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A SURVEY OF CALIBRATION TECHNIQUES FOR

ATMOSPHERIC OZONE MONITORS

NATIONAL BUREAU OF STANDARDS,

WASHINGTON, D.C

DEC 1976

' U.S. Department of Commerce

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PB263534

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NBSIR 76-1191

A SURVEY OF CALIBRATION

TECHNIQUES FOR ATMOSPHERIC

OZONE MONITORS

Jimmie A. Hogeson

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

Final Report

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter. Unthr S0cntaiy

Dr. Betsy Ancker-Johnson, Assistant SacretarY fpr Scianca and Tachno/ogy

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Acting Diractor

REPRODUCED BY; U S Department of Commerce

National Technical Information Sen/ice

Springfield, Virginia 22161

NHS

A Survey of Calibration Techniques for

Atmospheric Ozone Monitors

ABSTRACT

A survey is presented of recent studies on calibration

techniques for atmospheric ozone CO3) monitors. These

calibration techniques are based on iodometry, ultraviolet

photometry (UV) and gas phase titration (GPT) . The iodometric procedures include the 1 percent neutral buffered

potassium iodide (XBKI) technique used by the Environmental

Protection Agency (EPA) , a 2 percent NBKI method of the

California Air Resources Board and a 1 percent unbuffered

KI technique previously used by the Los Angeles Air Pollution

Control District (LAAPCD) . The UV and GPT approaches are of

rather recent application and brief descriptions of the

calibration procedures are given. In summary the data show

excellent agreement between O3 determinations by or GPT

and demonstrate that absolute measurements of trace O3 concentrations can be made by either technique. On the other

hand the NBKI methods yield O3 measurements 1 to 13 percent

higher than absolute values when O3 in dry air is analyzed.

In the presence of humid air the NBKI measurements are

high by factors ranging from 15 to 30 percent.
INTRODUCTION

As a result of the Clean Air Act of 1970 and subsequent

Federal regulations, ozone (O^) is one of the six criteria

air pollutants for which national primary and secondary air

quality standards have been established [1]. Compliance

monitoring has been implemented by many state and local air

pollution control agencies [2], throughout the country today.

Ozone has been recognized as an important air pollutant since

its discovery in the Los Angeles basin in the late 1940 's.

Since that time a considerable volume of literatature has

appeared dealing with techniques for and problems associated

with atmosphere 0^ monitoring. This literature is adquately

summarized in several recent reviews [3-6]. The purpose of

this discussion is to update these reviews by a description

of some recent, critical and unpublished activities in 0^

monitoring.

Atmospheric 0^ measurements can conveniently be divided

into the areas of sampling, calibration and analysis or

monitoring. Sampling procedures and manual and instrumental

analysis methods are adequately covered by prior reviews.

The attached appendix [3] provides a description of both

manual and continuous techniques for monitoring. The most

recent activities and the source of considerable controversy

lies in the area of 0^ calibration, and these activities

are discussed below.

2
The nature of the 0^ calibration problem is worth reviewing. Air pollution monitors, including those for 0^, do not,

in general, provide a measurement of the absolute concentra-

tion of the pollutant in the atmosphere. Instead they

provide an output signal which is linearly proportional to

pollutant concentration. The instrument must then be calibrated by sampling from a flowing air stream into which the

pollutant has been introduced at a known concentration.

Where feasible primary standards, such as National Bureau of

Standards certified gas cylinders or permeation tubes, are

used to generate known concentrations. In the case of the

unstable 0^ molecule, no primary standard is available.

Instead a photolytic generator [7] is used to produce trace

concentrations of 0^ in air and the air stream sampled and

analyzed by a manual, wet-chemical procedure. Various manual

procedures have been used in the past but the technique used

most predominantly now employs oxidation of a neutral buffered

potassium iodide solution [1]. The iodine produced is

determined spectrophotometrically

.

