Abstract: Abstract:Background，aim and scope Ammonium salt is one of the most important water-soluble ions, which are the main constituent of PM2.5. Ammonium salts have strong hygroscopicity and reduce visibility, and the wet-dry deposition of ammonium salt could be led to nitrogen saturation in a local ecosystem. We could understood the formation mechanism of fine particles, especially ammonium salt fine particles by sampling and monitoring ammonium salt in ammonia and PM2.5 simultaneously, that would provided scientific basis to control scientifically and reduce the pollution of fine particals as well as prevention and control the pollution of regional atmospheric environment. Materials and methodsSampling and monitoring the NH4+ in PM2.5 and the NH3 in air in three types of environment regions in Nanchang simultaneously, where are mixed areas, road areas and suburban areas respectively. The method of analysis and determinations mainly performed in accordance with Ambient air and exhaust gas -Determination of ammonia by Nessler's reagent spectrometry. ResultsDuring the sampling period in 2014-2015, the concentration of NH3 in air and NH4+ in PM2.5 were at high level in different regions of Nanchang. The spatial distribution difference of NH3 reflects the difference of source-strength of NH3 in different environmental regions. The concentration of NH4+ in road areas and suburban areas were higher than mixed areas because of the concentration of gaseous precursors in road areas and suburban areas were higher than mixed areas. The order of value of NH3/NH4+ in different environmental regions was mixed areas > road areas > suburban areas, which shows that the formation of NH4+ was greatly effected by gaseous precursors. And the concentration of NH3 was spring > autumn > winter > summer，which shows that the source-strength of NH3 was greatly influenced by seasonal meteorological conditions. The concentration of NH4+ was high in autumn and winter while low in spring and summer, and it indecated that the meteorological conditions in different seasons have different effects on the generation, removal and decomposition of ammonium salts. DiscussionThe daily distribution of value of NH3/NH4+ have the same trend of daily distribution of concentration of NH3. The formation of ammonium salts in PM2.5 were affected by different factors in different seaasons, and the main influencing factors were gaseous precursors, temperature and humidity. We can inferred that ammonium salt is sufficient from the value of NH4+ /SO42- exceeds 1.5. The forms of ammonium salt are mainly ammonium sulfate and ammonium nitrate. ConclusionsThe order of value of NH3/NH4+ in seasonal distribution was spring > summer > autumn > winter, while the concentration of NH4+ in seasonal distribution was the opposite. The concentration of NH3 between day and night distribution were different, and it was influenced by many factors,such as temperature difference between day and night, solar radiation, source-strength, temperature inversion and so on. The concentration of NH4+ changes in different seasons. Recommendations and perspectivesOn the study of concentration distribution of NH4+ in atmospheric PM2.5 and NH3 in air between different environment regions, or different seasons, or different periods of the same day. We could understood that source-strength of gaseous precursors, seasonal variation, temperature and humidity change, solar radiation intensity and inversion phenomenon all play an important role in the formation of ammonium salt. And it lead to the results, fine partical pollution could be controlled and reduced undamentally only by reducing and avoiding the emissions of gaseous precursors while meteorologic condition beyond our control.
Keywords: Key words：Gaseous precursor；Ammonia ；PM2.5；Ammonium