Spatial and Temporal Distribution of Atmospheric NH₃ and Partition of NH₃-NH₄⁺ Between Gas and Aerosol Phases in Guangdong Province

Research on the spatial and temporal distribution of atmospheric ammonia (NH₃) and the partition of NH₃-NH₄⁺ between gas and aerosol phases is beneficial for a deeper understanding of the formation and control factors of inorganic aerosols.Based on the data from the atmospheric monitoring network in 2023,the study analyzed the spatial and temporal distribution characteristics of NH₃ concentration in Guangdong Province.According to the data quality and regional differences,detailed analyses were conducted for two typical sites (Zimaling air quality monitoring station in Zhongshan City,Pearl River Delta,and the Technician College air quality monitoring station in Qingyuan City,northern Guangdong Province),focusing on NH₃ concentration differences,correlation between NH₃ and NH₄⁺,aerosol acidity,and sensitivity to precursor concentration changes.The results showed that there are regional differences in NH₃ concentrations across Guangdong Province,with levels ranking as follows:western Guangdong > northern Guangdong > Pearl River Delta > eastern Guangdong).And in the Pearl River Delta (PRD) region,NH₃ concentrations were significantly higher than NH₄⁺,indicating a deficiency of acidic substances,which reflects the effectiveness of SO₂ and NO_x mitigation measures.Seasonal variations revealed that NH₃ concentrations were lowest in summer and highest in winter.The suitable humidity and lower precipitation in winter in Guangdong are conducive to NH₃ generation,leading to higher average winter concentrations.Monthly average NH₃ concentrations peaked in March and December and reached troughs in June and September,reflecting the dual influence of agricultural activities and seasonal climatic conditions.Therefore,it is necessary to strengthen the control of agricultural sources in a timely and scientific manner.The diurnal variation of NH₃ concentration exhibited a single daytime peak pattern (noon to afternoon),indicating enhanced NH₃ volatilization under high daytime temperatures.Analysis of the Zimaling site and the Technician College site showed that the phase partitioning state of NH₃ and NH₃-NH⁺ ₄ in the surface atmosphere at both sites was dominated by gaseous NH₃,characterizing an ammonia-rich environment.Analysis using the ISORROPIA II model revealed that aerosols at both sites were acidic.Sensitivity analysis of aerosol responses to precursor concentration variations demonstrated that NH₄⁺ in aerosols was relatively sensitive to changes in total H₂SO₄ and total HNO₃,implying that reducing atmospheric H₂SO₄ and HNO₃ could effectively suppress aerosol generation.Therefore,SO₂ and NO_x emission reduction is the key to effectively reduce the pollution of fine particles with NH₄⁺.