The recent controversy involves the accuracy and reproducibility of iodometric calibration procedures. Questions

have arisen because of discrepancies observed in comparisons

of different variations of iodometric procedures and because

of the application of two alternative gas phase techniques

for absolute 0, measurement. These techniques employ
ultraviolet (UV) absorption by 0^ of 254 nm radiation and gas

phase titration (GPT) of 0^ with known concentrations of

nitric oxide (NO). The discussion below gives a brief

description of the UV and GPT calibration procedures. In

addition, results of recent comparisons of the various calibration techniques are summarized.

DISCUSSION

Calibration Procedures - UV and GPT

Ultraviolet Absorption Technique . Details of the absolute

measurement of 0^ in the subpart per million (ppm) range have

been given by Demore and Patapoff [8] and by Hodgeson, et al.

[9]. The basic absorption equation for determining ozone

concentrations by photometric measurements is:

0 "

where = 308.6 atm" ''^cm' (base e) is the 0^ absorption

coefficient at 253.7 nm, a value which has been determined

to within an accuracy of 1 percent by several investigators

[8]. In this equation Z is the pathlength in cm, Pq = 1 atm

and Tq = 273K.

4
The absorption coefficient and the optical pathlength

are known to within 1 per cent. Thus the absolute 0^ determination requires only the measurement of the ratio of the

transmitted light intensities in the absence of and in the

presence of 0^. It is instructive to examine the degree of

light attenuation expected for 0^ concentrations in the subppm range. At low ozone concentrations the light attenuation

is very small and the log term reduces to the linear form,

log^ I^/I = AI/I^ where AT = - I.

For an 0^ concentration of 0.1 ppm, an optical path of

100 cm and at P = 760 mm, T = 298K, the fractional

attenuation is

= 2.8 X 10"^

Thus, the determination of 0^ at the 0.1 ppm level requires

the measurement of a light attenuation of only 3 parts per

thousand (0.3%). This is a difficult task and indeed 0.1 ppm

is the approximate lower limit of detection for a 100 cm

photometer.

The laboratory photometer employed by the author in a previous study [9] is illustrated in figure 1. The optical

components were mounted on a shock mounted 2 meter optical
rail. The detector was a ultraviolet phototube with a high

rejection to room light. An interference filter was coupled

to the phototube to isolate the 253.7 nm component of the

low pressure mercury lamp. The absorption cell was a

1 meter Pyrex tube, 1 inch in diameter, with air inlet and

outlet connections at each end. The light pource was

collimated and apertured in a manner such that a parallel

beam of light, 1 to 2 mm in diameter, passed through the

center of the absorption tube to the phototube. This arrangement was chasen to avoid optical reflections off the walls of

the absorption tube and in order to define a well known

optical path length.

The relative light intensity is determined by measuring

the anode output current of the photodiode by either analog

or digital current measuring devices. In the single beam

system it is advantageous to integrate the output over

selected time intervals during both the sample and reference

cycles in order to obtain maximum precision. A digital

photometer output arrangement employing a charge-to-frequency

conversion and a multi-channel analyzer is described in

reference 9

.

The basic procedure for making 0^ measurements with a single beam photometer system was as follows. The reference

beam intensity, I^, measurement was made by purging the

6
photometer cell with clean air from an auxiliary air source.

When a stable reference intensity signal was obtained, the

ozonized air stream was pased through the cell and the

sample beam intensity, I, measured. Once a stable measurement

of I was obtained the cell was again purged with clean air to

remeasure I^. The total time required for the single beam

photometric measurement via this cycle was approximately

5 minutes.

Gas Phase Titration Technique . Gas phase titration (GPT) as

a technique applied to the calibration of atmospheric monitors of 0^ and nitrogen dioxide (NO2) has been described in

detail elsewhere [10, 9]. The GPT technique has been employed

extensively in recent years by the Environmental Protection

Agency (EPA) and other groups . Portable GPT apparatus are

commercially available for calibrations in the laboratory or

in the field.

