1

The Ambient Air

Precision and Accuracy

Program

1995 Annual Report

David Musick

Monitoring and Quality Assurance Group

Emissions, Monitoring, and Analysis Division

Office of Air Quality Planning

and Standards
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EXECUTIVE SUMMARY

Many important EPA decisions are based on the nationwide ambient

air monitoring data obtained by the State and Local agencies. This

data is collected by approximately 5,000 ambient air samplers which

make up the State and Local Air Monitoring Stations (SLAMS)

network. Data collected are used by the EPA to aid in planning the

Nation’s air pollution control strategy and to measure achievement

toward meeting the national ambient air quality standards (NAAQS).

Unfortunately, not all data are accompanied by estimates of its

quality. To assure the most knowledgeable and effective use of the

data, the quality of the national monitoring data should be

determined and made known to all data users. The Code of Federal

Regulations (CFR), Part 58, directed that precision and accuracy

checks be incorporated by the State and Local agencies to verify

the quality of the collected data. 

Precision is used in the sense of “repeatability of measurement

values under specified conditions.” Accuracy is used in the sense

of a measure of “closeness to the truth.” The CFR requires that

measures of data quality be reported on the basis of ‘reporting

organization.’ A reporting organization is defined as a State or

subordinate organization within a State which is responsible for a

set of stations which monitor the same pollutant and for which

precision and accuracy assessments can be. States must define one

or more reporting organizations for each pollutant such that each

monitoring station in the State SLAMS network is included in one,

and only one, reporting organization. The quality assurance

guidelines for precision is +/- 15 % and the guideline for accuracy

is +/- 20 % (see the Quality Assurance Handbook for Air Pollution

Measurement Systems, Volume II, section 2.0.11). 

A review of the yearly 1995 data for the six criteria pollutants:

Ozone (O3) Sulfur Dioxide (SO2) 

Carbon Monoxide (CO) Nitrogen Dioxide (NO2) 

Particles (PM10) Lead (Pb)

was performed on the precision and accuracy data for reporting

organizations as reported to the EPA’s Aerometric Information

Retrieval System (AIRS) database. This review yielded a national

average with upper and lower probability limits for each pollutant

which holds 95% of the stations data (see Chapter 40 Code of

Federal Regulations Part 58, Appendix A, Section 5 for exact

specifications and formulas).

A national review revealed that the overall quality of the nation’s

ambient air is within acceptable guidelines. The national average

of the precision probability limits is -7.0 and +7.5 and the

national average of the accuracy probability limits for level I was

-6.9 and +6.0 and level II was -5.6 and +4.4 respectfully. These
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numbers were taken by averaging all reporting organizations yearly

limits for the pollutants. 

The national review can be further aggregated into specific

pollutants. The precision results for the 150 reporting

organizations sampling for ozone average -6.0 and +5.9. The

precision results for the 134 reporting organizations sampling for

sulfur dioxide average -7.3 and +6.7. The precision results for

the 91 reporting organizations sampling for nitrogen dioxide

average -8.7 and +8.8. The precision results for the 105 reporting

organizations sampling for carbon monoxide average -4.5 and +6.2.

The precision results for the 171 reporting organizations sampling

for particulates average -8.4 and +9.8. 

A Regional review on the 1995 yearly precision and accuracy data

was also performed. The national percentage of Reporting

Organizations submitting data within acceptable guidelines for

ozone is 99.33 %. The national precision percentage for carbon

monoxide is 97.14%. The national precision percentage of Reporting

Organizations submitting acceptable precision data for nitrogen

dioxide is 90.11%. The national precision percentage for sulfur

dioxide is 91.79%. The national precision percentage for

particulates with a diameter of ten microns or less is 78.95%. 

The national percentage of Reporting Organizations submitting data

within acceptable guidelines for ozone is 95.95 %. The national

accuracy percentage for carbon monoxide is 98.27%. The national

accuracy percentage for nitrogen dioxide is 89.13%. The national

accuracy percentage for sulfur dioxide is 88.57%. The national

accuracy percentage for particulates with a diameter of ten microns

or less is 99.25%. 

This document fulfills the requirement within the 40 CFR Part 58

Appendix A for an annual report concerning the precision and

accuracy data submitted to the EPA from the State and Local

Agencies.
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ACKNOWLEDGMENTS

The author wishes to express thanks to the members of the technical

review team for their expertise and devoted time in the lengthy

review process. 

