REFERENCE*

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NBS TECHNICAL NOTE 840

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

Reference Materials

or Collaborative Tests

of Air Quality Methods

IOO

no. 540
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards * was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

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utilization of automatic data processing equipment; and serves as the principal focus within

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1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

3 Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.

* Part of the Center for Building Technology.
& CULL -Tfef1'

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L}0 Reference Materials for Collaborative

Tests of Air Quality Methods

Richard H. Johns and John K. Taylor

Analytical Chemistry Division

Institute for Materials Research

National Bureau of Standards Washington, D.C. 20234

T,

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U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued August 1974
Library of Congress Catalog Card Number: 74-600123

National Bureau of Standards Technical Note 840

Nat. Bur. Stand. (U.S.), Tech. Note 840, 17 pages (Aug. 1974) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1974

For sate by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 03.46:840). Price 55 cents.
REFERENCE MATERIALS FOR COLLABORATIVE

TESTS OF AIR QUALITY METHODS

Richard H. Johns and John K. Taylor

Reference materials and associated distribution

apparatus were developed for seven ambient air contaminants and for two smokestack contaminants. These established the reference base for collaborative tests of

ASTM procedures for ambient air quality and smokestack

emissions carried out under a three -year program known

as Project Threshold.

Key words: Air pollution; chemical analysis; Standard

Reference Materials.

1. Introduction

Analysis of the atmosphere for ambient -level contaminants

demands meticulous care in the handling of the sample. Gaseous

contaminants such as the oxides of nitrogen and sulfur are typically encountered at concentrations of 10-100 parts per

billion; at these concentrations they are prone to adsorption

or condensation within the sampling equipment and reaction

with its materials of construction. Similarly, particulate

contaminants are subject to sampling losses and physical

alteration within the sample collection train. Furthermore,

a group of contaminants may react among themselves at some stage of the sampling operation adding further complication

to the measurement. As a consequence of these problems,

ambient air samples are almost never stored; rather the

contaminant of interest is collected from a flowing air stream

by filtration, absorption or chemical reaction, using the

simplest and most inert plumbing arrangements possible.

Reference materials for atmospheric contaminants are subject to the same stability problems as the samples themselves. References are of considerable importance to this

field because only through their use may air quality measurements from widely separated laboratories be soundly compared.

Because of the storage problems of trace contaminant refer- ence mixtures, development effort has been focused on systems

wherein the contaminant is generated at the point of use.

Reference materials are ordinarily employed in chemical

analysis in one ot the other of two modes. In most laboratory

procedures, the standard is used in a control analysis to

ascertain that the procedure is producing accurate results.
This approach has the advantage of simplicity but is subject

to problems if the real sample has a complex matrix. The

matrix problem is largely circumbented when reference materials are used in the standard addition mode. By this procedure, the real sample is analyzed twice : At first alone,

and again after the addition of a known quantity of the

reference. The difference between the two results is due to

the reference and since its value is known accurately the

real sample can be evaluated by a simple ratio. It is by

this standard addition or spiking principle that reference

materials were employed in Project Threshold. It has the

important advantage that the reference spike is exposed to

the same matrix (the atmosphere) as the contaminant being

measured.

Seven reference materials were provided for the first

phase of Project Threshold through the ASTM Research Associateship at National Bureau of Standards. For two of the

contaminants, NBS -certified Standard Reference Materials were

employed. Standards for the remaining contaminants were

developed under the program, along with equipment and techniques for their use. In addition, spectrophotometer calibration service, using certified standards, was provided at the

test sites. The succeeding subsections of this report describe the development, calibration and testing of these

reference materials.

2. Permeation Tubes

The permeation tube has emerged as a useful source for

the generation of trace contaminant reference standards.