A laboratory calibration manifold used for GPT 0^ measurements [9] is illustrated in figure 2. Typical clean air flow

rates were of the order of 5 liters per minute. In the mode

illustrated in figure 2 the clean air flow was split such

that only 101 of the air passed through capillary 1 and

through the variable 0^ source. The remainder of the air

flow passed through capillary 2 and mixed with the ozonized

air stream downstream of the reaction flask. The reaction

7
flask and the mixing flask were approximately 250 cm in

volume. The split stream design was employed in order to

generate locally higher 0^ and NO concentrations in the

reaction flask and promote complete reaction over a wide

concentration range.

The GPT approach is based upon the rapid reaction between

NO and 0^.

NO (excess) + 0^ = NO2 + 0^ (6)

A constant NO concentration, (NO)^, in the ppm range is

produced by dilution of the flow from a cylinder containing

a known concentration of NO in nitrogen (50-100 ppm)

flow from NO cylinder

air flow through 0^ source

^NO ^^03

where F^^^

^3

^T

*In the case in which the air flow is split upstream of the

O3 source, Fq^ represents the sum of the flow through the

source and bypass arms.

8
Once the initial NO concentration is established, a series of

Oj samples at lower concentrations are added and the decrease

in NO observed with the chemiluminescence detector. Over the

range of 0^ concentrations for which the reaction is complete,

the following relation holds,

(NO)^ - (NO). = (O3). X Fq^/F^ = (NO^). (8)

where (03)^^ ^ Fo^/^T** ^3 concentration added and

(N02)^ is the concentration of NO2 produced. For the GPT

system described in this work, essentially complete reaction

was obtained at an initial NO concentration of 1 ppm for 0^

concentrations up to 0.7 ppm.

The GPT approach is a method for relating the concentration of the three components, NO, 0^ , and NO2. For an actual

measurement to be made the concentration of one of the species

must be known and the change in concentration observed upon

reaction. In the usual application the initial NO concentration is known based on a standard NO cylinder, which is

referenced to an NBS certified NO cylinder, and the measurement of a flow dilution ratio, F>,p^/F,p. The GPT measurement

**The flow ratio term, Fo^/Frj,, is included because the O3

concentration in the absence of added NO is desired. At

typical flow rates, e.g., Fq^ = 5000 cm^/min and T^^ = 100 cm^/min, this ratio is close to unity.
then yields a calibration of the 0^ source and the generation

of a known concentration of NO2.

Evaluations of Calibration Techniques

Early Studies . In the original version [11] of the Federal

Reference Method (FRM) now employed by EPA, a s toichiometry

factor (moles I2 released/moles 0^ absorbed) of 1.0 was

employed. This factor was later refuted by Boyd et al. [12]

who observed a factor of 1.5 upon static abosrption of

relatively high 0^ concentrations (10-100 ppm) . This work

was immediately followed be several investigations in the

early 1970 's all of which obtained stoichiometry factors near

unity for ppm concentrations of 0^ in flowing systems [ISIS] . These studies seemed to satisfactorily answer questions

over calibration uncertainties for a time. However, since

1973 extensive applications of the EPA-FRM and interagency

comparative and collaborative studies have yielded results

which have actively revived the issue of the accuracy and

the precision of iodometric methods.

For example in a recent interlaboratory collaborative

test conducted by EPA, different laboratories employing the

same reference method obtained a significant spread in

results upon the analysis of precalibrated 0^ generators

supplied by NBS [16]. Ozone generators were calibrated by

10
NBS at 5 concentration from 0,05 to 0.5 ppm and supplied to

ten different laboratories for analysis. The calibration of

the generators was then checked by NBS after the tests were

completed. The statistical analysis of results from this

study revealed that the mean percentage difference between

the average observed value and the NBS reference value at

these five concentration levels ranged from 16 to 37 percent.

Several factors might contribute to these observed interlaboratory biases, including instability of 0^ generators or

failure of collaborators to adhere to test procedures.

However, the nature of these studies indicated that the calibration procedure was a primary suspect cause for the observed

lack of reproducibility. This suspicion was reinforced by

data presented at a joint NBS-EPA workshop on ozone calibration. The summary of this workshop [17] discusses uncontrolled

variables in written procedures which may contribute to

uncertainties in iodometric 0^ analyses. These include such

factors as impinger design, reaction time after sampling and

reagent impurities.

