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Date: November 16, 2012 

Subject: 75 Percent CPMS Operating Limit Approach – MATS Reconsideration 

From: Nick Hutson, U.S. EPA Office of Air and Radiation 

To: Docket No. EPA-HQ-OAR-2009-0234 

As noted in the preamble to the proposed MATS reconsideration, the EPA is considering three 

PM CPMS compliance options for new EGUs. The third approach would allow an EGU owner 

or operator whose PM emissions as demonstrated during performance testing do not exceed 75 

percent of the PM emissions limit to set his PM CPMS operating limit by linearly scaling the 

average operating value obtained during all the runs to be equivalent to the value at 75 percent of 

the limit; an EGU owner or operator whose PM emissions as demonstrated during performance 

testing exceed 75 percent of the PM emissions limit would establish his operating limit as a 30-

day rolling average equal to the average PM CPMS values recorded during performance testing. 

Such an approach would prevent unnecessary retests for EGUs with low PM emissions. Should 

the EPA decide upon this third approach, the appropriate regulatory text would be as follows. 

1. Revise § 63.10023 paragraph (b) to read as follows: 

§ 63.10023 How do I establish my PM CPMS operating limit and 

determine compliance with it? 

* * * * * 

(b) Determine your operating limit as provided in paragraph 

(b)(1) or (b)(2) of this section. You must verify an existing or 

establish a new operating limit after each repeated performance 

test. 

(1) For an existing EGU, determine your operating limit based on 

the highest 1-hour average PM CPMS output value recorded during 

the performance test. 

(2) For a new EGU, determine your operating limit as follows. 

(i) If your PM performance test demonstrates your PM emissions 

do not exceed 75 percent of your emissions limit, you will use 

the average PM CPMS value recorded during the PM compliance 

test, the milliamp equivalent of zero output from your PM CPMS, 

and the average PM result of your compliance test to establish 

your operating limit. 

(A) Determine your instrument zero output with one of the 

following procedures. 

(1) Zero point data for in-situ instruments should be obtained 

by removing the instrument from the stack and monitoring ambient 

air on a test bench. 

(2) Zero point data for extractive instruments should be 

obtained by removing the extractive probe from the stack and 

drawing in clean ambient air. 
 

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(3) The zero point can also can be established obtained by 

performing manual reference method measurements when the flue 

gas is free of PM emissions or contains very low PM 

concentrations (e.g., when your process is not operating, but 

the fans are operating or your source is combusting only natural 

gas) and plotting these with the compliance data to find the 

zero intercept. 

(4) If none of the steps in paragraphs (A)(1) through (3) of 

this section are possible, you must use a zero output value 

provided by the manufacturer. 

(B) Determine your PM CPMS instrument average in milliamps, and 

the average of your corresponding three PM compliance test runs, 

using equation 10. 

ݔ ൌ భ

೙ ∑ ܺଵ ௡

௜ୀଵ , ݕ ൌ భ

೙ ∑ ܻଵ ௡

௜ୀଵ (Eq. 10) 

Where: 

X1 = the PM CPMS data points for the runs constituting the 

performance test, 

Y1 = the PM emissions value (in lb/MWh) for the runs constituting 

the performance test, and 

n = the number of data points. 

(C) With your instrument zero expressed in milliamps, your test 

average PM CPMS milliamp value, and your test average PM 

emissions value (in lb/MWh) from your compliance runs, determine 

a relationship of PM lb/MWh per milliamp with equation 11. 

  X z

Y

 

1

1 R (Eq. 11) 

Where: 

R = the relative PM lb/MWh per milliamp for your PM CPMS, 

Y1 = the three run average PM lb/MWh, 

X1 = the three run average milliamp output from you PM CPMS, and 

z = the milliamp equivalent of your instrument zero determined 

from (i)(A). 

(D) Determine your source specific 30-day rolling average 

operating limit using the PM lb/MWh per milliamp value from 

equation 11 in equation 12, below. This sets your operating 

limit at the PM CPMS output value corresponding to 75 percent of 

your emission limit. 

Ol = z + (0.75(L))/ R (Eq. 12) 

Where: 
 

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Ol = the operating limit for your PM CPMS on a 30-day rolling 

average, in milliamps. 

L = your source PM emissions limit in lb/MWh, 

z = your instrument zero in milliamps, determined from (i)(A), 

and 

R = the relative PM lb/MWh per milliamp for your PM CPMS, from 

equation 11. 

(ii) If your PM compliance test demonstrates your PM emissions 

exceed 75 percent of your emissions limit, you will use the 

average PM CPMS value recorded during the PM compliance test 

demonstrating compliance with the PM limit to establish your 

operating limit. 

(A) Determine your operating limit by averaging the PM CPMS 

milliamp output corresponding to your three PM performance test 

runs that demonstrate compliance with the emission limit using 

equation 13. 

ܱ௛ ൌ భ

೙ ∑ ܺଵ ௡

௜ୀଵ (Eq. 13) 

Where: 

X1 = the PM CPMS data points for all runs i, 

n = the number of data points, and 

Oh = your site specific operating limit, in milliamps. 

