September 2012

Environmental Technology 

Verification Report

Pall Corporation

Xact 625 Particulate Metals Monitor

Prepared by

Under a cooperative agreement with

 U.S. Environmental Protection Agency

EPA/600/R-12/680
i 

EPA/600/R-12/680

September 2012

Environmental Technology Verification

Report

ETV Advanced Monitoring Systems Center

Pall Corporation

Xact 625 Particulate Metals Monitor

By 

Thomas Kelly and Amy Dindal, Battelle

John McKernan, U.S. EPA 

Battelle

Columbus, Ohio 43201 
ii

Notice

The U.S. Environmental Protection Agency (EPA), through its Office of Research and 

Development, has financially supported and collaborated in the extramural program 

described here. This document has been peer reviewed by the Agency. Mention of trade 

names or commercial products does not constitute endorsement or recommendation by the 

EPA for use.

This report was prepared by Battelle to summarize testing supported by EPA’s Region 5 and 

Office of Air Quality Planning and Standards (OAQPS), and conducted in collaboration with 

the Ohio EPA (OEPA). Neither Battelle, EPA, OEPA nor any person acting on behalf of 

those organizations 

(a) Makes any warranty of representation, express or implied, with respect to the accuracy, 

completeness, or usefulness of the information contained in this report, or that the use 

of any information, apparatus, method, or process disclosed in this report may not 

infringe privately-owned rights; or 

(b) Assumes any liabilities with respect to the use of, or for damages resulting from the use 

of, any information, apparatus, method, or process disclosed in this report. 

Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise, does not necessarily constitute or imply its 

endorsement, recommendation, or favoring; nor do the views and opinions of authors 

expressed herein necessarily state or reflect those of the EPA or OEPA. 
iii

Foreword

The EPA is charged by Congress with protecting the nation’s air, water, and land resources. 

Under a mandate of national environmental laws, the Agency strives to formulate and 

implement actions leading to a compatible balance between human activities and the ability 

of natural systems to support and nurture life. To meet this mandate, the EPA’s Office of 

Research and Development provides data and science support that can be used to solve 

environmental problems and to build the scientific knowledge base needed to manage our 

ecological resources wisely, to understand how pollutants affect our health, and to prevent or 

reduce environmental risks. 

The Environmental Technology Verification (ETV) Program has been established by the 

EPA to verify the performance characteristics of innovative environmental technology across 

all media and to report this objective information to permitters, buyers, and users of the 

technology, thus substantially accelerating the entrance of new environmental technologies 

into the marketplace. Verification organizations oversee and report verification activities 

based on testing and quality assurance (QA) protocols developed with input from major 

stakeholders and customer groups associated with the technology area. ETV consists of six 

environmental technology centers. Information about each of these centers can be found on 

the Internet at http://www.epa.gov/etv/. 

Effective verifications of monitoring technologies are needed to assess environmental quality 

and to supply cost and performance data to select the most appropriate technology for that 

assessment. Under a cooperative agreement, Battelle has received EPA funding to plan, 

coordinate, and conduct such verification tests for “Advanced Monitoring Systems for Air, 

Water, and Soil” and report the results to the community at large. Information concerning 

this specific environmental technology area can be found on the Internet at 

http://www.epa.gov/etv/centers/center1.html. 
iv

Acknowledgments

The authors wish to acknowledge the support of all those who helped plan and conduct the 

verification test, analyze the data, and prepare this report. QA support was provided by 

Laurel Staley of EPA/ORD’s National Risk Management Research Laboratory, Rebecca 

Shircliff of Neptune and Company, Inc., and Zachary Willenberg of Battelle. The efforts of 

Darren Machuga, Steve Lowry, Dean Ponchak, Michael Murphy, and William Colon of the 

OEPA in conducting the field test are greatly appreciated. Finally, the authors thank Dennis 

Mikel of EPA’s OAQPS, Rudy Eden of California’s South Coast Air Quality Management 

District, and Emily Snyder of EPA’s Office of Research and Development for their review of 

this verification report.
v 

Contents

Notice ........................................................................................................................................ ii

Foreword .................................................................................................................................. iii

Acknowledgments .................................................................................................................... iv

List of Figures .......................................................................................................................... vi

List of Tables ............................................................................................................................ vi

List of Abbreviations ............................................................................................................... vii

Chapter 1: Background ............................................................................................................. 1

Chapter 2: Technology Description ......................................................................................... 2

Chapter 3: Test Design and Procedures ................................................................................... 4

3.1 Introduction ................................................................................................................... 4

3.2 Test Procedures ............................................................................................................. 5

3.2.1 Field Installation ................................................................................................ 5

3.2.2 Reference Sampling and Analysis ..................................................................... 6

3.2.3 Verification Sites and Schedule ........................................................................ 7

Chapter 4: Quality Assurance/Quality Control ........................................................................ 9

4.1 Amendments/Deviations ............................................................................................... 9

4.2 Reference Methods ........................................................................................................ 9

4.3 Review of Xact 625 QC Data ...................................................................................... 10

4.4 Audits .......................................................................................................................... 10

4.4.1 Technical Systems Audit ................................................................................. 10

4.4.2 Performance Evaluation Audit ........................................................................ 10

4.4.3 Data Quality Audit .......................................................................................... 12

4.5 QA/QC Reporting ........................................................................................................ 12

4.6 Data Review ................................................................................................................ 12

Chapter 5: Statistical Methods ............................................................................................... 13

5.1 Averaging of Xact 625 Hourly Data ........................................................................... 13

5.2 Comparability .............................................................................................................. 15

5.3 Correlation ................................................................................................................... 15

5.4 Bias .............................................................................................................................. 15

5.5 Data Completeness ...................................................................................................... 15

Chapter 6: Test Results ........................................................................................................... 17

6.1 Xact 625 Ambient Metals Results ............................................................................... 17

6.2 Comparability and Correlation .................................................................................... 23

6.3 Bias .............................................................................................................................. 25

6.4 Data Completeness ...................................................................................................... 26

6.5 Operational Factors ..................................................................................................... 27

Chapter 7: Performance Summary ......................................................................................... 29
vi

Chapter 8: References ............................................................................................................ 31

List of Figures

Figure 2-1. Xact 625 Installed in Field Trailer for Testing ..................................................... 3

Figure 3-1. Field trailer used in verification test, showing Xact 625 PM10 inlet, 

reference PM10 automated sampler, and meteorological sensors on the 

roof ....................................................................................................................... 6

Figure 3-2. Map view of Marietta, Ohio area showing location of OVESC sampling 

site (white triangle near top of figure) and of suspected metals emission 

source (red triangle at left center of figure) .......................................................... 8

Figure 6-1. Xact 625 hourly monitoring data for Mn, K, Fe, and Zn in Marietta, OH 

from December 10, 2011 to February 27, 2012 ................................................. 18

Figure 6-2. Example of elevated metals concentrations over a period of several 

hours ................................................................................................................... 18

Figure 6-3. Linear regression of Xact 625 daily averages against ICP/MS daily 

averages for Ca ................................................................................................... 20

Figure 6-4. Linear regression of Xact 625 daily averages against ICP/MS daily 

averages for Cu ................................................................................................... 21

Figure 6-5. Linear regression of Xact 625 daily averages against ICP/MS daily 

averages for Mn .................................................................................................. 21

Figure 6-6. Linear regression of Xact 625 daily averages against ICP/MS daily 

averages for Pb ................................................................................................... 22

Figure 6-7. Linear regression of Xact 625 daily averages against ICP/MS daily 

averages for Se ................................................................................................... 22

Figure 6-8. Linear regression of Xact 625 daily averages against ICP/MS daily 

averages for Zn ................................................................................................... 23

Figure 6-9. Percent bias results for Pb as a function of the reference concentration ............ 26

List of Tables

Table 4-1. Summary of PE Audits of Reference Analytical Method .................................. 11

Table 5-1. Calculation of the Xact 625 Daily QL for Elements Reported in 

Ambient Air at the Marietta Site and Comparison to ICP/MS Detection 

Limits .................................................................................................................. 14

Table 6-1. Summary of Hourly Values of All Metals Reported by the Xact 625 in 

Marietta, Ohio from December 10, 2011 to February 27, 2012 ......................... 19

Table 6-2. Results of Linear Regression of Xact 625 and Reference Data ......................... 24

Table 6-3. Bias of Xact 625 Results Relative to Reference Results .................................... 25

Table 6-4. Data Completeness for the Xact 625 .................................................................. 27

Table 7-1. Quantitative Performance Results for the Xact 625 ........................................... 29
vii

