA Method 102, 3 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. EPA Method 

25A did not receive a similar revision so the calibration spans were not grouped according to 

date. 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) 

Maximum THC Span 

(ppmvd) 

Coal 1,000 501 100 

Biomass 

(non-Bagasse) 1,510 1,500 113.4 

Biomass 

(Bagasse) 5,000 10,000 2,500 

Liquid 1,000 501 100.5 

Process Gas N/A1 86 252

1

 No top performers for process gas reported CO test data on or before May, 2008. 

2

 Span reported as 13 ppmvd in test report, but adjusted to 25 ppmvd to match EPA Method 10 protocol. 

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. 
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The reported 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: 

o CO: 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. 

o THC: VANewportNewsShipbuildingDryDock, 78-E1 (Test Data: 

November 2009) submitted a protocol gas value of 500 ppmvd. The 

protocol gas not representative of other span checks for the liquid 

subcategory and much higher than the calibration spans reported for the 

process gas and coal subcategories. This value was 400 ppmvd higher 

than the next highest span value. 

 Bagasse group: 

o CO: FLUSSugarCorp, Boiler #4. The test from boiler #7 was used to fill 

data gaps. This test report shows a maximum span of 10,000 ppmvd, 

which is 8,000 ppmvd higher than the next highest span for that date 

range. 

 

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

1, these data were used to compare to the reported CO or THC emissions data at the specific unit. 

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. 
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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) 

Maximum THC 

Measurement Error 

(ppmvd) 

Coal 100 51 12 

Biomass 

(non-Bagasse) 210 160 12 

Biomass 

(Bagasse) 510 1,100 300 

Liquid 100 51 12 

Process Gas 601 9 3 1

 No top performers for process gas reported CO test data on or before May, 2008. Maximum calibration error is 

based on the old version of EPA Method 10, which suggested a calibration span of 1,000 ppmvd. 

5.0 APPLICATION OF MEASUREMENT ERROR TO ANALYSIS 

Each test run for CO and THC 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 emission concentration 

was lower than the measurement error for that test run, the default 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 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. Westlin, Peter. Measurement Imprecision for Carbon Monoxide. s.l. : EPA Emissions 

Measurement Center, January 2011. 

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

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

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

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