Overview
ISO 10498:2004 - Ambient air: Determination of sulfur dioxide (SO2) by ultraviolet fluorescence specifies an automatic-analyser method for sampling and measuring SO2 in ambient air. The standard covers measurement ranges from a few micrograms per cubic metre up to a few milligrams per cubic metre (or, in volume terms, from µL/m3 to mL/m3). It defines the measurement principle, calibration requirements, sampling and instrument components, and routine quality-control procedures to ensure accurate, traceable SO2 measurements.
Key topics and technical requirements
- Measurement principle: Ultraviolet fluorescence - SO2 is excited by UV (≈200–220 nm) and emits fluorescence (≈240–420 nm); intensity is proportional to SO2 concentration.
- Instrumentation: Components include UV lamp (stabilized supply), reaction chamber, optical filters, photomultiplier detector, modulator, selective traps for interferents, flow controller, pressure regulator and pump.
- Calibration: Instruments are not absolute - regular calibration against primary calibration gas standards is required. Calibration protocol includes zero air, span gas and at least five calibration points across the measurement range. Calibration gas flow to the manifold should exceed instrument demand by ≥20%.
- Zero air and calibration gases: Zero air must contain no detectable SO2 and have O2 within ±2% of normal air (20.9%). Primary calibration methods referenced include static volumetric dilution, permeation tubes, TCM method and gravimetric gas preparation.
- Interferences and controls: Potential interferents: hydrogen sulfide (H2S), aromatic hydrocarbons, nitric oxide (NO), water vapor and low-molecular-weight mercaptans. Selective traps/scrubbers and optical filtering are required; temperature and pressure compensation or correction is necessary.
- Sampling line and materials: Use chemically inert materials (e.g., fluorocarbon polymer or glass). Minimize residence time; heat lines or cell above dewpoint to prevent condensation. Particulate inlet filters should be inert and not retain SO2.
- Quality assurance & maintenance: Routine zero/span checks (preferably daily, at least weekly), regular servicing (recommended semi‑annually or annually) and comparison of transfer standards with primary standards.
Applications and users
ISO 10498:2004 is used for:
- Regulatory ambient-air monitoring and compliance reporting
- Continuous urban/regional air quality networks and meteorological stations
- Environmental laboratories and reference measurement facilities
- Instrument manufacturers, calibration laboratories and field-service technicians
- Research applications requiring traceable SO2 time-series or concentration maps
Using ISO 10498 ensures consistency, comparability and traceability of SO2 data for health impact assessments, emissions control, air quality management and regulatory enforcement.
Related standards
Standards referenced by ISO 10498:2004 include:
These related standards support calibration, sampling best practice and performance verification for traceable SO2 measurement.