List of Abbreviations

AMS Advanced Monitoring Systems

As arsenic

Ba barium 

°C degrees Centigrade

Ca calcium

Cd cadmium

CES Cooper Environmental Services LLC

CI confidence interval 

Co cobalt

Cr chromium 

Cu copper 

DC data completeness

EDXRF energy-dispersive X-ray fluorescence

EPA U.S. Environmental Protection Agency 

ETV Environmental Technology Verification

Fe iron

HF hydrofluoric acid

Hg mercury

ICP/MS inductively coupled plasma mass spectrometry

K potassium 

L/min liter per minute

mm Hg millimeter of mercury

m3

/hr cubic meter per hour

MDL method detection limit

μg/L microgram per liter

μm micrometer

Mn manganese

Mo molybdenum 

ng/m3 nanograms per cubic meter 

Ni nickel

NIST National Institute of Science and Technology 

OAQPS Office of Air Quality Planning and Standards 

OEPA Ohio Environmental Protection Agency 

OVESC Ohio Valley Educational Service Center

Pb lead

Pd palladium 

PE performance evaluation

PM particulate matter

PM10 particulate matter of aerodynamic diameter ≤ 10 micrometers

QA quality assurance

QAPP quality assurance project plan

QC quality control 

QL quantitation limit
viii

QMP quality management plan 

r

2

 coefficient of determination

Rb rubidium 

RSD relative standard deviation

SAT School Air Toxics 

Sb antimony

SD standard deviation 

Se selenium

SEDO Southeast District Office

Sr strontium 

Th thorium 

Tl thallium

TSA technical systems audit

XRF X-ray fluorescence

Zn zinc
1 

Chapter 1 

Background 

The U.S. Environmental Protection Agency (EPA) supports the Environmental Technology 

Verification (ETV) Program to facilitate the deployment of innovative environmental 

technologies through performance verification and dissemination of information. The goal of 

the ETV Program is to further environmental protection by accelerating the acceptance and 

use of improved and cost-effective technologies. ETV seeks to achieve this goal by 

providing high-quality, peer-reviewed data on technology performance to those involved in 

the design, distribution, financing, permitting, purchase, and use of environmental 

technologies. 

ETV works in partnership with recognized testing organizations; with stakeholder groups 

consisting of buyers, vendor organizations, and permitters; and with the full participation of 

individual technology developers. The program evaluates the performance of innovative 

technologies by developing test plans that are responsive to the needs of stakeholders, 

conducting field or laboratory tests (as appropriate), collecting and analyzing data, and 

preparing peer-reviewed reports. All evaluations are conducted in accordance with rigorous 

quality assurance and quality control (QA/QC) protocols to ensure that data of known and 

adequate quality are generated and that the results are defensible. 

The EPA’s National Risk Management Research Laboratory and its verification organization 

partner, Battelle, operate the Advanced Monitoring Systems (AMS) Center under ETV. The 

AMS Center recently evaluated the performance of the Xact 625 Particulate Metals Monitor 

produced by Pall Corporation at an ambient air quality monitoring site in Marietta, Ohio. 

Systems for monitoring of metals in atmospheric particulate matter (PM) were identified as a 

priority technology category for verification through the AMS Center stakeholder process. 
2 

Chapter 2 

Technology Description 

The objective of the ETV AMS Center is to verify the performance characteristics of 

environmental monitoring technologies for air, water, and soil. This report provides results 

from verification testing of the Xact 625 Particulate Metals Monitor, which was developed 

and previously manufactured by Cooper Environmental Services LLC (CES) (Portland, OR). 

Commercial rights to the Xact 625 technology are now owned by Pall Corporation (Port 

Washington, NY). The following is a description of the Xact 625, based on information 

provided by the vendor. The information provided below was not verified in this test. 

The Xact 625, shown in Figure 2-1, determines metals in airborne PM less than 10 

micrometers (μm) in aerodynamic diameter (PM10). Metals determination by the Xact 625 is 

based on the principle of X-ray fluorescence (XRF), in which X-rays from a source cause 

removal of an electron from an inner electronic shell of a metal atom in a sample. The 

vacancy in the inner shell is then filled by an electron from an outer shell, with resulting 

emission of an X-ray with a wavelength longer than that of the original excitation and 

characteristic of the metal in question. The Xact 625 uses energy-dispersive XRF (EDXRF), 

in which the detector and electronics resolve emitted X-rays based on their energy. The 

EDXRF approach allows use of a relatively simple optical path and a relatively low power 

X-ray source, and thus reduces the instrument cost. The EDXRF approach also provides 

acquisition of the entire X-ray spectrum very rapidly, so that many elements in the periodic 

table can be detected within a few seconds. 

To monitor metals in atmospheric PM, the Xact 625 uses an automated moveable filter tape 

system, in which sample air is drawn through a small spot on the tape, collecting and 

concentrating PM10 onto that spot. The tape then advances, placing the collected sample spot 

in the X-ray excitation and analysis section of the instrument and initiating sampling onto a 

previously unexposed spot on the tape. The sequence of sampling and analysis can continue 

automatically, limited only by the supply of filter tape. The duration of sample collection at 

each spot can be set at a constant interval, or varied to maintain detection performance in the 

face of varying atmospheric PM10 levels. The Xact 625 samples ambient air at a constant 

flow rate of 16.7 liters per minute (L/min), i.e., 1 cubic meter per hour (m3/hr). The Xact 

625’s sample inlet is designed to provide uniform sample deposition, and the instrument 

analyzes approximately 90% of the sample spot area to minimize effects of sample 

inhomogeneity. The Xact 625 incorporates sensors for temperature and atmospheric 

pressure, and uses those data to maintain a constant volumetric sample flow and 
3 

consequently an accurate PM10 inlet size cut. In addition for this verification the vendor of 

the Xact 625 programmed the monitor to perform the following automatic internal QC

checks on a daily basis to assure data quality: 

• Internal energy alignment check, performed by XRF analysis of a copper (Cu) rod, 

conducted over a 15-minute period starting at midnight each day, 

• Upscale rod check, performed by XRF analysis of a metal rod containing chromium 

(Cr), lead (Pb), and cadmium (Cd), conducted once per day over a 15-minute period, 

• Flow check, conducted at the same time as the upscale rod check, to determine the 

Xact 625 sample air flow by insertion of a second mass flow meter into the flow path, 

• Palladium (Pd) rod stability check, conducted by XRF analysis of a Pd rod in every 

ambient sample analysis. 

Figure 2-1. Xact 625 installed in field trailer for testing; top to 

bottom are the control panel/X-ray source, computer, XRF analysis 

module with sampling tape drive, modem, and datalogger. 
4 

Chapter 3 

Test Design and Procedures 

3.1 Introduction 

Industrial communities are often impacted by emissions of toxic metals such as Pb, 

manganese (Mn), and Cd. For example, EPA’s School Air Toxics (SAT) Monitoring 

Initiative1 has reported that Mn, a neurotoxic metal, is one of the pollutants of greatest 

potential risk near schools in industrialized locations. Standard monitoring methods for 

metals in airborne PM have significant limitations, in that samples are collected on filters 

over a 24-hour time period and must be submitted for laboratory analysis, from which results 

may not be available for several weeks. In contrast, commercially-developed metals 

monitors can potentially determine 10 or more toxic metals simultaneously in ambient PM10 

with time resolution of 1 hour or less. The relatively fast response afforded by such monitors 

can provide advantages such as: 

• Improved ability to associate variations in metals concentrations with time of day or 

meteorological conditions, and thus to attribute metals risk to a particular source 

• Ability to compile datasets large enough to conduct source/receptor modeling, and 

• Cost reduction and time savings due to the generation of metals data onsite without 

waiting for laboratory analysis. 

Thus, continuous metals monitoring may lead to better characterization of environmental 

metals exposures and more effective source identification, allowing decision-makers to 

quickly target industries for enforcement action or voluntary emissions reduction.

This verification test was conducted according to a peer-reviewed quality assurance project 

plan (QAPP),

2

 and conformed to the quality system defined in the ETV3 and AMS Center4

Quality Management Plans (QMPs). As indicated in the QAPP2 the testing satisfied EPA 

QA Category III requirements. The QAPP and this verification report were reviewed by: 

• Rudy Eden, South Coast Air Quality Management District

• Dennis Mikel, U.S. EPA Office of Air Quality Planning and Standards (OAQPS). 

The purpose of this verification test was to generate performance data on metals monitoring 

technologies to inform users about the potential benefits of such technologies. The 

verification results reported here are from testing that involved the continuous operation of a 

Xact 625 monitor at an ambient air monitoring site in Marietta, Ohio, operated by the 

Southeast District Office (SEDO) of the Ohio Environmental Protection Agency (OEPA). 