These members include the internal OAQPS review team: 

Joe Elkins

David Musick

Michael Papp 

Randy Waite

Rhonda Thompson 

Lee Ann Byrd

David Lutz 

Ed Hanks

George Manire

Neil Berg 

Neil Frank

Nash Gerald 

The external review team includes:

Chris St Germain Region 1

Marcus Kantz Region 2

Herb Barden Region 4

Gordon Jones Region 5

Kuenja Chung Region 6

Manny Aquitania Region 9

William Puckett Region 10

Alice Westerinen California Air Resource

Board

LeRoy Gruber Dept. Of Environmental 

Services, Cincinnati, Ohio

The author also wishes to express thanks to Brenda Millar and

Jessie Williams for their administrative support.

 
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INTRODUCTION

Many important EPA decisions are based on the ambient air quality

monitoring data obtained by the State and Local agencies. This data

is collected by the approximately 5,000 ambient air samplers which

make up the State and Local Air Monitoring Stations (SLAMS)

network. Data collected and reported to the Aerometric Information

Retrieval System (AIRS) are used by the EPA to aid in planning the

Nation’s air pollution control strategy and to measure achievement

toward meeting national ambient air quality standards (NAAQS).

Further, the data in AIRS are made available to numerous

requestors, who may use the data for various research projects,

special studies, or other purposes.

Prior to the May 10, 1979 promulgation of the Regulations set forth

in chapter 40 of the Code of Federal Regulations (40 CFR) Part 58

(Federal Register notice: 44 FR 27558-27604), the quality assurance

and quality control practices of State and Local agencies were

strictly voluntary; although many forms of guidance and assistance

had been provided by the EPA Regional offices and the National

Exposure Research Laboratory (formally the Environmental Monitoring

Systems Laboratory), Research Triangle Park, North Carolina.

Consequently, there was a wide diversity among the State and Local

agencies in the scope and effectiveness of their QA program. 

Unfortunately, not all data are accompanied by estimates of its

quality. To assure the most knowledgeable and effective use of the

data, the quality of the national monitoring data should be

determined and made known to all data users. The Code of Federal

Regulations, Part 58, directed that precision and accuracy checks

be incorporated by the State and Local agencies to control and

evaluate the quality of the collected data. 

BACKGROUND 

Precision is used in 40 CFR Part 58, Appendices A and B, in the

sense of “repeatability of measurement values under specified

conditions.” Since specified conditions may vary considerably,

there are many levels of repeatability or precision. For example,

with an automated continuous air pollution sensor, the random

fluctuations in response over a short time (e.g., within a minute)

when an instrument is measuring a gas of constant pollutant

concentration is a very ‘local’ measurement of precision. Another

measure of repeatability would be the variation of one point

precision checks made at biweekly intervals on the same instrument

(Instrument Precision).

Accuracy is used in 40 CFR Part 58, Appendices A and B, in the

sense of a measure of “closeness to the truth.” Deviations from
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the truth result from both random errors and systematic errors.

Precision is associated with the random errors. The average

inaccuracy, or bias, of a measurement process over some time or set

of conditions is associated with the systematic error. For

example, the systematic error of a given instrument is associated

with average accuracy for that instrument over some specified

period of time. 

Although the ultimate truth cannot be known, the values of the

standards determined by National Institute of Science and

Technology (NIST) or other nationally recognized measurement

standards body are accepted as ‘truth’. In assessing the accuracy

of measurements of an air pollution monitoring agency, measurements

are made through the implementation of independent audits in which

the measurement systems are challenged with standards (materials or

devices) having traceability as directly as possible to NIST

standards.

Section 3 of Appendix A in 40 CFR Part 58, requires that measures

of data quality be reported on the basis of ‘reporting

organization.’ A reporting organization is defined as a State or

subordinate organization within a State which is responsible for a

set of stations which monitor the same pollutant and for which

precision and accuracy assessments can be. States must define one

or more reporting organizations for each pollutant such that each

monitoring station in the State SLAMS network is included in one,

and only one, reporting organization. Agency precision and

accuracy is the average values of all the instruments within a

reporting organization during the calendar quarter or calendar

year. Each reporting organization shall be defined such that

precision or accuracy among all stations in the organization can be

expected to be reasonably homogeneous, as a result of common

factors. Common factors that should be considered by States in

defining reporting organizations include: (1) operation by a

common team of field operators, (2) common calibration facilities,

and (3) support by a common laboratory or headquarters.

The precision and accuracy checks conducted by reporting

organizations are one component of a quality assurance program. At

the local level, the precision and accuracy data enable reporting

organizations to identify aspects of their quality assurance

programs that may need strengthening. They also enable the EPA to

determine ways in which the quality of ambient data can be

improved, such as additional research on measurement procedures,

increased quality control for certain types of measurements, or

technical assistance to areas of the country needing improved

quality control.

There are other potential uses of the precision and accuracy data.

First, when determining whether a site meets a National Ambient Air
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Quality Standard (NAAQS), it may be useful for decision makers to

know to what extent a concentration reported as either above or

below the standard is the result of measurement error. Second,

when setting NAAQS, policy makers must estimate the protection

afforded by existing and revised ambient standards on either a

national or regional basis. This judgment may be influenced by

measurement uncertainties. 

