Human-related volatile organic compound emissions and chemistry in indoor environments

Indoor air quality is impacted by human-related volatile organic compounds (VOCs) through dual pathways: direct emissions from breath and skin, and chemical reactions such as ozone-initiated oxidation of skin lipids. This review systematically examines the sources, mechanisms, and drivers of these emissions. We analyze physical transport processes, including exhaled breath and skin emissions, and quantify the emission levels of typical compounds globally. Heterogeneous chemistry, particularly ozone-squalene interactions via the Criegee mechanism, is elaborated to interpret VOC formation (for example, 6-methyl-5-hepten-2-one [6-MHO] or 4-oxopentanal [4-OPA]). Key impact factors, including temperature, relative humidity, air exchange rate, and clothing, are shown to modulate both emission characteristics and reaction kinetics. While advances in modeling and parameterization (such as diffusion/partition coefficients or reaction probability) have been achieved, gaps persist between laboratory-derived data and real-world scenarios. This review aims to provide a thorough understanding of human-related VOC emissions and chemistry, offering insights for adopting effective mitigation strategies to improve indoor air quality.