ISO 21501-1:2009

Overview

ISO 21501-1:2009 defines performance and test methods for light scattering aerosol spectrometers (LSAS) used to determine particle size distribution and particle number concentration of aerosols. The standard covers single-particle light-scattering techniques for particles approximately 0.06 µm to 45 µm in diameter and provides calibration and validation procedures to improve measurement accuracy and comparability between instruments. ISO 21501-1 applies where high concentrations (up to 1×10^11 particles/m3) are measured, but it explicitly states these instruments are not suitable for clean-room classification.

Key Topics and Requirements

• Measuring size range: nominal particle diameters from ~0.06 µm to 45 µm.
• Counting efficiency: defined as the ratio of measured to actual particle concentration; lower and upper size limits are conventionally at a counting efficiency of 0.5 ± 0.15.
• Size resolution: ability to distinguish neighbouring particle sizes; limited by instrument channel widths.
• Sizing accuracy: percentage difference between certified reference particle size and instrument-indicated size (ISO provides a sizing error formula).
• Sampling flow rate: volumetric flow through the LSAS; flow error must be within ±5% (typical flows 0.5–5 L/min).
• Effective detection flow rate: volumetric flow through the optical/aerodynamic sensing zone - to be measured or calibrated.
• Maximum particle number concentration & coincidence loss: instruments must specify maximum concentration (up to 10^11 particles/m3) and ensure coincidence loss ≤ 10% at that maximum.
• Test methods: standardized procedures for size calibration, effective detection flow determination, maximum concentration testing, size resolution, and counting efficiency (see Clauses 4.1–4.5 and informative Annexes).

Applications

ISO 21501-1 is used to ensure reliable aerosol measurements in:

• Pharmaceuticals: characterization of metered-dose inhalers (MDI), dry powder inhalers (DPI), nebulizers, and production control of active agents.
• Filter and separation testing: cut-off determination for impactors, cyclones, impingers and fractional separation efficiency of filters.
• Environmental and occupational monitoring: atmospheric aerosols, bio-aerosols, nebulized droplets, stables/composting facilities and street-tunnel measurements.
• Research & development: aerosol instrument calibration and inter-comparison studies.

Who uses this standard

• Instrument manufacturers (LSAS design, calibration, and specification)
• Test laboratories and QA teams in pharmaceutical and filter industries
• Environmental and occupational hygiene professionals
• Metrology institutes performing aerosol calibration and validation

Related standards

• ISO 21501 series:
  • Part 2 - Light scattering liquid-borne particle counter
  • Part 3 - Light extinction liquid-borne particle counter
  • Part 4 - Light scattering airborne particle counter for clean spaces

ISO 21501-1:2009 (ISO, 2009) is the reference for calibration, validation and performance requirements when using light scattering aerosol spectrometers for particle sizing and counting.