September 10, 2013

The Honorable Gina McCarthy

Administrator, EPA

Office of the Administrator

U.S. Environmental Protection Agency

Room 3000

Ariel Rios Building

1200 Pennsylvania Ave., NW

Washington, DC 20460

Melanie King

Energy Strategies Group

Sector Policies and Programs Division (D243-01)

U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

Lorie Schmidt

Associate General Counsel, Air and Radiation Law Office

Office of General Counsel

Mail Code: 2344A

U.S. Environmental Protection Agency

1200 Pennsylvania Ave., NW

Washington, DC 20460

RE: Petition for Reconsideration – National Emission Standards for Hazardous Air 

Pollutants for Reciprocating Internal Combustion Engines; New Source Performance 

Standards for Stationary Internal Combustion Engines, 78 Fed. Reg. 6674 (Jan. 30, 2013)

Dear Administrator McCarthy,

ICAC petitions the Environmental Protection Agency (EPA) for reconsideration of its January 

30, 2013 final rule amending the National Emission Standards for Hazardous Air Pollutants 

(NESHAP) for Reciprocating Internal Combustion Engines (RICE).The Institute for Clean Air 

Companies (ICAC) submitted comments on August 9, 2012. As explained below, the purpose of 

this petition is to address issues of central relevance to the outcome of the final rule, and to 

strengthen monitoring provisions to allow direct measurement of the primary hazardous air 

pollutant (HAP) – formaldehyde – that is the central focus of the final rule.
2

I. Summary

This petition contends that incorrect claims and conclusions submitted to the EPA in a previously 

submitted Petition for Reconsideration dated, October 18, 2010, by Dresser-Waukesha, and 

incorporated by EPA in the final rule, resulted in a final rule that does not adequately or 

accurately measure HAP from Four Stroke Spark Ignition Lean Burn (4SLBSI) or Four Stroke 

Rich Burn Spark Ignition Engines (4SRBSI). The final RICE NESHAP rule, signed on January 

14, 2013, allows owners of 4-stroke rich burn spark ignition engines to use non-reference EPA 

methods and non-correlated surrogate compounds for HAPs to demonstrate compliance with 

HAP surrogate emissions levels of formaldehyde. These surrogate compounds and nonreference EPA methods do not properly measure HAP from either 4SLBSI or 4SRBSI engines. 

II. Petition Request

ICAC requests that the EPA reconsider the following:

1. The use of THC or CO surrogate for HAP/formaldehyde for both SI 4SLB and SI 4SRB 

engines because the Dresser-Waukesha petition requesting this option was based on 

incorrect assumptions of formaldehyde reference method cost and no supporting data in 

the docket.

2. The use of THC or CO surrogate for HAP/formaldehyde for both SI 4SLB and SI 4SRB 

engines because there is no correlation between formaldehyde and THC or CO from 

these engines, and EPA did not adequately address the comments submitted by ICAC. 

3. The exclusion of EPA Method 320 and ASTM D6348 from the recommended test 

methods for each engine type and class.

III. Background

On January 14, 2013, EPA signed final amendments to the 2010 RICE NESHAP that reflect new 

technical information submitted by stakeholders after the 2010 standards were issued. EPA 

considered a previously submitted Petition for Reconsideration dated, October 18, 2010 by the 

engine manufacturer Dresser-Waukesha for reconsideration of the formaldehyde testing 

requirements on 4 stroke rich burn spark ignition engines (4SRBSI). In the petition for 

reconsideration, Dresser-Waukesha argued that formaldehyde is difficult and costly to measure. 

The Dresser-Waukesha petition requested that the HAP surrogate for 4SRB engines should be 

THC or CO rather than formaldehyde. Dresser-Waukesha submitted data from testing that does 

not support that THC reduction across the catalyst is an appropriate surrogate for HAP reduction 

across the catalyst; nevertheless, the data was used as the justification to use other surrogates for 

formaldehyde, THC or CO, as a surrogate for HAPs. EPA granted the petition for

reconsideration on January 5, 2011. 
3

FTIR Test Costs Are Not Expensive

The contention in the Dresser-Waukesha petition was that the cost of testing for HAP with the 

EPA and industry accepted surrogate compound, formaldehyde, with the EPA reference method 

for formaldehyde, EPA TEST METHOD 320 (Measurement of Vapor Phase Organic and 

Inorganic Emissions by Extractive Fourier Transform Infrared (FTIR) Spectroscopy), or the 

accepted alternative method, ASTM D6348–12 (Standard Test Method for Determination of 

Gaseous Compounds by Extractive Direct Interface Fourier Transform Infrared (FTIR) 

Spectroscopy) was “too costly and complex,” and that alternative test methods exist that would 

“provide a less expensive and less complex, but equally effective, method for demonstrating 

compliance than testing for formaldehyde.”

The Dresser-Waukesha petition also contended that other gases are “easier to measure”, or 

“much less expensive to measure.” No data were cited, listed, tabulated, or brought forward to 

demonstrate that these “other gas” measurements or alternative test methods are less expensive 

or easier to perform. In fact, 25 companies (see Appendix A) are performing formaldehyde 

measurements daily with FTIR technology at near or below the cost of the unsupported surrogate 

test for carbon monoxide (CO) monitoring. Moreover, the third party compliance-testing price 

in some cases is significantly below the cost of the inlet and outlet CO testing that is required to 

show reduction efficiency. 

Many of the companies listed in Appendix A have confidentially agreed to submit their costs for 

a complete RICE-MACT compliance test for formaldehyde using one of the EPA reference 

methods for formaldehyde (the accepted HAP surrogate for 4SRB and 4SLB engines), including 

other HAP monitoring. In many cases, the cost range is only $1,400 to $3,500 (see Appendix B). 

The final rule also added an exemption from testing for engines that are outside an arbitrary 

quarter-mile distance due to the costs and difficulty of testing companies to make it to these 

“rural” locations. The emission-testing companies listed below offer the same prices for RICEMACT engine tests, no matter their location.

