This grant funds a research project by Jonathan Williams, research group leader, Max Planck Institute for Chemistry, in collaboration with Pawel Wargocki, associate professor at the International Centre for Indoor Environment and Energy at the Technical University of Denmark (DTU) that will investigate the impact of exhaled and dermally emitted human emissions in climate chambers under different conditions of clothing, temperature, relative humidity, and ozone. Volatile organic compound (VOCs) emissions will be characterized by Williams and his team using state-of-the-art proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS). Novel analytical techniques developed by Williams for outdoor use will be used to measure OH reactivity of the human emissions, which will account for any “missing” emissions. Twin stainless steel climate chambers located at the DTU will be used to measure how human emissions vary between cold and dry versus hot and humid conditions, and how human emissions change with the presence of ozone and with different clothing. Williams’ experiments will allow for the isolation of exhaled versus dermally emitted bio effluents and the contribution if each to OH reactivity will be separately measured. These measurements will allow Williams to make the first ever OH reactivity–based budget of the human-influenced indoor environment and will reveal what proportion of human emissions currently can be measured and what proportion is “missing.” This new knowledge will be shared through peer-reviewed publications and conference presentations. At least one postdoctoral fellow will be trained.