The PM10 metals data produced hourly by the Xact 625 were averaged and compared to 

metals data from reference method samples collected daily and analyzed in the laboratory. 
5 

The Xact 625 was verified by evaluating the following performance parameters.

• Comparability 

• Correlation 

• Bias 

• Data completeness

• Operational factors

Comparability, correlation, and bias were assessed by comparison of Xact 625 results to 

those from inductively coupled plasma/mass spectrometry (ICP/MS) analysis of samples 

collected by a reference sampling method. Data completeness was determined from the 

number of hourly periods the metals monitor provided readings of PM10 metals 

concentrations. Data completeness was determined both relative to the entire field test period 

and relative to each 24-hour reference sampling period. Each of these performance factors 

was evaluated separately for those target metals detected by both the Xact 625 and the 

reference sampling/ICP-MS approach. Operational performance factors such as maintenance 

requirements, ease of use, and effectiveness of data acquisition were determined from 

observations by the field testing staff. This test was not intended to simulate long-term 

performance of the metals monitor at a monitoring site, but rather to assess the feasibility of 

its use for ambient metals monitoring in near-source locations. In long-term use, metals 

monitoring procedures might be tailored to address the specific conditions, metals 

concentrations, and sources for a given site. 

3.2 Test Procedures

3.2.1 Field Installation 

The Xact 625 used in this testing was purchased in 2011 by EPA’s OAQPS as a stand-alone 

monitoring system, designed and built by CES per EPA specifications. The Xact 625 

monitor was installed in an environmentally controlled trailer specially designed for field 

deployment of the monitor. Figure 3-1 shows an external view of the trailer at the Marietta 

test site with the Xact PM10 inlet, reference sampler (see Section 3.2.2) and meteorological 

sensors located atop the trailer. A view of the Xact 625 installed in the trailer is shown above 

in Figure 2-1. 

The PM10 inlet of the Xact 625 extended through the roof of the trailer and was positioned 

approximately 1.5 m (5 ft) from the inlet of the PM10 reference sampler, as shown in Figure 

3-1. A contractor employed by EPA/OAQPS transported and installed the Xact 625 trailer in 

the field, and performed startup checks on the Xact 625 monitor. The vendor of the Xact 625 

(Pall Corporation) trained OEPA staff in operation of the monitor, and those OEPA staff 

oversaw operation of the monitor during the field testing. The automated internal QC checks 

of the Xact 625 were programmed to take place between midnight and 12:30 am each day. 

As a result, on each test day, the Xact 625 reported 23 one-hour averages and one half-hour 

average measurement of metals in ambient PM10. All Xact 625 measurement data and QC 

results were recorded by the monitor’s datalogger, downloaded by EPA/OAQPS, and 

transferred to Battelle for use in data comparisons.
6 

Figure 3-1. Field trailer used in verification test, showing Xact 625 PM10 inlet, 

reference PM10 automated sampler, and meteorological sensors on the roof. 

3.2.2 Reference Sampling and Analysis 

Ambient PM10 samples for reference metals analysis were collected according to EPA 

Method IO-3.15 using a Partisol Plus 2025 Sequential Ambient Particulate Sampler (Thermo 

Scientific, Hopkinton, MA) equipped with a PM10 size-selective inlet. This sampler is 

designated by EPA as Reference Method RFPS-1298-127 for sampling of ambient PM10. 

The Partisol Plus 2025 uses 47 mm diameter Teflon® sample filters which are exchanged 

automatically after a pre-set sampling interval. The Partisol Plus 2025 can hold up to 16 

filter cassettes, sufficient for more than two weeks of unattended daily sampling. Sample air 

is pulled by an internal pump through the filter currently being sampled, with the sample air 

flow regulated by a mass flow controller. Ambient temperature and pressure readings are 

used along with mass flow control to maintain a constant volumetric sampling rate of 16.7 

L/min. Previously sampled and yet-to-be-sampled filters are sealed off within the Partisol 

Plus 2025 to prevent contamination. The sampler stores sampling and meteorological data in 

internal memory, including the average ambient temperature, ambient pressure, and average 

ambient relative humidity for each filter sample. 

The Partisol Plus 2025 sampler was installed on the roof of the field trailer as shown in 

Figure 3-1 and was operated by OEPA personnel. Samples were collected every day 

Partisol Plus 2025

Reference Sampler

Xact 625 PM10

Inlet

Meteorological 

Sensors
7 

throughout the field period with a 23.5 hour sampling duration, chosen so that reference 

sampling did not take place during the 0.5 hours per day when the Xact 625 performed its 

internal QC checks. Thus, the reference and Xact 625 sampling intervals were identical

throughout the test period. 

The ICP/MS laboratory contracted by EPA/OAQPS delivered blank 47 mm Teflon® filters to 

the field site in individual pre-labeled containers accompanied by chain of custody forms. 

Collected filter samples were removed from the Partisol Plus 2025 sampler approximately 

once per week without interruption of sampling. Collected samples were then shipped to the 

ICP/MS laboratory for extraction and analysis approximately every 2 weeks. 

The reference PM10 filter samples were extracted and analyzed by the ICP/MS laboratory for 

metals content according to the procedures of EPA Method IO-3.5,6

 but using a modified 

acid digestion that included hydrofluoric acid (HF) to improve digestion for some elements. 

The extraction and analysis were performed according to Standard Operating Procedures 

that are incorporated into the laboratory’s QAPP for sampling and analysis in EPA’s national 

monitoring programs.7 The QC requirements of Method IO-3.56 were followed, including 

the use of blanks, QC samples, laboratory fortified blanks, internal standards, and tuning 

solutions. An instrument performance demonstration program included duplicate samples, 

standards, blanks, interference check standards, continuing calibration blanks and verification 

standards, and laboratory control and matrix spikes.7

 The ICP/MS laboratory’s stated 

detection limits for the PM10 metals are summarized in Table 5-1 in Section 5.1. 

3.2.3 Verification Sites and Schedule

The Xact 625 operated from August 19 to November 3, 2011 at an OEPA field site in East 

Liverpool, Ohio. Battelle conducted a technical systems audit (TSA) of the field procedures 

and a performance evaluation (PE) audit of the Partisol Plus 2025 reference sampler at the 

East Liverpool site that confirmed both adherence to the field procedures and valid reference 

sampler operation. However, during operation at the East Liverpool site, clearly erroneous 

ambient temperature and pressure readings were reported by the Xact 625 sensors. Because 

of those readings it was determined that the reliability of the monitor’s sample flow (and 

consequently its PM10 particle size cut) was questionable. The temperature and pressure 

sensors in the Xact 625 were not repaired until the end of the sampling period in East 

Liverpool, and therefore it was concluded that none of the Xact 625 data from the East 

Liverpool site were of sufficient quality to be used for performance verification. It should be 

noted that the failure of those sensors was not caused by a fault in the Xact 625 itself, but by 

the exposed location of the wiring connections for those sensors on the roof of the field 

trailer in which the Xact 625 was installed. The design of those connections was 

subsequently corrected by installation of more durable and weather resistant connections. 

Following repair of the ambient temperature and pressure sensors in the Xact 625, the field 

trailer and Partisol Plus 2025 reference sampler were installed at an OEPA site at the Ohio 

Valley Educational Service Center (OVESC) in Marietta, Ohio. The Xact 625 operated 

continuously at the Marietta site from December 10, 2011 to February 27, 2012, and with 

minor interruptions daily reference samples were collected with the Partisol Plus 2025 

sampler from December 23, 2011 through February 25, 2012. Thus, data for comparison of 
8 

Xact 625 and reference results were obtained over a 65-day period, within an approximately 

80-day period of continuous operation of the Xact 625. The daily reference method samples 

were collected over 23.5-hour sampling intervals, i.e., from 12:30 am to midnight each day. 

This sampling schedule synchronized the reference and Xact 625 sampling periods and 

avoided reference sampling during the half hour each day when the Xact 625 performed its 

internal QC checks. Throughout the period in which the Xact 625 was operating at the 

Marietta site, the monitor’s automated QC check results were reviewed frequently and 

confirmed proper operation of the instrument. 

Both the East Liverpool and Marietta air quality monitoring sites were located in 

industrialized areas near the Ohio River characterized by restricted air flow due to local 

terrain. Both sites were chosen in part based on elevated levels of Mn and other metals found 

in ambient total suspended particulate in EPA’s SAT Monitoring Initiative. Figure 3-2 

shows a map view of the Marietta area, indicating the location of the OVESC sampling site 

and of an industrial facility thought to be a key source of metals emissions in the area.

