Indoor Air Quality measurements: volatile & non-volatile particle number (PN) measurement in a domestic environment during normal activities

Links between low Air Quality and long term heath consequences are well established1. Legislation and shifting behaviour have driven improvements in outdoor air quality over the last 20 years.

The EU has identified Particle Number (PN) concentration as an additional measurement metric for outdoor air pollution2, since Particle Mass (PM) concentration may not fully correlate with dose, as Ultrafine particles (UFPs) penetrate deep into the lung. Since studies3 suggest that ~70% of subjects’ time was spent indoors at home, exposure in the home must be included in understanding individual total exposure to PN.

The health effects of volatile organic compounds (VOCs) have been widely studied4. However, the health effects of inhaled volatile or semi-volatile particles containing VOCs requires further investigation. Domestic processes including cooking, aerosol use, combustion etc. all have the potential to release volatile or semi-volatile particles. Although small Ultrafine Particles (UFPs, <100 nm) may contribute little to PM concentration, they can penetrate deeply into the lung and be absorbed into the body and bloodstream. Their prevalence in a domestic environment with the potential for high dose due to prolonged occupancy therefore merits further study.

We demonstrate the application of a fast response Condensation Particle Counter5 (CPC) with active and inactive catalyst substrates, enabling quantitative near real-time measurement of both volatile and non-volatile indoor PN during a range of daily activities. We show that prolonged exposure to high PN can result from even short-lived activities, due to inadequate ventilation and extraction, which may not be identified as a risk by conventional PM measurements. Public awareness of the health consequences of outdoor air pollution has grown through research and education, with Air Quality Alerts and behavioural guidance. An increased focus on indoor air quality is essential for this guidance to consider the full picture and raise awareness of the importance of air quality within the home.

References
[1] Health risks of air pollution in Europe: HRAPIE-2 project: updated guidance on concentration–response functions for health risk assessment of air pollution in the WHO European Region, WHO Report 2025
[2] EU Directive 2024/2881
[3] Matz CJ, Stieb DM, Davis K, Egyed M, Rose A, Chou B, Brion O. Effects of age, season, gender and urban-rural status on time-activity: Canadian Human Activity Pattern Survey 2 (CHAPS 2). Int J Environ Res Public Health. 2014 Feb 19;11(2):2108-24
[4] Xihe Zhou, Xiang Zhou, Chengming Wang, Handong Zhou, Environmental and human health impacts of volatile organic compounds: A perspective review, Chemosphere, Volume 313, 2023, 137489
[5] J. Symonds, S. Payne, J. Pongetti, M. Tofts, Asian Aerosol Conference (2024)