Ammonia in urban atmosphere can be substantially reduced by vehicle emission control: A case study in Shanghai, China

To investigate the impact of emission controls on ammonia (NH₃) pollution in urban atmosphere, observation on NH₃ (1 hr interval) was performed in Shanghai before, during and after the 2019 China International Import Expo (CIIE) event, along with measurements on inorganic ions, organic tracers and stable nitrogen isotope compositions of ammonium in PM_2.5. NH₃ during the CIIE period was 6.5±1.0 µg/m³, which is 41% and 32% lower than that before and after the event, respectively. Such a decrease was largely ascribed to the emission controls in nonagricultural sources, of which contribution for measured NH₃ in control phase abated by ∼20% compared to that during uncontrol period. Molecular compositions of PAHs and hopanes further suggested a dominant role of the reduced vehicle emissions in the urban NH₃ abatement during the CIIE period. Our results revealed that vehicle exhaust emission control is an effective way to mitigate NH₃ pollution and improve air quality in Chinese urban areas.