Finally, the 1990 Clean Air Act Amendments (CAAA) identified

nonattainment areas for pollutants. These nonattainment areas were

classified by levels of pollutant concentration in the atmosphere

(marginal, moderate, serious, severe, and extreme). For an area or

site to change its classification, it must show reductions in

pollutant concentration levels. The monitoring data must be of

acceptable quality to support the reclassification of nonattainment

areas or for attainment areas to become classified as

nonattainment. 

CURRENT REGULATIONS

Precision of Automated Methods

A one-point precision check must be carried out at least

once every 2 weeks on each automated analyzer used to measure

SO2, NO2, O3, and CO. The precision check is made by challenging

the analyzer with a precision check gas of known concentration

between 0.08 and 0.10 parts per million (ppm) for SO2, NO2, O3

analyzers and between 8 and 10 ppm for CO analyzers. To check

the precision of SLAMS analyzers operating on ranges higher than

1.0 ppm for SO2, NO2, O3 or 0 to 100 ppm for CO, precision check

gases of appropriately higher concentration can be used once

approved by the appropriate Regional Administrator or designee. 

However, the results of precision checks at concentration levels

other than those stated need not be reported to EPA. 

Except for certain CO analyzers (40 CFR Part 58), analyzers must

operate in their normal sampling mode during the precision check,

and the test atmosphere must pass through all filters, scrubbers,

conditioners, and other components used during normal ambient

sampling and as much of the ambient air inlet system as is

practicable. If a precision check is made in conjunction with a

zero or span adjustment, it must be made prior to such zero or span

adjustments. Randomization of the precision check with respect to

time of day, day of week, and routine service and adjustments is

encouraged where possible. Report the actual concentrations of the

precision check gas and the corresponding concentrations indicated

by the analyzer. The percent differences between these

concentrations are used to assess the precision of the monitoring

data (Reference 3).
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Accuracy of automated methods

Each calendar quarter (during which analyzers are operated), audit

at least 25 percent of the SLAMS analyzers that monitor for SO2,

NO2, O3, or CO such that each analyzer is audited at least once per

year. If there are fewer than four analyzers for a pollutant

within a reporting organization, randomly reaudit one or more

analyzers so that at least one analyzer for that pollutant is

audited each calendar quarter. Where possible, if there are fewer

than 4 analyzers, EPA strongly encourages more frequent auditing,

up to an audit frequency of once per quarter for each SLAMS

analyzer.

The audit is made by challenging the analyzer with at least one

audit gas of known concentration from each of the following ranges

that fall within the measurement range of the analyzer being

audited:

 Concentration range, ppm

Audit Level SO2, O3 NO2 CO 

I............ 0.03-0.08 0.03-0.08 3 - 8

II............ 0.15-0.20 0.15-0.20 15 - 20

III........... 0.35-0.45 0.35-0.45 35 - 45

IV............ 0.80-0.90 --------- 80 - 90

 

NO2 audit gas for chemiluminescence-type NO2 analyzers must also

contain at least 0.08 ppm NO.

Precision of manual methods

For each network of manual methods, select one or more monitoring

sites within the reporting organization for duplicate, collocated

sampling as follows: for 1 to 5 sites, select 1 site; for 6 to 20

sites, select 2 sites, and for over 20 sites, select 3 sites. This

selection should be reviewed periodically to ensure all new NAAQS

updates are included (i.e., proposed PM2.5 regulations). Where

possible, additional collocated sampling is encouraged. For

particulate matter, a network for measuring PM10 shall be separate

from a TSP network. Sites having annual mean particulate matter

concentrations among the highest 25 percent of the annual mean

concentrations for all the sites in the network must be selected

or, if such sites are impractical, alternate sites approved by the

Regional Administrator may be selected.

In determining the number of collocated sites required, monitoring

networks for Pb should be treated independently from networks for

particulate matter, even though the separate networks may share one

or more common samplers. However, a single pair of samplers

collocated at a common-sampler monitoring site that meets the
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requirements for both a collocated lead site and a collocated

particulate matter site may serve as a collocated site for both

networks. The two collocated samplers must be within 4 meters of

each other, and particulate matter samplers must be at least 2

meters apart to preclude airflow interference. Calibration,

sampling and analysis must be the same for both collocated samplers

and the same as for all other samplers in the network. For each

pair of collocated samplers, designate one sampler as the primary

sampler whose samples will be used to report air quality for the

site, and designate the other as the duplicate sampler. Each

duplicate sampler must be operated concurrently with its associated

routine sampler at least once per week. The operation schedule

should be selected so that the sampling days are distributed evenly

over the year and over the 7 days of the week. The every-6-day

schedule used by many monitoring agencies is recommended. Report

the measurements from both samplers at each collocated sampling

site, including measurements falling below the specified limits.

