Dr. Chris Laroo

Environmental Scientist

US Environmental Protection Agency

Office of Transportation and Air Quality

Assessment and Standards Division

2000 Traverwood Dr.

Ann Arbor, MI 48105

Subject: Transient Partial Flow PM Measurement Peer Review

Dear Dr. Laroo:

I have reviewed those parts of the EPA FRM (U.S. EPA, 2009) that relate to the use of 

partial flow sampling systems (PFSS) for transient PM measurements. These are sections 40 

CFR Part 1065,140(e), 1065.170(c)(1)(vi), and 1065.545. With regard to the review I find the 

following:

1) Clarity/Understandability – The sections referenced are clear and understandable.

2) Reasonableness of methodology and assumptions - The methodology associated with use of 

the partial flow sampling system is reasonable and given the reference material provided the 

assumptions on which parameters used in these sections are selected is also reasonable.

3) Appropriateness of data – The data used in locking down the parameters used in these 

sections is very appropriate. However, I have some comment on the thoroughness of one of 

the references used. See the attached review.

4) Recommendations for any alternate methodologies and/or data – I have made some 

recommendations and comments on the sections reviewed. These are included in the 

attached review.

Sincerely,

Dr. Bruce Cantrell

BKC Consulting

2504 Lake Crossing Dr.

Greenwood, IN 46143-8598

Phone: (317) 889-6402

e-mail: BKC Consulting@comcast.net

Enclosure
Review of 

Use of partial flow systems for transient PM measurement

By

Bruce Cantrell, BKC Consulting

September 7, 2007

Summary Comments

This is a review of those parts of the EPA FRM (U.S. EPA, 2009) that relate to the use of partial 

flow sampling systems (PFSS) for transient PM measurements. These are sections 40 CFR Part 

1065,140(e), 1065.170(c)(1)(vi), and 1065.545. In locking down the parameters used in these 

sections, the EPA has relied on two published studies; (CRC, 2007) and (Sierra Instruments, 

(2006). Review of the FRM requires comment on each of these studies.

The Sierra Instruments study cited is rather shallow and reads more like an Executive Summary 

than report of a study. The correlation testing results are skimmed over and the correlations are 

not cited. Rather two comparison plots are offered. No Regressions are offered and the statistics 

are simply stated rather than backed up with data. The variance in results of engines running 

with CCRT devices are attributed to problems in filter gravimetrics that are simply alluded to, 

and the impact on the paired–t and F- tests is not discussed. Rather, the claim is repeated that the 

results conform to Part 1065 without substantiation. This leaves the reader in the position of 

taking their word for the results stated and that is not acceptable.

The CRC report (CRC, 2007) describing a more complete study of several commercially 

available PFSS reports the characteristics of each system under a variety of conditions. Sample 

flow correlations with a full flow CVS are presented and standard error is calculated for each 

correlation. Most of these correlations yielded r2 values greater than 99 percent and standard 

error less than 5%. In addition, measured PM concentrations are compared with those obtained 

using the CVS for a range of emission concentrations from <10 to 85% of the 2007standard. 

This permitted exploration of particle and filter artifact formation under condition similar to 

those pertaining when a diesel particulate filter (DPF) is in use. The effect of sample residence 

time was also studied. As with the Sierra report (Sierra, 2006) gravimetric analysis of collected 

samples shows high variability when a DPF is used and PM concentrations are very low, less 

than 10% of the 2007 standard. This is explored in terms of particle and filter artifact using 

OC/EC analysis.

Specific Comments

40 CFR Part 1065,140(e) – This section is a fairly faithful adaptation of the results reported in 

the CRC report and, taken at face value, the Sierra report. It mixes the traditional dilution 

procedures with those necessary to accomplish partial flow dilution using the available 

commercial partial flow sampling systems. Aside from temperature control of the dilution 

process the most critical parameter here is residence time of the sample before it reaches the 
sample collection device, be it a filter or real-time monitor. This needs to be as short as possible. 

Subsection (3) states that the PFSS residence time should be at least 0.5s. I would change this to 

read the PFSS residence time should be at most 0.5s. Also, the assumed flow temperature should 

be 47±5oC in keeping with the temperature requirement of the collection media. Sample 

temperature should be measured at the collection media as part of the temperature control 

process.

1065.170(c)(1)(vi) – Filter media is critical for collection of representative PM. All collection

media will collect hydrocarbon artifact, including PTFE. Using support bonded to the back of a 

PTFE filter will enhance this because of the increase in available surface area. When using filter 

media other than pure PTFE, which will collect a minimum amount of artifact, this must be taken 

into account. For example, PTFE-coated glass fiber filter will collect a substantial amount of 

artifact and should be used with a back-up filter which can be used to correct for artifact build-up 

on the filter. Corrections on the order of 50 to 80% in this case are not acceptable. This problem 

is significant when a DPF is used and emission concentration is less than 10% of the 2007

standard; quite often, concentration measurements using filter collection are indistinguishable 

from that obtained as a tunnel blank (CDC,2007).

Should the subtended angle in the filter holder transition from inlet to the filter be 14o rather than 

12.5o ? This is the angle for minimum loss that has been a rule of thumb reported for turbulent 

deposition in studies of expansion sections of PM transport lines. Another study (Sparrow,

2009) finds that10o is the angle where flow separation stops. The authors should make a final 

determination of this before the rule is published.

1065.545 – Several commercially available PFSS units can meet the prescribed requirements 

(CRC, 2007and Sierra, 2006). They exhibit both linearity, as evidenced by correlation with total

sample flow, and response times that permit mean sample flow rates to be accurately determined 

during each component of a transient test cycle. In addition to the specifications listed, I would 

add the certification of the flow meters using a NIST traceable transfer standard.

References:

Coordinating Research Council, (2007). 2007 DIESEL PARTICULATE MEASUREMENT 

RESEARCH, Report NO. E-66-3, Alpharetta, GA, 49 pp.

Sierra Instruments, Inc. (2006). Sierra Instruments Model BG-3 vs. CVS Multiple Engine 

Correlation Study, Monterey, CA, 7 pp.

Sparrow, E.M., Abraham, J.P.,Minkowskycz, W.J. (2009). Flow separarion in a diverging 

conical duct: Effect of Reynolds number and divergence angle. International journal of Heat 

and Mass Transfer, vol. 52 (2009), pp. 3079-3083.

U.S. EPA, (2009). 40 CFR, Part1065 FINAL with Changes from C3 Marine – FRM. Office of 

Transportation and Air Quality, Assessment and Standards Division, Ann Arbor, MI , 238 pp.