The Surrogacy Issue

Alternative testing that does not scientifically act as a surrogate for formaldehyde or HAPs is 

now going to be accepted as a surrogate for HAPs emissions. The EPA reference method for 

formaldehyde is self-validating, has a high degree of QA/QC performed, and is legally 

defensible in a court of law. The surrogate testing requested, THC or CO, in the DresserWaukesha petition does not correlate with formaldehyde surrogate HAP testing. The data 

submitted on surrogate compounds for formaldehyde were flawed in its statistics and 

conclusions. 
4

The ICAC submitted its specific comments to these issues on August 9, 2012. ICAC’s 

comments clearly pointed out the problems with the surrogate methods for measuring 

formaldehyde accurately, the lack of correlation in the data submitted in the Dresser-Waukesha 

petition, and championed the accuracy, excellent QA/QC requirements, and the lack of 

complexity in the EPA reference method for formaldehyde. Additional data from 53 field 

compliance source tests was submitted with the ICAC comments letter to refute the data and 

conclusions in the Dresser-Waukesha petition. EPA has received sufficient data to demonstrate 

that no correlation between formaldehyde and THC or CO exists. In Appendix C, data are again 

presented that demonstrate why CO should not be and is not a surrogate for HAP or 

formaldehyde for any type of RICE-MACT engine.

ICAC’s comments explained why there is limited to no correlation. Formaldehyde present in the 

emission exhaust from these engines is not generated during the primary combustion, but during 

the exhaust transport, i.e.; formaldehyde is not generated when CO is generated during the 

primary combustion. Therefore, there can be no correlation that is statistically based on CO. 

In a SI 4SLB engine exhaust, significant formaldehyde emissions are possible and probable even 

when there is little to no CO or VOC emission, because formaldehyde is generated by the partial 

oxidation of the CH4 slip through the exhaust train at temperatures between 750°F and 1,000°F. 

The main contributing factors to the formaldehyde emission are CH4 slip, O2 concentration, 

linear flow rates, exhaust temperatures, and catalyst age, and are not correlated to CO or VOC 

emissions. These findings are appended below, and can be duplicated in any catalyst-research 

laboratory throughout the country.

An additional assertion made in the Dresser-Waukesha petition was that CO is allowed for other 

engine types, specifically SI 4SLB engines, as a surrogate for HAP and/or formaldehyde based 

on a limited study performed at Colorado State University, so they should be allowed for SI 

4SRB as well. In that study, the correlations were questionable at best, and the testing was 

performed under very tightly controlled conditions, which clearly do not exist in the field during 

actual natural gas compression. ICAC’s comments presented real engine-exhaust test data 

(collected during compliance tests) on a cross section of RICE-MACT engines both SI 4SLB and 

SI 4SRB that demonstrated there is limited to no correlation between VOC:CO:formaldehyde for 

either engine type.

Portable Hand-Held CO Measurements Do Not Follow EPA Reference Test methods

The final rule also allows a hand-held portable electro-chemical cell device to be used to 

measure CO. This is not an EPA reference method, has minimal QA/QC due to numerous 

interferences, and may only be used for a period of 2 minutes of testing. If a portable is used, 

then the instrument must be an ETV certified instrument and all testing must meet USEPA’s 

CTM-034. It is well known by anyone who performs these tests routinely in the field, that these 
5

engines may vary in their CO emissions concentrations by thousands of parts per million by 

volume (ppmv) during an hour period and this assertion is supported by the data submitted in 

ICAC’s comments. 

Normal EPA reference test methods require a minimum of three, one-hour test periods as 

described in the EPA Test Methods 25A, 10, and 320, published in 40CFR Part 60. By allowing 

the substitution of EPA Reference Test Method 320 or ASTM Test Method D6348-12 for 

formaldehyde, to demonstrate compliance, with a surrogate test by EPA Test Method 10, 

instrumental method for CO, that is a surrogate for an EPA Test Method 25A instrumental THC 

test, with a non-reference test method using a hand held not validated, non-reference method for 

CO for a two minute period, there now exists an option for a “compliance test” that contains no 

scientifically proven representative test as measured by an EPA Reference Method to prove 

HAPs emissions from these affected engines covered in the final rule. This is an unprecedented 

move away from the EPA reference test methods to demonstrate compliance with a NESHAP 

emissions rule.

Finally, in the final rule, EPA has neglected their own reference method for monitoring gas 

emissions, specifically EPA Method 320 (and with extension ASTM D6348) by not explicitly 

stating them as valid methods for all RICE-MACT engine testing. These methods are fully selfvalidating methods that allow for the accurate measurement of many compounds simultaneously, 

including CO, CO2, NOx, N2O, NH3, H2O, formaldehyde, and VOC. They are also the only 

methods that provide an avenue for post-data validation that allow for confirmation of the test 

data. Many of the companies listed below not only perform the RICE-MACT compliance testing 

using this technology at costs less than the more traditional methods, they also have 3rd parties 

validate the data at no additional cost to the client or the regulatory agency.

 

IV. Specific Arguments

There were several inaccuracies in the Dresser-Waukesha petition, and in the EPA’s ultimate 

decision to accept them in the final rule. The following points show why CO should not be 

allowed as surrogate for HAP in any RICE-MACT engine, lean or rich burn.

1. There was no evidence presented by Dresser or any other organization in the docket that 

demonstrated formaldehyde was difficult to measure as a surrogate for HAP. There are 

numerous emission testing companies in the US, today, providing this service as a turnkey analytical service, with the capability of full data validation to pass the EPA 

Reference Method 320 or EPA accepted ASTM D6348-03 reference methods for 

formaldehyde (See Appendix A). Additionally, there is an EPA promulgated self-
6

validating method (U.S. EPA Method 320 and 318) and an ASTM method (ASTM 

D6348-03) for measuring formaldehyde and other HAPs. 

