Final Report 68‐D‐02‐079 10/2/2007  Page 1 

FINAL REPORT

LAB WORK TO EVALUATE PM 2.5 COLLECTION WITH A DILUTION MONITORING

DEVICE FOR DATA GATHERING FOR EMISSION FACTOR DEVELOPMENT

Work Assignment 5‐10  

EPA Contract _68‐D‐02‐079_

By

Eastern Research Group, Ray Merrill, PhD, Project Manager

1600 Perimeter Park Drive

Morrisville, NC 27560

By subcontractors:

Baldwin Environmental Inc.

405 Western Rd #33

Reno NV 89506

Allan L. Budd, Project Manager and Investigator

Tom A Baldwin, Principal Investigator

&

Desert Research Institute

University and Community College System of Nevada

2215 Raggio Parkway,  

Reno, NV 89512

Judith C. Chow, Sc.D.

John G. Watson, Ph.D.

David A. Sodeman, Ph.D.
Final Report 68‐D‐02‐079 10/2/2007  Page 2 

Table of Contents

FINAL REPORT ................................................................................................................................. 1

List of Tables ................................................................................................................................... 3

List of Figures.................................................................................................................................. 4

EXECUTIVE SUMMARY .................................................................................................................... 5

1. INTRODUCTION....................................................................................................................... 6

1.1 Background....................................................................................................................... 6

1.2 Rationale of proposed approach for establishing emission factors ................................ 7

1.3 Project Objectives ............................................................................................................ 8

2. EXPERIMENTAL METHODS...................................................................................................... 8

2.1 Wet Stack Simulator......................................................................................................... 9

2.2 Dilution Sampler Configuration...................................................................................... 10

2.2.1 In‐Stack Dilution Stage............................................................................................ 10

2.2.2 Stack Dilution Sampler............................................................................................ 11

2.2.3 PM Size and Mass Quantification ........................................................................... 11

2.3 Test Matrix and Procedure............................................................................................. 13

2.4 Quality Control and Quality Assurance.......................................................................... 14

2.5 Data Reduction............................................................................................................... 14

3. Results and Discussion.......................................................................................................... 18

4. Summary, Conclusions, and Future Work ............................................................................ 27

4.1 Summary and Conclusions............................................................................................. 27

4.2 Future work .................................................................................................................... 27

References .................................................................................................................................... 29
Final Report 68‐D‐02‐079 10/2/2007  Page 3 

List of Tables

Table 2‐1: Test matrix of the experiments that have been completed........................................ 15

Table 3‐1: Theoretical salt concentrations, measured concentrations (accounting for dilution)

and percent of salt measured compared to theoretical salt concentrations for each test

performed..................................................................................................................................... 20

Table 3‐2: Average and standard deviation of the measured salt concentration compared to

theoretical stack salt concentration for each group of tests. The tests were grouped by salt

concentrations. ............................................................................................................................. 21
Final Report 68‐D‐02‐079 10/2/2007  Page 4 

List of Figures

Figure 2‐1: Experimental set‐up ................................................................................................... 16

Figure 2‐2: Schematic of cylindrical filter probe........................................................................... 17

Figure 3‐1: Number and mass size distribution for Test #29........................................................ 22

Figure 3‐2: PM2.5 Comparison between DustTrak and BAM with the gravimetric samples for all

Na2SO4 tests.................................................................................................................................. 23

Figure 3‐3: PM2.5 Comparison between DustTrak and BAM with the gravimetric samples for

Na2SO4 tests with concentrations less than 1.0 g/L. .................................................................... 24

Figure 3‐4: PM10 Comparison between DustTrak and BAM with the gravimetric samples for all

Na2SO4 tests.................................................................................................................................. 25

Figure 3‐5: PM10 Comparison between BAM and the gravimetric samples for Na2SO4 tests with

concentrations less than 1.0 g/L................................................................................................... 26
Final Report 68‐D‐02‐079 10/2/2007  Page 5 

EXECUTIVE SUMMARY

This project explores the feasibility of using a modified dilution system combined with filters

and a continuous beta attenuation monitor (BAM) similar to ambient PM2.5 and PM10 reference

and equivalent methods.  Sample recovery of >75% with a standard deviation of ±6% on

replicated measurements is shown.  Most of the missing salt is believed to have deposited to

the walls of the wet stack simulator.  A linear regression slope of 1.04 was demonstrated

between the BAM and the manual filter method results for PM10 which is a good measure of

overall correspondence since very little or the sampled mass is >PM10 .  The PM2.5 data from the

BAM had a linear regression slope of 1.25 with the PM2.5 manual method.  This positive

discrepancy wasfound previously and is believed to be due to an inaccurate calibration

standard and/or a cut point discrepancy in the Kimoto Virtual Impactor.  These problems are

being addressed.

These results demonstrate the feasibility of applying the dilution sampling method and an

instrumental mass measurement method to PM10 and PM2.5 from wet stacks.  An effective

simulator of wet stack conditions is also demonstrated.

As a result of this pilot study, improvements to the test apparatus and the sampling system

have been identified that will further increase sample recovery and measurement precision.  

Future efforts are proposed to enhance the method and demonstrate its field applicability.
Final Report 68‐D‐02‐079 10/2/2007  Page 6 

1. INTRODUCTION

1.1 Background

There is increasing concern in health and environmental circles about particulate matter (PM)

in the atmosphere, especially in the inhalable PM10 and respirable PM2.5 fractions. Larger

particles (>10μm) are filtered by the human respiratory tract but smaller particles bypass our

natural filters and carry allergens and disease causing chemicals to the lungs. There are a

significant number of articles in the technical literature on this topic. Pope and Dockeryi(2006)

and Chow et. al. (2007)ii provides the most recent summary of PM health effects.  In 1997, the

USEPA established National Ambient Air Quality Standards for PM2.5 which was revised in 2006.