State of California Studies . Comparative studies began in the

State of California in 1973 to check the accuracy obtainable

with iodometric calibration procedures. Two separate procedures were used in that state, each different from the FPA-FRM.

Throughout California outside the county of Los Angeles, the

11
California Air Resources Board (CARB) employed a method similar to EPA, differing in that 2% NBKI (vs 1% for EPA) was

used and humidified air was passed through the 0^ generator.

The Los Angeles Air Pollution Control District (LAAPCD)

calibrated their analyzers by a method in which 21 unbuffered

KI was used and in which the liberated iodine was determined

by titration with thiosulfate.

Significant measurement discrepancies between the LAAPCD

and CARB were first observed in 1973, during studies in which

a CARB mobile van obtained oxidant data within 2 miles of the

LA Pomona station (Spring 1973) and then adjacent to the LA

Azusa station (Summer 1973) . In Pomona averaged LAAPCD

oxidant data were 38 percent lower than simultaneous CARB

data and in Azusa 30 percent lower than CARB measurements

[18, 19]. The measurement discrepancy was traced to the

different calibration procedures employed in laboratory

studies conducted by calibration teams from CARP and the

California Air and Industrial Hygiene Laboratory [19, 20].

These studies demonstrated that the county calibration method

gave results 27 to 30 percent lower than the CARB method when

analyzing the same ozone sample.

In order to further investigate the measurement disparity

and provide a recommended course of action, CARB in the

summer of 1974 appointed an "ad hoc" committee to evaluate

12
various calibration procedures. In October 1974, this cominittee conducted a study at the CARB El Monte Laboratory, in

which the following calibration procedures were simultaneously

compared by sampling from a common manifold - 1% NBKI (EPA),

2% NBKI (CARB), 2% UBKI (LAAPCD) , UV and GPT. Six 0^ concentrations over the nominal concentration range, 0.1-0.8 ppm,

were analyzed on 3 consecutive days. The iodometric measurements were performed by representatives from each of the

agencies involved. The data were analyzed by linear

regression with the UV measurement as the reference and the

following relations were obtained [21].

0.003

0.005

0.035

0.032

The following comments should be made regarding these

data. Both the CARB and the EPA results are significantly

higher than the absolute UV measurements while the LAAPCD

measurements are slightly lower. The discrepancy observed

between the CARB and LAAPCD measurements was approximately

f°3)EPA ' l-^l C"3)UV

-

(°3)lAAPCD = "-5^ (°3W -

13
the same as observed previously. The EPA* and LAAPCD

iodometric results show significant negative intercepts.

The effect of the negative intercept is that the EPA and UV

measurements tend to converge at lower concentrations. The

GPT procedure was not the same as that normally applied by

EPA, but a late modification especially designed to be

compatible with the sampling manifold employed. Finally,

according to GARB practice the air stream was humidified to

a 50 percent RH upstream of the 0^ source.

EPA Study . Shortly after the El Monte study, a similar

investigation was undertaken at EPA's research facility at

Research Triangle Park, NC. In this study the CARB, EPA and

LAAPCD methods were compared to GPT as the reference. Three

ozone concentrations (0.1, 0.3 and 0.5) were analyzed over

a 9 day study in a random fashion such that 12 determinations/

concentration/method resulted. In this study dry air was used

for the 0^ source as specified in the EPA-FRM. The GPT measurement was performed at the start and conclusion of each

experiment. The GPT measurement was traceable both to an NBS

standard reference NO cylinder and to the generated

from an NBS certified N0~ permeation device. The results of

*In a separate study [9] employing the same reagents and

impingers used here, a negative intercept was also observed

and by indirect evidence attributed to an O3 demand of the

reagents or distilled water used. In the absence of this

demand the slope would not be affected.

14
this study are summarized below in terms of the average

ratio of the iodometric results to CPT [22].