This device consists simply of a sealed plastic capsule con- taining the contaminant of interest as a liquefied gas. The

contaminant permeates the wall of the capsule at a constant

rate which may be measured by weight loss. Rates are typically 1-10 micrograms /minute . The capsule is usually made

from FEP fluorocarbon because of its inertness. Sulfur

dioxide permeation tubes are available from the National

Bureau of Standards as a Standard Reference Material (SRM

1625) and these were used for generation of the sulfur

dioxide reference "spikes" in the first phase of Project

Threshold. Nitrogen dioxide permeation tubes (not yet available in SRM form) were obtained from a commercial source,

calibrated at the Bureau, and used to generate the nitrogen

dioxide reference spikes. Calibration data for these devices

showed them to possess permeation rates in the range of 1-10

yg/min.
Field application of permeation devices is complicated

by the requirement for rigid temperature and flow control. In

use, the tube is placed in a simple, thermostated glass

generator and swept with dry air at a metered rate. The

generator and dilution apparatus used in the field for spiking

is diagrammed in Figure 1. For an exemplary spike, a permeation

tube possessing a rate of 5 yg/min might be swept with dry air

at 0.2 1/min and the resulting stream diluted with ambient air

into a total flow of 100 1/min, to provide a spike of 50 yg/m 3

. The total flow must be measured with great accuracy and the

dilution apparatus must provide perfect mixing of the sample

before it is delivered to the collaborating laboratories.

The orifice flow meters used in the dilution manifold are accurate to ± 1 percent. Since permeation rates are a function

of temperature to the extent of nearly 10 percent per degree

centigrade, the generator temperature must be controlled within

narrow limits to maintain the calibration accuracy of the permeation device. In practice, temperature was easily maintained

within ± 0.05°, corresponding to ± 0.4 percent constancy in

output of the devices.

The fact that the dilution apparatus operates under a slight positive pressure (10 cm water) raises the question

whether system pressure might affect the output rates of

permeation tubes. To answer this question, an NBS-certified

sulfur dioxide tube was recalibrated gravimetrically after

exposure to flowing conditions at - , 1 and 2 atmospheres

absolute pressure, respectively, for 2 -day periods. No change

in calibration was observed under these exaggerated pressure

conditions

3. Ozone

Ozone is the least stable of the atmospheric contaminants

measured in these studies. It may be present in the atmosphere at

concentrations of 20-200 ug/m 3 at ground level and approaches

a maximum of 2,000 yg/m 3 at 20,000 feet altitude. It is produced by the action of solar ultraviolet radiation on atmospheric

oxygen , and its altitude profile arises from the opposing effects

of air density and the shielding effect of the lower atmosphere

toward ultraviolet energy.

An ozone spiking system was developed, calibrated and

tested under the ASTM Program, although collaborative testing

of ozone methods has been deferred to a later date. Ozone

reference standards must of necessity be generated at the

point of use. Ozone generators are based on the irradiation

of air or oxygen by ultraviolet light, gamma radiation, or an
BLOWER

AMBIENT

SAMPLE

ORIFICE FLOWMETERS

PERMEATION TUBE

THERMOMETER

CONSTANT-TEMPERATURE CIRCULATOR

SPARE

LINE

UNSPIKED

LINE

SAMPLING

PORTS

SPIKED

LINE

ROTAMETER

0.2i/min

Figure 1. Spike Generator and Sampling Manifold
electric discharge. Commercial equipment for generating

low atmospheric-level concentrations of ozone has recently

appeared on the market, and such an instrument was purchased

for Project Threshold. The ozone generator which was obtained employs a carefully-regulated ultraviolet source

acting on a metered stream of air to produce ozone concen- trations of 20-2,000 yg/m 3

. The ultraviolet lamp is provided

with thermal compensation of its power input, a photometric

intensity reference, and telescoping shutters for control

of ozone concentration. At maximum output, the instrument

will produce 5 1/min of ozone at a concentration 2,000 yg/m 3 in air. This stream is to be diluted with ambient air into

a total flow of 100 1/min for distribution to the collaborators. The resulting spike is 100 yg/m 3

, a suitable level.

The instrument was tested at the Bureau and found to

be reproducible in its output to the 5 percent precision

which is claimed. Because the distribution manifold operates

under a slight positive pressure (10 cm water) , it was felt

necessary to examine the effect of pressure on the generator

output. Measurements with an electrochemical oxidant meter,

Figure 2, showed that there is no measureable change in oxone production over the pressure range of 0-25 cm water

at the generator output tap. The generator was calibrated

over its output range using the neutral potassium iodide

method in preparation for its use in the field. Calibration

data are given in Table I.

4. Off -Stream Reference Spikes

In the procedures for nitrogen dioxide, sulfur dioxide

and ozone, collaborators were provided with live, on-stream

spiked ambient samples. For these analyses, their samples

were drawn from distributors on two parallel mixing manifolds (Figure 1) , differing only in the respect that one carried the injected contaminant spike.