Along with the PM10 NAAQS, these form the basis for Air Quality Management (AQM) systems

that protect human health (Bachman 2007)iii.

To date, continuous emissions and certification methods have not provided data that allows

accurate relationships to be established between source emissions and ambient air

concentrations. Being able to relate the ambient concentrations of PM10 and PM2.5 to source

emissions is key to reducing human exposure.  PM10 Stack certification methods using hot filters

followed by impingers have been found to be poor estimators of actual PM emissions.   

An alternative method that is used for mobile source certification dilutes the emissions to near

ambient temperatures prior to PM quantification.  There is a large body of research going back

almost 30 years that strongly supports a dilution method that simulates what happens when

source emissions exit the stack and are dispersed in the atmosphere.  EPA’s certification

Method 5G for wood stoves uses a dilution system: (www.epa.gov/ttn/emc/promgate/m‐

05g.pdf, even though the alternative, Method 5H for the same type of source uses the impinger

condenser system www.epa.gov/ttn/emc/promgate/m‐05h.pdf).

The Atmospheric Dispersion Simulator (ADS) has evolved as a means of quantifying PM10, PM2.5,

and PM10‐2.5mass more accurately than existing methods (Method 5, 40, Opacity, etc.) The

combination of dilution, dispersion and reduced temperature stabilizes condensation,

nucleation and agglomeration, simulating processes that occur in the atmosphere. If the stack

sample is diluted by 20:1 or greater with clean dry air and allowed at least 10 seconds to

equilibrate, PM mass concentrations approach those that are expected soon after effluent exits

a stack (Chang et. al. 2004)iv

.  An ASTM committee is finalizing an ADS procedure for PM2.5

based on this work.v

The USEPA released a Conditional Test Method, CTM 039(04_Rev 2) in July of 2004. This

method is an ADS which may be used on a wide range of sources to measure PM2.5 and PM10

emissions but is not applicable to wet sources.
Final Report 68‐D‐02‐079 10/2/2007  Page 7 

Previous studies have not demonstrated the ability to measure PM10 and PM2.5 from wet stacks

that contain free water droplets.  This often is the situation with stacks on sources with wet

scrubbers.  In these, much of the PM exists as entrained particles and dissolved material that,

when dried, become PM.  

Budd et. al (2005)vi demonstrated the feasibility of applying a commercially available ambient

air Beta Attenuation Monitor (BAM) that simultaneously measures PM10, PM10‐2.5 and PM2.5 to

this measurement problem.   In this project they demonstrated the ability to measure capture

and measure of the mass of salt crystals generated by evaporation of water from fine droplets

with dissolved salt in them.

This feasibility study is focused on extending that work to the conditions expected in a stack

after a wet scrubber.

1.2 Rationale of proposed approach for establishing emission factors

There is strong experimental evidence that the ADS method directly measures the PM

formation potential of stack emissions using methods that are identical to the devices used to

measure PM in the atmosphere.  This method measures PM whether it is from condensable

material or salts entrained in water droplets.  It is suitable as a method for both certification

and continuous monitoring.

Hot filter/impinger stack certification methods evolved in the 1960’s and 1970’s based on

methods from the 1950’s.  The understanding that much of the PM, especially PM2.5 derives

from condensable material has come to light in recent years.   

Numerous workers in the field have demonstrated that physical and chemical changes to the

sample.  Several things occur during this process:

• Many toxic and carcinogenic materials are gases at stack temperature but condense into

fine particles as the stack gas is dispersed and cooled to ambient conditions.  

• When a facility has a wet scrubber to remove SO2 there are salts of materials like

Na2SO4, CaSO4, NH4NO3 etc. plus the scrubber reagents like Ca(OH)2 dissolved in water

droplets in the stack.  When the entrained droplets disperse, and the water evaporates,

fine particles composed of these materials is left, most of which have documented

health effects.  While the water droplet is larger than 10 micrometers when observed in

the stack, the resulting particle after evaporation of the water are fine particles in the

PM2.5 category.

Budd et. al. (2005) demonstrated the feasibility of ADS methods with integrated filter and

instrumental methods compatible with ambient FRMs and FEMs. Laboratory experiments

demonstrated quantitative results with sample recoveries close to 100% on a routine basis.
Final Report 68‐D‐02‐079 10/2/2007  Page 8 

This prior work demonstrated the ability to sample and measure salts that are entrained and

dissolved, in fine water droplets.  The measurement principle was to drive off the water and

allow the salt to crystallize.  A water droplet of around 50 μm with a typical dissolves salt results

in PM2.5 particles when the water is driven off and the crystal is allowed to equilibrate with

clean ambient air for about 15 seconds.  The problem has been how to do this without losing a

large and variable percentage of the salt in the measurement system.  Many of these losses

occur within the stack itself, owing to gravitational settling and deposition to the stack walls.  

This implies that emissions samples should be taken as close to the exit point as possible.  

These losses should not be included as part of sampler losses, as they remain in the source.  

Sampler losses may occur in the sample probe, the dilution/mixing zone, in the aging chamber,

and in the sampling inlets.  These losses have yet to be quantified for wet stack emissions

sampled with ADS.

Two‐stage dilution in the proposed configuration addresses the water droplet loss by drying

them within the stack near the exit to minimize scavenging of large, wet particles once they are

extracted into the ADS.   A portion of the stack flow enters a chamber through a short tube in

the stack and is immediately mixed with hot air.  The hot air evaporates the water leaving

behind the fine particle which is then drawn into ADS to complete the

cooling/dilution/dispersion process.  The purpose of this project is to demonstrate the

feasibility of this double dilution process.

