THE OHIO CHAMBER OF COMMERCE,

THE OHIO MANUFACTURERS ASSOCIATION,

AND

THE OHIO CHEMISTRY TECHNOLOGY COUNCIL

COMMENTS ON

U.S. EPA’S PROPOSED DISAPPROVAL

OF OHIO’S CONTINUOUS OPACITY MONITORING RULE

70 Fed. Reg. 36901 RME ID No. RO5-OAR-2005-OH-0002

(June 27, 2005)

LINDA WOGGON JACK R. POUNDS

Vice President, Governmental Affairs President

Ohio Chamber of Commerce Ohio Chemistry Technology Council

230 East Town Street 88 East Broad Street, Suite 1490

Columbus, Ohio 43215 Columbus, Ohio 43215

(614) 228-4201 (614) 224-1730

KEVIN SCHMIDT

Director of Public Policy

Ohio Manufacturers Association

33 North High Street

Columbus, OH 43215

(614) 224-5111

Prepared by

PORTER, WRIGHT, MORRIS & ARTHUR LLP

Robert L. Brubaker

Andrew S. Bergman

41 South High Street

Columbus, Ohio 43215

August 24, 2005
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OHIO CHAMBER OF COMMERCE,

OHIO MANUFACTURERS ASSOCIATION,

AND

OHIO CHEMISTRY TECHNOLOGY COUNCIL

COMMENTS ON U.S. EPA’S PROPOSED DISAPPROVAL

OF OHIO’S CONTINUOUS OPACITY MONITORING RULE

70 Fed. Reg. 36901 (June 27, 2005)

I. INTRODUCTION

The Ohio Chamber of Commerce, the Ohio Manufacturers Association, and the Ohio

Chemistry Technology Council present these comments on the United States Environmental

Protection Agency’s (U.S. EPA) proposed disapproval of Ohio’s Continuous Opacity Monitoring

(COM) Rule, published at 70 Fed. Reg. 36901 on June 27, 2005. The Ohio Chamber of

Commerce represents the interests of over 4,000 member companies, including manufacturers,

utilities, and small businesses. The Ohio Manufacturers Association represents the interests of

over 1800 member companies with a focus on manufacturers. The Ohio Chemistry Technology

Council represents over 80 chemical industry and related companies that do business in Ohio.

Members of all three of these trade associations are subject to the requirements set forth in the

Clean Air Act and Ohio Air Pollution Control Law and their implementing regulations.

The Ohio COM Rule establishes COM as an alternative method for assessing compliance

with opacity limits for certain sources. U.S. EPA’s proposed disapproval incorrectly assumes

that the method of measuring opacity was germane to Ohio’s prior attainment demonstrations for

the PM NAAQS, and fails to properly consider the distinction between periodic opacity

monitoring in accordance with Reference Method 9 and a continuous opacity monitoring method

for judging compliance.
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II. OHIO’S COM RULE

Until passage of the COM Rule, Ohio’s rule-based method for assessing compliance with

the opacity provisions of OAC 3745-17-07(A) was Reference Method 9 (as set forth in Appendix

A to 40 CFR part 60). See OAC 3745-17-03(B)(1)(a). The COM Rule adds COM as an

alternative compliance monitoring method for coal-fired boilers with heat input capacities equal

to or greater than 250 BTU that have particulate control equipment. OAC 3745-17-03(B)(1)(b).

The COM Rule excludes COM readings in excess of 20 percent opacity during operating periods

not otherwise exempted as long as (a) they are less than 1.1 percent of the six-minute average

opacity values, (b) they do not exceed 60 percent opacity, and (c) the total amount of time, in

hours, of nonexempt and certain exempt opacity values greater than 20 percent and less than 60

percent does not exceed one tenth of the actual number of hours the emission unit was in

operation during the calendar quarter. OAC 3745-17-03(B)(1)(b)(i), (ii) and (iii).

Ohio EPA believes that this compliance approach uses a COM system for a specific

source category in a way that does not affect the total amount of exemptible time or maximum

exemptible opacity values under the previous Method 9–only scheme. Ohio EPA

Responsiveness Summary (dated March 6, 2003) at p. 10 (copy attached as Attachment 1).

III. HISTORY OF OHIO’S OPACITY REQUIREMENT

AP-3 was Ohio EPA’s first set of particulate matter regulations. AP-3-07 set forth the

requirements for regulating opacity:

AP-3-07 – Control of visible air contaminants from stationary

sources.