2. The Dresser-Waukesha petition argued that formaldehyde is costly to measure. There is 

no credible data to back up this claim. The emissions testing companies listed in 

Appendix B quote an average price of a RICE-MACT compliance test from ASTM 

Method D6348-03 measuring for CO / NOx / VOCs / H2O and Formaldehyde is in the 

$2,000 to $3,500 range and as low as $1,400. This price is far from an onerous burden on 

the oil and gas industry and nowhere near twice as much as mentioned in the DresserWaukesha petition. The statement was made that “the EPA estimates that replacing 

formaldehyde testing with THC testing would result in substantial compliance cost 

savings annually while achieving the same reduction in HAP emissions,” This comment 

by the EPA has painted the FTIR manufacturing and testing services industry with a wide 

brush and publicly labeled them as “too complex and costly” without having data of any 

kind to support that statement or conclusion.

3. The Dresser-Waukesha petition submitted data attempting to demonstrate that CO was an 

adequate surrogate for HAP and/or formaldehyde. In their own study, they had

demonstrated R2values of 0.5 to 0.65 for correlation between CO and formaldehyde for a 

single engine speed. An R2value of 0.50, simply stated, means that only 50% of variance 

of the formaldehyde measurement can be explained by the CO measurement. This does 

not mean that 50% of the time the measurement is correct rather that only 50% of the 

understanding of the emission has been described. In the social sciences that would 

indicate a level of correlation; however, in the physical sciences an R2less than 0.90 

suggests that a significant degree of variability exists between the known and the 

predicted, and an R2of 0.50, would suggest very little correlation. Furthermore an R2of 

0.50 with the condition that the engine is running at specific set points further reduces its 

predictive ability. For further explanation of this lack of correlation, see Appendices C &

D. 

4. Data submitted in the ICAC’s comments from actual SI 4SLB and 4SRB compliance test 

data showed that there was little to no correlation between the CO, VOCs and 

formaldehyde. It was also demonstrated that the formaldehyde emission from SI 4SLB 

engines is mostly due to CH4 partial oxidation in the exhaust system, not due to the 

primary combustion (See Appendix D). Similar results were also shown for SI 4SRB 

engines. Formaldehyde that is ultimately emitted from these sources is generated by a 

different mechanism than the CO and VOCs. The reason there is little to no correlation is 

because the formaldehyde concentration in both SI 4SLB and 4SRB is due to the 

oxidation of the CH4 slip (which can be significant, 1,000’s ppm), the O2 level, the flow 

rate through the catalyst or exhaust train and the temperature of that exhaust train and 
7

catalyst. The formaldehyde emission in a properly running exhaust system from a natural 

gas fired engine is not due to the primary combustion, or related to CO and VOCs. The 

catalyst data presented below clearly show that the formaldehyde from the engine exhaust 

is eliminated by the catalyst and then recreated as the temperature of the catalyst (and 

exhaust manifolds) rises towards the operating range. Thus, the conclusions drawn from 

the data in the Dresser-Waukesha petition are erroneous and not based upon proper 

scientific principles, and their acceptance should be questioned, especially considering 

that direct HAP measurements could be performed less expensively.

V. Conclusion

The data provided demonstrate that there is no correlation and why there is no correlation 

between VOC: CO: formaldehyde for either SI 4SLB or SI 4SRB engines for real world engineexhaust data. The industry provided no recent cost data demonstrating that HAP (formaldehyde) 

monitoring has any overly burdensome cost on the industry. In fact, with current RICE-MACT 

testing costs in the $1,400 to $3,500 range for these compliance tests anywhere in the contiguous 

US, there appears to be no reason to allow for surrogates to HAP/formaldehyde testing for either 

SI 4SLB or SI 4SRB engines. 

Finally, as provided in the appendices, there are many small businesses that have spent 

significant sums of money to buy state-of-the-art technology to be able to perform this testing. 

These companies will be harmed if this final rule is not reconsidered and modified. Lastly, there 

are a number of small businesses that create the catalysts for these engines that will also be 

negatively affected. These companies hire hundreds of workers throughout the US and pay local, 

state, and federal taxes, and develop innovative new technologies.

Thank you for your consideration of the above issues. If you have any questions, please do not 

hesitate to call me at (202) 367-1260.

Sincerely,

Betsy Natz,

ICAC Executive Director
8

Appendix A

RICE-MACT FTIR Emission and Energy Testing Groups

This appendix contains a list of source emission testing companies and energy companies that 

have spent significant resources preparing their companies to offer low cost high quality testing 

for RICE-MACT JJJJ and ZZZZ engine testing by FTIR EPA Method 320 or ASTM D6348 

Methods. Most have also received training by industry experts to assure the quality of the data 

collected. All of these source testing companies have already purchased the necessary equipment 

to measure CO/NOx/VOCs and HAPs cost effectively by FTIR from RICE-MACT engines.

As can be observed in this list there are companies throughout the US that are offering these 

testing services, so that the tests can be performed anywhere in the continental US with very low 

cost to the Natural Gas Industry. (See Appendix B for RICE-MACT test pricing by EPA 

Method 320 or ASTM D6348).