1.3 Project Objectives

Project objectives are:

• Determine the accuracy and precision of PM2.5 (and PM10) measurements made with the

double dilution system generated in a wet stack simulator;  

• Evaluate comparability of different PM2.5 and PM10 FRM and FEM methods on the ADS

for wet stack emissions;  

• Identify follow‐up research to further clarify PM sampling efficiencies for wet stacks.

Supporting tasks are:

• Create a wet stack simulator to represent worst‐case conditions for droplets in

industrial stack emissions;

• Modify the Baldwin ADS to handle wet stack effluences, l including the development of

an in‐stack primary diluter to remove liquid water.

2. EXPERIMENTAL METHODS

The ADS being developed under SBIR project EP‐D‐06‐071 to continuously measure coarse and

fine particulate matter was used in these tests.  This is a variation of the design described by

England et al. (2007a, 2007b)vii.  A wet stack simulator was developed to produce controlled

emissions similar to those that might be found following a wet scrubber system.  Both the stack

dilution system and the wet stack simulator were instrumented to measure temperatures,

relative humidity, flow rates, and pressures at different parts of the system.
Final Report 68‐D‐02‐079 10/2/2007  Page 9 

2.1 Wet Stack Simulator  

The wet stack simulator is illustrated in Figure 2‐1.  The objectives for this device are:

• Provide stack gas with water droplets containing varying amounts of salts found in

industrial wet stacks.   These droplets often result from a wet scrubbing system and

typically include calcium hydroxide, calcium sulfate, sodium hydroxide, sodium sulfate,

ammonium sulfate, and ammonium nitrate.

• Allow for varying stack exit velocities, droplet concentrations, temperatures, and

relative humidity.

• Facilitate rapid changes in variables and their measurement.

Target exit velocities were 15 – 40 ft/s and target temperatures were 145 – 175 °F.  These

targets were selected based on discussions with stack testers and EPA personnel as typical of

many wet stacks.  The diameter of the stack was selected based on the velocity desired and

enough space to insert the in‐stack dilution apparatus, an S‐Pitot system for flow measurement

in accordance with Method 2.  These conditions required a volumetric flow of up to 500

ft3/min.  A blower was obtained that would produce this flow with an expected back pressure

of <1 inch H2O pressure in the 6” duct.  The blower was equipped with a variable speed control

to allow flow and velocity adjustments.

Commercially available space heaters with heat inputs varying from 30,000 to 130,000 BTU/hr

were used as heat and combustion product (CO2) sources.  These devices were selected due to

cost‐effectiveness, ease of use, and compactness.   One heater was powered by propane with

variable heat outputs of 30, 40 and 50,000 BTU/hr and the other was a 70,000 BTU/hr unit fired

by kerosene.  Using these in combination allowed for variable heat inputs.   

These space heaters were installed on the inlet of the blower.  This configuration was necessary

as these heaters are not configured to push flow against measurable resistance.  

Water droplets were generated with a spray nozzle through which saturated salt solutions were

nebulizer.  Droplet sizes were to be <100μm with a peak between 30 and 50viii (spreadsheet

from a private communication with R. Myers of USEPA, 2007).   Supersaturated conditions were

maintained as indicated by water saturation tables from Perry’s Chemical Engineering

handbook, using a spreadsheet provided by Walter Smith of Walter Smith and Associatesix

.  

Upon consultation with Spray Systems, the supplier, a Model 1/4JAC+SU29 siphon sprayer was

selected.  Siphon type sprayers operate with high air pressure and water flow rates in the range

of interest.   

Droplets were created with a single sprayer for the tests described here, but it was found

during the tests that super saturation was not always attainable. After these tests were

completed, a second pure water sprayer will be added before the blower to saturate the

stream before injecting the salt solution.  This will be evaluated in a future test.  The lack of
Final Report 68‐D‐02‐079 10/2/2007  Page 10 

super saturation may be one of the reasons that salt losses occurred in the stack and result in

less than 100% recovery of anticipated salt by the dilution sampler.

The in‐stack dilution sampler quantifies the clean air to stack air ratio by measuring CO2 in the

stack gas, the dilution air, and the diluted mixture.  The over‐fire air running through the space

heater results in a stack CO2 level that is ~15 times the ambient level (~5000 ppm).  Additional

CO2 can be added to the stack gas from a cylinder to obtain more precise dilution ratios.

The CO2 measurement system consists of a 0‐3000 ppm range CO2 analyzer that is multiplexed

between ambient air (340 ‐ 370 ppm), the stack CO2 measured from a dilution probe and the

CO2 in the dilution chamber.  A dilution probe measured the stack CO2 on a wet basis which is

the same basis as the diluted sample out of the dilution chamber.  This introduces a much

smaller error into the overall measurement than does having a basis difference that would

require measurement or estimation of water concentration.  In the case of wet stacks that are

saturated, the estimation of water from the stack temperature may provide an accurate water

measurement.  This will be evaluated in the future.

Stack velocity was measured with an S‐Pitot tube system, in accordance with Method 2

(www.epa.gov/ttn/emc/methods/method2.html). The stack temperature probe needed for

flow and other calculations was a type K thermocouple in the Pitot probe.  Static pressure in the

stack was, for these tests, assumed to be ambient pressure taken from the weather station at

the DRI test site.  In‐stack pressure will be measured in future experiments.

