1 MEMORANDUM
TO: Brian Shrager, US EPA\OAQPS\SPPD
FROM: Eastern Research Group, Inc.

DATE: November 2011
SUBJECT: Incorporating Measurement Erro r in Reported Carbon Monoxide (CO) Data – Updated for Reconsideration Proposal

1.0 INTRODUCTION This memorandum describes the methods used to incorporate measur ement error into the reported emission values of carbon monoxide (CO) where the reported meas ured emission values are uncharacteristically low. This analysis invol ved 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 calibra tion error to emission testing data. Subsequent analys es for CO were based on the adju sted 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 (Bo iler MACT) in March 2011 a dditional test reports from best performing boilers in each subcategor y were collected and reviewed to refine the analysis. Since no further reviews of the THC test re ports 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 a nd emission reductions analyses for this proposal. 12 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 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.

= Error Measurement כ 3ሺ√ሺ כ 3 ሺ ܽ݊݌ݏ݊ ݋݅ݐܽݎ݈ܾܿܽ݅ .ݔ݉ܽ כ 0.02 ሻ ଶ ሻሻ (1 Equation ( Where: Calibration span is greater than 25 ppmvd

Measurement Error = 3 כ ሺ√ሺ3 כ ሺ 0.5 ሻ ଶ ሻሻ ൌ 3 (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. 2

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 along with other units whic h submitted test reports that had previously3 been reviewed for CO from each subcategory were investigated for reported instrument calibration data. Whereas the maximum value betw een the calibration span and the protocol gas certificate from each test report was used in the initial CO measurement error analysis 2 , 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 mi d-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, ye t practical CO calibration value as it relates to the data. In most cases, th e high-level calibration gas value was specified in the report. Since revisions were made to EPA Method 10 3,4 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 ac cording to the date of the test. Appendix A shows a detailed list of each of the test reports reviewed, alon g 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 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) Coal 1,000 506 Biomass (non-Bagasse) 2280 1720
Biomass (Bagasse) 8991 N/A (no tests from after May 2008) Liquid 897 4844 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 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. 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 ppm vd higher than the next highest span. This was based on reported gas certificate only and no calibration spans were reported.

 NENebraskaCityStation, Auxiliary Boile r 2 (Test date: June 2007) shows conflicting span values in the repo rt, 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 monitore d 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 repo rted CO emissions data at the specific unit.5 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.

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) 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 MEASUREM ENT ERROR TO ANALYSIS Each test run for CO was reviewed to de termine 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 r un, the measurement errors were used in lieu of the reported concentration. For th e units in Appendix A that had te sts reports available to extract a test-specific calibration span, the specific measur ement 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. Eastern Research Group, Inc. Incorpor ating 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.