The spiking technique was not feasible for five of the

procedures of Project Threshold. Two of these are "effects

methods" which require month-long sampling periods. Two

others involve particulate reference standards, the problems

of which are legion. Finally, the spiking of atmospheric

lead vapor would require a level of a few parts per trillion

for a 5-day period.
OZONE GENERATOR

PRESSURE EFFECTS

Figure 2. Ozone Generator, Pressure Data.
Table I Ozone Generator

Calibration Data

Instrument as Received

Indicated Sample Measured3- Output, VV h Liters Ozone, ppb

100 15.1 128

300 15.2 389

500 12.1 654

500 12.2 647

After Final Recal ibration

500 10.0 486

500 10.0 498

500 10.0 526

500 11.0 510

500 10.0 499

500 10.0 481

500 5.0 505

500 mean 501

Neutral bufferred p otassium iodide method

(D 2912)
For these latter methods, procedures were developed at

NBS for spiking the collected sample rather than the ambient

air. Collaborators were given prepared, packaged spikes for

addition to their collected samples prior to analysis. The

development and testing of these reference materials is

related in subsequent paragraphs.

5. Sulfation

The sulfation procedure (ASTM D 2010) , an effects method,

is based on the exposure of a reactive "candle" which collects

atmospheric sulfur compounds as lead sulfate over an exposure

period of a month. After exposure, the loaded candle is

digested and analyzed for sulfate by a classical gravimetric

procedure. For reference spikes, measured quantities of

solid potassium sulfate were provided for the collaborators,

to be added to the digestion mixtures prior to analysis. The

samples were packaged in gelatin capsules, packed with filter

pulp, so that no further quantitative transfer measurements

would be required.

The spiking procedures were tested at NBS with unexposed

candles and found to give good sulfate recovery. The potassium

sulfate standard, a reagent commercial chemical, was assayed

and found to be 99.3 percent pure.

6. Dust fall

This simple but useful effects method (ASTM D 1739) is

almost explicit in its name. Settleable atmospheric particulate

is collected in a pail of water over a period of a month. Using

the known mouth area of the bucket, the result is calculated

in grams/sq meter/month of collected dust.

The method involves separation of the collected material

into water-soluble, water-insoluble and benzene-soluble

fractions by a laboratory procedure. An off -stream spike was devised to check this separation. Known mixtures of salt, sand

and granular polystyrene were provided to the collaborators

in vials. Alternate buckets were spiked by addition of the

entire contents of vials containing this material, prior to

analysis

7. Airborne Particulate (Tape Sampler)

This second particulate method was subjected to collaborative testing during the program. With the tape sampler, ambient

air is drawn at a measured rate through a circular area on a filter paper tape, which is fed mechanically between supply
and take-up spools. A dirt spot results and is quantitated

by the reduction in light transmission of the paper, as measured

by a simple photometer. The instrument is fully automatic and

is provided with an adjustable timer for selection of its

sampling period ordinarily in the range of a fraction of an hour to several hours.

Neither on-stream nor off-stream spiking seemed feasible

for this procedure, owing to uncertainties in the preparation

and dispersion of uniform particulate samples. It was decided

instead to provide a calibration service for the collaborating

instruments. A number of Schott neutral density filters were obtained and precisely calibrated in absorbance at the Bureau

of Standards. For tape sampler calibration, filters were positioned over the tape, in the light path of the instrument,

to check photometric accuracy. The results were discouraging. Reflection from the tape caused erroneous measurements, and

light losses resulted from the displacement of the photometer

due to the insertion of the filters. Although no further

work is anticipated, it would be possible to retrieve and

calibrate the samplers if a better procedure could be devised.

8. Lead

Atmospheric lead is measured by a procedure (ASTM D 2681)

which provides for segregation of the sample into particulate

and vaporous fractions at the point of collection. The

particulate material, which generally accounts for more than

95 percent of the lead, is collected on an in-line filter;

vaporous lead is trapped in a charcoal absorber placed

immediately downstream of the filter. The collected samples

are digested and analyzed separately by a dithizone colorimetric

procedure

.