2.2 Dilution Sampler Configuration

The ADS for wet stacks, also shown in Figure 2‐1 has an in‐stack section where the stack gas is

diluted with >150°C air to evaporate the droplets, leaving the salt crystals.  The BEI ADS takes its

sample from the top of this in‐stack dilutor and further dilutes the sample with clean ambient

air to in the dilution and aging chamber to obtain an equilibrium size distribution.   For the flow

rates used in these experiments, the sample aged for at least 15 s prior to quantification.

2.2.1 In­Stack Dilution Stage

The most important issue for sampling from wet stacks is the behavior of water droplets.  

Droplets that contain dry PM10 and PM2.5 are in the range of 1‐100 μm, and isokinetic sampling

is needed to capture them in their wet state.  When droplets collide with a surface, they are

lost, and direct velocity measurements prior to sampling must be avoided.  Large water drops

also have a large settling velocity that counteracts the upward motion of the stack flow, so

many of the large ones will fall to the bottom of the stack.  

Figure 2‐2 shows the in‐stack dilutor, which consists of a pipe mounted coaxially with the stack,

with the inlet probe at the bottom. This dilution system is supported by brackets in the stack.  

This design allows the in‐stack dilutor to be inserted into an industrial wet stack via a standard

flange and a hinged brace system to keep it steady.
Final Report 68‐D‐02‐079 10/2/2007  Page 11 

The stack gas velocity drives the sample into the in‐stack dilutor.  The diluent air is metered

through a flow meter, passes through a temperature controlled heater and is sent to the in‐

stack dilutor.  Typical dilution ratios ranged from 1:1 to 4:1 during the experiments. A small

blower can be added to draw sample into the in‐stack dilutor that would be controlled by a

flow sensor in the system after the dilutor.   A larger in‐stack diluter can be added to determine

the extent to which further in‐stack drying improves recovery and precision.  An >8:1 length to

diameter ratio is maintained to ensure plug flow needed for uniform delay time by avoiding

channeling.  Flow rates are always in the laminar region.  A cylindrical filter to introduce the

diluent air can also be added in future experiments (Figure 2‐2).

2.2.2 Stack Dilution Sampler

The Baldwin ADS is a compact, practical system that is intended to be more convenient,

efficient, and representative that the current PM10 Method 201/202 certification method.  

Features include:

• A >6:1 length to diameter ratio to ensure no channeled flows and uniform aging times.

• Concentric mixing of dilution air with sample air to minimize turbulence and impaction

losses.

• Mass flow meters and controls to maintain long‐term flow stability and dilution ratios.

• CO2 dilution ratio measurement for accurate quantification.

• Sampling ports for a variety of detection systems, including ambient FRM and FEM

sampling for PM10 and PM2.5.

• A two channel Beta Attenuation Monitor for continuous quantification of PM10, PM2.5,

and PM10‐2.5.

2.2.3 PM Size and Mass Quantification

The bottom of the dilution chamber expands from 6” to a 9” diameter plate with holes and

fittings for different PM quantification systems.  Mass and related particulate methods for

these tests are: 1) manual filter collection systems that are similar to ambient FRM PM2.5 and

PM10 measurements for NAAQS compliance; 2) TSI Dust Track light scattering measurements to

monitor PM variations throughout each test; 3) semi‐continuous Kimoto dichotomous BAM

that uses a virtual impactor to separate PM2.5 and PM10‐2.5; 4) Grimm optical particle counter

(OPC) to quantify the accumulation and coarse modes of the size distribution; and 5) MSP wide

range particle spectrometer to quantify the ultrafine and accumulation modes of the size

distribution and Grimm DustMonitor.

2.2.3.1 FRM/Manual Filter Collection and Analysis

The FRM SA 246 PM10 impactor and the FRM BGI Very Sharp Cut PM2.5 cyclone were located

before pre‐weighed 47mm Teflon membrane filters   Each of these inlets drew 16.7 L/min from

the dilution chamber.  Dry gas meters determined the volume of air sampled during each 20 to

40 min test.   The DustTrak reading was monitored during each test to obtain at least 300 μg

deposit on each filter so that the laboratory filter weight uncertainty of ±6 μg would result in <

2% uncertainty in the mass quantification.  After each test the exposed Teflon membrane filters

were taken to the DRI filter laboratory for FRM conditioning and weighing.   
Final Report 68‐D‐02‐079 10/2/2007  Page 12 

2.2.3.2 Beta Attenuation Monitor

The Kimoto Model 613 D Beta Attenuation Monitor (BAM) sampled at 16.7 l/min through

another of the sampling ports.  This BAM contains a virtual impactor to separate PM10 into

PM2.5 and PM10‐2.5 size fractions.  Samples are a collected on a Teflon membrane tape that

advances when a sufficient loading is obtained.  The particles absorb the beta rays, whose

source is located above the tape. The attenuation of the beta rays is proportional to the

amount of mass on the filter. Earlier tests have shown that with the factory calibration the

Kimoto BAM is highly correlated with filter measurements but gives results 5‐40% higher than

the filter values.  The bias is consistent and is a simple multiple factor.  Reasonable correlation

factors were developed as part of project, EP‐D‐02‐029.  A new version of the BAM unit that

addresses calibration is to be made available for upcoming tests.   

The Kimoto BAM generates 1 min average mass readings.  Tests were finished on the minute so

that values could be averaged over the sample duration.

2.2.3.3 Grimm and MSP Particle Size Distribution Analyzers

The Grimm Dust Monitor (Model 1.108) is a Laser Particle Spectrometer (LPS). The LPS

determines the size of a sampled particle from the amount of light scattered (by the particle)

and focused onto a photodetector using a system of mirrors.  Since the amount of light from a

particle depends on its size, precise and repeatable sizing of particles is possible.

