Personal reactive clouds: Introducing the concept of near-head chemistry

The “personal cloud” effect and its impact on human exposure to airborne pollutants are well documented. A great deal is also known regarding indoor air chemistry, particularly as related to ozone reactions with mono-terpenes. In this paper we hypothesize the presence of personal reactive clouds that result from ozone reactions with terpenes and terpenoids emitted from personal care products. A proof of concept assessment was completed based on reaction rates between ozone and five reactive organic compounds that are found in personal care products. Screening experiments were also completed with three perfumes and two hairsprays to determine the extent of secondary organic aerosol formation in the breathing zone of a subject who had applied these products. The results of screening calculations and preliminary experiments confirm that chemistry occurs in the near-head region of individuals who apply scented personal care products to their hair or facial skin. Additional research is needed to characterize reaction products and health consequences associated with near-head chemistry and associated personal reactive clouds.