Dynamic variations of ammonia in various life spaces and seasons and the influences of human activities

Ammonia (NH3) in occupied indoor environments is significantly higher than those outdoors and poses a serious threat to human health. Here we conducted highly time-resolved measurements of NH3 in three occupied academic offices and a gym using cavity ring-down spectroscopy to explore the sources, sinks and dynamic processes of NH3 in indoor environments. The open-close windows, cooking and cleaning experiments were also performed to investigate the effects of human activities on indoor NH3 levels. Our results showed that the NH3 levels in different offices of the same season did not differ a lot, yet the average concentration in fall was much higher than that in winter due to the increased NH3 emission from more skin exposure. The indoor NH3 presented pronounced diurnal variations and the changes in excess NH3 were highly correlated with CO2 and temperature, demonstrating its dominant source of human activities and the influence of temperature. While the enhanced ventilation reduces indoor NH3 levels, we found that the surfaces can act as an important reservoir to control NH3 concentration by gas-surface equilibrium. Cleaning experiments also showed increases in NH3, yet dominantly from the emissions of occupants under high relative humidity and temperature conditions. Cooking of meat-containing protein quickly releases high concentration of NH3 to the indoor environment. Our results demonstrate the significant impacts of human activities on indoor NH3 concentration and dynamic processes. Future measurements across different indoor spaces and in different seasons are needed to better understand the sources, sinks and dynamic variations of indoor NH3.