The MSP wide range particle spectrometer (WPS Model 1000XP) combines a Scanning Mobility

Particle Sizer (SMPS) and a Laser Particle Spectrometer (LPS) housed and operated together as a

single unit. The SMPS consists of a differential mobility analyzer (DMA) and a condensation

particle counter (CPC). The sampled particles are charged to a known charge distribution by a

radioactive source. The particles enter the DMA near the top of two concentric tubes.  The

outer tube is held at ground potential while the center tube has an applied voltage that

changes with time. At a given center tube voltage, only a narrow size range of charged particles

will have the correct electrical mobility to exit the DMA and enter the CPC. The CPC condenses

alcohol onto the particles, growing them into droplets large enough to be counted by the

detection of light scattered by the particles. By varying the voltage, a large range of particles

can be classified. The LPS operates similar to the Grimm DustMonitor. The SMPS has a size

range of 0.01 to 0.5μm, while the LPS has a size range of 0.5 to 10 μm.   

Normally, these devices are collocated with the direct mass methods to determine the particle

size distribution.  Changes in the size distribution with distance into the dilution chamber can

be measured by inserting a probe up the length of the chamber.  Attainment of a stable size

distribution that doen’t vary between the sample plenum and ~20% higher in the dilution

chamber is the best indication that equilibrium has been achieved.
Final Report 68‐D‐02‐079 10/2/2007  Page 13 

2.2.3.4 TSI Model 8520 Dust Trak

The TSI DustTrak (Model 8520) draws samples air into the sensing chamber where it is

illuminated by a 780 nm light from a laser diode.  Light is scattered from the sampled particles a

(780 nm diode). and a lens focuses the scattered light onto the photodetector. The amount of

scattered light is proportional to the mass concentration of the aerosol.  DustTrak output is

calibrated for a coarse particle distribution and gives a higher reading than actual mass for

PM2.5.  It is used as an indicator of the mass being sampled onto the filters and helps to control

the duration of each experiment.      

2.2.3.5 CO2 Analyzer

The LI‐840 CO2 Gas Analyzer is a non‐dispersive, infrared gas analyzer based upon a single path,

dual wavelength, and infrared (IR) detection subsystem. The CO2 measurements are a function

of the absorption of IR energy as it travels through the optical path. Concentration

measurements are based on the difference ratio in the IR absorption between a reference (3.45

μm) and sample signal (4.26 μm). The LI‐840 measures CO2 concentration in the stack and in

the dilution chamber (in‐stack plus dilution air CO2).  Before and after a triplicate of tests,

ambient CO2 is measured to represent the concentration in dilution air.

For a typical stack test, the CO2 concentration after dilution was in the range of 2000 to 5000

ppm.  However, due to the high over‐fire air in the heat source 500 to 700 ppm was found.  

Background typically contains 340 – 370 ppm of CO2.    

Manual switching between the stack probe and dilution chamber probe was used to determine

CO2 variation in the stack and in the dilution chamber.   

2.2.3.6 Laboratory Analysis of Filter Samples

As described in the QAPP, filter samples were equilibrated for 24 hours at constant

temperature and relative humidity prior to weighing.  Filters were charge neutralized and

weighed on a ±1 μg balance prior to and after sampling.

2.3 Test Matrix and Procedure

The tests are defined in Table 2‐1.  The first series of tests were intended to  evaluate that the

wet stack simulator was operating within its design parameters:

• Water concentration – 15 – 25%

• Stack Velocity – 30 – 40 ft/s

• Stack temperature 145 – 175 F

The following adjustments are being made as a result of this testing:

• CO2 from a cylinder was added into the stack to enhance the CO2 generated by the

kerosene heater.   
Final Report 68‐D‐02‐079 10/2/2007  Page 14 

• Water evaporation in the in‐stack diluter was less than expected, so more heat was

added to the system.

2.4 Quality Control and Quality Assurance

The QAPP specifies the quality control (QC) and Quality Assurance (QA) activities.  Procedures

for calibrating critical hardware, recording data in notebooks, sample security and custody,

cross checking all calculations with a colleague etc. were followed.   

2.5 Data Reduction

Data reduction and display were done using Microsoft Excel.  Standard USEPA calculations were

used where possible.  All calculations were cross checked by a team member, knowledgeable in

the process being checked.
Final Report 68‐D‐02‐079 10/2/2007  Page 15 

Table 2‐1: Test matrix of the experiments that have been completed

Test # Composition Conc (g/L)