(A) Emission limitation

(1) No person shall discharge into the atmosphere from

any single source of emission whatsoever any air contaminant of a

shade or density equal to or darker than that designated as No. 1 on

the Ringelmann chart or 20 percent opacity, except as set forth in

subsection (A)(2) and section (B) of this regulation.
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(2) A person may discharge into the atmosphere from

any single source of emission for a period or periods aggregating

not more than three minutes in any sixty minutes or for a period of

time deemed necessary by the Board, air contaminants of a shade

or density not darker than No. 3 on the Ringelmann chart or 60

percent opacity.

(B) Uncombined water

It shall be deemed not to be a violation of this regulation where the

presence of uncombined water is the only reason for failure of an

emission to meet the requirements of this regulation.

AP-3 was promulgated in 1972 as part of the original Ohio SIP. The original opacity

regulations were based on using the Ringelmann chart that compared a stack plume with

progressive shades of darkness. See AP-3-01(H) (defining “Ringelmann Chart” as a “chart

published and described in the United States Bureau of Mines Information Circular 8333 (May

1967)”). The regulation established opacity standards that were uniform across the State,

regardless of air quality, and regardless of the source type, size or emission controls.

The opacity regulations were recodified in 1977 and amended in 1980. The control of

visible air contaminants was placed in a new Ohio Administrative Code section 3745-17-07 that

retained the twenty percent opacity standard with an allowance for one six-minute exceedance up

to 60% opacity for each sixty minute period of operation. The new opacity regulation removed

the reference to the Ringelmann Chart and, in its place, adopted a new regulatory section that

specified Reference Method 9 in Appendix A to 40 CFR part 60 to determine compliance with

opacity requirements. OAC 3745-17-03(B)(1).

IV. RELATIONSHIP OF OPACITY TO PARTICULATE MASS EMISSIONS

U.S. EPA claims that allowing certain sources to use an alternative method of measuring

opacity may interfere with satisfying relevant state planning requirements contrary to section

110(l) of the Clean Air Act. 70 Fed. Reg. at 36901. The state planning requirements U.S. EPA
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refers to appear to be those in section 110(a)(2) of the Clean Air Act that call for the State’s

demonstration of attainment and maintenance of the PM NAAQS. The particulate mass

emission limits that Ohio EPA promulgated to support Ohio’s prior PM NAAQS attainment

demonstrations are unchanged and not at issue. There is no factual basis for U.S. EPA’s premise

that the proposed opacity standard compliance monitoring method is relevant and material to a

prior demonstration of attainment and maintenance of the PM or PM-10 NAAQS in Ohio.

Therefore, the alternative COM method of determining compliance with the opacity standard

cannot be a potential “interference” within the scope of section 110(l).

Opacity is “the degree to which emissions reduce the transmission of light and obscure

the view of an object in the background.” 40 C.F.R 60.2. U.S. EPA has consistently recognized

from its earliest air regulations, however, that opacity is not directly correlated to particulate

mass emissions, and that opacity is not a precise surrogate for particulate emission rates.

By defining “increase in emissions” in terms of kg/hr, the proposed

regulations could not be interpreted as considering an increase in

opacity of emissions as a modification unless there is a

corresponding increase in mass rate of pollutant emissions. Under

certain conditions, an increase in opacity is not accompanied by an

increase in mass emission rate.

39 Fed. Reg. 36946, 36947 (1974).

U.S. EPA published guidance around the same time that further established the

subservient role that the opacity standards relative to the mass emission standard:

Opacity standards are a necessary supplement to mass emission

standards. Opacity standards help assure that source and emission

control systems continue to be properly maintained and operated

so as to comply with mass emission standards.
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U.S. EPA Publication No. EPA-450/2-74-023 (November, 1974). See also U.S. EPA

Publication No. EPA-454/R-00-039 (September, 2000) at 2-1 (“Opacity is used as a surrogate for

PM emissions and provides qualitative information on the operation and maintenance of

particulate control equipment.”).

Moreover, if a source meets the mass emission standard for particulates but does not meet

the opacity standard, U.S. EPA will adjust the opacity limit.

