Understanding Endogenous and Exogenous Volatile Organic Compounds in Human Breath with respect to Indoor Air Quality

Thousands of volatile organic compounds (VOCs) are inhaled by humans in indoor environments. These chemicals are originating from diverse sources, such as human volatilome (Roberts et al., 2020), human activities (Farmer et al., 2019), human and building microbiome (Misztal et al., 2018), house contents and other indoor sources (Liu et al., 2019). One characteristic feature of indoor air is relatively low dilution rate of indoor emission sources relative to outdoor air which is reflected in typically 2 orders of magnitude higher VOC concentrations (Liu et al., 2019). Compared to outdoors, indoor air has from 10 billion to 10 trillion higher intake fraction (IF) defined as the mass inhaled to mass emitted (Lai et al., 2000; Nazaroff, 2008). With respect to the inhaled indoor air, the exhaled air components can either be depleted (exogenous indoor pollutants taken up), remain unchanged, or enhanced in endogenous metabolites. Knowledge of emission rates of the endogenous compounds from humans are important in modeling indoor VOC composition in populated spaces. On the other hand, the fates of the exogenous VOCs are not well understood for the most VOCs and how they might affect human health and well-being. Many hydrophobic compounds such as terpenoids, benzenoids and furanoids are able to cross the blood brain barrier (BBB) and therefore may directly affect mood, cognition, and other aspects of human brain function. It has been recently suggested based on Tedlar bag analysis that human respiratory system is both a source and a sink for different VOCs (He et al., 2019). Here we focus on holistic understanding of both microbial and nonmicrobial chemical contributions to indoor air composition and follow their fate in exhaled and inhaled air in real time by proton transfer reaction time of flight mass spectrometry (PTRTOF-MS).