ISO 4225:2020

Overview

ISO 4225:2020 - "Air quality - General aspects - Vocabulary" is the ISO international standard that defines fundamental terms and definitions used in air quality assessment. The document provides a consistent, unambiguous vocabulary for describing air quality, air pollution, aerosols, sampling and measurement of gases, vapours and airborne particles. ISO 4225:2020 is applicable to all ISO International Standards, Technical Reports, Technical Specifications and Guides related to air quality, and includes an alphabetical index of terms (Annex A).

Key topics

• Core definitions: clear definitions for concepts such as air quality, air pollutant, ambient air, indoor air, workplace air, and air quality standard.
• Aerosols and particles: terminology for aerosol, bioaerosol, nanoparticle, nanostructured particle, agglomerate, particle aerodynamic diameter, and related concepts.
• Agents and exposure: terms for biological agent, chemical agent, breathing zone, inhalation exposure, and dermal exposure.
• Meteorology and transport: vocabulary covering cyclone, stability, chimney effect, lapse rate, dispersion parameters and effective chimney height.
• Sampling and measurement: standardized terms addressing samples, sampling equipment, sampling methods, measurement methods, and averaging time to support consistent use across laboratories and protocols.
• Aerosol phenomena: definitions for fog, mist, haze, droplet, wash‑out and rain‑out.
• Editorial notes: no normative references; harmonization with related standards (e.g., ISO 18158:2016) and removal of obsolete terms in the 2020 revision.

Applications (who uses it)

ISO 4225:2020 is a foundational resource for:

• National and regional regulators drafting air quality legislation and standards.
• Environmental and public‑health agencies performing monitoring and reporting.
• Testing laboratories and instrument manufacturers ensuring consistent terminology for sampling and measurement methods.
• Occupational health and safety professionals assessing workplace air.
• Consultants, researchers and standard developers who need interoperable, unambiguous vocabulary when preparing protocols, reports, standards or guidance.

Practical benefits include improved clarity in technical documents, fewer ambiguities in measurement protocols, consistent interpretation of air quality criteria (e.g., averaging time and concentration metrics), and better comparability of monitoring data.

Related standards

• ISO 18158:2016 (harmonized terminology where appropriate)
• ISO 29464:2017 (referenced for specific aerosol/mist definitions)
• ISO/TC 146 suite (air quality sampling and measurement standards)

Keywords: ISO 4225:2020, air quality vocabulary, air pollutant definitions, aerosol terminology, sampling methods, measurement methods, ambient air, indoor air, workplace air.