Upon receipt from such owner or operator of the written report of

the results of the performance tests required by § 60.8, the opacity

observation results and observer certification required by §

60.11(e)(1), and the COMS results, if applicable, the Administrator

will make a finding concerning compliance with opacity and other

applicable standards. . . . If the Administrator finds that an affected

facility is in compliance with all applicable standards for which

performance tests are conducted in accordance with § 60.8 of this

part but during the time such performance tests are being

conducted fails to meet any applicable opacity standard, he shall

notify the owner or operator and advise him that he may petition

the Administrator within 10 days of receipt of notification to make

appropriate adjustment to the opacity standard for the affected

facility.” [Emphasis added.]

40 C.F.R. 60.11(e)(6).

Courts in Ohio have found that the opacity standard is not independently enforceable

when a source is in compliance with the applicable mass emission limitation for particulate

matter. In Dayton-Walther Corp. v. Williams, 1980 WL 35334B (Ohio App. 10

th Dist. 1980), the

State court of appeals considered whether the Ohio opacity standard in OAC 3745-17-07 is

independent of the specific regulations for the emission of hydrocarbons and particulates such

that a source in compliance with those specific regulations can be in violation of the opacity

standard. Id. at *4. Guided by the U.S. EPA policies expressed above, as well as the D.C.

Circuit’s concerns with the reliability and purpose of the opacity standard expressed in Portland
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Cement Ass’n. v. Ruckelshaus, 486 F.2d 375, 401 (D.C. Cir. 1973), cert. denied, 417 U.S. 921

(1974), the Dayton-Walther court concluded that:

The only reasonable interpretation of OAC 3745-17-07, as

demonstrated by the record before us, is that it is not a regulation

that may be applied to an applicant independently of the

hydrocarbon and particulate ambient air quality standards, but,

rather, like its federal counterpart, is to be used only as a

supplement to those standards.

Ohio opacity standards, as applied to a particular applicant, may be

used only as a means of determining, in the first instance, whether

a pollution source appears to be violating a mass emission

standard. It may not be used as the primary test where other

reliable data is available to indicate compliance with emission

standards.

Dayton-Walther at *6.

In 1985, a federal district court in Ohio relied on Dayton-Walther Corp., Portland

Cement, and 40 C.F.R. § 60.11(e)(6) to conclude that, whereas a violation of Ohio’s opacity

standard is a sufficient basis to commence an enforcement action, it is not sufficient proof of a

violation of Ohio’s SIP to support judgment in the enforcement action. United States v. New

Boston Coke Corp., No. C-1-84-1427, Opinion and Order (U.S. Dist. Ct., S.D. Ohio) (August 16,

1985) (copy attached as Attachment 2). The court found that the opacity standards were

subservient to the mass emission standard; the opacity standard offered a threshold indication of

a potential mass emission standard violation but not definitive and sufficient evidence of such a

violation.

Around the same time as the Dayton-Walther Corp. and New Boston Coke Corp. cases,

U.S. EPA evaluated Ohio EPA’s SIP submittal addressing Ohio’s particulate matter control plan.

U.S. EPA acknowledged that Ohio EPA believed that, although visible emissions were useful in

enforcing the mass emission limits, they were not an integral part of the State’s control strategy

and never were meant to be independently enforceable.
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The State has indicated to EPA that it does not consider the opacity

limitations in 3745-17-07 for stack sources to be an integral part of

its overall control strategy to reduce particulate emissions and

achieve the TSP ambient air quality standards. The State has

asserted that, with the exception of the V.E. limits for coke oven

batteries, which reflect a certain level of control technology, the

V.E. limits of 3745-17-07 are of primary importance in enforcing

the applicable mass emission limits in rules 3745-17-09 through

11.

Notice of Proposed Rulemaking, 47 Fed. Reg. 41584, 41589 (1982). U.S. EPA also understood

that the opacity regulation was useful in enforcing the mass standards and not as a separate,

independently enforceable standard.

In evaluating Ohio’s Part D SIP, EPA’s primary concern in regard

to those sources proposed by Ohio to be covered by rule

3745-17-07, was that the associated mass particulate emission

limits in 3745-17-09 through 11 require the implementation of

reasonably available control measures, and that, at a minimum,

rule 3745-17-07 contains clear, specific and enforceable visible

emission limits which will be of use in enforcing the mass

particulate limitations.

Id.