Nominal

Concentration EPA/GPT CARB/GPT LAAPCD/GPT

0.1 1.05 1.07 0.592

0.3 0.964 1.01 0.604

0.5 1.01 1.04 0.650

Average Ratio 1.01 1.04 0.615

The results of this study differ from the El Monte data

in that the EPA and GARB measurements were only slightly

higher than the reference 0^ values obtained in this case by

GPT. The large discrepancy between the NBKI and the

unbuffered KI measurements was again confirmed.

Effect of Water Vapor . The most disturbing disparity between

the El Monte and EPA-RTP studies was the different relations

observed between the iodometric techniques and the reference

techniques employed, since both UV and GPT presumably provide

an absolute measure of the 0^ concentration. A substantial

portion of the descrepancy was subsequently accounted for in

three separate studies by EPA at their research laboratories

in Las Vegas, NV [23] and Research Triangle Park, NC [24] and

by GARB in California [25]. These studies demonstrated that

humidified air has a significant effect upon some of the

techniques employed.

15
In these studies the responses of the various techniques

and instruments to 0^ in dry air were compared to responses

obtained when air containing the same 0^ concentration and

relative humidities of 20 to 80 per were analyzed. A portion

of these data are summarized in Table I. The Dasibi and GPT

measurements are unaffected by the presence of water vapor.

The chemiluminescence 0^ detector shows a net positive

response of 5-8 per cent. The unbuffered KI procedure has a

slight negative response to water vapor whereas the NBKI

procedures have positive responses of 6-13%. Thus in presence

of water vapor the NBKI results will be ca. 10 per cent higher

with respect to reference UV or GPT measurements. A correction

of the El Monte NBKI data for water vapor would give closer

agreement to the EPA-RTP measurements. Some discrepancy would

remain which may be attributed to different procedures followed

in the GPT measurements or unknown variables in the KI

procedures.

Recent Individual Investigations . Most of the previous

investigations discussed involved interagency or interlaboratory investigations of several procedures. While such

studies have been useful for the rapid generation of qualitative information, they suffered several shortcomings which

have limited the definitive determination of the quantitative

relations among the various calibration procedures. The

involvement of several investigators and laboratories requires

16
that rigid procedural protocols be written and followed.

Such protocols leave little room for changes in direction

of the experiment detailed by the nature of the data obtained.

In addition such studies were conducted within such a

relatively short time frame that it is almost impossible to

repeat suspect experiments or to perform problem solving.

Finally, the involvement of many different people and apparatus

makes the problem of quality control over the whole experiment

quite complex.

The most definitive information about relations among

calibration procedures can be obtained in one laboratory over

an unlimited time frame by a single investigator who is able

to control all aspects of the study. Fortunately several

studies of this sort have recently been completed for 0^.

In an August 1975 meeting of the ASTM in Boulder Colorado,

three separate papers discussed observed relations among UV,

GPT and NBKI. These reports were based on carefully controlled experiments in which multiple, simultaneous analyses of

were performed by the various procedures. DeMore and

Patapoff [8] used a 5 meter laboratory photometer and

observed agreement within 1 per cent between UV and GPT

measurements over the concentration range of 0.05 to 1 ppm.

Similar agreement was obtained by Paur [26], who used 2 separate modified Dasibi analyzers to make absolute UV

measurements. Hodgeson et al . [9] used a 1 -meter laboratory

17
photometer for comparison of UV to GPT and the 1 per cent

NBKI method employed by EPA. Again a 1:1 agreement was obtained between UV and GPT over the concentration range from

0.1 to 0.8 ppm. However, the NBKI method gave measurements

that were ca. 10 per cent higher than either of the gas

phase techniques. Finally, results obtained at the Statewide Air Pollution Research Center in California, showed

good agreement between absolute 0^ measurements by IJV

photometry and long-path infrared spectrophotometry [27].