Company Location

Air Compliance Consultants 1050 William Pitt Way, Pittsburgh, PA 15238

Air Hygiene 1600 W. Tacoma Street, Broken Arrow, OK 74012

Additional offices in Shreveport, LA; Fort Worth, TX; 

Houston, TX; and mobile laboratories in Atlanta, GA; Las 

Vegas, NV; and Philadelphia, PA

B.enviroSAFE 601 Lonesome Prairie Trail, Haslet, TX 76052

Additional office in Tulsa, OK

CET 400 S. Bloomfield Blvd., Bloomfield, NM 87413

CST 10935 Argonite Dr. NW, Albuquerque, NM 87114

Envirotech Inc 5796 US Highway 64, Farmington, NM 87401

ESS Inc. 436 Raleigh Street, Wilmington, NC 28412

Liberty Testing LLC 113 CR 2213, Cleveland, TX 77327

EQT EQT Plaza, 625 Liberty Avenue, Suite 1700, Pittsburgh, 

PA 15222
9

Additional offices throughout Northeast and Mid-Atlantic

States

EMIT 772 Airfield Lane, Sheridan Wyoming 82801

Additional offices in Fort Worth, TX; Houston, TX; 

Farmington, NM; Oklahoma City, OK and Grand Junction, 

CO

Empire Stack Testing, LLC 5252 Ramsey Road Ashville, NY 14710

Enerven 15505 Wright Brothers Dr. Addison, TX 75001

Now (J-W Energy Company) Additional offices throughout US

EnRUD Resources, Inc 1006 Vista Road, Pasadena, TX 77504 

 

Entech Eng 4 South Fourth Street, P.O. Box 32, Reading, PA 19603-

Additional offices in Mountaintop, PA; Pottsville, PA; 

Lititz, PA

Exterran 16666 Northcase Dr., Houston, TX 77060

Additional offices all over the world

Golden Specialty 931 Seaco Ct, Deer Park, TX 77536

Graystone 1551 N. Hwy 69, Atoka, OK 74525

McClung 234 Johnny Clark Road, Longview, TX 756034-4319

MEI 2525 E. Interstate 20 Midland, TX 79701

Additional offices in Weatherford, TX

Nordon Corporation P.O. Box 1415, Round Rock, TX 78680

Oasis Emission Consultants, Inc 44 Fort Road, Sheridan, WY 82801

Additional offices in Rock Springs, WY and Gillette, WY

Pace Analytical Inc 1800 Elm Street SE, Minneapolis, MN 55414

Additional offices throughout US

STORM 4219 Rosewood Rd. Schnecksville, PA 18078 

TRC Environmental Corp. 9225 U.S. Highway 183 South, Austin, TX 78747

Additional offices throughout US
10

Windrock – 1832 Midpark Rd., Suite 102, Knoxville, TN 37921

Additional offices throughout Northeast and Mid-Atlantic 

States
11

Appendix B

RICE-MACT FTIR NO/CO, JJJJ, ZZZZ Test Costs

The Dresser-Waukesha petition suggested that HAP testing for RICE-MACT engines is a costly 

burden on the natural gas industry, yet it did not provide any costs to demonstrate this burden. 

Below are approximate 2012 price ranges from 12 companies, listed by their main testing 

headquarters state, for RICE-MACT engine testing for NO/CO, JJJJ and ZZZZ testing. These 

companies perform testing in the Northeast, Mid-Atlantic, Southeast, Midwest, Mountain, 

Southwest, and West regions. As seen in the table below, the cost for a single full NO/CO, JJJJ, 

ZZZZ compliance test is in-line if not lower than traditional CO testing. Pricing could be even 

lower given more competition and a larger engine base to test. If inlet/outlet CO testing is used 

to demonstrate compliance, that testing can be more expensive than performing EPA Method 

320 or ASTM D6348 where CO/NOx/VOCs and HAP (formaldehyde) directly. Many of these 

companies listed have traditional portable testing capability, and most if all will agree that FTIR 

testing (through the above methods) is easier and provides greater confidence in the final data. 

By using newer technology with EPA Method 320 or ASTM D6348, better data are collected 

that can be validated, at lower or equivalent costs and allows for the direct reading of HAPs such 

as formaldehyde. 

The EPA also added a rural rule based on economic and logistical reasons for not testing a 

certain set of engines. In the emission testers list below, all of these companies have built or 

purchased fully self-contained measurement systems that can be mobilized to nearly any location 

without need for local power or assistance. Also, in most cases the price to perform the RICEMACT test by EPA Method 320 or ASTM D6348 is the same no matter the location of the 

engine. 

Please note that the price ranges in the table below are not all base prices. Some include travel 

and some do not; some companies vary their prices based on the number of engines tested and 

allow discounts for multiple engines; higher prices may reflect special testing circumstances, 

such as inlet/outlet testing.

Main Location NO/CO JJJJ ZZZZ

Oklahoma $1,500 - $2,500 $1,850- $3,500 $1,850 - $5,000

Pennsylvania $2,000 - $7,500 $2,000 - $7,500 $2,000 - $7,500

Texas $1,400 - $3,150 $1,400 - $4,500 $1,400 - $5,900

Wyoming $1,800- $4,800 $2,500 - $4,800 $2,500 - $4,800
12

Appendix C

No Correlation between CO/VOCs and HAP for SI-4SLB or SI-4SRB RICE

In ICAC’s comments, data were submitted demonstrating why CO should not be allowed as a 

surrogate for HAP in either a SI-4SLB or a SI-4SRB engine no matter the engine horsepower. 

The data also demonstrated how the CO, VOCs, and formaldehyde vary in real life engines 

during actual compliance tests. The following data are being resubmitted and are a subset of 

data collected over the last year from a number of testing firms.

Fifty-six lean burn compliance data sets were performed following ASTM D6348. Each test had 

CO, VOC, and formaldehyde data collected and were from 5 emission testing firms. These data 

are tabulated below for each of the 3-one hour tests. As can be observed from these data, the CO 

can be 10 times or more than the formaldehyde level and at other measurements 3 times less or 

lower. From these 56 randomly selected tests on engines that were prepped for the impending 

compliance test, there appears to be no correlation between CO and formaldehyde.

It also has been suggested that VOCs could be used a surrogate for HAP as well. Again from the 

data below, the formaldehyde is shown to be anywhere from 3 times lower to 8 times higher than 

the respective VOC. 

