Indoor NH_3 variation and its relationship with outdoor NH_3 in urban Beijing

摘要

Online measurements of indoor and outdoor ammonia (NH_3) were conducted at auniversity building in Haidian District, Beijing, to investigate their variation characteristics,indoor-outdoordifferences, influencing factors, and possible contributionof indoor NH_3 to atmospheric NH_3. Indoor NH_3 mixing ratios varied greatly amongthe rooms of the same building. Indoor NH_3 mixing ratio peaked at 1.43 ppm in atoilet. Both indoor and outdoor NH_3 mixing ratios exhibited higher values duringsummer and lower values during winter and correlated significantly with relative humidityand temperature. Moreover, their daily mean mixing ratios were significantlycorrelated with each other. But indoor and outdoor NH_3 in cold months exhibitedquite different diurnal variations. During the measurement period, indoor NH_3 mixingratios were substantially higher than those outdoors, by an average factor of 3.1(1.0–6.6).This indicates that indoor NH_3 could be a source of outdoor atmosphericNH_3. The contribution of indoor NH_3 to atmospheric NH_3 was estimated at 0.7 ± 0.5Gg NH_3-N·a~(−1), accounting for approximately 1.0 ± 0.7% of total emissions in Beijingand being comparable to industry, biomass combustion, and soil emissions, but lowerthan transportation emissions. The influence of COVID-19control measures causedindoor and outdoor NH_3 mixing ratios to decrease by 22.8% and 19.3%, respectively-attributableto decreased human activity and traffic flow.