Changing the opacity standard cannot be found to interfere with a prior demonstration of

PM NAAQS attainment and maintenance because opacity only roughly correlates to PM

emissions, and the particulate mass emission limits that ensure attainment and maintenance of

the PM NAAQS are enforceable independent from the opacity standard. Furthermore, the sixminute average level of opacity is not a metric capable of being used to demonstrate PM

NAAQS attainment. The NAAQS are uniform national standards for a discrete set of pollutants

that are set at a level requisite (i.e., sufficient but not more than necessary) to protect public

health from the adverse effects of the pollutants in the ambient air. Whitman v. American

Trucking Ass’n., 531 U.S. 457, 473 (2001). Opacity is measured in 6-minute intervals, which is

not even remotely correlated with the PM NAAQS averaging time periods. Moreover, the
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variation in opacity standards from state-to-state for similar sources, including greater than 20

percent opacity allowed by some States, indicates the absence of a source-receptor relationship

basis for opacity standards. See e.g. N.C. Admin. Code tit. 15A, § 2D.0521(c) (2005); Ga.

Comp. R. & Regs. r. 391-3-1-.02(2)(b) (2005). Finally, the one-size-fits-all opacity standard,

applied universally throughout the state without regard to relevant modeling factors such as

topography, meteorology, and stack height, is inconsistent with a consideration of sourcereceptor relationships.

U.S. EPA itself has recently rejected the notion underlying the proposed disapproval of

Ohio’s COM Rule that any change in a SIP requirement requires a case-by-case, fact-specific

review to determine whether the requirements of section 110(l) are met. Final Rule on

Nonattainment Major New Source Review Implementation Under 8-Hour Ozone National

Ambient Air Quality Standard: Reconsideration, 70 Fed. Reg. 39413, 39420 (July 8, 2005).

Modeling the impact of the change was not needed, for instance, where the measures being

changed were not needed for demonstrating attainment because the state did not rely on the

measures in its attainment planning to attain the relevant NAAQS. Id. at 39421. The agency

emphasized “Congress’ intent that States play the primary role in pollution control and

Congress’ desire that States retain the maximum possible flexibility to balance environmental

and economic controls in designing plans to clean up nonattainment areas,” id., and thus guarded

against an “overly restrictive interpretation of section 110(l).” Id. at 39422. Selecting the

particular type of opacity monitoring method was not relevant and material to a prior

demonstration of attainment and maintenance of the PM NAAQS, and the proposed disapproval

burdens Ohio with an obligation not required by section 110(l).
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If U.S. EPA still believes that Ohio’s COM Rule may interfere with Ohio’s PM NAAQS

attainment demonstration, it must issue a statement of basis and purpose that includes a summary

of the factual data relied on by U.S. EPA, as well as the methodology used in obtaining and

analyzing the data, before it can disapprove Ohio’s SIP submittal. CAA § 307(d)(3)(A) and (B).

U.S. EPA must show in the rulemaking record how Ohio’s COM Rule conflicts with the

attainment demonstration for the PM NAAQS, most particularly, the basis for a finding that

Ohio’s current method for monitoring compliance with the opacity standard is necessary to

demonstrate attainment with the PM NAAQS, and allow an opportunity for interested parties to

comment. U.S. EPA has not satisfied this statutory obligation.

V. A CONTINUOUS OPACITY MONITORING SYSTEM IS MORE STRINGENT

THAN METHOD 9

In proposing to disapprove Ohio’s COM Rule, U.S. EPA believes that the COM Rule is

less stringent than the previous Method 9–only rule. Even if U.S. EPA could establish that

Ohio’s opacity rule is necessary for an attainment demonstration of the PM NAAQS (an

impossibility), the agency fails to take into account that a COM method of monitoring opacity

compliance is inherently more stringent than periodic tests in accordance with Reference Method

9, and therefore adjustment factors such as those included in the COM Rule are necessary.

Courts have consistently recognized that the test method used to enforce an emission

standard is part and parcel of the standard itself. Courts have held that the test method used to

develop the standard and the test method used to enforce the standard must be consistent, or else

the standard itself can be called into question. “[A] significant difference between techniques

used by the agency in arriving at standards, and requirements presently prescribed for

determining compliance with standards, raises questions about the validity of the standard.”