While excellent agreement has been obtained between the

photometric and GPT measurements, the situation is still

somewhat vague regarding the relation between iodometric and

absolute 0^ measurements. Paur [28] has summarized recent

published and unpublished data in which iodometric measurements

were compared to UV or GPT determinations. This summary is

repeated here as table II. The EPA II NBKI yields 0^ measurements higher than obtained by UV or GPT by factors

ranging from 1 to 11% for studies conducted in the absence

of water vapor. It is interesting to note that if the ratios

from references 24 and 21 are corrected by 101 for the water

vapor effect, then ratios of 1.02 and 1.13 are obtained for

the II NBKI method. With attention focused on the EPA

method, it is apparent that a factor of 1.07 + 0.06 would

encompass all the data given here. It should be emphasized

that these are best possible results obtained by trained

18
personnel in dedicated experiments and therefore may not

represent the accuracy obtainable in routine field calibrations .

SUMMARY AND CONCLUSIONS

The studies discussed above demonstrate that excellent

agreement can be obtained between UV and GPT calibration

procedures and that either technique may be used for the

absolute measurement of sub-ppm concentrations of 0^. On the

other hand results obtained in separate studies by the EPA

1 percent NBKI procedure (using dry air) have been higher

than absolute 0^ measurements by factors ranging from 1.01

to 1.13. A factor of 1.07 +_ .06 encompassed all the studies

discussed here. This small deviation from unity and the

relatively large uncertainty which must be assigned to the

factor dictates against the application of correction

factors to NBKI calibration results at the present time. In

the presence of moist air, 0^ measurements by NBKI procedures

are higher than absolute values by 15 to 30 percent. The

reasons for the observed water vapor effect are unknown at

the present time.

The main conclusion is that greater accuracy can be

achieved by a replacement of iodometric calibration procedures

by UV photometry or GPT. At the present time the choice of

19
UV or GPT is a matter of convenience. In principal calibrations by the UV procedure are simpler because this technique

is inherently flow independent. A lack of absolute laboratory

photometers is the primary limitation, since at the present

time there are only three operational systems - at the Jet

Propulsion Laboratory, F.PA-Las Vegas and NBS. Absolute

determination of 0^ by the GPT procedure requires the accurate

measurement of a flow dilution ratio. However, the technique

may be readily applied now by many calibration groups through

the availability of NBS certified NO cylinders and commercially

available GPT apparatus.

20
REFERENCES

1. Title 40 CFR Part 50, "National Primary and Secondary

Air Quality Standards", Federal Register 56 , No. 228,

pp. 22384-223970 (Nov. 25, 1971).

2. Title 40 CFR Part 51, "Requirements for Preparation,

Adoption and Submittal of Implementation Plans," ibid,

pp. 22398-22417.

3. J. A. Hodgeson, Intern J. Environ. Anal. Chem . 2^, 113 (1972).

4. USDHEW, National Air Pollution Control Administration, "Air

Quality Criteria for Photochemical Oxidants," NAPCA Publication AP-63, Washington, DC, U.S. Government Printing

Office, 1970.

5. "Photochemical Oxidant Monitoring Instrumentation," in

Instrumentation for Environmental Monitoring-Air , Environmental Instrumentation Group, Lawrence Berkeley Laboratory,

University of California, Berkeley, 1973.

6. P. K. Mueller, "Measurement Methods," Chapter VI, Ozone

and Other Photochemical Oxidants , National Research Council,

Washington, DC (to be published, 1976) .

7. J. A. Hodgeson, R. K. Stevens and B. E. Martin, ISA

Transactions , U, 161 (1972).

8. W. B. DeMore and M. Patapoff, "Comparison of Ozone Determinations by Ultraviolet Photometry and Gas Phase Titration,"

publication preprint, submitted to Environ. Sci. Techn., 1975.

9. J. A. Hodgeson, C. L. Bennett, H. L. Kelly and B. A. Mitchell,

"Ozone Measurements by lodometry. Ultraviolet Photometry

and Gas Phase Titration," Publication preprint, presented

at ASTM Symposium on Calibration in Air Monitoring, University

of Colorado, Boulder, August 5-7, 1975.