Figure 3-2. Map view of Marietta, Ohio area showing location of OVESC sampling site 

(white triangle near top of figure) and of suspected metals emission source (red triangle 

at left center of figure). 

OVESC
9 

Chapter 4 

Quality Assurance/Quality Control 

QA/QC procedures and all verification testing were performed in accordance with the QAPP

for this verification test and the QMP for the AMS Center except where noted below. 

QA/QC procedures and results are described below.

4.1 Amendments/Deviations 

Three deviations to the test/QA plan were prepared, approved, and retained in the test 

documentation. Those deviations collectively established the following modifications and 

corrections to the test/QA plan and the test procedures: 

• The period of testing at the East Liverpool site was shortened due to startup 

difficulties with the Partisol Plus 2025 sampler. 

• At the request of the analytical laboratory, reference filter samples were shipped from 

the field site to the analytical laboratory every 2 weeks, rather than every week as 

stated in the QAPP, to provide more efficient handling and analysis of each batch of 

samples.

• Testing was conducted at one site (Marietta) rather than two sites as originally 

planned, due to the failure of the Xact 625’s ambient temperature and pressure 

sensors at the East Liverpool site, as noted in Section 3.2.3. 

• The filters used in the Partisol Plus 2025 sampler were not weighed before shipment 

to the field because determination of PM10 mass concentration was not needed. 

• The analytical laboratory returned ICP/MS analysis results within 7 days of the end of 

the week in which samples were received, rather than within 7 days of sample receipt.

• The sample extraction procedure used by the analytical laboratory was modified 

slightly from the procedure in Method IO-3.5, by the inclusion of HF in the digestion 

reagent. This fact was specified in the laboratory’s standard operating procedure but 

was not stated in the QAPP. 

These deviations are not considered to have had any significant effects on the verification 

data obtained at the Marietta site.

4.2 Reference Methods

The QA/QC procedures for the reference metals sampling and ICP/MS analysis adhered to 

the requirements of the methods used.5-7 The QC results were reported to EPA/OAQPS by 

the analytical laboratory as part of the analytical data package for the reference samples.
10

4.3 Review of Xact 625 QC Data 

The results of the automated daily internal QC checks performed by the Xact 625 were 

reviewed approximately weekly, each time data were downloaded from the instrument. 

Those results showed stability in Xact 625 operations throughout the entire period of 

operation at both the East Liverpool and Marietta sites. Over that entire period the relative 

standard deviation (RSD) of the Pd internal standard readings determined in every Xact 625 

XRF analysis was 2.04%. The instrument’s average flow error was -0.69% (± 0.004%), 

where the value in parentheses is the standard deviation (SD) of the daily flow check results. 

The average accuracy relative to upscale rod check standards analyzed daily was 100.21% 

(±0.004%) for Cr, 100.55% (±0.013%) for Cd, and 99.79% (±0.007%) for Pb, where 

accuracy of 100% represents perfect agreement with the upscale rod check standard. 

4.4 Audits

Three types of audits were performed during the verification test: a TSA of the verification 

test performance, a PE audit of the reference method sampling and analysis, and a data 

quality audit. Audit procedures are described further below. 

4.4.1 Technical Systems Audit 

The Battelle QA Officer performed two TSAs as part of this verification test. The field TSA 

was performed at the East Liverpool test site on October 6, 2011, and focused on observation 

of the sampling material handling, Xact 625 oversight, reference method sampling, and field 

data recording procedures. The first two deviations listed in Section 4.1 were noted in that 

TSA. The second Battelle TSA consisted of a visit on February 23, 2012 to the analytical 

laboratory contracted by EPA/OAQPS to conduct the ICP/MS analyses. That TSA focused 

on laboratory QA/QC, chain of custody, and analytical procedures. No significant findings 

resulted from the laboratory TSA. 

An EPA QA representative also conducted a field TSA at the East Liverpool site on October 

13, 2011. Two findings from that audit addressed communication among the several 

organizations involved in the test, and the failures of the temperature and pressure sensors in 

the Xact 625 that are described in Section 3.2.3. Those sensor failures were the cause of the 

third deviation listed in Section 4.1. Both of these findings were addressed prior to the start 

of testing at the Marietta site, the former by instituting regular conference calls among all 

parties, and the latter by replacement of the temperature and pressure sensor and 

confirmation of their correct operation. 

4.4.2 Performance Evaluation Audit 

A PE audit of the Partisol Plus 2025 reference method sampler was performed at the East 

Liverpool site on December 2, 2011, prior to moving the field test to the Marietta site. The 

PE flow audit was conducted by measuring the sample air flow rate through the sampler by 

means of a National Institute of Science and Technology (NIST)-traceable flow transfer 

standard (BIOS DryCal, Serial No. 103777). The results of that PE audit showed that the 

Partisol 2025 sample flow rate was within 1.9% of the target rate of 16.7 L/min, well within 
11

the target ±5% tolerance of the flow rate. The PE audit of the ambient temperature and 

pressure sensors of the Partisol Plus 2025 sampler was conducted using a Kestrel® Model 

4500 Pocket Weather Tracker (Nielsen-Kellerman, Boothwyn, PA) obtained from Battelle’s 

Instrumentation Services Laboratory (No. LN-269475). The PE audit showed that the 

Partisol Plus 2025 temperature and pressure sensors agreed with the PE audit device within 

0.3 degrees Centigrade (°C) and 1 millimeter of mercury (mm Hg) pressure, respectively. 

These PE audit results were well within the target tolerances of ± 2 °C and ± 4 mm Hg (i.e., 

± 5.3 millibars), respectively. 

Battelle also conducted a PE audit of the reference metals analysis by submitting sample 

solutions of eight target metals to the reference laboratory for analysis. Those PE audit 

samples were prepared by Battelle by dilution of individual aqueous metals standards 

traceable to NIST. The metals concentrations in the PE audit samples were unknown to the 

reference laboratory. Two PE audit samples containing different levels of the eight metals 

were submitted for analysis, and the reference laboratory analyzed each sample both with and 

without dilution. The results from those two analyses agreed closely for each target metal in 

each of the two PE audit samples, so the average of the undiluted and diluted sample results 

was used for comparison to the spike value for each metal. The acceptance criterion for the 

PE audit was that the concentrations reported by the laboratory should be within ±10% of the 

prepared concentrations. The results of the laboratory PE audit are summarized in Table 4-1, 

and show that the reference analyses met that acceptance criterion for all metals in both PE 

audit samples. 

Table 4-1. Summary of PE Audits of Reference Analytical Method

Sample Metal

Standard 

Concentration 

(μg/L)a

Measured 

Concentration 

(μg/L)

Percent 

Difference

# 1 

As 8.0 8.27 3.4

Cd 2.0 2.06 2.8

Cr 8.0 8.34 4.2

Mn 2.0 1.97 -1.3

Ni 2.0 2.14 6.9

Pb 2.0 2.06 3.0

Sb 2.0 1.86 -7.0

Se 8.0 8.77 9.6

# 2 

As 30 30.3 1.1

Cd 7.0 7.36 5.1

Cr 30 30.4 1.3

Mn 7.0 7.12 1.7

Ni 7.0 7.37 5.3

Pb 7.0 7.21 3.0

Sb 7.0 6.73 -3.9

Se 30 32.9 9.7

a: μg/L = microgram per liter
12

4.4.3 Data Quality Audit 

At least 10% of the data acquired during the verification test were audited. Battelle’s QA 

Officer traced the data from the acquisition, through reduction and statistical analysis, to final 

reporting, to ensure the integrity of the reported results. All calculations performed on the 

data undergoing the audit were checked. Only minor and readily correctable data issues were 

noted in the data quality audit, with no effect on the overall quality of the verification results.

4.5 QA/QC Reporting

Each audit was documented in accordance with Sections 3.3.4 and 3.3.5 of the QMP for the 

ETV AMS Center. The Battelle Verification Test Coordinator prepared formal responses to 

all audit findings and observations, including any corrective actions taken. The results of the 

audits and Battelle’s corrective actions were reviewed, approved, and submitted to EPA.

4.6 Data Review 

All data received from EPA for the Xact 625 and the reference method underwent 100% 

review and validation by Battelle technical staff before being used for any statistical 

calculations. Records generated in the verification test received a one-over-one review 

before these records were used to calculate, evaluate, or report verification results. Data 

were reviewed by a Battelle technical staff member involved in the verification test. 
13

Chapter 5 

Statistical Methods 

The statistical methods used to evaluate the quantitative performance factors listed in Section 

3.1 are described in this chapter. All results from the Xact 625 monitor and from the 

reference sampling and ICP/MS analysis were reported as ambient metals concentrations in 

nanograms per cubic meter (ng/m3

) of air at ambient (i.e., not standard) conditions. Nondetect results from the reference method for any metal were flagged as such, and excluded 

from any data comparisons. 

