CWA 18407:2026

This document specifies a Human-Centric Exposure Modelling (H-CEM) approach to estimate human exposure in occupied indoor environments. The H-CEM method integrates information on indoor particle concentrations, environmental and airflow conditions, and human physiological characteristics to assess inhaled particulate matter under realistic conditions.
Standardized reference measurement of PM2,5 mass concentration is defined in ISO 16000-37. General sampling strategy principles for indoor air are defined in ISO 16000-1. The present CWA complements these standards and does not replace reference sampling or laboratory-based measurement methods defined in the ISO 16000 series. Where regulatory or compliance measurements are required, relevant ISO 16000 standards apply.
To support the accurate application of the H-CEM method, this document also includes a complementary methodology for quantifying the relationship between indoor and outdoor PM2,5 concentrations. This supporting methodology uses simultaneous, high temporal-resolution measurements obtained from low-cost particle sensors (LCSs), together with statistical analysis for quality control (QC) procedures assurance, to estimate the infiltration factor (Finf) and to distinguish between outdoor-origin and indoor-generated particulate matter. The resulting parameters provide essential input data that enhance the reliability and representativeness of H-CEM exposure estimations.
The guidelines presented in this document cover the installation and deployment of low-cost sensors, the sampling methodology, and the data-processing procedures required to obtain valid particle concentration measurements for exposure modelling. These procedures are designed to address practical challenges associated with assessing human exposure in indoor environments, where individuals spend the majority of their time, more than 90 %, and where particle levels may show significant spatial and temporal fluctuations.
This document is applicable to a wide range of indoor environments; residential, educational, offices, and other occupied indoor environments where the objective is to characterize PM2,5 exposure under typical occupancy and ventilation conditions.
This document does not specify procedures for:
- regulatory compliance assessment of indoor or outdoor air quality;
- real-time indoor air quality control or operational monitoring;
- source apportionment of emissions arising exclusively from indoor activities such as cooking or smoking;
- characterization of pollutants outside the PM2,5 size fraction.
The guidelines are intended for researchers, practitioners, digital-twin developers, building engineers, and exposure modelers requiring a harmonized framework for conducting indoor particulate exposure investigations and for applying the Human-Centric Exposure Modelling (H-CEM) method.