The percent differences in measured concentration (μg/m ) between

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the two collocated samplers are used to calculate precision.

Accuracy of manual methods

The accuracy of manual sampling methods is assessed by auditing a

portion of the measurement process. For particulate matter methods,

the flow rate during sample collection is audited. For SO2 and NO2

methods, the analytical measurement is audited. For Pb methods, the

flow rate and analytical measurement are audited.

Particulate matter methods. Each calendar quarter, audit the flow

rate of at least 25 percent of the samplers such that each sampler

is audited at least once per year. If there are fewer than four

samplers within a reporting organization, randomly reaudit one or

more samplers so that one sampler is audited each calendar quarter.

Audit each sampler at its normal operating flow rate, using a flow

rate transfer standard. The flow rate standard used for auditing

must not be the same flow rate standard used to calibrate the

sampler. However, both the calibration standard and the audit

standard may be referenced to the same primary flow rate standard.

The flow audit should be scheduled so as to avoid interference with

a scheduled sampling period. 

Report the audit flow rates and the corresponding flow rates

indicated by the sampler's normally used flow indicator. The

percent differences between these flow rates are used to calculate

accuracy. Great care must be used in auditing high-volume

particulate matter samplers having flow regulators because the

introduction of resistance plates in the audit flow standard device

can cause abnormal flow patterns at the point of flow sensing. For

this reason, the flow audit standard should be used with a normal

filter in place and without resistance plates in auditing
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flow-regulated high-volume samplers, or other steps should be taken

to assure that flow patterns are not perturbed at the point of flow

sensing. 

 

SO2 Manual Methods. Prepare the audit solutions from a working

sulfite-tetrachloromercurate (TCM) solution as described in section

10.2 of the SO2 Reference Method (appendix A of part 50 of this

chapter). These audit samples must be prepared independently from

the standardized sulfite solutions used in the routine calibration

procedure. Sulfite-TCM audit samples must be stored between 0 and

5 degrees Celsius and expire 30 days after preparation. Prepare

audit samples in each of the concentration ranges of 0.2-0.3,

0.5-0.6, and 0.8-0.9 μg SO2/ml. Analyze an audit sample in each of

the three ranges at least once each day that samples are analyzed

and at least twice per calendar quarter. Report the audit

concentrations (in μg SO2/ml) and the corresponding indicated

concentrations (in μg SO2/ml). The percent differences between

these concentrations are used to calculate accuracy. 

 

NO2 Manual Methods. Prepare audit solutions from a working sodium

nitrite solution as described in the appropriate equivalent method.

These audit samples must be prepared independently from the

standardized nitrite solutions used in the routine calibration

procedure. Sodium nitrite audit samples expire in 3 months after

preparation. Prepare audit samples in each of the concentration

ranges of 0.2-0.3, 0.5-0.6, and 0.8-0.9 μg NO2/ml. Analyze an audit

sample in each of the three ranges at least once each day that

samples are analyzed and at least twice per calendar quarter.

Report the audit concentrations (in μg NO2/ml) and the

corresponding indicated concentrations (in μg NO2/ml). The percent

differences between these concentrations are used to calculate

accuracy.

Pb Manual Methods. For the Pb Reference Method (appendix G of 40

CFR part 50, the flow rates of the high-volume Pb samplers shall be

audited as part of the TSP network using the same procedures. For

agencies operating both TSP and Pb networks, 25 percent of the

total number of high-volume samplers are to be audited each

quarter. Each calendar quarter, audit the Pb Reference Method

analytical procedure using glass fiber filter strips containing a

known quantity of Pb. 

These audit sample strips are prepared by depositing a Pb solution

on 1.9 cm by 20.3 cm ( 3/4 inch by 8 inch) unexposed glass fiber

filter strips and allowing them to dry thoroughly. The audit

samples must be prepared using batches of reagents different from

those used to calibrate the Pb analytical equipment being audited.

Prepare audit samples in the following concentration ranges: 
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Equivalent 

 Pb concentration ambient Pb 

Range μg/strip concentration 

 {1} μg/m 

3

 

1 .................. 100- 300 0.5-1.5 

2 .................. 600-1000 3.0-5.0 

 {1} Equivalent ambient Pb concentration in μg/m is based on

3

sampling at 1.7 m /min for 24 hours on a 20.3 cmX25.4 cm (8 inchX10 3

inch) glass fiber filter. 

