Human Ammonia Emission Rates under Various Indoor Environmental Conditions.

Ammonia (NH ₃ ) is typically present at higher concentrations in indoor air (∼10-70 ppb) than in outdoor air (∼50 ppt to 5 ppb). It is the dominant neutralizer of acidic species in indoor environments, strongly influencing the partitioning of gaseous acidic and basic species to aerosols, surface films, and bulk water. We have measured NH ₃ emissions from humans in an environmentally controlled chamber. A series of experiments, each with four volunteers, quantified NH ₃ emissions as a function of temperature (25.1-32.6 °C), clothing (long-sleeved shirts/pants or T-shirts/shorts), age (teenagers, adults, and seniors), relative humidity (low or high), and ozone (<2 ppb or ∼35 ppb). Higher temperature and more skin exposure (T-shirts/shorts) significantly increased emission rates. For adults and seniors (long clothing), NH ₃ emissions are estimated to be 0.4 mg h ^-1 person ^-1 at 25 °C, 0.8 mg h ^-1 person ^-1 at 27 °C, and 1.4 mg h ^-1 person ^-1 at 29 °C, based on the temperature relationship observed in this study. Human NH ₃ emissions are sufficient to neutralize the acidifying impacts of human CO ₂ emissions. Results from this study can be used to more accurately model indoor and inner-city outdoor NH ₃ concentrations and associated chemistry.