5.1 Averaging of Xact 625 Hourly Data 

The Xact 625 readings on each test day consisted of one half-hour measurement and 23 onehour measurements, with all sampling done at the same flow rate (i.e., 16.7 L/min). 

Consequently, integration of the Xact 625 results over a daily 23.5-hour time period required 

simple arithmetic averaging of the 24 total concentration results, but with the 0.5-hour result 

given half the weight of the 23 1-hour results, i.e.: 

23.5 Hour Average = (0.5c1 + c2 + ...c24)/23.5 (1)

where c1, c2, ...c24 are the metals concentrations reported each hour by the Xact 625. 

Before the resulting daily average results from the Xact 625 monitor were compared to the 

corresponding daily integrated sample results from the reference method, they were

compared to a daily quantitation limit (QL) of the Xact 625 for each target metal. The QL is 

a defined value for each target metal and roughly corresponds to 10% uncertainty in an 

interference-free situation.8

 Three distinct hourly QL values were applicable to the Xact 625 

data for each metal, and were used to determine the daily QL value for each metal. Those 

three hourly QL values were:

• The normal hourly QL value for a Xact 625 sample collected over 1 hour and 

analyzed by XRF over the following hour. This QL value applies to 22 of the 24 

hourly readings reported each day by the Xact 625. 

• The QL value for an Xact 625 sample collected between 11:00 pm and midnight, 

which was collected over 1 hour but only analyzed by XRF for 0.5 hour (due to the 

internal QC checks performed by the Xact 625 between midnight and 12:30 am). 

This QL value equals the normal hourly QL value times √2 (i.e., times 1.414). 
14

• The QL value for a Xact 625 sample collected between 12:30 am and 1:00 am, which 

was collected for 0.5 hour (due to the internal QC checks performed by the Xact 625 

between midnight and 12:30 am) but analyzed by XRF for 1 hour. This QL value 

equals the normal hourly QL value times 2. 

Daily QL values for each metal reported by the Xact 625 were determined as the 

appropriately weighted average of the three different hourly QL values. Table 5-1 lists the 

three hourly QL values for each of the 23 metals reported by the Xact 625, along with the 

resulting daily QL value. A footnote to the table illustrates the calculation procedure used. 

Daily average Xact 625 results for any metal that were less than the Xact 625 daily QL for 

that metal were excluded from the statistical calculations summarized below. For 

comparison, the detection limits reported by the ICP/MS analysis laboratory for each metal 

are also shown in the last column of Table 5-1. 

Table 5-1. Calculation of the Xact 625 Daily QL for Elements Reported in Ambient Air 

at the Marietta Site and Comparison to ICP/MS Detection Limits

Element

Xact 625 Quantitation Limits Laboratory 

ICP/MS 

Detection Limit

(ng/m3) 

Normal 1-

hour QL 

(ng/m3)

a

11:00 pm to 

Midnight QL 

(ng/m3)

b

12:30 to 1:00 

am QL 

(ng/m3)

c

Calculated 

Daily QL

(ng/m3)

d

As 0.81 1.14 1.62 0.84 0.17

Ba 6.68 9.45 13.4 6.95 0.66

Br 1.31 1.85 2.61 1.35 e

Ca 6.38 9.02 12.8 6.62 113

Cd 40.6 57.5 81.3 42.2 0.01

Co 2.24 3.17 4.48 2.32 0.03

Cr 2.04 2.88 4.08 2.12 24.2

Cu 1.89 2.67 3.78 1.96 2.51

Fe 5.37 7.59 10.7 5.57 e

Hg 1.33 1.89 2.67 1.38 0.05

K 16.7 23.7 33.5 17.4 e

Mn 2.00 2.83 4.00 2.08 0.32

Mo 6.94 9.81 13.9 7.21 0.19

Ni 1.60 2.26 3.19 1.66 0.40

Pb 1.54 2.18 3.09 1.60 0.07

Rb 2.43 3.44 4.86 2.52 0.02

Sb 4.69 6.63 9.38 4.88 0.28

Se 0.99 1.41 1.99 1.03 0.35

Sr 3.16 4.47 6.33 3.29 0.09

Th 11.3 16.0 22.6 11.7 0.01

Ti 2.69 3.80 5.37 2.80 e

Tl 1.30 1.84 2.60 1.35 0.003

Zn 1.64 2.31 3.27 1.70 5.93

a: Sample collected over 1 hour and analyzed by XRF over 1 hour; b: Sample collected over 1 hour and 

analyzed by XRF over 0.5 hour; c: Sample collected over 0.5 hour and analyzed by XRF over 1 hour.

d: Calculated as (22 × Normal QL + (11 pm to midnight QL) + 0.5 × (12:30 to 1:00 am QL))/23.5; e.g., for As 

daily QL = (22 × 0.81 + 1.14 + 0.5 × 1.62)/23.5 = 0.84 ng/m3

. 

e: Element not reported from ICP/MS analysis.
15

5.2 Comparability

For each target metal, comparability was determined by a linear regression of the data using 

the reference method results as the independent variable and the Xact 625 results as the

dependent variable, as follows. 

Ci = (m•Ri) + b (2) 

where Ri is the ith daily reference measurement, Ci is the average of the Xact 625 

measurements over the same 23.5-hour time period, and m and b are the slope and intercept 

of the linear regression, respectively. Comparability is reported in terms of the m and b

values obtained from the linear regression for each metal determined by the Xact 625 and the 

reference method. Comparability results also indicate whether each reported slope or 

intercept value is significantly different from 1.0 or from zero, respectively (i.e., whether the 

95% confidence interval [CI] excludes a slope of 1.0 or an intercept of zero, respectively). 

5.3 Correlation

The degree of correlation between the Xact 625 results and the reference method results was

determined by the coefficient of determination (r2

) of the linear regression between the daily

reference method results and the corresponding daily averages of the Xact 625 measurements 

over the same time periods. The r2 value was determined separately for each metal

measured.

5.4 Bias 

The bias of the Xact 625 readings was evaluated in terms of the percent difference of the 

daily average Xact 625 readings relative to the corresponding daily average reference method 

results. That is, for each target metal (i) in each 23.5-hour reference method period (j), bias

for that metal in that period (Bi, j) was calculated as:

Bi,j = (Average Monitor Reading - Reference Reading) × 100 (3) 

Reference Reading 

The bias results are reported in terms of the mean, median, range, and SD of the individual 

Bi,j results for each metal. Also, the individual Bi,j results for each metal were compared to 

the ambient metal concentrations to determine whether bias is a function of the ambient 

concentration of the metal.

5.5 Data Completeness

Data completeness (DC) was determined in two ways. The first was as the percentage of all 

hours in the field period in which the metals monitor reported ambient metals data, relative to 

the total number of hours in the field period: 

DC1 = (# Hours data return/Total hours in period) × 100 (4) 
16

DC was also calculated as the percentage of all 23.5-hour reference measurement periods 

during which the monitor reported at least 12 hours of monitoring data (i.e., produced data 

for at least half of the reference monitoring period): 

DC2 = (# Periods with ≥ 12 hours monitor data/# Reference periods) × 100 (5) 

Both forms of DC were calculated for each target metal.
17

Chapter 6 

Test Results 

This chapter summarizes the metals monitoring results from the Xact 625 at the Marietta site, 

and the comparisons of those results to the corresponding results of the reference sampling 

and ICP/MS analysis. Section 6.1 shows illustrative results from the Xact 625 and the 

reference method, and Sections 6.2 through 6.4 show results for the quantitative performance 

parameters identified in Section 3.1. Section 6.5 summarizes observations on operational 

factors of the Xact 625. 

6.1 Xact 625 Ambient Metals Results

Mn was the predominant toxic metal determined in ambient air during the field period in 

Marietta, OH. To illustrate the ambient levels observed, Figure 6-1 shows the hourly Xact 

625 readings of Mn, potassium (K), iron (Fe), and zinc (Zn) from December 10, 2011 to 

February 27, 2012. Although most hourly Mn concentrations were below 10 ng/m3

, Figure 

6-1 shows approximately 20 hourly Mn concentrations exceeding 1 μg/m3, with a maximum 

hourly reading of 5.9 μg/m3

 on February 7. K, Fe, and Zn are shown in Figure 6-1 because 

analysis of the Xact 625 data showed those metals to have the highest degree of correlation 

with the Mn data. Figure 6-1 shows that K and Fe concentrations were similar, and that peak 

concentrations of these metals often, but not always, coincided with peak concentrations of 

Mn. The peak concentrations of Mn usually exceeded the simultaneous concentrations of Fe 

and K. The median hourly Zn concentration was 12 ng/m3, but the maximum Zn 

concentration was 965 ng/m3, and occurred on February 7, coincident with the maximum 

hourly Mn concentration. The concentrations of other metals in Marietta were much lower in 

this time period. For example, Pb exhibited mean and median concentrations of 5.2 and 3.9 

ng/m3

, respectively, with a maximum hourly reading of 98 ng/m3. 