Separate spikes were provided for particulate and vaporous

lead. For the particulate spike, NBS certified Orchard Leaves

SRM 1571 was used. This material is a natural particulate

containing 44 ug lead per gram of the standard. Considering the

problems of dispersion and control associated with on-stream

particulate spiking, the standard was used instead to spike

the collected sample. For this purpose, weighed quantities of

the standard were packaged in coded gelatin capsules. Each

collaborator was then able to combine for analysis an encapsulated spike and his collected particulate sample, without the

need for quantitative transfer of the reference material. Tests

of this spiking procedure showed good recovery of lead from the

SRM, as shown in Table II

For spiking of the vaporous lead fraction, samples of

lead-doped charcoal were added to the respective absorbers
Table! II

Test of LeadI Standards

ASTM D-•2681

Lead Recovery from Orchard Leaves (SRM- 1571)

Sample Lead, yg

Reagent Blank

Empty Capsule

Empty Capsule

Ink-Coded Capsule

Ink-Coded Capsule

Standard "0" (30.1 yg

Standard "6 M (26.0 yg

Pb)

Pb)

0.9

1.9

1.3

1.1

0.9

28.4

26.7

Lead Recovery from Doped Carbon

Sample Lead, yg

Reagent Blank

Reagent Blank

Reagent Blank

1.0

1.0

1.0

Carbon Blank (10 g)

Carbon Blank (10 g)

Carbon Blank (10 g)

1.2

1.4

1.4

1.00 ml TML-Methanol

1.00 ml TML-Methanol

1.00 ml TML-Methanol

1.00 ml TML-Methanol

10.2

9.8

10.4

10.5

Carbon, 10.1 yg lead

Carbon, 10.1 yg lead

Carbon, 10.1 yg lead

Carbon, 10.1 yg lead

10.0

8.7

8.6

8.7

10
prior to sample collection. The doping material was a solution of tetramethyl lead in methanol prepared by the Ethyl

Corporation. The material was analyzed by the supplier and

checked at the Bureau and found to contain 10.1 yg lead per

milliliter. This material was pipetted onto 2-gram samples of

a cnarcoal which had been previously analyzed for residual

lead. These samples were supplied to the collaborators in

coded vials to be added to the spiked absorbers prior to

sample collection. A number of these spikes were tested for

lead recovery both at the Bureau and at Ethyl Corporation.

Results of these tests are also shown in Table II.

9. Reference Materials for Stack Emissions

The development of reference standards for source

monitoring analytical procedures is a considerably different

problem from that of the ambient standards used in the first

phase of Project Threshold. Nitrogen and sulfur oxides, the

prominent gaseous contaminants, are present in process stacks

at concentrations which are larger than ambient by a factor

of about 10 5

. Compared to atmospheric sampling, which can

be done under near-laboratory conditions, source sampling must

be done in an industrial environment which may be dirty, noisy,

and unprotected from the weather. Moreover, the variety and

concentration of interfering substances in stacks, and the

elevated temperature of the effluent mixture, make interfering

reactions more rapid and more significant.

Several procedures have been devised for applying reference

standards to source measurements. The gaseous contaminant may

simply be diluted with air or nitrogen and stored in a pressure vessel, to be used later as a reference standard. Aside

from the problem of deterioration during storage, such a standard fails to represent the contaminant under true stack

conditions. Another procedure is to build a standard emissions generator -- that is, a small furnace -- but conditions

are difficult to control and the equipment is unwieldy for use

in the field. For Project Threshold, a "spiking" or standardaddition procedure was desired which would permit the reference

standard to be placed in the same matrix as the contaminant

itself, the matrix in this case being the stack gas mixture.

By way of example, parallel samples of stack gas are analyzed

for sulfur oxides, but to one of these samples a known amount

of pure sulfur dioxide is added as an internal standard. The

difference in the response of the method to the two samples is

that which is due to the known spike and this provides calibration of the method, given that response is linear with concentration.

11
The spiking of an industrial facility fueled at rates

measured in tons per hour is impractical. Accordingly, field

tests on such facilities were confined to the determination of

repeatability and reproducibility -- the precision of the

methods under test. Accuracy tests, using a spiking system

developed at NBS , were conducted in a small pilot plant at

Battelle Columbus Laboratories. The system is illustrated in

Figure 3. A portion of the effluent from a furnace was piped

to an adjoining laboratory via a branched line whose flow

parameters could be measured accurately. To one of these

branches was added a gaseous spike at a flow rate controlled

by calibrated metering orifices. Previously-analyzed high

purity cylinder gases were used for the purpose. The pilot

plant effluent was spiked with nitric oxide and sulfur dioxide

for the respective tests at spiking rates ranging up to one mole per hour. Analyses of the standard gases are given in

Table III.

