1 MEMORANDUM
TO: Brian Shrager, US EPA\OAQPS\SPPD
FROM: Amanda Singleton and Graham Gibson, ERG
DATE: January 2011
SUBJECT: Incorporating Meas urement Error in Reported Ca rbon Monoxide (CO) and Total Hydrocarbon (THC) Data

1.0 INTRODUCTION

This memorandum describes the methods used to incorporate measur ement error into the reported emission values of carbon monoxide (C O) and total hydrocar bons (THC) where the reported measured emission values are uncharact eristically low. This analysis involved identifying calibration spans from the test repor ts 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 te sting 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 References2 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 ex ample, the allowable calibration error, system bias, and drift requirements are directly proportio nal to the site-specific instrument calibration span (i.e., ± 2.0 percent of the calibration span value). For in strument 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 detectio n 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 ൈ ሺ ሺ0.02 כ ݉ܽݔ. ݈ܾܿܽ݅ݎܽݐ݅݋݊ ݌ݏܽ݊ሻ ଶ ሻ ሻ (Equation 1) Where: Calibration span is greater than 25 ppmvd

3 ൈ ሺ√ሺ3 ൈ ሺ ሺ0.5ሻ ଶ ሻ ሻ = 0.9 (Equation 2) Where: Calibration span is 25 ppmvd or less

A discussion of the derivation of this equati on 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 e rror, 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 ca libration span was specified in the report. If no span value was reported, the maximum concentrati on from a protocol gas certificate was used in lieu of the span. If both a calibration span and prot ocol 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 wa s not available to the Agency to extract the calibration span or protocol gas cer tificates. 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 to3 identify a likely calibration span for these lo w 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 10 2, 3 in May, 2008, it was common that units with CO test data reported on or before May 2008 were using the prescripti ve span guidance of 1,000 ppmvd that was listed in the old method. The current ve rsion of EPA Method, 10 does not include these older span require ments but instead requires the te ster 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 ma ximum calibration span or protocol gas concentration determined from the test report reviewed in each subcategory.

Table 1 – Summary of Maximum Spa n 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/A 1 86 25 2

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 si gnificant difference in reported calibration spans for bagasse and other types of biomass, wh ich is consistent with comments received from the bagasse industry on wide CO emission swings at their boilers. As a re sult, we identified the maximum calibration span for each separate group of biomass.4 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 (Tes t 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 re ported gas certificate only and no calibration spans were reported.

o THC: VANewportNewsShipbuildin gDryDock, 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 th e calibration spans reported for the process gas and coal subcategorie s. 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 da ta at the specific unit.

4.0 CALCULATION OF MAXIMU M MEASUREMENT ERROR

Using the equations provided in section 2.0 and the maximum calibration spans identified in Table 1 above, we estimated the maximum m easurement errors for each subcategory, as
outlined in Table 2.5 Table 2 – Summary of Default Me asurement 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 60 1 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 MEASUREM ENT 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 reduc tions. 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 concentra tion. For the units in Appendix A that had tests reports available to extract a test-specific calibration span, the meas urement 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 de fault measurement error from Table 2.6 

### 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.