One the most fascinating, important, but difficult-to-understand features of indoor environmental chemistry is how the human occupants of an indoor space shape the chemical processes taking place within it. In response to this challenge, a group of European researchers led by Jonathan Williams at the Max Plank Institute for Chemistry came together in 2018 to study this issue. Williams’s Indoor Chemical Emissions and Reactivity (ICHEAR) project designed a series of experiments set in twin stainless steel climate chambers that aimed to measure the chemicals emissions from human breath and skin across a variety of conditions. ICHEAR set important baseline data about human emissions to the indoor environment and how those emissions vary depending on common environmental variables like room temperature, humidity, abient ozone levels, and the type of clothing being worn. This grant funds a second round of the ICHEAR experiments (known as ICHEAR2), allowing Williams and his co-investigator, Pawel Wargocki of the Technical University of Denmark, to build on their initial results. In a new set of experiments using the same twin-climate-chamber design, Williams and Wargocki will probe how a new set of variables affect human emissions in indoor air, including exercise, hygiene (washing frequency, clothing), and deodorant and fragrance use. This experiments will inform how indoor emissions and chemistry associated with humans are altered by real-world lifestyle choices.