[A-CG42] Biogeochemical linkages between the surface ocean and atmosphere

[ACG42-06] Impacts of ammonia on gas-particle partition and AWC during the 2016 APHH-Beijing campaign: inducing effects of nitrate ammonium

*baozhu Ge¹, Xiaobin Xu², Zhiqiang Ma³, Xiaole PAN¹, Zhe WANG^1,4, Weili Lin⁵, Bin Ouyang⁶, Danhui Xu¹, James Lee⁷, Mei Zheng⁸, Dongsheng Ji¹, Yele Sun¹, Huabin Dong⁸, Freya Anne Squires⁷, Pingqing Fu¹, Zifa Wang¹ (1.State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China, 2.State Key Laboratory of Severe Weather & Key Laboratory for Atmospheric Chemistry of China Meteorological Administration, Chinese Academy of Meteorological Sciences, Beijing 100081, China, 3.Institute of Urban Meteorology, China Meteorological Administration, Beijing, China, 4.Research Institute for Applied Mechanics (RIAM), Kyushu University, Fukuoka, Japan, 5.College of Life and Environmental Sciences, Minzu University of China, Beijing 100081, China, 6.Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK, 7.National Centre for Atmospheric Science Department of Chemistry, University of York, York, YO10 5DD, UK, 8.State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, 100871, China)

Keywords:Ammonia, partition, aerosol acidity, APHH-Beijing, PM2.5, NCP

Atmospheric NH₃ plays a vital role not only in the environmental ecosystem but also in atmosphere chemistry. To fully understand the effects of NH₃ on the formation of haze pollution in Beijing, ambient NH₃ and related species were measured at high resolutions during the wintertime Air Pollution and Human Health-Beijing (APHH-Beijing) campaign in 2016. Simulations were made to gain insights into impacts of NH₃ on the formation of secondary inorganic aerosols (SIAs) and regional fine particle pollution. We found that the total NH_x (gaseous NH₃+particle NH₄⁺) was mostly in excess of the SO₄^2--NO₃^--NH₄⁺-water equilibrium system during our campaign. This NH_x excess made medium aerosol acidity, with the median pH value being 3.6 and 4.5 for polluted and non-polluted conditions, respectively, and enhanced the formation of particle phase nitrate. During polluted periods, SIAs contributed most to PM_2.5 and were highly correlated with aerosol water content (AWC), indicating the importance of heterogeneous reactions in haze formation. Our analysis suggests that NH₄NO₃ is the most important factor driving the formation of AWC, with NO₃^- controlling the prior pollution stage and NH₄⁺ the most polluted stage. Increased formation of NH₄NO₃ under excess NH_x, especially during the nighttime, may trigger the decreasing of aerosol DRH and hence lead to hygroscopic growth even under lower RH conditions 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. Both our observational and modelling results suggest that the control of NH₃ may be more effective in reducing PM_2.5 under current emissions conditions in the North China Plain (NCP).