The episodes of elevated Xact 625 metals readings in Marietta did not typically consist of 

single hourly spikes, but rather were periods of elevated concentrations lasting from a few 

hours to several hours. As an example, Figure 6-2 shows the period from February 5 to 7, 

2012, in which the highest Mn levels were observed. Figure 6-2 shows that those levels 

occurred as two separate peaks in an episode that lasted approximately 12 hours.

Table 6-1 summarizes the 1,829 hourly readings of the 23 metals reported by the Xact 625 in 

continuous operation at the Marietta site. That table shows the mean, median, maximum, and 

minimum hourly reading of each metal, and for comparison the Xact 625’s hourly method 

detection limit (MDL) and hourly QL for each metal, in ng/m3

. 
18

0

1000

2000

3000

4000

5000

6000

12/7 12/17 12/27 1/6 1/16 1/26 2/5 2/15 2/25

Concentration, ng/m3

Mn

Fe

K

Zn

Figure 6-1. Xact 625 hourly monitoring data for Mn, K, Fe, and Zn in Marietta, OH 

from December 10, 2011 to February 27, 2012. 

Figure 6-2. Example of elevated metals concentrations over a period of several hours. 

0 

1000

2000

3000

4000

5000

6000

2/5/2012 15:00 2/6/2012 3:00 2/6/2012 15:00 2/7/2012 3:00 2/7/2012 15:00

Concentration, ng/m3

Mn

Fe

K

Zn
19

Table 6-1. Summary of Hourly Values of All Metals Reported by the Xact 625 in 

Marietta, Ohio from December 10, 2011 to February 27, 2012 

Metal

Ambient Concentrationa (ng/m3) MDLb

(ng/m3)

QLb

(ng/m3 Mean Median Maximum Minimum )

As 0.15 < MDL 31.5 < MDL 0.11 0.81

Ba 1.82 < MDL 148 < MDL 0.95 6.68

Br 4.09 3.22 126 < MDL 0.18 1.31

Ca 212 142 1,830 < MDL 0.90 6.38

Cd < MDL < MDL 21.1 < MDL 5.75 40.64

Co < MDL < MDL 0.43 < MDL 0.32 2.24

Cr 0.73 < MDL 106 < MDL 0.29 2.04

Cu 3.11 2.37 450 0.77 0.27 1.89

Fe 126 95.1 1,711 7.91 0.76 5.37

Hg < MDL < MDL 0.62 < MDL 0.19 1.33

K 158 122 4,970 49.8 2.37 16.7

Mn 95.5 6.45 5,910 < MDL 0.28 2.00

Moc 11.8 11.3 37.3 9.02 0.98 6.94

Ni 0.48 0.30 31.2 < MDL 0.23 1.60

Pb 5.21 3.92 97.7 0.79 0.22 1.54

Rb 0.36 < MDL 26.9 < MDL 0.34 2.43

Sb < MDL < MDL 3.65 < MDL 0.66 4.69

Se 1.28 0.95 11.6 < MDL 0.14 0.99

Sr 1.33 1.07 37.7 < MDL 0.45 3.16

Th < MDL < MDL 4.68 < MDL 1.60 11.3

Ti 9.64 5.93 491 < MDL 0.38 2.69

Tl < MDL < MDL 2.78 < MDL 0.18 1.30

Zn 19.2 12.0 965 1.25 0.23 1.64

a: Based on 1,829 hourly readings.

b: MDL = method detection limit, QL = quantitation limit, for normal hourly data. QL corresponds to 10% 

uncertainty in an interference-free situation.8

 MDL corresponds to ±1 SD interference free, consistent with 

EPA Method IO 3.3.8,9

c: See text.

Of the 23 metals reported by the Xact 625, 19 were also determined by the ICP/MS analysis 

of reference samples. For those 19 metals, the daily 23.5-hour averages of the Xact 625 data 

were calculated as described in Section 5.1 and compared to the respective daily QL values 

listed in Table 5-1. For 12 of those 19 metals (arsenic [As], barium [Ba], Cd, cobalt [Co], Cr, 

mercury [Hg], nickel [Ni], rubidium [Rb], antimony [Sb], strontium [Sr], thorium [Th], and 

thallium [Tl]), the resulting daily averages of the Xact 625 hourly data were almost always 

below the respective daily QL values of the Xact 625, and consequently no statistical 

comparison could be made to the reference metals data. 

Also, the Xact 625 reported ambient molybdenum (Mo) concentrations that were almost 

always approximately 12 ng/m3 throughout the entire field period. This observation is 

illustrated in Table 6-1, in that the minimum hourly Mo value was over 9 ng/m3, and the 

mean and median were 11.8 and 11.3 ng/m3, respectively. Those Xact 625 Mo results were 

identified as a detection artifact by the vendor through inspection of Xact 625 spectral data. 

Although the Mo data from the field test were affected by this artifact and cannot be used for 
20

comparison to reference data, the vendor indicates that in the future this artifact can be 

prevented by narrowing the X-ray energy window used for determination of Mo. 

For the remaining six metals determined by the Xact 625 (calcium [Ca], Cu, Mn, Pb, 

selenium [Se], and Zn) quantitative comparisons could be made between the daily average 

Xact 625 results and the daily ICP/MS results. Figures 6-3 through 6-8 show the linear 

regression of Xact 625 daily average results against the ICP/MS method results for Ca, Cu, 

Mn, Pb, Se, and Zn, respectively. Each of these figures also shows the linear regression 

equation and r2 value.

Figure 6-3. Linear regression of Xact 625 daily averages against ICP/MS daily averages 

for Ca. 

y = 0.8219x - 30.635

R2 = 0.9792

0 

100

200

300

400

500

600

700

800

0 200 400 600 800 1000 1200

Xact 625 Result, ng/m3 

ICP/MS Result, ng/m3 
21

Figure 6-4. Linear regression of Xact 625 daily averages against ICP/MS daily averages 

for Cu.

y = 1.0377x - 0.0938

R2 = 0.9985

0 

200

400

600

800

1000

1200

0 200 400 600 800 1000 1200

Xact 625 Result, ng/m3 

ICP/MS Result, ng/m3 

Excluded

Figure 6-5. Linear regression of Xact 625 daily averages against ICP/MS daily averages 

for Mn.

y = 0.3039x + 2.0701

R2 = 0.3408

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0.0 2.0 4.0 6.0 8.0 10.0

Xact 625 Result, ng/m3 

ICP/MS Result, ng/m3 
22

Figure 6-6. Linear regression of Xact 625 daily averages against ICP/MS daily averages 

for Pb.

y = 0.9862x + 0.0116

r2 = 0.9264

0 

0.5

1 

1.5

2 

2.5

3 

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

Xact 625 Result, ng/m3 

ICP/MS Result, ng/m3 

Figure 6-7. Linear regression of Xact 625 daily averages against ICP/MS daily averages 

for Se.

y = 1.0595x + 1.5557

R2 = 0.943

0 

2 

4 

6 

8 

10

12

14

16

18

20

0 2 4 6 8 10 12 14 16 18

Xact 625 Result, ng/m3 

ICP/MS Result, ng/m3 
23

Figure 6-8. Linear regression of Xact 625 daily averages against ICP/MS daily averages 

for Zn.

It should be noted that one data point for Mn in Figure 6-5 has been excluded from the linear 

regression calculation shown in that figure. That data point is from January 9, 2012, on 

which day the Xact 625 reported only 13 hourly readings, for reasons that are described in 

Section 6.4. This data point is markedly offset from all other Mn results in Figure 6-5, and 

has a substantial effect if included in the regression. It is likely given the great variability 

observed in Mn concentrations that the 13 hourly values reported by the Xact 625 on January 

9 do not adequately indicate the daily average Mn over that entire day, and as a result agree 

poorly with the reference sample result. The data for other metals from that same day were 

also reviewed, and were found not to be outliers and consequently were not excluded from 

the corresponding regressions. Note that on January 6, 2012 the Xact 625 recorded only 14 

hourly readings (see Section 6.4), but no reference sample was collected on that day so there 

is no impact on the comparison of Xact 625 and reference results. 

