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Environmental Measurements

Ozone Measurements


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Technical Contact:
James Norris
Tel: 301-975-3936
E-mail: james.norris@nist.gov

Please contact the technical staff before shipping instruments or standards to the address listed below.

Mailing Address:
National Institute of Standards and Technology
100 Bureau Drive, Stop 8393
Gaithersburg, MD 20899-8393

Service ID
Number
Description of Services Fee ($)
37510C Ozone Instrument Calibrations 1905
37515S Additional Special Tests for Ozone Instruments At Cost
37520C NIST Standard Reference Photometer (NIST SRP)
87937
37525S NIST Standard Reference Photometer Maintenance
At Cost
37530C Validation of NIST Standard Reference Photometer (NIST SRP) 4139
37535S Additional Special Tests for Validation of NIST Standard Reference Photometer (NIST SRP) At Cost

Fees are subject to change without notice.

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Ozone Instrument Calibrations (37510C-37515S)

NIST provides calibration of many types of ozone measuring instruments. The calibrations are done by comparison against the NIST Standard Reference Photometer (SRP) which serves as the reference standard for the United States and is traceable to the International Bureau of Weights and Measures (BIPM).

Maximum Calibration Range: 0 nmol/mol (ppbv) to 1000 nmol/mol
Minimum Calibration Range: 0 nmol/mol to 100 nmol/mol
Minimum Concentration Point: 15 nmol/mol.

A single calibration run is performed over the customer specified concentration range consisting of ten independent concentration points, and a zero ozone concentration point at the beginning and end of each calibration run.

Calibrations of most commercial ozone instruments are done using an automated control system which reads the analog signal, or RS-232 (serial) port of the instrument under calibration. Calibrations can also be performed manually by entering the values from the instrument under calibration into the SRP control system. In general, the source for the ozone sample and reference air (if necessary) is provided by NIST instrumentation. If requested, the ozone sample can come from a commercial ozone instrument.

Calibration runs utilizing analog or serial communication are generally performed overnight and consists of 5-10 independent calibration runs. Manual calibrations will consist of only one independent calibration run.

Independent special tests (37515S) require additional costs.

Delivery and return shipment of the instrument under calibration must be handled by the instrument owner.

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NIST Standard Reference Photometer (NIST SRP)(37520C-37525S)

The NIST Standard Reference Photometer (NIST SRP), developed by NIST and the U.S. Environmental Protection Agency, is a photometric instrument for the assay of up to 1000 nmol/mol of ozone in calibration atmospheres. The measurement is based on the application of the Beer-Lambert Law using an absorption cross-section of 1147 x 10-20 cm2/molecule. The NIST SRP design consists of a dual cell system where each cell alternates between sample and reference during a variable length instrument cycle. This minimizes affects of lamp drift, and absorption cell or detector biases. The NIST SRP has served as the reference standard for all ozone measurements at NIST since 1983, and has recently been adopted as the Bureau International des Poids et Mesures (BIPM) reference standard for international ozone traceability. More than 25 years of NIST SRP inter-comparisons show agreement within 1.0 percent over the 0 nmol/mol to 1000 nmol/mol concentration range against NIST SRP 2, most agree to better than 0.3 %. The spread in the agreement of all NIST SRPs is 0.7%. Recent bias improvement upgrades are showing an improved agreement spread between all SRPs. The uncertainty estimate for a NIST SRP is located in Appendix I.

The current NIST SRP Network consists of 42 instruments located worldwide in the following countries: Australia (1), Austria (1), Canada (2), China (1), Czech Republic (1), Finland (1), France (7), Germany (2), Hong Kong S.A.R., China (1), Japan (1), Mexico (1), Portugal (1), Russia (1), Spain (1), Switzerland (4), Sweden (1), Taiwan R.O.C. (1), United Kingdom (1), and the United States (13).

General Comment: Each request for construction of an instrument will be considered individually and customers, especially other National Laboratories and Metrology Institutes, are encouraged to enter into a research collaboration with NIST establish worldwide traceability for ozone measurements.

Power Requirements: 115 VAC, 50/60 Hertz. A power transformer (if necessary) will be adequate. The control computer (not included) can operate on an independent power service separate from the NIST SRP.