 

Audit samples must be extracted using the same extraction procedure

used for exposed filters. Analyze three audit samples in each of

the two ranges each quarter samples are analyzed. The audit sample

analyses shall be distributed as much as possible over the entire

calendar quarter. Report the audit concentrations (in μg Pb/strip)

and the corresponding measured concentrations (in μg Pb/strip)

using unit code 77. The percent differences between the

concentrations are used to calculate analytical accuracy.

The accuracy of an equivalent Pb method is assessed in the same

manner as for the reference method. The flow auditing device and Pb

analysis audit samples must be compatible with the specific

requirements of the equivalent method.

QUALITY ASSURANCE GUIDELINE

The stated guideline for determining compliance to precision and

accuracy guidelines is found is the Quality Assurance Handbook,

Volume 2, Section 2.0.11 which states, “As a goal, the 95%

probability limits for precision (all pollutants) and TSP accuracy

should be less than +/- 15%. At 95% probability limits, the

accuracy for all other pollutants should be less than +/- 20%.”

The collected data can be taken from the EPA Aerometric Information

Retrieval System (AIRS), Air Quality Subsystem, precision/accuracy

reporting organization summary report. 

DATA RESULTS

National Review

Each Reporting Organization submitted data for 1995 into the EPA’s

Aerometric Information Retrieval System (AIRS) database. AIRS

calculated yearly average precision and accuracy acceptance limits

for each Reporting Organization (Section 5, reference 3). The

calculation was based upon data submitted from January 1, 1995 to
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December 31, 1995. The percentages are based upon the yearly

precision and accuracy (P&A) results. A reporting organization is

said to be outside of the acceptable quality assurance limits if

either of the upper probability limit or lower probability limit is

outside of the acceptable quality assurance limit. All reporting

organization acceptance limits were then averaged for a national

results profile. The national results were aggregated into

separate categories for automatic and manual methods of sampling.

The national results indicate the precision and accuracy data

average well within the quality assurance guidelines. All of the

criteria pollutant’s precision acceptance limits average nationally

at -7.0 and +7.5 respectfully. The criteria pollutant’s accuracy

acceptance limits average nationally for level I at -6.9 and +6.0

and level II at -5.6 and +4.4 respectfully. (Note: The precision

and accuracy data for lead was excluded from these calculations.

The standard for lead is 1.5 ug/m but the national average

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concentration (the arithmetic mean of the maximum quarterly

concentration as reported in the EPA National Trends Report) is

0.04 ug/m . This represents only 2.6 percent of the standard.

3

These calculations and the lead program are being evaluated for

revision to show a true representation of the lead samplers.

Automated Methods 

Table 1.0 shows the national precision summary for automated

methods. All of the automated methods averaged together nationally

yield a precision average of -6.6 for the lower probability limit

and +6.9 for the upper probability limit. Each of the four

pollutants were also reviewed separately. There were 150 Reporting

Organizations sampling for ozone (O3) and the national precision

average for ozone is -6.0 and +5.9. There were 134 Reporting

Organizations sampling for sulfur dioxide (SO2) and the national

precision average for sulfur dioxide is -7.3 and +6.7. There were

91 Reporting Organizations sampling for nitrogen dioxide (NO2) and

the national precision average for nitrogen dioxide is -8.7 and

+8.8. There were 105 Reporting Organizations sampling for carbon

monoxide (CO) and the national precision average for carbon dioxide

is -4.5 and +6.2. 

The national accuracy averages are within the acceptable quality

assurance limits. The accuracy averages are separated by

concentration level. The national average for level I accuracy for

automated methods is -7.7 and +6.4. The national average for

level II accuracy for automated methods is -5.6 and +4.4. The

national average for level III accuracy for automated methods is

-5.6 and +4.2. Table 1.0 shows the national summary of accuracy

for automated methods.

There were 73,986 precision audits for automated methods and 4,364
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accuracy audits for automated methods in 1995 performed by a total

of 2,356 analyzers. 

Manual Methods

Table 2.0 shows the national summary of precision for manual

methods. The national precision average for particulates with

diameters under 10 microns (PM10) is -8.4 for the lower probability

limit and +9.8 for the upper probability limit. The national

precision average for lead (Pb) reflect the current monitoring

procedures which are currently under revision. The standard for

lead is 1.5 ug/m but the national average concentration (the

3

arithmetic mean of the maximum quarterly concentration as reported

in the EPA National Trends Report) is 0.04 ug/m . This represents 3

only 2.6 percent of the standard. The low numbers on the table

represent precision and accuracy calculations which are based upon

these very low concentrations which in turn lead to a high number

of reporting organizations submitting precision results outside of

the acceptable limits. These calculations are being revised to

show a true representation of the precision of lead samplers. 

The national accuracy averages are within the acceptable quality

assurance guidelines. The accuracy averages are separated by

concentration level. The national average for level I accuracy for

manual methods is -5.5 and +5.0. The national average for level

II accuracy for manual methods is -6.2 and +4.5. The national

average for level III accuracy for manual methods is -9.8 and +6.6.