(iii) Your PM CPMS must provide a 4-20 milliamp output and the 

establishment of its relationship to manual reference method 

measurements must be determined in units of milliamps. 

(iv) Your PM CPMS operating range must be capable of reading PM 

concentrations from zero to a level equivalent to two times your 

allowable emission limit. If your PM CPMS is an auto-ranging 

instrument capable of multiple scales, the primary range of the 

instrument must be capable of reading PM concentration from zero 

to a level equivalent to two times your allowable emission 

limit. 

(v) During the initial performance test or any such subsequent 

performance test that demonstrates compliance with the PM limit, 

record and average all milliamp output values from the PM CPMS 

for the periods corresponding to the compliance test runs. 

(vi) For PM performance test reports used to set a PM CPMS 

operating limit, the electronic submission of the test report 

must also include the make and model of the PM CPMS instrument, 

serial number of the instrument, analytical principle of the 

instrument (e.g. beta attenuation), span of the instruments 

primary analytical range, milliamp value equivalent to the 

instrument zero output, technique by which this zero value was 

determined, and the average milliamp signal corresponding to 

each PM compliance test run. 
 

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2. Amend the Appendix by revising Table 4 to Subpart UUUUU of 

Part 63 to read as follows: 

Table 4 to Subpart UUUUU of Part 63 — Operating Limits for EGUs 

As stated in §§63.9991, you must comply with the applicable 

operating limits: 

If you demonstrate 

compliance using... 

You must meet these operating 

limits... 

1. PM CPMS for an 

existing EGU 

Maintain the 30-boiler operating day 

rolling average PM CPMS output at or 

below the highest 1-hour average 

measured during the most recent 

performance test demonstrating 

compliance with the filterable PM, 

total non-mercury HAP metals (total 

HAP metals, for liquid oil-fired 

units), or individual non-mercury HAP 

metals (individual HAP metals 

including Hg, for liquid oil-fired 

units) emissions limitation(s). 

2. PM CPMS for a new 

EGU 

Maintain the 30-boiler operating day 

rolling average PM CPMS output 

determined in accordance with the 

requirements of §63.10023(b)(2)and 

obtained during the most recent 

performance test run demonstrating 

compliance with the filterable PM, 

total non-mercury HAP metals (total 

HAP metals, for liquid oil-fired 

units), or individual non-mercury HAP 

metals (individual HAP metals 

including Hg, for liquid oil-fired 

units) emissions limitation(s). 

3. Amend the Appendix by revising Table 6 to Subpart UUUUU of 

Part 63 to read as follows: 

Table 6 to Subpart UUUUU of Part 63 — Establishing PM CPMS 

Operating Limits 

As stated in §63.10007, you must comply with the following 

requirements for establishing operating limits: 

If you And you choose And... Using... According to the 
 

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have an 

applicable 

emission 

limit 

for... 

to establish PM 

CPMS operating 

limits, you 

must... 

following 

procedures... 

1. 

Filterable 

Particulat

e matter 

(PM), 

total nonmercury 

HAP 

metals, 

individual 

nonmercury 

HAP 

metals, 

total HAP 

metals, or 

individual 

HAP metals 

for an 

existing 

EGU. 

 

 

Install, 

certify, 

maintain, and 

operate a PM 

CPMS for 

monitoring 

emissions 

discharged to 

the atmosphere 

according to 

§63.10010(h)(1)

. 

Establish 

a sitespecific 

operating 

limit in 

units of 

PM CPMS 

output 

signal 

(e.g., 

milliamps

, mg/acm, 

or other 

raw 

signal). 

Data from 

the PM 

CPMS and 

the PM or 

HAP metals 

performanc

e tests. 

1. Collect PM 

CPMS output data 

during the entire 

period of the 

performance 

tests. 

2. Record the 

average hourly PM 

CPMS output for 

each test run in 

the performance 

test. 

3. Determine the 

highest 1-hour 

average PM CPMS 

measured during 

the performance 

test 

demonstrating 

compliance with 

the filterable PM 

or HAP metals 

emissions 

limitations. 

2. 

Filterable 

Particulat

e matter 

(PM), 

total nonmercury 

HAP 

metals, 

individual 

nonmercury 

HAP 

metals, 

total HAP 

metals, or 

individual 

Install, 

certify, 

maintain, and 

operate a PM 

CPMS for 

monitoring 

emissions 

discharged to 

the atmosphere 

according to 

§63.10010(h)(1)

. 

Establish 

a sitespecific 

operating 

limit in 

units of 

PM CPMS 

output 

signal 

(e.g., 

milliamps

, mg/acm, 

or other 

raw 

signal). 

Data from 

the PM 

CPMS and 

the PM or 

HAP metals 

performanc

e tests. 

1. Collect PM 

CPMS output data 

during the entire 

period of the 

performance 

tests. 

2. Record the 

average hourly PM 

CPMS output for 

each test run in 

the performance 

test. 

3. Determine the 

PM CPMS operating 

limit in 

accordance with 

the requirements 
 

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HAP metals 

for a new 

EGU. 

 

 

of 

§63.10023(b)(2)fr

om data obtained 

during the 

performance test 

demonstrating 

compliance with 

the filterable PM 

or HAP metals 

emissions 

limitations.