1

Review of Draft EPA Test Methods 201A and 202 related to 

the Use of High Temperature and Out-of-Stack Collection 

Methods 

Introduction 

Southern Research Institute (SRI or Southern) was tasked by Eastern Research Group, under 

contract to EPA (Work Assignment No. 3-05, Contract No. EP-D-07-064) to review and provide 

advice on two issues related to proposed revisions to Method 201A. The first deals with the 

reduction or elimination of cyclone thread galling resulting from exposure of PM10 and PM2.5 

cyclones to high temperature sources. The second deals with the possibility of locating the 

cyclone(s) outside the duct to be sampled and using heated probes to convey the sample stream 

to the sizing device(s) which would be maintained at a suitable temperature. 

Reduction or Elimination of Cyclone Thread Galling 

Stainless steel should be OK for temperatures to 1,200 °F. If such cyclones are to used, one (or 

both) of each of each mating thread surfaces should have a hard chrome plating applied and a 

high-temperature anti-seize compound should be used. For higher temperature applications 

Southern has constructed samplers of both Hastelloy, and Haynes 230 alloys. A Haynes 230 

alloy sampler has been used successfully at temperatures as high as 1,840 °F and the 

specifications of the alloy suggest that it should be good to about 2,500 °F. These samplers all 

used bolt-together rather than screw-together assemblies. Details on one such impaction-type 

sampler can be found in “Development of Particle Size Test Methods for Sampling High 

Temperature and High Moisture Source Effluents” prepared for the California Air Resources 

Board (NTIS PB95-170221).1 The latter document also describes a method for making gaskets 

for use at high temperatures. Fairly straight-forward modifications of the PM10 and PM2.5 

cyclone designs should be possible to allow the same type of assembly of the cyclones. This may 

necessitate larger sampling port diameters. Boron nitride is an excellent anti-seize compound for 

this application. (Paint a thin slurry of boron nitride on the bolts before assembling the sampler. 

Use “break-away” bolts to facilitate disassembly in case the bolt threads gall. Over-torqueing 

such bolts causes them to break at the bolt head without damaging the flanges. 

Locating the Cyclone(S) Outside the Duct to Be Sampled 

Locating the cyclone(s) outside the duct to be sampled can be done only if the transport losses 

for particles in the size range of interest are low enough that the measurement results would not 

be materially affected. These losses would be caused by deposition primarily by impaction in the 

sampling nozzle and (at the flow rates used in PM10 and PM2.5 sampling) settling losses in 

horizontal probes. 

In order to use extractive sampling, the sampling nozzle will have to turn the gas stream through 

a 90° angle before the sample enters the probe. Losses in such nozzles for even given particle 

size depend on the gas velocity, the gas viscosity, and the diameter of the tubing from which the 

nozzle is constructed. Losses in nozzles occur as a result of mechanical deposition in the straight 

section of the nozzle immediately downstream of the nozzle inlet2 and, in the case of Method 5 
2

or similar nozzles, in the bend(s) used to turn the sample stream to enter the probe. Losses in the 

straight (entry section) of the nozzle are ignored here because they would be expected to be 

comparable to losses in the nozzles called for by the current PM10 sampling method. As a test of 

the feasibility of using extractive sampling for PM10 sampling, a set of calculations were carried 

out for based on sampling a source in which the gas was standard air at a temperature of 300 °F. 

Figure 1 shows a plot of the velocity at which sampling would be isokinetic at the PM10 flow 

rate (0.61 acfm or 17 lpm) at these conditions. 

Figure 1. Isokinetic velocity versus nozzle diameter for PM10 flow rate at 300 F in standard 

air. 

Particle losses in bends are dominated by impaction of particles on the “back side” of the bend. 

Particles that have too much inertia to allow them to follow the flow streamlines will continue 

moving toward the back wall of the bend as the gas turns, and if the inertia is great enough, they 

will contact the wall and be subject to capture. The penetrations through bends can be calculated 

from empirical relationships developed by Pui, et al., as follows: 

 P = 10-0.963Stk

For 90° bends where Stk (the particle Stokes number), is calculated in each case based on the 

tube diameter and gas velocity immediately upstream of the bend.3 

0

5

10

15

20

25

30

35

40

45

2 3 4 5 6 7 8 9 10

Nozzle Diameter, mm

Gas Velocity, m/s
3

Selecting two test cases, using velocities of 10 m/s and 20 m/s, which span the range of gas 

velocities commonly encountered in the field, losses were calculated for the bends in tubes 

having the corresponding nozzle diameters in Figure 1. Figure 2 shows a plot of the results as 

percent penetration by particle size for each case. 

