Atmospheric NH3 plays a vital role not only in the environmental ecosystem but also in atmosphere chemistry. To further understand the effects of NH3 on the formation of haze pollution in Beijing, ambient NH3 and related species were measured and simulated at high resolutions during the wintertime Air Pollution and Human Health-Beijing (APHH-Beijing) campaign in 2016. The excess NHx was calculated upon the equilibrium system of SO42--NO3--NH4+-water during this campaign. We applied ISORROPIA II model to calculate the aerosol acidity, aerosol water content (AWC) as well as its sensitivity to the SOx(SO2+SO42-),NOx(NO2+NO3-), NHx(NH3+NH4+) inputs. We also run the 3 D model NAQPMS to quantify the effects of NH3 to the heavy pollution in NCP. We found the Increased formation of NH4NO3 under excess NHx, especially during the nighttime, may trigger the decreasing of aerosol deliquescence relative humidity (DRH) even down to less than 50% and hence lead to hygroscopic growth even under RH conditions lower than 50% and the wet aerosol particles become better medium for rapid heterogeneous reactions. A further increase of RH promotes the positive feedback "AWC-heterogeneous reactions" and ultimately leads to the formation of severe haze. Modelling results by NAQPMS show the control of 20% NH3 emission may affect 5~11% of PM2.5 formation under current emissions conditions in the North China Plain (NCP).

Supplement to: Ge, Baozhu; Xu, Xiaobin; Ma, Zhiqiang; Pan, Xiaole; Wang, Zhe; Lin, Weili; Ouyang, Bin; Xu, Danhui; Lee, James; Zheng, Mei; Ji, Dongsheng; Sun, Yele; Dong, Huabin; Squires, Freya Anne; Fu, Pingqing; Wang, Zifa (2019): Role of Ammonia on the Feedback Between AWC and Inorganic Aerosol Formation During Heavy Pollution in the North China Plain. Earth and Space Science (ESS), 6(9), 1675-1693