1 12255 136 90 180 157 90 100 31 N/A 0 0 0

2 12141 135 90 180 156 90 100 31 N/A 0 0 0

3 12040 134 90 180 155 90 100 31 N/A 0 0 0

4 12077 135 60 180 155 90 100 32 N/A 0 0 0

5 12031 133 60 180 155 90 100 32 N/A 0 0 0

6 12019 132 60 180 154 90 100 32 N/A 0 0 0

7 11775 133 30 180 151 90 100 34 N/A 0 0 0

8 11765 132 30 180 151 90 100 32 N/A 0 0 0

9 11683 130 30 180 150 90 100 34 N/A 0 0 0

10 12474 58 90 180 160 90 100 29 Na2SO4 15.2 185 225

11 12460 57 90 180 160 90 100 29 Na2SO4 15.2 185 226

12 12727 61 90 180 163 90 100 30 Na2SO4 15.2 185 221

13 12541 61 60 180 161 90 100 29 Na2SO4 15.2 185 224

14 12534 61 60 180 161 90 100 28 Na2SO4 15.2 218 264

15 12418 63 60 180 160 90 100 28 Na2SO4 15.2 248 304

16 12013 58 10 180 154 90 100 27 Na2SO4 1.02 175 14.9

17 12154 47 10 180 156 90 100 25 Na2SO4 1.02 175 14.7

18 12369 49 10 180 159 90 100 25 Na2SO4 1.02 175 14.5

19 12639 67 10 180 162 90 100 25 Na2SO4 1.02 150 12.1

20 12770 68 10 180 164 90 100 25 Na2SO4 1.02 150 12.0

21 12563 67 10 180 161 90 100 25 Na2SO4 1.02 150 12.2

22 12343 48 10 180 159 90 100 20 Na2SO4 1.02 175 14.5

23 12377 44 10 180 159 90 100 20 Na2SO4 1.02 175 14.5

24 12594 47 10 180 162 90 100 20 Na2SO4 1.02 175 14.2

25 12683 67 10 180 163 80 100 19 Na2SO4 0.51 150 6.1

26 12705 64 10 180 163 80 100 19 Na2SO4 0.51 150 6.1

27 12689 63 10 180 163 80 100 19 Na2SO4 0.51 150 6.1

28 12409 64 10 180 159 80 100 19 Na2SO4 0.51 150 6.2

29 12677 71 10 180 163 80 100 18 Na2SO4 0.51 150 6.1

30 12681 71 10 180 163 80 100 19 Na2SO4 0.51 150 6.1

31 13203 47 10 180 170 80 100 20 Na2SO4 0.51 148 5.8

32 12969 53 10 180 167 80 100 20 Na2SO4 0.51 149 5.9

33 13030 52 10 180 167 80 100 20 Na2SO4 0.51 150 5.9

34 12693 74 10 180 163 80 100 24 Na2SO4 0.51 149 6.0

35 12554 74 10 180 161 80 100 23 Na2SO4 0.51 174 7.1

36 12627 74 10 180 162 80 100 23 Na2SO4 0.51 158 6.4

Probe Flow 

(lpm)

In-Stack Dilutor Salt Solution Stack 

Flow Rate 

(lpm) Temp. (C)

Dilution Tunnel

Stack 

Temp. (C)

Dilution 

Air (lpm) Temp. (C)

Dilution 

Air (lpm)

Total Flow 

(lpm)

Sprayer 

Flow Rate 

(ccm)

Theor. 

Stack Salt 

Conc (mg 

m-3) 
Final Report 68‐D‐02‐079 10/2/2007  Page 16 

Figure 2‐1: Experimental set‐up
Final Report 68‐D‐02‐079 10/2/2007  Page 17 

Figure 2‐2: Schematic of cylindrical filter probe.
Final Report 68‐D‐02‐079 10/2/2007  Page 18 

3. Results and Discussion

Tables 3‐1 and 3‐2 summarize the results of each experiment described in Table 2‐1.  These

results show that salt recovery, determined as a fraction of that recovered in the ADS mass

measurement with respect to that injected by the sprayer,  was >75% for PM10 67% for PM2.5

range.  The standard deviation of 12 replicate measurements in each category was ±6% of

reading as a percentage of theoretical salt concentration in the stack on a mass basis on the

0.51 gm/L concentration in the nebulized solution.

The PM10 impactor and the PM2.5 cyclone were examined after all of the tests, and there was

visible accumulation of fine particles in the cup of the PM2.5 cyclone.  There were a few visible

(>10 μm) crystals present in the PM10 impactor, indicating that some of the solid particles left

after water evaporation were large.  theThis is a partial reason why PM10 and PM2.5 recoveries

are less than 100%, as these larger particles are removed by the inlets.   

Figure 3 ‐1 displays the number and mass concentration size distribution in the dilution

chamber measured by the MSP wide range particle spectrometer for Test #29.  This example is

typical of size measurements for the other tests.  The number distribution peaks around 0.03

micrometers. The mass distribution has two peaks, one around 0.5 – 0.6 micrometers, with the

second near 1.5 micrometers. These distributions were consistent throughout the testing

period, both in the shape of the distribution and the concentration. This illustrates that the

dilution system is stable and reproducible.  It also shows the expected distribution of particle

sizes.  Most of the particles are in the ultrafine region (<0.1 μm) while most of the particle mass

is in the accumulation mode region (0.1 to 2.5 μm).   

Tests were completed for several salt concentrations in the sprayer solution.  Similar recoveries

and precision were observed for all levels except the highest of 1.5 g/L in the water solution, a

concentration higher than be expected in wet scrubber effluent.  Repeatability and recovery

was better at lower concentrations the  (Table 3‐2).  Figures 3‐2, 3‐3, 3‐4 and 3‐5 demonstrate

that the different mass measurements were highly correlated for all but the highest spray

water concentrations.   

It is likely that most of the losses take place in the wet stack simulator prior to entering the first

dilution probe.   The spray is large and some of the droplets impact directly onto the edge of

the stack.  This could be minimized by using a more focused spray nozzle and increasing the

diameter of the stack.  It also appears that the stack is not always at supersaturated (RH=100%)

conditions that would retain the droplet size.  This can be alleviated by adding an additional

sprayer with pure water prior to the blower.   

The BAM still reports high values for PM2.5 and lower values for PM10‐2.5 when compared to

gravimetric results.  See Figures 3.2 and 3.3 where the coefficient of correlation is 1.22 and 1.24

for PM2.5.  When the two values (PM2.5 and PM (10‐2.5)) are added together to report PM10 the

expected result is were obtained, with slopes of 1.02 and 1.04.  These data and the earlier
Final Report 68‐D‐02‐079 10/2/2007  Page 19 

results reported under EP‐D‐02‐029; suggest that this is most likely due to an issue with the

Virtual Impactor cut point, as well as a possible calibration bias relating the beta attenuation to

mass.  The manufacturer, Kimoto, has announced a new version of the unit that was used in

these tests, with the Virtual Impactor removed, allowing use of standard cyclone or impactor

devices.  This change is expected to eliminate the issue of difference in cut point.    
Final Report 68‐D‐02‐079 10/2/2007  Page 20 

Table 3‐1: Theoretical salt concentrations, measured concentrations (accounting for dilution)

and percent of salt measured compared to theoretical salt concentrations for each test

performed.