Hundreds of other data sets demonstrate the same conclusion that there is little to no correlation 

between formaldehyde and CO or formaldehyde and VOC within a standard compliance test on a 

SI- 4 stroke lean burn engine. Also, all of these data were collected using a single FTIR gas 

analyzer so there were no additional costs to collect the formaldehyde information as is 

suggested by the industry. Since there is limited correlation and limited to no additional costs for 

measuring formaldehyde, the question arises as to why would one want to depend on a surrogate 

when the information is available with current EPA recognized technology following recognized 

protocol.

In the data provided, if CO were used as a surrogate, there are potentially times when the 

formaldehyde would be grossly overestimated causing an apparent failure of the compliance test. 

This scenario is certainly every bit as possible as the converse where the CO is low and the 

formaldehyde is high as the data below clearly demonstrate.
13

Compliance 

Test Run 1 Run 2 Run 3 Run 1 Run 2 Run 3 Run 1 Run 2 Run 3

1 25.2 25.3 25.5 26.8 26.7 26.8 6.9 6.9 6.9

2 3.4 3.5 3.5 9.2 9.3 9.3 < 2 < 2 < 2

3 25.8 26.1 26.6 14.3 14.3 15.1 5.4 5.4 5.6

4 15.3 15.5 15.6 6.2 6.2 6.2 2.5 2.5 2.6

5 25.0 25.0 25.0 20.2 21.0 21.5 8.0 8.0 8.0

6 18.3 18.4 18.4 21.9 22.0 21.9 7.3 7.3 7.1

7 22.8 22.9 23.0 26.0 26.4 26.3 5.7 5.7 5.6

8 22.0 21.6 21.7 19.2 19.2 19.2 6.5 6.5 6.5

9 8.7 10.9 11.5 25.0 29.2 31.6 22.0 33.3 34.0

10 19.9 17.5 18.9 99.4 91.9 101.0 34.4 30.0 35.2

11 0.7 0.6 0.6 0.2 0.2 0.2 2.4 4.7 6.5

12 1.5 1.5 1.4 1.7 1.6 2.1 7.7 5.7 4.4

13 0.0 0.0 0.0 -0.4 -0.5 -0.4 2.4 2.0 2.0

14 2.7 2.8 3.0 0.6 0.6 0.8 3.1 3.3 3.0

15 -0.1 -0.2 -0.3 67.3 64.1 39.8 2.4 2.1 2.1

16 4.7 4.5 4.5 11.6 11.2 11.3 2.1 2.2 1.8

17 5.8 5.7 5.5 5.1 4.8 4.5 7.1 4.9 4.1

18 6.2 6.6 6.8 12.4 13.3 13.3 16.2 14.1 13.5

19 7.7 7.7 6.9 12.2 12.0 10.6 19.1 17.7 16.3

20 10.5 11.8 12.9 24.1 24.2 24.5 15.8 15.4 16.1

21 10.5 11.7 11.9 27.4 26.1 25.8 14.3 16.1 16.1

22 10.1 12.6 12.6 11.2 12.0 11.9 12.0 13.8 13.2

23 13.1 14.9 16.8 10.7 10.5 10.7 21.4 20.3 22.0

24 10.4 11.0 11.2 12.1 10.9 9.7 30.9 30.7 29.0

25 11.9 11.6 12.5 22.0 20.6 21.5 14.7 17.1 14.7

26 11.2 10.7 11.9 24.5 22.5 23.1 32.1 31.5 33.9

27 25.9 26.7 27.3 50.2 50.5 51.3 39.0 39.2 39.2

28 11.3 11.4 11.2 2.8 2.8 3.0 44.6 43.8 45.4

29 21.2 21.1 20.4 43.0 40.1 38.6 45.8 45.7 42.9

30 9.4 11.2 12.3 19.0 20.0 20.5 24.6 26.7 28.7

31 4.7 7.8 10.5 6.4 6.4 6.5 43.6 42.3 42.9

32 12.3 12.9 13.1 13.2 13.2 13.1 5.0 5.0 9.8

33 22.1 22.1 24.6 43.6 43.0 42.9 40.6 40.2 40.0

34 18.6 18.6 18.7 15.6 15.5 15.4 6.5 6.8 6.9

35 21.5 24.0 25.7 23.7 23.5 23.5 9.3 9.5 9.7

36 24.8 27.9 29.6 41.5 42.2 42.2 13.7 13.7 13.8

37 21.9 22.6 25.1 32.1 33.8 33.6 6.0 6.1 6.3

38 30.0 33.7 35.6 41.8 42.5 42.7 14.1 14.1 14.1

39 18.1 17.9 18.1 33.5 33.3 33.2 7.7 7.4 7.2

40 22.4 29.6 31.5 11.5 11.5 11.5 6.9 6.7 6.7

41 34.8 38.1 42.1 50.8 51.5 52.5 6.7 6.4 6.3

42 62.5 62.2 62.6 396.9 397.9 398.0 21.6 21.7 22.4

43 8.5 8.4 9.3 4.3 3.7 3.8 7.3 7.2 8.1

44 14.5 14.6 14.3 5.5 5.5 5.4 6.5 6.4 6.6

45 22.1 22.9 22.2 41.8 40.0 38.6 10.1 9.9 9.4

46 26.8 26.8 26.7 54.2 54.9 56.6 10.2 9.5 9.1

47 26.7 26.5 26.4 30.3 30.5 30.2 12.7 14.2 14.1

48 52.7 52.1 51.9 415.6 415.8 416.2 66.4 66.8 66.9

49 6.3 6.2 6.2 4.2 4.1 4.1 4.2 4.0 4.2

50 13.4 13.6 13.5 9.6 8.6 9.0 15.8 17.3 23.5

51 2.5 2.5 2.6 0.7 0.6 0.7 15.6 15.8 18.2

52 -0.1 -0.2 -0.2 100.0 191.2 237.5 4.2 10.5 11.9

53 13.1 13.5 13.6 3.0 3.0 3.0 9.2 9.7 9.0

54 21.0 20.7 20.8 7.9 7.6 7.6 11.6 11.8 11.0

55 43.6 44.3 45.5 335.3 337.1 336.6 10.2 10.1 10.2

56 52.8 55.5 55.4 461.9 463.9 466.5 35.3 36.8 37.8

Formaldehyde

(ppm) dry

CO

(ppm) dry

VOCs as Propane

(ppm) dry

2012 Lean Burn Compliance Test Data

***Data reviewed from 5 separate emission testing firms***
14

Rich burn engines, when running correctly, produce less formaldehyde than their lean burn 

counterparts on average. However, if the purpose is to use CO or VOCs as a surrogate for 

formaldehyde, it must be demonstrated that a correlation exists. In the table below are 30 

compliance tests on rich burn engines where the formaldehyde was below detection.