Figure 2 shows penetration versus particle diameter for simple 90° bend nozzles at the PM10 

flow rate (isokinetic at gas velocities of 20 m/s and 10 m/s respectively). The gas conditions used 

were those for standard air at a temperature of 300 F. 

As can be seen from Figure 2, losses in the bend would in these cases be too large to be 

acceptable for PM10 measurement in both cases and might be marginally acceptable for use for 

PM2.5 measurement. 

Method 5 nozzles are effectively three 90° bends in series. Thus losses for Method 5 (“button 

hook”) nozzles would be expected to be even greater than those for the cases of simple 90° bends 

used in the calculations for Figure 2. The projected cut diameter (D50) for Method 5 nozzles 

sampling isokinetically at the PM10 flow rate are shown below at two gas stream velocities at 

the same conditions used in Figure 2. These results indicate that Method 5 nozzles would be 

totally unsuited for either PM 10 or PM2.5 sampling. 

Gas Velocity, m/s Nozzle ID, mm 90° Bend D50, μm M5 D50, μm 

10 6.15 6.4 3.56 

20 4.32 3.7 2.05 

Figure 2. Penetration versus particle diameter for simple 90° bend nozzles at the PM10 flow 

rate (isokinetic at gas velocities of 20 m/s and 10 m/s respectively). 
4

Figure 3. Penetration versus particle diameter for a 2.44 m long, 1.27 cm ID (8 foot long, 0.5 

inch ID) horizontal tube at the PM10 flow rate for the same gas conditions used in the 

previous examples. 

Probe Losses 

Probe losses versus particle size were calculated using the model developed by Fan, et al.2, for 

the same PM10 flow conditions used in the discussions above for sampling nozzles. A plot of the 

results are shown in Figure 3. 

As can seen from the Figure 3, probe losses for a probe of the size modeled here would not be 

expected be of much consequence compared to nozzle losses. Losses in sampling nozzles and 

transport systems are discussed more thoroughly by Farthing, et al. in “Instrumental Monitoring 

of Particulate Mass Emissions from Stationary Sources.” 4

Conclusions 

Extractive sampling probably cannot be allowed in the case of measuring PM10 emissions but 

might be acceptable, at least in many cases, for PM2.5 sampling at dry sources. Losses in 

extractive systems preclude their use in measuring PM10 emissions and make it impossible to 

account for dissolved or suspended droplets larger than about 3 um to 4 um in the case of wet 

sources for both PM10 and PM2.5. 

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.1 1 10 100

Particle Diameter, micrometers

Percent Penetration

4.32 mm

6.15 mm
5

References 

1. McCain, Joseph. D. and C. S. Fowler. Development of Particle Size Test Methods of 

Sampling High Temperature and High Moisture Source Effluents. Final Report on California 

Air Resources Board Contract A132-084, June, 1994. NTIS PB95-170221. 

2. Pui, David Y. H., Francisco Romay-Novas, and B. Y. H. Liu. Experimental Study of Particle 

Deposition in Bends of Circular Cross Section. Aerosol Science and Technology. 7:301-315, 

1987. 

3. Fan, Bijian, Andrew R. McFarland, and N. K. Anand. Aerosol Particle Losses in Isokinetic 

Sampling Probe Inlets. Environmental Science and Technology. 26:390-394, 1992. 

4. Farthing, William E. , J. D. McCain, A. D. Williamson, R. R. Wilson, T. R. Snyder, and L. 

G. Felix. Instrumental Monitoring of Particulate Mass Emissions from Stationary Sources. 

Southern Research Institute Final Report on Cooperative Agreement No. 822049 with EPA 

Methods Research and Development Division, Atmospheric Research and Exposure 

Assessment Laboratory, Research Triangle Park, NC 27711, EPA Project Officer: Thomas 

E. Ward, April 1999.