It is noted that there are two separate accuracy audits for lead.

One audit concerns the analytical chemical analysis and the other

concern a flow check. 

Regional Review

Table 3.0 summarizes the regional precision results. For automated

methods, the precision percentages ranged from 90% to 99% of the

Reporting Organizations submitting data within acceptable quality

assurance limits. The percentages are based upon the yearly

precision results for the reporting organizations. A reporting

organization is said to be outside of the acceptable quality

assurance limits if either the upper limit or lower limit is

outside of the acceptable quality assurance guideline. 

The table shows the total number of Reporting Organizations

sampling for each specific pollutant as well as how many submitted

data within acceptable quality assurance guidelines. For example,

of the 150 reporting organizations sampling for ozone, 149

submitted yearly data within acceptable quality assurance limits

which is 99.33 %. The national percentage for carbon monoxide is

97.14%. The national percentage for nitrogen dioxide is 90.11%.

The national percentage for sulfur dioxide is 91.79%. The national
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percentage for particulates with a diameter of ten microns or less

is 78.95%. 

Table 4.0 summarizes the regional accuracy results. For automated

methods, the accuracy percentages ranged from 88% to 98% of the

reporting organizations submitting data within acceptable quality

assurance limits. The percentages are based upon the yearly

accuracy results for the reporting organizations. 

The national percentage of reporting organizations submitting

acceptable data of ozone is 95.95 %. The national percentage for

carbon monoxide is 98.27%. The national percentage for nitrogen

dioxide is 89.13%. The national percentage for sulfur dioxide is

88.57%. The national percentage for particulates with a diameter

of ten microns or less is 99.25%. The national percentage for lead

is separated into two distinct accuracy audit categories. The

national percentage of reporting organizations submitting

acceptable data of lead from an analytical laboratory audit is

83.33%. The national percentage of reporting organizations

submitting acceptable data of lead from an annual flow audit is

100% respectfully. Table 5.0 offers an explanation of the

terminology used in the tables.
15

REFERENCES

1. Guideline on the Meaning and Use of Precision and Accuracy

Data Required by 40 CFR 58, Appendices A and B. U.S. Environmental

Protection Agency, Research Triangle Park, North Carolina (EPA600/4-83-023. 1983.

2. The Use of Precision and Accuracy Data in Air Quality

Management. A.D. Thrall, C.S. Burton, Systems Applications, Inc.

N.H. Frank, W.F.. Hunt, U.S. EPA Research Triangle Park, North

Carolina. 1984.

3. Code of Federal Regulations, Title 40, Part 58, Ambient Air

Quality and Surveillance. 1993 (44 FR 27571).

4. Quality Assurance Handbook for Air Pollution Measurement

Systems, Vol II, Ambient Air Specific Methods, U.S.EPA , Research

Triangle Park, North Carolina, April 1994. EPA-600/4-77-027a.

5. Issues Concerning The Use of Precision and Accuracy Data,

Special report, U.S. EPA, Office of Air Quality Planning and

Standards, Research Triangle Park, North Carolina, EPA 450/4-84-

006. February 1984.

6. Precision and Accuracy Assessments for State and Local Air

Monitoring Networks 1981-1986. Supplement to EPA/600/4-88/007.

U.S. EPA, Environmental Monitoring Systems Lab, Research Triangle

Park NC 27711, EPA/600/4-88/037.

7. Precision and Accuracy Assessments for State and Local Air

Monitoring Networks, 1982, U.S. EPA, Environmental Monitoring

Systems Lab, Research Triangle Park NC 27711, EPA/600/4-85/031.

8. Precision and Accuracy Assessments for State and Local Air

Monitoring Networks, 1983, U.S. EPA, Environmental Monitoring

Systems Lab, Research Triangle Park NC 27711, EPA/600/4-86/012.

9. Precision and Accuracy Assessment for State and Local Air

Monitoring Networks, 1984. U.S. EPA, Environmental Monitoring

Systems Lab, Research Triangle Park, NC 27711, EPA/600/4-86/031.

10. Precision and Accuracy Assessments for State and Local Air

Monitoring Networks, 1985, U.S. EPA, Environmental Monitoring

Systems Lab, Research Triangle Park NC 27711, EPA/600/4-87/003.

11. Precision and Accuracy Assessments for State and Local Air

Monitoring Networks, 1986, U.S. EPA, Environmental Monitoring

Systems Lab, Research Triangle Park NC 27711, EPA/600/4-88/007.
16

12. Precision and Accuracy Assessments for State and Local Air

Monitoring Networks, 1987, U.S. EPA, Environmental Monitoring

Systems Lab, Research Triangle Park NC 27711, EPA/600/4-89/015.