In these tests, the CO 1 hour average varied from 16 ppm up to almost 700 ppm, yet no 

formaldehyde was detected. Also, there were significant variations in the CO concentration 

between the test runs that demonstrates the need for longer testing times. Since these compliance 

tests were not reporting VOCs they were not calculated and to do so would have required 

significant effort and time that was not available. These data could be provided if required by 

the EPA to demonstrate the lack of correlation between VOC and formaldehyde.

Instead, since methane (CH4) had been measured, its concentration was utilized as a predictor of 

the potential VOC. Certainly as stated above, there may or may not be a great correlation 

between methane and VOC but it just demonstrates that with almost a 10 fold change in average 

methane levels (~260 ppm to ~2600 ppm), no formaldehyde was observed.

That leads to the question of why the formaldehyde does not correlate to other combustion 

byproducts like CO and VOCs during real compliance tests of a natural gas fired SI-4SLB and 

SI-4SRB reciprocating internal combustion engines. The data presented in Appendix D explain 

why there is no correlation between CO/VOCs and formaldehyde for these natural gas fired 

engines.
15

Engine

Average CO

3 Runs

(ppm)

Std Dev. CO

3 Runs

(ppm)

Average

Formaldehyde

3 Run

(ppm)

Average

H2O

(%)

CH4

(ppm)

1 211.0 32.5 < 0.3 19.2 466.3

2 225.7 10.1 < 0.3 19.3 556.6

3 17.7 0.5 < 0.3 20.0 731.2

4 302.2 9.9 < 0.3 18.9 371.5

5 275.3 89.1 < 0.3 18.1 437.0

6 50.3 14.7 < 0.3 18.7 1037.0

7 44.3 0.1 < 0.3 18.6 270.0

8 501.4 124.4 < 0.3 20.0 666.2

9 639.0 43.0 < 0.3 18.6 347.6

10 360.9 180.1 < 0.3 19.5 365.2

11 16.6 0.4 < 0.3 18.3 306.6

12 129.7 13.3 < 0.3 17.9 437.1

13 608.0 228.5 < 0.3 18.1 329.4

14 651.1 361.6 < 0.3 19.2 1087.0

15 22.6 0.7 < 0.3 19.2 782.2

16 36.2 3.6 < 0.3 18.4 906.6

17 137.4 19.6 < 0.3 18.8 264.2

18 27.7 2.0 < 0.3 19.7 323.0

19 199.9 230.8 < 0.3 20.1 436.7

20 342.7 14.4 < 0.3 20.5 1691.0

21 283.7 87.6 < 0.3 20.2 1948.0

22 124.0 32.6 < 0.3 20.1 817.6

23 47.1 1.6 < 0.3 19.3 660.9

24 109.6 13.9 < 0.3 20.4 1195.0

25 622.8 68.1 < 0.3 20.0 2574.0

26 584.8 2.1 < 0.3 20.6 351.6

27 352.1 2.0 < 0.3 20.2 397.2

28 46.6 2.7 < 0.3 18.0 859.6

29 128.3 38.2 < 0.3 19.5 1197.0

30 672.9 201.8 < 0.3 18.8 297.3

Minimum 16.6 0.1 < 0.3 17.9 264.2

Maximum 672.9 361.6 < 0.3 20.6 2574.0

Median 205.4 14.5 < 0.3 19.2 511.4

Std Dev. 225.1 91.0 - 0.8 546.8

Recent Data from Cross Section of Rich Burn Engines

with No Formaldehyde detected
16

Appendix D

Why there is no correlation between CO/VOCs and Formaldehyde

Why is the formaldehyde concentration not correlated to CO and VOCs in either lean or rich 

burn engines? It is most likely due to the formaldehyde being formed by a different chemical 

pathway. What different pathways are present? One in particular is the catalyst chemistry itself. 

When the gases interact at the catalytic surface, CO, formaldehyde and VOCs react differently 

and the resultant mixture can and does change.

To determine if this was possible, both lean burn and rich burn catalyst cores were obtained and 

simulated combustion mixtures were passed through them at varying temperatures and flow 

rates. Gas mixture measurements were performed just prior to the catalyst and just after the 

catalyst. The percentage of formaldehyde remaining was calculated for different catalyst 

temperatures and flows (GHSV – Gas Hourly Space Velocities).

In the lean burn experiment tabulated below the formaldehyde dropped to a few percent of its 

original concentration very quickly at low temperatures and at all flow rates. However, as the 

catalyst temperature was raised to near the normal operating temperatures the formaldehyde 

returned at levels exceeding 60% of the original concentration. What happened in these 

experiments? Does formaldehyde not react at these higher temperatures and flows? 