Laboratory Requirements: A laboratory with reasonably stable temperature, pressure, and humidity control. Large temperature drifts and cyclical changes can affect instrument stability. Humidity levels above 50 % have been shown to cause SRP detector drift. The whole SRP system will fit on a normal desktop or laboratory bench top.

Physical Dimensions: Electronics Module: 18.75 x 12.75 x 7.5 inches, (47.6 x 32.4 x 19.1 cm).
Pneumatics Module: 18.75 x 12.75 x 7.5 inches, (47.6 x 32.4 x 19.1 cm).
Optical Bench: 46.0 x 5.0 x 4.875 inches, (116.8 x 12.7 x 12.4 cm).

The SRP system can be set up on a laboratory bench top with the optical bench setting on a stand and the electronics and pneumatics modules situated underneath. The required bench top space is 46.0 x 17.0 inches (116.8 cm x 43.1 cm) with a necessary clearance height of approximately 27 inches (68.6 cm). Additional space is then required for the control computer, which will need to be located near the instrument, and another lab bench will be necessary for setting up guest instruments to be calibrated.

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Shipping Dimensions and Weight Included with a NIST SRP purchase are two customs shipping containers.

Container 1: Instrument Modules and associated cables and interface components.
25 x 24 x 18 inches (63.5 x 61 x 45.7 cm) at 102 pounds (46.4 kg)

Container 2: Optical Bench Module
9 x 9 x 53 inches (12.9 x 12.9 135 cm) at 58 pounds (26.4 kg)

All shipment costs including customs fees, duty, and taxes must be handled by the customer.

Air Supply: Minimum input pressure of 15 psig (34.7 psia, 239.2 kPa) of clean, dry air.
Preferably, zero air containing no significant impurities, having less than 1 ppm (parts per million) total hydrocarbons by volume, and containing 20 - 21% oxygen. The NIST SRP has internal devices to control the amount of air required for operation. No external control is necessary. A zero air supply of 20 standard liters/min. (SLPM) will be adequate for most calibration work. These units are available through commercial suppliers of air monitoring equipment.

An SRP draws 2 SLPM into each cell (4 SLPM total), plus some excess is required in the sample and reference manifolds, and additional flow requirements for instruments under calibration.

General Items needed in the Laboratory for SRP operation and Maintenance

- Zero air supply - specifications stated above under Air Supply.
- 115 VAC power - listed above under Power Requirements.
- Pressure Standard with traceability to primary standard.
- Digital multimeter - preferably with mV scale and frequency measurement capability.
- Digital temperature measurement meter - thermocouple device is suitable.
- Wrenches, preferably English, but Metric will work.
- Screwdrivers, both straight and Phillips, several sizes, especially small for potentiometers.
- Teflon tubing, clean ¼ inch (6.35 mm) outside diameter.

SRP control system: allows for fully automated calibration of commercial ozone instruments. Details on the Control software are below:

  • Operates under Windows XP or Vista (U.S. version recommended)
  • Uses Excel 2003 (U.S. version recommended) or later for report output
  • Reports are customizable
  • Calibration is done using scripts, which are customizable
  • Up to three instruments can be compared to the SRP, including multiple SRPs
  • Guest instruments can be an SRP, Analog input, or Serial input
  • Guest ozone generator can be used in calibration (RS232 only)
  • Calibration methods can be saved
  • Methods can be linked for totally automated runs

This new software requires a newer computer to operate. The computer requirements are:

  • 2 GHz or better processor recommended
  • 2 GB or more memory
  • Microsoft Excel (2003 or later)
  • Windows XP or Vista (U.S. version recommended)
  • 250 GB Hard Drive recommended
  • 20 inch monitor (Wide screen recommended)
  • Two free PCI slots
  • CDRom drive

Included with the NIST SRP Instrument:

- Control circuit cards and inter-connection cables
- Operating software (Windows based fully automated control system)
- Standard operating procedures manual (currently being updated)
- Product information on commercial components used in the NIST SRP
- Complete set of instrument drawings and circuit diagrams
- A built-in Ozone Generator
- Temperature Calibrator
- Custom SRP shipping cases
- Validation against NIST SRP 2 (NIST’s highest level ozone standard)

