Overview
ISO 13964:1998 - Air quality - Determination of ozone in ambient air - Ultraviolet photometric method - defines a standardized procedure for measuring ozone in ambient atmospheres using UV photometry. The standard specifies the measurement principle (monochromatic 253.7 nm radiation from a low‑pressure mercury lamp), calibration approach, instrument requirements, sampling precautions and performance considerations. It also includes informative annexes on chemical interferents, correction for ambient nitric oxide, and typical analyser performance.
Key topics and technical requirements
- Measurement principle: UV absorption at 253.7 nm and application of the Beer–Lambert law to relate transmittance to ozone concentration; use of an ozone catalytic converter (scrubber) for zeroing.
- Calibration: Ultraviolet photometry is specified as the primary reference procedure; secondary transfer standards may be used if traceable to the primary method (see ISO 6879 referenced).
- Range and reference conditions: The standard gives applicable concentration ranges and uses reference conditions (25 °C, 101.25 kPa), with alternatives (0 °C or 20 °C) allowed; temperature and pressure compensation methods are described.
- Instrument components: Requirements for UV source (low‑pressure Hg lamp with 185 nm removed), detector sensitivity (predominantly 253.7 nm), inert absorption cell materials, flow control, temperature and pressure measurement, particle filter and ozone converter.
- Sampling and handling: Use of ozone‑inert sample lines, minimization of residence time (recommendation to keep residence time short; up to 5 s allowed), particle filtration (regular replacement), and precautions against condensation.
- Interferences and corrections: Discussion of known interferents (e.g., NO, NO2, SO2 at elevated concentrations), particulate losses, and specific corrections for ambient nitric oxide (Annex B). Annex A lists reported chemical interferents for scrubber types.
- Safety: Ozone is toxic; the standard warns about handling and specifies venting/scrubbing excess ozone.
Applications and users
ISO 13964 is intended for:
- Environmental and air quality monitoring agencies operating ozone monitoring networks.
- Calibration and testing laboratories establishing traceability for ozone analysers.
- Manufacturers of UV photometric ozone analysers designing instruments to meet performance specifications.
- Researchers and compliance officers evaluating ambient ozone concentrations for regulatory or health studies.
Practical applications include routine ambient ozone monitoring, instrument calibration and quality assurance, regulatory compliance monitoring, and research on ozone trends and exposure.
Related standards and resources
- ISO 6879 (referenced for definitions and transfer standards)
- Informative annexes within ISO 13964: Annex A (chemical interferents), Annex B (NO correction), Annex C (typical performance specifications)
Keywords: ISO 13964, ozone determination, ultraviolet photometric method, ambient air, UV photometric ozone analyser, ozone monitoring, air quality standard, calibration, interferences.