6.2 Comparability and Correlation 

Table 6-2 summarizes the outcome of linear regression of the daily average Xact 625 results 

against the corresponding reference results for each target metal for which this comparison 

could be made. For each metal Table 6-2 shows the number of data points in the regression, 

the slope and intercept of the regression line, and the r2

 value. The slope and intercept results 

are shown with their associated 95% CI values. Slope results that do not include a value of 

1.0 within the 95% CI, and intercept values that do not include a value of 0.0 within the 95% 

CI, are highlighted by bold font in Table 6-2. 

Table 6-2 shows that the regression slopes for Mn, Pb, Se, and Zn are relatively close to 1.0, 

although a slope of 1.0 falls slightly outside the 95% CI range of the slope for Mn. The slope 

y = 0.9713x - 3.0144

r2 = 0.9883

0 

20

40

60

80

100

120

140

160

180

200

0 50 100 150 200

Xact 625 Result, ng/m3 

ICP/MS Result, ng/m3 
24

Table 6-2. Results of Linear Regression of Xact 625 and Reference Data 

Metal

Number of 

Data 

Points

Slopea

(±95% CI)

Interceptb

(ng/m3) 

(±95% CI)

Coefficient of 

Determination 

(r2)

Ca 47 0.822

(± 0.035)

-30.6

(± 11.9) 0.979 

Cu 26 0.304

(± 0.169)

2.07

(± 0.647) 0.341 

Mn 48 1.038

(± 0.012)

-0.094

(± 2.13) 0.999 

Pb 52 1.059

(± 0.072)

1.56

(± 0.301) 0.943 

Se 25 0.986

(± 0.114)

0.012

(± 0.219) 0.926 

Zn 53 0.971

(± 0.029)

-3.01

(± 0.977) 0.988 

a: Values in bold indicate 95% CI does not include slope of 1.0.

b: Values in bold indicate 95% CI does not include intercept of zero.

for Ca, and especially the slope for Cu, are substantially less than 1.0. Table 6-2 also shows 

that the regression intercepts for Ca, Cu, Pb, and Zn differ significantly from zero. As shown 

in Figures 6-3 to 6-8, the concentration ranges of the target metals and the numbers of data 

points available for regression analysis differ greatly among the six metals. In that regard the 

strikingly different regression results for Cu and Se are noteworthy, given the similarly low 

concentration ranges and the relatively small numbers of data points available for these 

metals (Figures 6-4 and 6-7, respectively). A likely cause of the weak regression for Cu is 

that the Cu concentrations were near both the detection limit of the ICP/MS analysis and the 

QL of the Xact 625. In addition, after the field period in Marietta was completed the vendor 

of the Xact 625 investigated Xact 625 XRF spectra, including a spectrum of a blank section 

of the Xact 625’s filter tape obtained prior to the start of monitoring in Marietta. The vendor 

indicated a Cu reading on the blank tape equivalent to approximately 6 ng/m3

. A single 

blank analysis result must be viewed with caution, but this observation suggests that Xact 

625 tape background may have contributed to the regression results for Cu, and that analysis 

of a blank spot on the filter tape should be part of the routine daily QC checks of the Xact 

625. Such a blank analysis is generally recommended by the vendor but was not included 

among the automated QC procedures implemented by the vendor for this verification. 

With the exception of Cu Table 6-2 shows strong correlation of the Xact 625 and reference 

method results, with r2 values ranging from 0.926 for Se to 0.999 for Mn. 

The regression plots for Ca, Mn, Pb, and Zn (Figures 6-3, 6-5, 6-6, and 6-8) each show one 

data point that is at a much higher concentration than all other data points. To assess whether 

these single data points unduly influenced the regression results shown for those metals in 

Table 6-2, the regressions were also calculated without these single data points. The impact 

of these single points on the respective regression results was found to be minimal. For 

example, for Ca, Mn, and Zn the regression slope changed by 0.018 or less upon exclusion of 

the highest data point, r2 values also changed only slightly, and no changes occurred in the
25

significance of the difference of slope values from 1.0 or intercept values from 0.0. A small 

effect was seen for Pb, for which exclusion of the highest data point increased the regression 

slope from 1.059 to 1.149 (the latter significantly different from 1.0), decreased the intercept 

from 1.556 to 1.305 (both significantly different from 0.0), and reduced r2 from 0.943 to 

0.914. Nevertheless, these small differences do not alter the overall picture of the Xact 625’s 

performance relative to the reference method in determining Pb. It was concluded that the 

single high data points in the regressions for Ca, Mn, Pb, and Zn do not exert undue effect on 

the regression results for these metals, and these data points were included in the regressions.

6.3 Bias

Table 6-3 summarizes the bias results for the six metals for which Xact 625 results can be 

compared to the ICP/MS results. The bias values were calculated according to Equation 3 in 

Section 5.4. Shown in Table 6-3 for each metal are the mean (± SD), median, and range of 

the individual bias values found by this comparison. 

Table 6-3. Bias of Xact 625 Results Relative to Reference Results 

Metal

Number of 

Data Points

Bias (%)

Mean (± SD) Median Range

Ca 47 -31.3

(± 9.5) -31.0 -57.0 to -9.8 

Cu 26 -5.6

(± 22.1) 1.2 -56.0 to 26.2 

Mn 48 1.1

(± 21.8) -0.6 -33.3 to 103 

Pb 52 74.8

(± 54.3) 61.9 8.7 to 339 

Se 25 -0.70

(± 8.1) -1.3 -15.9 to 17.7 

Zn 53 -20.5

(± 15.4) -17.9 -59.3 to 27.6 

The percent bias results in Table 6-3 appear to present a different picture than the regression 

results in Section 6.2, in that (e.g.) a low average bias is indicated for Cu and a relatively 

large average bias for Pb. The bias results are sensitive to the magnitude of the 

concentrations being compared, i.e., a small quantitative difference in measurement results 

can equate to a large percent bias if the reference result is a small concentration. 

Consequently, a regression equation and r2 value indicating similarity of results may not 

correspond to low percent bias values. A good example is Pb, for which the regression line 

is shown in Figure 6-5. Although the regression slope for Pb is only slightly above 1.0 (i.e., 

1.059), the positive intercept of approximately 1.5 ng/m3 is relatively large compared to the 

reference Pb concentrations, more than half of which are less than about 3 ng/m3

. 

After the field period in Marietta was completed the vendor of the Xact 625 analyzed the 

XRF spectrum of a blank section of the Xact 625’s filter tape obtained prior to the start of 

monitoring in Marietta, and observed a blank Pb level equivalent to approximately 1 ng/m3

. 
26

This observation indicates that the Xact 625 filter tape background may have contributed 

significantly to the positive intercept for Pb, reinforcing the suggestion made in Section 6.2 

that analysis of the blank filter tape should be part of the routine daily QC checks of the Xact 

625. 

In the case of Ca, the combination of a relatively low slope and relatively large negative 

intercept (Figure 6-3) contribute to the negative bias values shown in Table 6-3. On the other 

hand, in the case of Cu the relatively random magnitude and direction of the differences 

between Xact 625 and ICP/MS results shown in Figure 6-3 result in an overall average 

percent bias close to zero despite a wide range of individual bias values.

The influence of the absolute magnitude of the measured concentrations on the percent bias 

results is illustrated in Figure 6-9, which plots the individual percent bias values for Pb as a 

function of the reference method concentrations for that metal. The percent bias values for 

Pb are all positive, but clearly decline sharply as the reference Pb concentration increases. 

Figure 6-9. Percent bias results for Pb as a function of the reference concentration.

6.4 Data Completeness

The DC for the Xact 625 in operation at the Marietta site was calculated in two ways as 

described in Section 5.5. DC for each metal was calculated both as the percentage of hourly 

data collected during the verification testing period, and as the percentage of the 23.5-hour 

daily averaging periods in which the Xact 625 provided at least 12 readings. Hourly DC was

calculated over both the entire period of operation of the Xact 625 in Marietta (December 10, 

2011 to February 27, 2012; 1,905 total possible hours) and over the 65-day period during 

which the reference samples were collected (December 23 to February 25; 1,560 total 

0 

50

100

150

200

250

300

350

400

0 5 10 15 20

Bias of Xact 625 Result, %

ICP/MS Pb Result, ng/m3 
27

possible hours). Completeness relative to daily 23.5-hour periods was calculated only for the 

latter period. Table 6-4 summarizes the DC results.