13. Precision and Accuracy Assessments for State and Local Air

Monitoring Networks, 1988, U.S. EPA, Environmental Monitoring

Systems Lab, Research Triangle Park NC 27711, EPA/600/4-90/008.
17

Table 1.0 National Results for Precision and Accuracy Data for Automated Methods

Pollutant Number Precision Precision Number Number Number Audit Audit Audit Audit Audit Audit 

Reporting Lower Upper Precision Analyzers Accuracy Level Level Level Level Level Level 

Organizations Limit Limit Checks Audits 1 1 2 2 3 3

Lower Upper Lower Upper Lower Upper

Limit Limit Limit Limit Limit Limit

O3 150 - 6.0 5.9 26,431 933 1,727 - 6.2 5.7 - 4.6 3.8 - 4.5 3.6

SO2 134 - 7.3 6.7 19,271 559 1,037 - 9.1 5.2 - 7.2 4.3 - 7.3 4.3

NO2 91 - 8.7 8.8 10,546 370 697 - 9.8 7.7 - 6.9 5.1 - 6.3 4.5

CO 105 - 4.5 6.2 17,738 494 903 - 5.6 7.0 - 3.9 4.5 - 4.2 4.3

National n/a - 6.6 6.9 73,986 2,356 4,364 - 7.7 6.4 - 5.6 4.4 - 5.6 4.2

Totals 

and

Average

 Note: The Upper and Lower Limits represent national averages of the 95% probability limits for the yearly data. For example: The value 5.9 is the national yearly

 average for the upper precision limit of all the data submitted by the 150 reporting organizations sampling for ozone; 95% of the ozone data would be defined

 between the upper and lower probability limit of -6.0 and +5.9.
18

Table 2.0 National Results for Precision and Accuracy Data for Manual Methods

Pollutant Number Precision Precision Number Number Number Audit Audit Audit Audit Audit Audit 

Reporting Lower Upper Collocated Collocated Accuracy Level Level Level Level Level Level 

Organizations Limit Limit Sites Samples Audits 1 1 2 2 3 3

Lower Upper Lower Upper Lower Upper

Limit Limit Limit Limit Limit Limit

PM10 171 - 8.4 9.8 338 12,863 4,377 - 3.8 4.4 - - - -

Pb 55 - 21.0 16.4 73 3,122 452 - 8.8 6.0 - 9.0 6.1 - 9.8 6.6

Class A

Pb 58 n/a n/a n/a n/a 272 - 3.8 4.5 - 3.4 3.0 - -

Class F

National n/a - 14.7 13.1 411 15,985 5,101 - 5.5 5.0 - 6.2 4.5 - 9.8 6.6

Totals 

and

Average

 Note: The Upper and Lower Limits represent national averages of the 95% probability limits for the yearly data. For example: The value 9.8 is the national yearly

 average for the upper precision limit of all the data submitted by the 171 reporting organizations sampling for PM10; 95% of the data is defined by the upper and

 lower probability limits of -8.4 and +9.8. 
19

Table 3.0 Percentage of Regional Reporting Organizations Submitting Data 

Within the Acceptable Quality Assurance Precision Limits

Region Ozone CO NO2 SO2 PM10 Pb (A)

I 100 100 100 100 85 NR

II 100 100 100 75 0 *** 50

III 100 100 100 100 71 50

IV 100 95 82 92 82 0

V 100 100 92 96 82 0

VI 100 100 80 70 71 0

VII 100 88 83 100 60 0

VIII 100 100 100 100 85 0

IX 100 93 90 82 73 NR

X 87.5 100 100 80 100 0

*Note 1

NAT.

AVG.

149/150 102/105 82/91 123/134 135/171 2/17

99.33 % 97.14 % 90.11 % 91.79 % 78.95 % 11.76 %

**Note 2

Automated Methods Manual Methods

* Note 1: The percentages are based upon the yearly P&A results. A reporting organization is said to be outside of the acceptable quality

assurance limits if either and/or both of the upper limit or lower limit is outside of the acceptable quality assurance limit. The nationa

average represents the number of reporting organizations submitted data within acceptable limits divided by the toal number of reporting

organizations submitting data.

**Note 2: The percentages for Lead (Pb) are due to the current procedures for monitoring which are under revision and will be corrected.

The standard for Lead is 1.5 ug/m but the national average concentration (the arithmetic mean of the maximum quarterly concentration as 3

reported in the EPA National Trends Report) is 0.04 ug/m . This represents only 2.6 percent of the standard. The low numbers on the table 3

represent precision calculations which are based upon these very low concentrations which in turn lead to a high number of reporting

organizations submitting P&A results outside of the acceptable limits. This is evident in the fact that only 17 reporting organizations had

valid data to report and only two were within acceptable guidelines. These calculations are being revised to show a true representation of

the precision of Lead samplers. 