Portland Cement Ass’n., 486 F.2d at 396.
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Determining the appropriate test method used to enforce an emissions standard is critical

because “[t]est methods and the frequency of testing for compliance with emission limitations

are surely ‘substantive’ requirements; they impose duties and obligations on those who are

regulated.” Appalachian Power Co. v. EPA, 208 F.3d 1015, 1027 (D.C. Cir. 2000). Thus,

“changing the method of measuring compliance with an emission limitation can affect the

stringency of the limitation itself.” Id. See also Donner Hanna Coke Corp. v. Castle, 464 F.

Supp 1295 13 (W.D. NY 1979) (court struck down U.S. EPA’s application of a modified version

of Method 9 that strayed so far from the original substance and intent of Method 9 that it in

effect created a new and different standard.)

The method of measuring compliance thus is fundamental to a performance standard and

to the level of stringency imposed by a standard. See Clean Air Implementation Project (CAIP)

v. EPA, 150 F.3d 1200, 1205 (D.C. Cir. 1998). U.S. EPA has recognized that any evidence used

to establish compliance or noncompliance with Clean Air Act requirements must be equivalent

to the application of Reference Methods or other compliance test methods established by rule

contemporaneously with the creation of the performance obligation. 62 Fed. Reg. 8314, 8319

(1997) (Credible Evidence rule).

1 Credible evidence may not be applied in the place of a

reference test where the result is to alter an obligation to comply or “affect” the stringency of the

underlying standard. CAIP, 150 F.3d at 1205.

Courts have applied the principle that continuous emissions monitoring methods are

inherently more stringent than periodic emissions monitoring methods to opacity monitoring in

order to evaluate the validity of COM adjustment factors. In National Parks Conservation Ass’n.

v. TVA, 175 F. Supp 2d 1071 (E.D. Tenn. 2001), the court considered a permit term issued by

the Tennessee Department of Environment and Conservation (TDEC) that allowed a source to

1 We note that the Credible Evidence rule is not self-executing and is not included in the Ohio SIP.
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substitute COM data for Method 9 data and authorized unexcused levels to exceed 20 percent up

to 2 percent of the time during each calendar quarter. The TDEC had not sought U.S. EPA

approval for this exception because it believed that the use of COMS was more restrictive than

Method 9, which was specified in the SIP, and EPA approval for a more restrictive standard was

not necessary. Id. at 1075. The court agreed:

Obviously, monitoring the smokestack emissions continuously

with equipment capable of reliably measuring the opacity will

identify many more exceedances than will be identified by an

operator “eyeballing” the smokestack emissions once a day, or

less. I believe that it was completely reasonable for TDEC to

consider the COM monitoring by TVA at its plants to be a more

restrictive standard than the Tennessee SIP required and therefore

concluding that EPA approval of that more restrictive standard was

not necessary.

Id. at 1079.

In another case, Sierra Club v. TVA, 2004 U.S. Dist. LEXIS 28080 (N.D. AL; September

14, 2004), the court similarly considered the stringency of COM data as compared to Method 9.

The court reviewed a COM practice (later codified) by the Alabama Department of

Environmental Management (ADEM) to exclude excess emissions that do not exceed 2 percent

of the source’s operating hours. The court agreed with the court in National Parks that a

continuous monitoring system is more restrictive and stringent than Method 9, and so ADEM’s

practice could be used to establish compliance with the underlying opacity limit. Id. at *20. The

validity of Ohio’s application of the COM method is even stronger because, unlike ADEM, Ohio

EPA followed all appropriate rulemaking procedures to specifically provide for even more

rigorous use of COMs on a prospective basis.

Because a COM compliance determination method is more stringent than Method 9,

establishing compliance under a COM system must include an adjustment factor such as those
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accepted by the National Parks and Sierra Club courts. If a 2 percent adjustment factor is

acceptable, the 1.1 percent adjustment factor found in the revised Ohio opacity rule must be also.

An adjustment factor is also necessary when substituting continuous for periodic opacity

monitoring methods given that opacity standards are inherently subject to statistical

measurement error and uncertainty, and an agency does not have the authority to find a violation

of a quantitative standard where the exceedences of the standard are within statistical

measurement error.

The possibility of statistical measurement error, which is often

unavoidable where regulations set quantitative standards, does not

detract from an agency’s power to set such standards. It merely

deprives the agency of the power to find a violation of the

standards, in enforcement proceedings, where the measured

departure from them is within the boundaries of probable

measurement error.

