Total OH Reactivity of Emissions from Humans: In Situ Measurement and Budget Analysis

Abstract

Humans are a potent, mobile source of various volatile organic compounds (VOCs) in indoor environments. Such direct anthropogenic emissions are gaining importance, as those from furnishings and building materials have become better regulated and energy efficient homes may reduce ventilation. While previous studies have characterized human emissions in indoor environments, the question remains whether VOCs remain unidentified by current measuring techniques. In this study conducted in a climate chamber occupied by four people, the total OH reactivity of air was quantified, together with multiple VOCs measured by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) and fast gas chromatography–mass spectrometry (fast-GC–MS). Whole-body, breath, and dermal emissions were assessed. The comparison of directly measured OH reactivity and that of the summed reactivity of individually measured species revealed no significant shortfall. Ozone exposure (37 ppb) was found to have little influence on breath OH reactivity but enhanced dermal OH reactivity significantly. Without ozone, the whole-body OH reactivity was dominated by breath emissions, mostly isoprene (76%). With ozone present, OH reactivity nearly doubled, with the increase being mainly caused by dermal emissions of mostly carbonyl compounds (57%). No significant difference in total OH reactivity was observed for different age groups (teenagers/young adults/seniors) without ozone. With ozone present, the total OH reactivity decreased slightly with increasing age.

Emission Rates of Volatile Organic Compounds from Humans

“…The abundance of skin lipids has been found to decrease with the increase in age, 58 which may result in less lipid ozonolysis among the seniors. 59 …”

Liquid crystal display screens as a source for indoor volatile organic compounds

“…5 demonstrate that LCD screens can make substantial contributions to indoor VOCs under certain conditions. Additionally, we recognize that the relative contributions may be smaller under specific scenarios [e.g., human breath contains high isoprene mixing ratios (55)]. We also note that the ER TVOC of LCD screens (1.5 to 4.9 μg • h -1 • unit -1 ; SI Appendix, Table S5) are substantially lower than the ER TVOC of, for example, hardboard, plywood, and new furniture (> 10 mg • h -1 • unit -1 ) (56,57).…”

The effects of warmth and CO 2 concentration, with and without bioeffluents, on the emission of CO 2 by occupants and physiological responses

“…If occupant emission rates of bioeffluents and CO 2 increase at temperatures that cause thermal discomfort, the ventilation rates prescribed by ventilation standards should be adjusted accordingly, but at present only the Australian standard recommends higher ventilation rates when the air temperature is 27°C and above, presumably to deal with an increased emission of bioeffluents 7 . Furthermore, recent studies found that human emissions of VOCs 8 and ammonia 9 change with the thermal conditions.…”