Table 6-4. Data Completeness for the Xact 625

Measure of Completeness Time Period Value (%)

Completeness of Hourly 

Data 12/10/11 to 2/27/12 96.0

Completeness of Hourly 

Data 12/23/11 to 2/25/12 95.4

Percentage of Days with 

≥12 Hours of Data 12/23/11 to 2/25/12 96.9

Table 6-4 shows that the completeness of the Xact 625’s hourly data was greater than 95% 

over both its entire operational period at the Marietta site and over the 65-day period of 

reference sampling. By far the largest episode of missing Xact 625 data was from 3:00 pm 

on Friday, January 6 to 11:00 am on Monday, January 9, 2012. This loss of data resulted 

when the Xact 625 software opened a second XRF control screen, causing routine sampling 

to be interrupted. No reason could be found for this event, but because the data loss began on 

a Friday afternoon, the problem was not discovered and corrected until site operators visited 

the site on the following Monday. This event caused the Xact 625 to produce only 14 hourly 

readings on January 6, none on January 7 and 8, and 13 hourly readings on January 9. On all 

other sampling days between December 23 and February 25, the Xact 625 returned at least 

22 hourly readings. Thus, the Xact 625 provided hourly readings for less than 12 hours on 

only two days out of the 65 days on which reference sampling occurred. 

6.5 Operational Factors

The Xact 625 was installed in the field trailer shown in Figure 3-1 prior to its arrival at the 

field site. Consequently, installation of the Xact 625 was not evaluated in this test. Startup 

of the Xact 625 was straightforward upon setup of the field trailer at the test site, and the 

analyzer was ready for routine operation within about one day after electrical power was 

connected to the trailer. The Xact 625 operated reliably throughout the field test, as indicated 

by the DC results in Section 6.4, and required minimal operator attention. The filter tape in 

the analyzer was replaced approximately every 2 weeks, but no other routine maintenance 

was needed. During the period in which the Xact 625 was installed at the East Liverpool 

site, the temperature and barometric pressure sensors of the analyzer malfunctioned, 

invalidating the Xact 625 data from that site. However, that malfunction was caused by the 

design and installation of connectors for those sensors in an exposed location on the roof of 

the field trailer, and not by an issue with the Xact 625 itself.

The Xact 625 was programmed to carry out several internal automated QC checks on a daily 

basis, and did so without interruption during the field period. The results of these QC checks 

are summarized in Section 4.3, and demonstrated stable performance, minimal flow

variation, and close agreement with calibration standards throughout the entire field period at 

both the East Liverpool and Marietta sampling sites. Analysis of the Xact 625’s blank filter 
28

tape to determine background metals levels was not part of the monitor’s automated daily QC 

checks. However the results reported above, and investigations conducted by the vendor 

after the Marietta field period, indicate that inclusion of blank filter analysis in such QC 

checks may be valuable. 

The data files produced by the Xact 625 clearly distinguished the QC analysis periods from 

the normal hourly ambient sampling periods, and included a variety of analyzer operating 

data in addition to the measured ambient metals concentrations in ng/m3. Those operating 

data included ambient and internal analyzer temperatures, ambient barometric pressure and 

tape pressure drop, sample flow rates in actual and standard units, sample volumes, and 

alarm and QC indications. The data files were well organized and allowed quick review to 

assess Xact 625 operations and QC results, such as those summarized in Section 4.3. Xact 

625 data files were reviewed at least weekly by a Pall Corporation representative to assess 

the analyzer’s operating stability, but the data files were clear enough that a similar review 

could be performed by any user familiar with the file format. 

The purchase price of the Xact 625 at the time of preparation of this report was

approximately $180,000. This price is subject to change.
29

Chapter 7 

Performance Summary

Of the 23 ambient PM10 metals determined by the Xact 625 in this verification, 19 were also 

determined by the ICP/MS analysis of reference samples. Of those 19 metals, Xact 625 

results for 12 metals were almost always below the respective QLs of the Xact 625, and for 

one other metal (Mo) the Xact 625 reported a nearly constant and unrealistic ambient 

concentration due to an incorrect energy window for that metal in the XRF analysis. The 

vendor of the Xact 625 indicates that this problem can be avoided in the future by narrowing 

the energy window. Table 7-1 presents a summary of the quantitative performance results of 

the Xact 625 for the remaining six metals, showing the performance parameters and resulting 

performance metrics. 

Table 7-1. Quantitative Performance Results for the Xact 625 

Performance 

Parameter Metal Metric

Comparability 

Slope Intercept (ng/m3)

Ca 0.822 -30.6

Cu 0.304 2.07

Mn 1.038 -0.094

Pb 1.059 1.56

Se 0.986 0.012

Zn 0.971 -3.01

Correlation

Coefficient of Determination (r2)

Ca 0.979

Cu 0.341

Mn 0.999

Pb 0.943

Se 0.926

Zn 0.988

Bias

Mean (%) Median (%)

Ca -31.3 -31.0

Cu -5.6 1.2

Mn 1.1 -0.6

Pb 74.8 61.9

Se -0.7 -1.3

Zn -20.5 -17.9

Data 

Completeness 

Hourly Data 

(%)

Daily Averages 

with ≥ 12 Hours 

(%)

All 95.4 to 96.0 96.9
30

Table 7-1 indicates that the daily average Xact 625 results were highly correlated and in 

close quantitative agreement with ICP/MS analysis results for most of the six metals, and that 

the Xact 625 achieved data completeness of over 95%. The regression results for Cu reflect 

the fact that Cu concentrations were often near the detection limit of the ICP/MS analysis and 

the QL of the Xact 625. In addition, investigations conducted after the verification test 

suggest that the regression results for Cu and the bias results for Pb may have been affected 

by the levels of these metals in the Xact 625’s blank filter tape.

The Xact 625 required minimal operator attention during testing, with routine maintenance 

consisting of changing the sampling tape approximately every 2 weeks. The monitor 

conducted several automated internal QC checks on a daily basis, and provided readily 

understandable data files that distinguished QC from ambient monitoring results and 

included analyzer flow and internal readings. The RSD of the Pd internal standard readings 

determined in every Xact 625 XRF analysis was 2.04%. The monitor’s average flow error 

was -0.69% (± 0.004%), where the value in parentheses is the SD of the daily flow check 

results. The average accuracy relative to upscale rod check standards analyzed daily was 

100.21% (±0.004%) for Cr, 100.55% (±0.013%) for Cd, and 99.79% (±0.007%) for Pb, 

where accuracy of 100% represents perfect agreement with the upscale rod check standard. 

However, the test results noted above for Cu and Pb strongly indicate that analysis of blank 

portions of the filter tape should be a component of the Xact 625’s automated internal QC 

checks. 
31

Chapter 8

References

1. School Air Toxics Monitoring Initiative, information available at 

http://www.epa.gov/ttn/amtic/airtoxschool.html. 

2. Quality Assurance Project Plan for the Verification of the Xact 625 Ambient Particulate 

Metals Monitor, Battelle, Columbus, Ohio, August 2011 

3. U.S. EPA, Environmental Technology Verification Program Quality Management Plan, EPA 

Report No: 600/R-08/009 EPA/600/R-03/021, U.S. Environmental Protection Agency, 

Cincinnati, Ohio, January 2008. 

4. Battelle, Quality Management Plan for the ETV Advanced Monitoring Systems Center, 

Version 7.0, U.S. EPA Environmental Technology Verification Program, prepared by 

Battelle, Columbus, Ohio, November 2008. 

5. Compendium method IO-3.1, Selection, Preparation, and Extraction of Filter Material, in 

Compendium of Methods for the Determination of Inorganic Compounds in Ambient Air, 

EPA/625/R-96/010a, U.S. Environmental Protection Agency Office of Research and 

Development, June 1999. 

6. Method IO-3.5, Determination of Metals in Ambient Particulate Matter Using Inductively 

Coupled Plasma/Mass Spectrometry (ICP/MS), in Compendium of Methods for the 

Determination of Inorganic Compounds in Ambient Air, EPA/625/R-96/010a, U.S. 

Environmental Protection Agency Office of Research and Development, June 1999. 

7. Quality Assurance Project Plan for Support for the EPA National Monitoring Programs 

(NMOC, UATMP, PAMS, HAPs, and NATTS), EPA Contract EP-D-09-048, ERG, 

Morrisville, North Carolina, 2011. 

8. Currie, Lloyd A., Detection and Quantitation in X-Ray Fluorescence Spectrometry. In Xray Fluorescence Analysis of Environmental Samples, Dzubay, Thomas B., ed.; Ann 

Arbor Science, Ann Arbor, MI, 1978; pgs. 289-305. 

9. Method IO-3.3, Determination of Metals in Ambient Particulate Matter Using X-Ray 

Fluorescence (XRF) Spectroscopy, in Compendium of Methods for the Determination of 

Inorganic Compounds in Ambient Air, EPA/625/R-96/010a, U.S. Environmental 

Protection Agency Office of Research and Development, June 1999.