*** There were three reporting organizations and each submitted data outside the stated guidelines.
20

Table 4.0 Percentage of Regional Reporting Organizations Submitting Data 

Within the Acceptable Quality Assurance Accuracy Limits

Region Ozone CO NO2 SO2 PM10 Pb (A) Pb (F)

I 100 100 100 100 100 NR NR

II 100 100 100 100 100 100 100

III 100 100 75 100 100 100 100

IV 100 100 80 89 100 0 100

V 100 89 60 69 100 100 100

VI 100 100 100 86 100 66 100

VII 66 100 100 100 89 100 100

VIII 100 100 100 100 100 100 100

IX 75 100 100 80 100 NR NR

X 100 100 100 100 100 100 100

* Note 1

NAT.

AVG.

71/74 57/58 41/46 62/70 133/134 15/18 22/22

95.95 % 98.27 % 89.13 % 88.57 % 99.25 % 83.33 % 100 %

** Note 2

Automated Methods Manual Methods

Note 1: The percentages are based upon the yearly P&A results. A reporting organization is said to be outside of the acceptable quality assurance limits

is either and/or both of the upper limit or lower limit is outside of the acceptable quality assurance limit. The national average represents the number of

reporting organizations submitted data within acceptable limits divided by the toal number of reporting organizations submitting data.

Note 2: The percentages for Lead (Pb) are due to the current procedures for monitoring which are under revision and will be corrected. The standard for

Lead is 1.5 ug/m but the national average concentration (the arithmetic mean of the maximum quarterly concentration as reported in the EPA National 3

Trends Report) is 0.04 ug/m . This represents only 2.6 percent of the standard. The low numbers on the table represent precision calculations which are 3

based upon these very low concentrations which in turn lead to a high number of reporting organizations submitting P&A results outside of the acceptable

limits. These calculations are being revised to show a true representation of the accuracy of Lead samplers. 
21

Table 5.0 Explanations of the terms for Tables 1, 2, 3, and 4

Title Explanation

Pollutant This will be one of the six criteria pollutants - Ozone, Sulfur

Dioxide, Carbon Monoxide, Nitrogen Dioxide, Particles, Lead

Number Reporting

Organizations

This is the total number of reporting organizations that

submitted data into the EPA’s Aerometric Information

Retrieval System (AIRS) database for that particular

pollutant

Precision Lower Limit This is the lower limit for precision checks which represent

the lower boundary of the 95% probability limits

Precision Upper Limit This is the upper limit for precision checks which represent

the upper boundary of the 95% probability limits 

Number Precision Checks This is the total number of precision checks performed on

that particular pollutant within that specific year

Number Analyzers The total number of analyzers that monitored that particular

pollutant within that specific year

Number Accuracy Audits The total number of accuracy audits performed during that

specific year

Audit Level I Lower Limit This is the lower boundary of the 95% probability limits for

the level one audit as defined by 40CFR58, Appendix A

Audit Level I Upper Limit This is the upper boundary of the 95% probability limits for

the level one audit as defined by 40CFR58, Appendix A

Audit Level 2 Lower Limit This is the lower boundary of the 95% probability limits for

the level two audit as defined by 40CFR58, Appendix A

Audit Level 2 Upper Limit This is the upper boundary of the 95% probability limits for

the level two audit as defined by 40CFR58, Appendix A

Audit Level 3 Lower Limit This is the lower boundary of the 95% probability limits for

the level three audit as defined by 40CFR58, Appendix A

Audit Level 3 Upper Limit This is the upper boundary of the 95% probability limits for

the level three audit as defined by 40CFR58, Appendix A

Number Collocated Sites This is the total number of collocated sites within the

pollutants network of monitors
Table 5.0 Explanations of the terms for Tables 1, 2, 3, and 4

Title Explanation

22

Number Collocated This is the total number of valid collocated samples that was

Samples submitted to the EPA’s AIRS database
23

Table 6.0 Explanations of the terms of Table 3.0 and 4.0

Title Explanation

Region This will specify one of the ten EPA regions

Percentages The percentages are based upon the total number of

reporting organizations that submitted data into EPA’s AIRS

database and the total number of reporting organizations

that submitted data within acceptable guidelines. For

example, 149 reporting organizations submitted data within

acceptable guidelines and 150 reporting organizations

submitted data. The percentage is then 149/150 or 99.33%

PM10 Precision This is based upon the percent differences between two

collocated samplers

PM10 Accuracy This is the annual flow check

Lead Precision This is based upon the percent differences between two

collocated samplers

Lead (A) Accuracy This is a quarterly audit of the laboratory

Lead (F) Accuracy This is an annual flow check