Not included:

- Customs Charges, Taxes, or Duty on the instrument
- Control Computer or Printer (A PC is necessary for operation of the SRP)
- Zero air supply system. (necessary for SRP operation)
- Power transformer for 115V power. (necessary for SRP operation)
- Written Warranty (although NIST will ensure the SRPs proper operation as built, and work with your personnel to have it operate correctly in your lab)
- Shipment of new NIST SRP to your lab
- Round-trip shipment of our traveling NIST SRP 0 to your lab
- Travel costs for initial setup and operations training in your lab
SRP Uncertainty Budget Summary

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Appendix 1 - SRP Uncertainty Budget Summary

Component
(y)
Source Distribution Standard
Uncertainty
Combined
Standard
Uncertainty
µ(y)
Sensitivity
Coefficient
ci = ∂x/∂y
Contribution to
µ(x), |ci|• µ(y)/nmol
mol-1
Optical Path-length, L Measurement scale
Variability
Divergence
Rectangular

Rectangular
Rectangular
0.005 cm

0.03 cm
0.52 cm

0.52 cm

x/Lopt

2.89 x 10-3 x
Pressure, P P Gauge
P difference between cells
Rectangular
Rectangular
0.029 kPa
0.017 kPa

0.034 kPa

x/P

3.37x10-4 x
Temperature, T T probe
T gradient
T heating bias
Rectangular
Rectangular
Rectangular
0.029 K
0.058 K
-1.0 x 10-3 x
0.07K x/T
2.29 x 10-4x
Bias
Ratio of intensities, D Scaler resolution
Repeatability
Rectangular
Triangular
8×10-6
1.1×10-5

1.4×10-5

x/Dln(D)

0.28
Absorption cross-section,σ Conventional value
1.22×10-19
cm2/molecule
1.22×10-19
cm2/molecule
x 1.06×10-2 x

The effective number of degrees of freedom for all components is large therefore, the conventional 95% coverage factor of 2 is appropriate.

The uncertainty budget above is summarized in one equation describing the uncertainty as a function of ozone mole fraction:

 equation for uncertainty as a function of ozone mole fraction

Removing the absorption cross-section uncertainty, the equation becomes:

equation removing the absorption cross-section uncertain 

This summarizes the above uncertainty budget for an SRP without the absorption cross-section uncertainty or the temperature probe heating bias included. Without the temperature probe bias, the 95% level of confidence expanded uncertainty is:

U95 = x ± 2 × u(x) nmol/mol

With the temperature probe bias, the 95% level of confidence expanded uncertainty is:

U+95 = 2 × u(x) nmol/mol, U95 = (-2 × u(x) - 0.001 × x) nmol/mol


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Validation of NIST Standard Reference Photometers (37530C-37535S)

NIST provides ozone reference standard instruments called Standard Reference Photometers (NIST SRP) to government laboratories around the World. It is recommended that the NIST SRP be validated bi-annually. This validation service is provided by NIST for any existing NIST SRP instrument.

The validation of a NIST SRP is done by comparison against the NIST SRP, serial number 2 (NIST SRP 2) which serves as the reference standard for the United States and is traceable to the International Bureau of Weights and Measures (BIPM). An SRP validation is performed up to a maximum ozone concentration of 1000 nmol/mol (ppbv), or a lower ozone concentration range if requested. The minimum ozone concentration range for a validation of an SRP is 250 nmol/mol. The minimum ozone concentration point which can be accurately measured is 15 nmol/mol. A single validation run is performed over the desired concentration range consisting of ten independent concentration points, and a zero ozone concentration point at the beginning and end of each calibration run. In general, the source for the ozone sample and reference air is provided by NIST instrumentation. If requested, the source for the ozone sample and reference air can come from the guest SRP.

An official SRP validation consists of multiple inter-comparison runs over multiple days to look at within day, and between day variations. The data is summarized and provided in a report.

Independent special tests require additional costs.

Delivery and return shipment of the NIST SRP to be validated must be handled by the owner.

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Program questions: Calibrations 
Phone: 301-975-2200, Fax: 301-975-2950
NIST, 100 Bureau Drive, Stop 8363, Gaithersburg, MD 20899-8363