To try to understand what was happening, the experiment was repeated with no formaldehyde in 

the simulated engine exhaust mixture heading to the catalyst. When that was done, almost 

identical levels of formaldehyde were observed at the post catalyst measurement point. So the 

conclusion drawn initially was the following: formaldehyde appears to be forming on the catalyst 

GHSV T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17

Flow 19 7.9 4.9 4.6 2.3 4.0 0.9 1734.7 3.0 14.6 49.6 67.0 44.1 26.5 2.4 -0.1 0.1 0.3

Flow 18 7.3 7.2 4.3 2.5 2.7 0.8 1.1 2.8 12.9 47.9 67.2 40.0 25.4 2.2 0.0 0.2 0.0

Flow 17 7.2 5.8 4.0 2.9 3.7 0.4 0.8 2.6 13.7 47.9 62.4 38.5 23.8 2.0 -0.4 -0.6 0.0

Flow 16 7.5 4.8 4.4 3.1 3.2 0.6 1.0 2.6 13.7 51.5 57.4 34.4 17.3 1.3 -0.1 -0.3 -0.2

Flow 15 6.6 4.1 4.1 3.1 3.2 0.7 0.9 3.0 13.5 46.8 55.2 29.9 14.6 0.7 -0.6 -0.1 0.2

Flow 14 6.2 4.8 4.8 3.9 3.4 0.9 0.8 2.8 13.4 47.1 51.4 27.0 12.5 0.6 -0.2 -0.3 0.1

Flow 13 5.3 4.2 3.8 3.6 2.1 0.5 1.2 2.9 14.3 42.1 44.7 21.5 9.6 0.6 0.3 -0.4 0.0

Flow 12 4.6 3.6 4.0 4.0 3.5 0.7 1.6 2.3 12.4 41.9 39.8 21.8 8.1 0.6 0.0 -0.5 -0.1

Flow 11 5.5 3.1 3.4 3.8 3.1 0.7 0.8 2.2 12.6 43.5 39.4 18.0 6.5 0.3 -0.6 -0.5 0.2

Flow 10 4.5 1.1 3.3 2.6 1.9 0.5 1.3 2.6 10.7 36.6 33.2 14.3 4.1 0.1 -0.5 -0.4 -0.1

Flow 9 4.4 3.1 3.4 3.9 2.7 0.5 0.6 1.7 9.4 28.5 31.2 12.0 3.3 0.0 0.2 -0.2 -0.2

Flow 8 3.7 2.5 3.1 3.1 3.0 0.6 1.1 2.1 9.2 29.3 21.7 10.8 1.4 0.2 -0.1 -0.1 -0.3

Flow 7 3.6 2.5 1.7 3.8 1.7 0.7 1.1 1.9 7.7 25.3 18.1 7.7 1.0 -0.1 -0.3 0.1 -0.3

Flow 6 3.0 2.6 2.2 2.6 2.5 0.1 0.5 1.6 6.2 20.5 15.7 5.7 0.4 -0.2 -0.1 -0.4 0.0

Flow 5 2.6 3.4 2.3 2.6 2.9 0.3 0.7 1.4 4.7 16.2 12.2 3.2 0.1 -0.3 -0.2 0.0 0.0

Flow 4 3.6 2.1 2.2 2.2 2.3 0.1 0.0 1.3 3.5 8.1 6.1 1.1 0.1 -0.4 0.0 -0.2 0.0

Flow 3 2.2 2.3 2.8 2.5 2.6 0.1 0.1 0.6 1.5 4.0 3.7 1.1 -0.1 -0.4 0.1 -0.1 -0.4

Flow 2 2.7 2.1 3.4 2.8 3.3 0.3 0.0 0.9 0.8 2.3 1.9 0.3 0.0 0.1 -0.2 -0.2 -0.2

Flow 1 3.3 3.3 2.9 3.1 2.6 0.0 0.5 0.7 0.5 1.0 0.7 0.5 -0.1 0.1 0.1 -0.2 -0.1 Increasing Flow --------------->

% Formaldehyde Emission from Lean Burn Catalyst

Increasing Catalyst Temperature ------------------>
17

or the reactor walls due to the partial oxidation of methane (100s to 1000s of ppm are present in 

the lean burn exhaust). The formaldehyde emission from a lean burn engine would not be 

expected to correlate to the combustion gases but be correlated to the methane exhaust 

concentration, the oxygen concentration, the catalyst (or exhaust) temperature, the age of the 

catalyst and the gas flow rate through the catalyst. Therefore, the use of combustion gases as 

surrogates or predictors of the HAP or formaldehyde is flawed since they are not generated 

during the same reaction chemistry.

Two additional experiments were also performed to further understand what might be happening 

to generate the observed formaldehyde. First, a more limited test was performed with and 

without CO to make sure that the post catalyst formaldehyde was not somehow related to the CO 

concentration. With or without CO in the simulated exhaust had no effect on the formaldehyde 

formation and similar post catalyst formaldehyde concentrations were observed in both. In the 

second test the lean burn catalyst was replaced with a blank core to determine if it is potentially a 

hot metal surface affect and not the catalyst. When this experiment was performed, up to a 

200% formaldehyde post response was observed. This suggests that the hot metal in the exhaust 

may be playing a significant role in the formation of formaldehyde and that the catalyst role 

might be minimal. It would also further suggest as a catalyst ages its ability to oxidize this 

generated formaldehyde would be reduced and the emission level would further increase. 

Additional research needs to be performed to understand the contribution of both to the final 

exhaust. However, it is clear that formaldehyde seen at the higher catalyst temperatures and seen 

during many SI-4SLB engine compliance tests is most likely due to CH4 partial oxidation in the 

exhaust and not due to the original engine combustion.