Test #

10 225 84689 95010 105177 69530 124062 38 42 47 31 55

11 226 78677 77141 85081 65946 40702 35 34 38 29 18

12 221 77901 94873 105116 103887 72978 35 43 48 47 33

13 224 75854 90117 98928 63270 104722 34 40 44 28 47

14 264 66320 95419 103279 59700 97853 25 36 39 23 37

15 304 64985 78872 85424 58093 95139 21 26 28 19 31

16 14.9 13013 12748 12491 9916 11608 87 86 84 67 78

17 14.7 17293 14925 14241 12918 15621 117 101 97 88 106

18 14.5 14994 15275 14005 10356 13448 104 106 97 72 93

19 12.1 9490 9766 9341 7438 8836 78 80 77 61 73

20 12.0 9053 10468 10908 7033 8893 75 87 91 59 74

21 12.2 8754 9872 9427 7372 8519 72 81 77 60 70

22 14.5 12723 12137 11933 N/A 12951 88 84 82 N/A 89

23 14.5 10005 9926 9701 8404 9373 69 69 67 58 65

24 14.2 8013 7958 7633 6445 7253 56 56 54 45 51

25 6.1 4972 5599 5439 3979 4794 82 92 89 65 79

26 6.1 4754 4769 4583 3915 4400 78 79 75 64 72

27 6.1 4979 5367 5167 4088 4589 82 88 85 67 75

28 6.2 4870 5402 5256 3994 4140 78 87 85 64 67

29 6.1 4578 4649 4483 3488 4220 75 76 74 57 69

30 6.1 4412 4552 4388 3863 4102 73 75 72 63 67

31 5.8 5004 5589 5404 4127 4784 87 97 94 71 83

32 5.9 4943 4990 4800 4151 4555 84 84 81 70 77

33 5.9 4759 5025 4799 3947 4437 80 85 81 67 75

34 6.0 5787 6010 5847 4932 5031 96 99 97 82 83

35 7.1 5844 5074 4792 4335 N/A 82 71 67 61 N/A

36 6.4 6217 6020 5808 4641 N/A 97 94 91 72 N/A

taking into account dilution ratio

Kimoto 

PM10

Kimoto 

PM2.5

DustTrak 

PM2.5

Ratio of Instrument response to Theoretical Stack Conc 

express as percent

Filter 

PM10

Filter 

PM2.5

DustTrak 

PM2.5 

Conc 

(μg/m3)

Kimoto 

PM2.5 

Conc 

(μg/m3)

Kimoto 

PM10 

Conc 

(μg/m3)

Filter 

PM2.5 

Conc 

(μg/m3)

Filter 

PM10 

Conc 

(μg/m3)

Theor. 

Stack Salt 

Conc (mg 

m-3) 
Final Report 68‐D‐02‐079 10/2/2007  Page 21 

Table 3‐2: Average and standard deviation of the measured salt concentration compared to

theoretical stack salt concentration for each group of tests. The tests were grouped by salt

concentrations.

Tests # avg stdev avg stdev avg stdev avg stdev avg stdev

10-15 15.2 31 ± 6 37 ± 6 41 ± 7 30 ± 10 37 ± 13

16-24 1.02 83 ± 19 83 ± 15 81 ± 14 64 ± 12 78 ± 16

25-36 0.51 83 ± 7 86 ± 9 83 ± 9 67 ± 6 75 ± 6

Salt Conc Kimoto PM10 Filter PM2.5 Filter PM10

(g/L)

DustTrak Kimoto PM2.5
Final Report 68‐D‐02‐079 10/2/2007  Page 22 

Number and Mass Distribution of Dried Salt for Test # 29

0

20000

40000

60000

80000

100000

120000

140000

0.01 0.1 1 10

Particle Diameter (micrometers)

Number Concentration (dN / dLogD)

0

20

40

60

80

100

120

140

Mass Concentration (dM / dLogD)

Figure 3‐1: Number and mass size distribution for Test #29
Final Report 68‐D‐02‐079 10/2/2007  Page 23 

PM2.5 Comparison: all Na2SO4 tests

Gravimetric vs DustTrak and BAM

y = 1.10x

R2

 = 0.80

y = 1.22x

R2

 = 0.87

0

200

400

600

800

1000

1200

1400

0 200 400 600 800 1000 1200

Gravimetric Mass Conc (μg m-3)

DustTrak and BAM Mass Conc (

μg m-3)

DustTrak

BAM

Figure 3‐2: PM2.5 Comparison between DustTrak and BAM with the gravimetric samples for all

Na2SO4 tests
Final Report 68‐D‐02‐079 10/2/2007  Page 24 

PM2.5 Comparison: [Na2SO4] = 1.0 g L-1 or less

Gravimetric vs DustTrak and BAM

y = 1.24x

R2

 = 0.93

y = 1.27x

R2

 = 0.87

0

100

200

300

400

500

600

700

800

900

0 50 100 150 200 250 300 350 400 450 500

Gravimetric Mass Conc (μg m-3)

DustTrak and BAM Mass Conc (

μg m-3)

DustTrak

BAM

Figure 3‐3: PM2.5 Comparison between DustTrak and BAM with the gravimetric samples for

Na2SO4 tests with concentrations less than 1.0 g/L.
Final Report 68‐D‐02‐079 10/2/2007  Page 25 