Amoco Oil Co. v. EPA, 501 F.2d 722, 743 (D.C. Cir. 1974)

U.S. EPA has acknowledged the measurement error in Method 9 itself. 40 CFR Part 60,

Appendix A, Method 9 (setting forth the results of field studies that establish positive error

statistics for black and white plumes.). The agency has also acknowledged the measurement

error of COM systems. See U.S. EPA Proposed Method 203: “Determination of the Opacity of

Emissions from Stationary Sources by Continuous Opacity Monitoring Systems” (describing

acceptable COM performance audits).

A very small adjustment factor such as the one adopted by Ohio is consistent with the

principle that that an agency can “overlook circumstances that in context may fairly be

considered de minimis. It is commonplace, of course, that the law does not concern itself with

trifling matters and this principle has often found application in the administrative context.”

Alabama Power Co. v. Costle, 636 F.2d 323, 360 (D.C. Cir. 1979). The opacity rule already
13

exempts opacity exceedences for start-ups, shutdowns, and malfunctions, and for some other

exceedences between 20 and 60 percent opacity. OAC 3745-17-07(A)(2) and (3). The 1.1

percent adjustment factor can rightly be considered in context to be within the discretion of Ohio

EPA to avoid regulation of de minimis circumstances, especially as it involves a more stringent

monitoring method with some degree of measurement uncertainty. For U.S. EPA to disapprove

such small adjustment factor in conjunction with a more stringent monitoring program defies

common sense and goes against the wishes of Congress that states’ environmental programs be

allowed to be flexible within the Clean Air Act’s cooperative federalism structure.

The COM Rule’s adjustment factor is also consistent with U.S. EPA’s exercise of

enforcement discretion not to bring an enforcement action for small opacity violations. U.S.

EPA Region V has had a long-standing enforcement policy not to bring a notice of violation

unless the percent of operating time with excess opacity exceeds five percent per calendar

quarter. See Directive No. AEB-600-4 (November 12, 1981) (copy attached as Attachment 3).

See also Ohio EPA Responsiveness Summary at p. 7 (U.S. EPA acknowledges that the COM

Rule allows such a small number of exceedences that the agency “would commonly apply

enforcement discretion and choose not to take action in such cases.”). As a practical matter,

neither U.S. EPA nor Ohio EPA has ever used opacity monitoring data in a manner that would

demand opacity readings of less than 20 percent for 100 percent of the time.

Ohio EPA expects its COM Rule to be “a clearly enforceable, technically-supported, 24-

hour per day compliance approach using a continuous monitoring system for a specific source

category.” Ohio EPA Responsiveness Summary at p. 10. Ohio is trying to improve its

monitoring program in precisely the way U.S. EPA wants states to do:

The EPA believes that it will be more effective, more equitable,

and more efficient to improve inadequate monitoring in applicable
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requirements, where necessary, through rulemakings to revise the

applicable requirements themselves or through other programmatic

approaches, rather than by addressing inadequate monitoring on a

case-by-case basis in the issuance and renewal of title V operating

permits.

Request for Comment on Potentially Inadequate Monitoring in Clean Air Act Applicable

Requirements and on Methods To Improve Such Monitoring, 70 Fed. Reg. 7905 (February 16,

2005). Ohio’s attempt to develop its opacity monitoring program through rulemaking should be

encouraged by U.S. EPA.

Finally, U.S. EPA claims that Method 9 might potentially detect opacity from a detached

plume of sulfate emissions that would not be detected by a COM method. As pointed out by

Ohio EPA, however, compliance with the mass particulate emissions limitation is determined

using reference methods that only count the “front half” of the sampling train and thus “it would

[not] be appropriate (or practically enforceable) to use Method 9 to evaluate a detached plume

when the procedure used to evaluate the particulate mass emissions does not count the same

sulfate emissions.” Ohio EPA Responsiveness Summary at p. 13. As we discussed earlier,

opacity is only an approximate surrogate for particulate emissions and an opacity exceedence

should not lead to a violation where the source is complying with the mass particulate emission

limitation. Further, Ohio EPA’s long-standing practice not to apply the opacity rule to detached

plumes, a practice supported by U.S. EPA’s own admonition not to read detached plumes that

contain water vapor, see 40 CFR part 60, Appendix A, Method 9, section 2.3.2, ensures that

opacity remains tied to the particulate emissions emitted from the stack and does not end up

measuring emissions that result from chemical reactions in the atmosphere.