A similar experiment was constructed for rich burn catalysts. In this experiment it was noted 

that formaldehyde was reduced effectively at most temperatures and flows. But formaldehyde 

was still observed near the midpoint of the temperature range at the lower flow rates. Once again 

there are conditions that can be present in the exhaust stream that would be conducive to 

formaldehyde formation at the catalyst or within the exhaust housing. Again it would not be 

prudent to base the formaldehyde concentration or other HAP concentration on a surrogate, when 

so many unmeasured variables determine the exhaust HAP concentration (CH4 slip, O2

concentration, linear flow rate, exhaust temperature, and catalyst age); especially when 

HAP/formaldehyde can be measured directly at no additional cost.
18 GHSV T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17

Flow 19 8.8 4.8 4.0 5.5 2.0 21.7 20.2 4.6 2.6 25.6 2.7 3.6 1.6 0.0 -0.1 -0.7 -0.1

Flow 18 7.2 4.8 2.7 3.3 2.1 17.4 13.7 4.5 2.4 13.4 2.0 12.2 1.0 -0.1 -0.4 -0.1 -0.2

Flow 17 7.5 6.5 4.2 3.8 1.4 8.8 9.5 7.1 2.2 10.0 25.9 1.5 1.2 -0.5 -0.6 0.3 2.3

Flow 16 6.8 6.6 3.5 5.6 8.1 8.3 9.5 2.7 2.0 1.7 7.9 1.8 1.0 -0.5 -0.3 0.3 1.3

Flow 15 5.9 3.8 5.0 3.2 10.4 11.0 4.5 2.3 1.4 14.4 1.2 1.3 36.8 -0.1 -0.1 2.7 1.5

Flow 14 4.8 19.1 4.7 3.1 9.7 11.4 2.5 1.1 1.4 3.4 2.2 1.0 1.2 -0.2 -0.7 27.9 1.3

Flow 13 4.4 28.8 4.6 2.8 9.5 8.8 2.0 3.7 4.1 14.3 1.9 1.3 0.9 -0.3 0.0 2.3 1.5

Flow 12 3.8 4.0 3.4 3.5 10.4 11.6 10.0 3.1 16.2 1.2 1.6 1.1 0.8 0.0 -0.5 1.8 2.4

Flow 11 3.3 2.7 6.4 3.5 9.8 12.2 11.4 6.4 0.8 20.7 1.5 1.0 0.5 -0.2 -0.3 0.8 0.5

Flow 10 3.0 1.8 4.4 3.3 16.3 5.8 9.2 7.1 0.3 0.7 1.4 1.9 0.7 -0.4 -0.5 1.1 0.5

Flow 9 2.5 3.1 4.6 4.2 8.2 7.7 9.4 7.2 1.1 0.6 1.5 1.7 0.5 -0.5 -0.6 0.4 0.9

Flow 8 2.5 1.5 4.4 4.2 9.2 9.8 8.4 8.8 10.8 0.9 1.3 2.0 0.4 -0.3 -0.6 -0.1 0.8

Flow 7 1.8 1.5 4.5 2.9 7.5 10.9 8.4 2.9 13.5 0.6 1.1 2.1 0.2 -0.3 -0.5 -0.3 1.7

Flow 6 1.2 4.4 3.7 1.2 8.8 10.7 10.7 12.6 1.0 1.2 1.1 1.5 0.5 -0.4 -0.1 -0.2 1.1

Flow 5 1.1 0.9 2.9 1.1 11.3 9.5 19.1 13.1 20.3 1.3 2.3 2.6 0.4 -0.2 -0.8 0.0 1.0

Flow 4 1.0 0.9 4.1 1.1 14.9 15.4 13.9 9.7 5.3 1.9 2.5 2.4 0.5 -0.4 -0.8 0.4 1.1

Flow 3 0.6 7.2 2.7 0.9 14.7 9.1 30.8 43.2 15.4 2.4 2.4 1.7 0.4 -0.2 -0.1 0.6 5.5

Flow 2 1.6 0.5 2.2 2.0 20.2 22.8 33.4 14.1 24.0 3.7 2.5 41.7 0.7 -0.2 -0.2 0.6 3.7

Flow 1 4.8 9.5 5.6 3.1 25.2 18.4 29.2 21.9 7.1 45.8 2.2 52.1 0.9 -0.2 0.7 1.3 0.5

Increasing Catalyst Temperature ------------------> Increasing Flow --------------->

% Formaldehyde Emission from Rich Burn Catalyst
19

Appendix E

Example of Rich Burn Engine Variability

An engine emission data set from just prior to and then during a rich burn compliance test are 

displayed below. As is observed, just prior to the rich burn test the CO, VOCs, NH3 and NOx 

are all very high and yet no formaldehyde is observed. So, once again CO and VOCs would not 

be a good predictor of the formaldehyde concentration for this rich burn engine at any setting.

These high CO and NOx emission levels suggest that the engine requires tuning to pass a 

compliance test. Subsequent to that engine tuning, the 3-one hour compliance test proceeds. 

During this compliance test, significant variations in all but the formaldehyde concentrations are 

still observed. This exhaust variability and initial tuning demonstrates that these rich burn 

engines if not monitored or tested annually could allow for significant emission amounts of CO 

and NOx. It also demonstrates why 15 minute tests are not adequate to provide an accurate 

picture of the true exhaust.

Allowing engines to operate untested or tested for very short periods would nearly guarantee that 

they would all be running similar to the section in yellow below. As these gases move from 

“rural” to populated areas of the country, the air quality would be further negatively affected and 

could potentially cause non-attainment to occur more frequently as more and more engines are 

added to the pipeline.

At a minimum the EPA should at least review the current operating status of some of these 

“rural” engines or discuss procedures with emissions testing companies before making sweeping 

decisions with little to no factual information.

This source test data from a Rich Burn Engine clearly demonstrates that there is no correlation to 

THC, CO, and formaldehyde and that CO concentration clearly vary by very large concentration 

changes over any 1 hour period.

Measurement 

Point

Formaldehyde

(ppm) dry

CO

(ppm) dry

VOCs

as Propane

(ppm) dry

NH3

(ppm) dry

NOx

(ppm) dry

Prior to Test > 0.3 9,129.58 93.90 1,459.12 689.79

Run 1 > 0.3 1,000.80 42.18 521.85 139.67

Run 2 > 0.3 570.14 33.37 335.92 78.67

Run 3 > 0.3 637.45 31.89 398.77 73.47

Rich Burn Compliance Test