PM10 Comparison: all Na2SO4 tests

Gravimetric vs BAM

y = 1.02x

R2 = 0.80

0

200

400

600

800

1000

1200

1400

1600

0 200 400 600 800 1000 1200 1400 1600

Gravimetric Mass Conc (μg m-3)

DustTrak and BAM Mass Conc (

μg m-3)

BAM

Figure 3‐4: PM10 Comparison between DustTrak and BAM with the gravimetric samples for all

Na2SO4 tests
Final Report 68‐D‐02‐079 10/2/2007  Page 26 

PM10 Comparison: [Na2SO4] = 1.0 g L-1 or less

Gravimetric vs BAM

y = 1.04x

R2

 = 0.90

0

100

200

300

400

500

600

700

800

900

0 100 200 300 400 500 600 700 800 900

Gravimetric Mass Conc (μg m-3)

DustTrak and BAM Mass Conc (

μg m-3)

BAM

Figure 3‐5: PM10 Comparison between BAM and the gravimetric samples for Na2SO4 tests

with concentrations less than 1.0 g/L
Final Report 68‐D‐02‐079 10/2/2007  Page 27 

4. Summary, Conclusions, and Future Work

4.1 Summary and Conclusions

These pilot project tests have shown reasonable recovery and precision of fine (and coarse)

particulate matter with ADS, a dilution based system, operating in the “wet” (water saturated

or super‐saturated) stack environment.  Earlier work has shown comparable results for dry (non

water saturated) stacks.  The significance here is that a single method might be applicable to all

stacks for coarse (PM10) and fine (PM2.5) in wet and dry stacks.

The ADS intends to simulate PM2.5 and PM10 as they would be measured at a receptor location

by diluting and cooling the stack extract to allow for condensation, nucleation, and coagulation

and determining mass with methods identical to those used by FRM and FEM ambient

monitors.  This is in contrast to PM10 stack certification Method 201/202 which collects particles

on a hot in‐stack filter followed by collection of the transmitted gases in impingers.   

Wet stack effluents which follow wet scrubbers present a difficult problem for any stack

sampling method.  These effluents are simulated and sampled with the ADS to demonstrate

that high and repeatable recoveries are achievable.  

More than 75% of the calcium sulfate salt nebulized into the wet stack was measured by the

ADS and a primary dilution combination.  It is believed that most of the difference remained in

the stack, owing to gravitational settling and deposition to the stack walls, rathern than being

lost in the dilution system.  This can be definitively evaluated in follow‐on experiments that

would modify the wet stack simulator to minimize losses and evaluate deposition by stack and

probe washing at various points in the system.

4.2 Future work

These results and earlier work with the dilution method indicate the potential for this approach

to PM2.5 stack emissions monitoring.  This approach appears to simulate the effect of dilution

and cooling on emissions, making them more compatible with ambient PM.

Follow‐up to these initial experiments include the following:

• Modify the wet stack simulator, as described in the body of this report, to minimize

deposition, settling, and evaporationof the droplets.

• Wash ADS and stack surfaces at various locations to better quantify losses.

• Peform additional tests with different salts typical of a variety of wet stack emissions.

• Further clarify the calibration and size cuts of the Kimoto BAM.

In the longer term, the following tasks need to be completed:
Final Report 68‐D‐02‐079 10/2/2007  Page 28 

• Generate data on simulated sources that demonstrate recovery, precision of the

method.  This involves refining both the simulation system, embracing both wet and dry

stacks and the physical implementation of the proven dilution method.   

• Gather field data to support (or refute) the hypothesis stated above.  This involves a

project to deploy systems to the field to gather data on typical sources to compare with

the methods that these sources are presently using.

• Develop correlation data between source emissions measured by the dilution method

and ambient air results.  This project, if it could be designed would punctuate the

advantage and provide the Agency with compelling arguments to promulgate

provisional rules.   

• Demonstrate the improved precision and comparison data with existing methods such

as Methods 5, 201 and 202.  This project will be to run comparisons with existing

methods on common sources.  At present, this is only feasible on dry sources.   
Final Report 68‐D‐02‐079 10/2/2007  Page 29 

References

                                                      

i

Pope and Dockery 2006) Pope C.A. III; Dockery,  D.W.; Health Effects of Fine Particulate Air

Pollution, Lines that Connect–A Critical Review, JAWMA 6,709‐742, 2006

ii Chow et. al. Will the Circle be unbroken: a History of the U.S, National Ambient Air Quality

Standards, A Critical Review; JAWMA 57, 1151‐1161, 2007

iii Bachman, J.D.; JAWMA 57, 652‐697, 2007

iv Chang, M.C., Chow, J.C., Watson, J.G., Hopke, P. K., Yi, S‐M., England, G.C.; JAWMA 54(2004),

1494‐1505

v ASTM WK752 “Test Method for Determination of PM2.5 Mass and Species Emissions from

Stationary Combustion Sources by Dilution Sampling”, Glenn England, Technical Contact.  

Initiated 4/23/2003; http://www.astm.org/

vi Budd, Allan L.; Baldwin, Tom A.; Final Report SBIR contract EP‐D‐05‐021 August 31, 2005

vii England et al. ;J. Air & Waste Manage. Assoc. 57:79–93; 2007a, J. Air & Waste Manage. Assoc.

57:65–78; 2007b)   viii Myers, Ron, USEPA OAQPS personal communication of data from work at the University of

North Carolina in the form of an Excel spreadsheet that shows the relationship of a salt bearing

water droplet size to expect particle size if the water is evaporated; 7/2007

ix Smith, Walter – Private Communication, 7/2007