10. K. A. Rehme, B. E. Martin and J. A. Hodgeson, "Tentative

Method for the Calibration of Nitric Oxide, Nitrogen

Dioxide and Ozone Analyzers by Gas Phase Titration,"

EPA-R2-73-246 , U.S. Environmental Protection Agency,

Washington, DC 20460, March 1974.

11. D. H. Byers and B. E. Saltzman, Adv. Chem. Series , No. 21

American Chemical Society, Washington, DC, 1959, pp 93-101.

^1
12. A. W.

13. J. A.

K. A.

14. S. L.

15, R. N.

16. H. C.

Study

Boyd, C. Willis and R. Cyr , Anal. Chem . 42 , 670 (1970).

Hodgeson, R. E. Baumgardner , B. E. Martin and

Oxidants in the Atmosphere", EPA-650/4-75-016 , U.S. Environmental Protection Agency, Washington, DC 20460, February 1975.

17. J. B. Clements, "Summary Report: Workshop on Ozone Measurement by the Potassium Iodide Method," EPA-650/4-75-007

,

ibid, February, 1975.

18. "Oxidant Measurements and Emergency Plan Episode Criteria

Levels," Staff Report No. 74-16-6, California Air Resources

Board, Sacramento, CA, August 15, 1974.

19. Communications from Jerry Wendt, California Air Resources

Board, El Monte Laboratory.

20. J. Tang, E. Jeung and M. R. Imada , "Collaborative Study

of Manual Ozone Method," AIHL Report No. 158, Air and

Industrial Hygiene Laboratory, California State Department

of Health, Berkeley, CA, November 1973.

21. "Comparison of Oxidant Calibration Procedures -A Report of

the Ad Hoc Oxidant Measurement Committee of the California

Air Resources Board," Sacramento, CA, February 3, 1975.

22. K. Rehme, R. Paur, W. A. McClenny and R. K. Stevens, "Ozone

Calibration Study," Internal Report, Environmental Protection

Agency, Research Triangle Park, NC, November 25, 1974.

23. H. L. Kelly and J. A. Hodgeson, Unpublished data. Environmental Protection Agency, Las Vegas, Nevada, November 1974.

24. R. E. Baumgardner and R. Paur, Internal Report, Environmental

Protection Agency, Research Triangle Park, NC, May 1975.

25. "A Study of the Effect of Atmospheric Humidity on Analytical

Oxidant Measurement Methods - Report of a Joint Study by the

Los Angeles Air Pollution Control District and the California

Air Resources Board with the assistance of the Environmental

Protection Agency Region IX Conducted in Temple City,"

California Air Resources Board, Sacramento CA, July 9, 1975.
26. R. Paur and R. E. Baumgardner, presented at ASTM Symposium

on Calibration in Air Monitoring, University of Colorado,

Boulder, CO, August 5-7, 1975.

27. J. N. Pitts, Jr., J. M. McAfee, W. 0. Long and A. M. Winer,

Environ. Sci. Technol

.

, (Submitted for Publication, 1975).

28. R. J. Paur, R. E. Baumgardner, W. A. McClenny and

R. K. Stevens, "Status of Methods for the Calibration

of Ozone Monitors," Extended Abstract, presented at

the Division of Environmental Chemistry, American Chemical

Society, New York, April 1976.

TABLE I

EFFECT OF HUMIDIFIED OZONE SAMPLES

Relative Response, Wet/Dry

Re£. 23 Re£. 24 Re£. 25

Technique (40IRH) (50IRH) (60IRH)

1% KI 1.05 1.08 1.10

21 KI - 1.06 1.13

1% UBKI - - 0.96

GPT - 0.990

Dasibi 1.00 0.995 1.00

Chemilum. 1.05 1.08 1.07
> +-> •H 'H

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OO o o o LO LTl in I t / /

oo

a in in LO 00 oo oo o • (X r—I o u o o o o o o o

p: " 1 o <u 1 1 1 1 1 1 o o o o U-) 00 a rH r-t t—i

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