Table III

Analysis of Reference Gases

(Battelle, Mass Spectrometer)

Impurity Nitric Oxide Sulfur Dioxide

C0 2 0.08 percent 0.16 percent

N 2 0.36 percent 0.04 percent

N 2 0.33 percent

Assay 99.23 percent 99.80 percent

Fabrication and calibration of the metering orifices were

major tasks in design of a reliable spiking system. Four

orifices were fabricated from watch jewels having bore

diameters of 0.06 to 0.14 mm. These established gas flows

ranging from 75-500 milliliters per minute from a 15-psig

source. The spike was subsequently diluted in a duct system

flowing at 200-300 liters per minute, to produce spiking

levels from two hundred to several thousand parts per million.

The metering orifices were calibrated by a gravimetric

procedure. Attempts at calibration by chemical and volumetric

means were fraught with experimental difficulties. The gravimetric method proved simple and reliable. A small cylinder

of the pure contaminant gas was fitted with a regulator, a precision pressure gage and the orifice undergoing calibration,

Gas pressure was adjusted to 15 psig, the spiking condition,

and the entire assembly was placed on a 10-kg top-loading

12
COOLING LOOP

u

MULTI-FUEL FURNACE

FLUE

S UNSPIKED / LINE SAMPLING

PORTS ^/ SPIKED

LINE

METERING ORIFICE

SPIKING GAS

Figure 3. Stack Spiking System

13
balance. A balance -reading device was devised to reduce

parallax error. The weight loss of the assembly was monitored

manually over a period of several hours and the resulting data

used to determine a gravimetric rate for the orifice using a least squares fit. Rates for the four orifices are shown in

Table IV. In a separate experiment, it was determined that

the orifice rates are unaffected by a downstream back-pressure

of 12 inches of water, a pressure several times that existing

in the duct system. A subsequent experiment demonstrated that

the rates are independent of ambient temperature over the range

of 15-30 °C.

Table IV

Orifice Rates, grams/second

Orifice , mm NO, 15 psig SO2 , 15 psig

0.06 0.001464 (not used)

0.08 0.002349 0.003390

0.12 0.004751 0.006998

0.14 0.006468 0.009702

In addition to the pilot plant spiking procedure, it was desired to assess the precision and accuracy of the analytical

procedures for nitrogen and sulfur oxides, apart from the

respective sampling operations. For this purpose, simulated

stack samples were prepared as aqueous solutions of inorganic

salts. The samples were packaged in 20-ml ampoules for distribution to the collaborators. Test samples were checked through

the respective analytical procedures at NBS for NO and SO

and were also checked for accuracy by a gravimetric procedure.

Each collaborator was supplied with triplicate ampouled

samples representing three discrete levels of nitrogen and

sulfur oxides chosen to be typical of the samples collected

in the field. The sets of coded samples were distributed to

the collaborators at three times during the program to be

fun in parallel with actual stack samples collected at

industrial sites. Analysis of the resulting data provided an assessment of the accuracy of the chemical analysis procedures

of the collaborators , independent of the sampling procedures

in the field.

14
NBS-114A [REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-8402. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE Reference Materials for Collaborative Tests of Air

Quality Methods

5. Publication Date August 1974

6. Perfotming Organization Code

7. AUTHOR(S)

Richard H. Johns and John K. Taylor

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as 9.

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES Library of Congress Catalog Number: 74-600123

16. ABSTRACT (A 200-word or less tactual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) Reference materials and associated distribution apparatus were developed

for seven ambient air contaminants and for two smokestack contaminants.

These established the reference base for collaborative tests of ASTM

procedures for ambient air quality and smokestack emissions carried

out under a three-year program known as Project Threshold.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicoions)AiT pollution; chemical analysis, Standard Reference

Materials

18. AVAILABILITY XX Unlimited

^j For Official Distribution. Do Not Release to NTIS

1 Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CB .46-840

I Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

17

22. Price

55 cents

USCOMM.DC -29042-P74



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