Ammonia Emission Characteristics Of No-agricultural Sources And Construction Of Nitrogen Isotope Fingerprints

With the formation of SO₂,NO_x and NH₃ as precursors,secondary inorganic aerosols?including sulfates,nitrates and ammonium salts?occupy about half or more of the mass concentration of PM_2.5 in China.Under the background that SO₂ and NO_x emission reductions have risen to the national level but NH₃ emission reductions have not yet been implemented,the impact of NH₃ emissions on China's atmospheric fine particulate pollution will gradually increase and become more prominent.Previous studies on NH₃ emissions have focused on agricultural sources?mainly livestock and fertilizer application?,but more and more measured data indicate that there are complex and diverse non-agricultural sources of NH₃ emissions in urban areas,which has caused atmospheric NH₃ concentrations are close to or even higher than agricultural areas.In view of this,this study starts from the emission of NH₃,and systematically studies the high-frequency evolution of NH₃-NH₄⁺in the urban atmosphere and its grain conversion,especially for non-agricultural ammonia.The main research conclusions are as follows:?1?The average concentration of NH₃ in the four seasons of Nanjing's urban atmosphere changed significantly:the average concentrations of NH₃ in spring,summer,autumn,and winter were 13.77±8.48,18.58±9.30,15.23±6.54 and 9.81±5.52?g·m^-3,respectively.The average changes of NH₄⁺concentration in the four seasons were 11.03±7.77,6.74±4.62,10.59±7.17 and 12.00±6.62?g·m^-3,respectively.The high NH₃ concentration in Nanjing indicates that urban areas may be hot spots for NH₃ emissions.?2?The pollution of Nanjing's urban atmosphere was accompanied by the occurrence of pollution events.For the cause of the daily variation of NH₃ in the pollution events,this study excludes the impact of a sharp increase in emission source strength and external transmission,and attributed it to NH₃-NH₄⁺gas particle conversion.And during the pollution event,the contribution rate of NH₄⁺to PM_2.5 is about 33%,which is 36%higher than that under non-polluting weather.?3?When the concentration of NH₃ in the atmosphere is low,the rate of gas-solid conversion between NH₄⁺/NH_x increases;and vice versa.As the conversion of NH₄⁺from gaseous to granular phase increases,the formation of PM_2.5 aerosols also increases.And under low temperature and high humidity?temperature 7.5??12.5?,humidity 50%?90%?conditions,the gas-solid conversion speed of NH₃ and NH₄⁺is accelerated.NH₄⁺mainly combines with to form NH₄Cl.The increased formation of?NH₄?₂SO₄ and NH₄NO₃ leads to aggravation of pollution events.?4?For the first time,an online gas aerosol monitor was used to monitor and compare the concentration of NH₃ in the human waste from urban buildings and the surrounding environment in real time.The observed 2 to 3 orders of magnitude higher concentration than that in the environment,indicating that human waste from urban construction is one of the important sources of NH₃ in urban areas and may strongly affect the surrounding NH₃concentration.The NH₃ concentration presents seasonal changes.Generally,the NH₃concentration in the exhaust pipe of human settlements in urban buildings is following order:summer>autumn>winter,and there is an excellent correlation between temperature and summertime concentrations vacation?R²=0.95?.Human activity is the most important factor in the ammonia emissions from human waste pipes in urban buildings.?5?Under smoldering and open flame conditions,K⁺was significantly correlated with Cl^-during smoldering?R=0.97?,indicating that K⁺mainly exists in the form of chloride.NH₄⁺is significantly correlated with Cl^-,NO₂^-,SO₄^2-and NO₃^-during open flame,indicating that these four anions are more easily combined with K⁺and NH₄Cl,?NH₄?₂SO₄,NH₄NO₃.In addition to Na⁺and Cl^-,the correlation coefficients of NO₂^-,SO₄^2-and NO₃^-reached above 0.72,indicating that Na⁺is more likely to form soluble compounds with these anions.Under different combustion states,there is a significant difference in ammonia emissions from straw.In different combustion stages,when the particulate removal device is used,the ammonia emission rate in the first 30s of straw combustion is 1.78?gm^-3for wheat>0.97?gm^-3 for rice>0.63?gm^-3 for corn>0.62?gm^-3for branch.?6?Directly measure the?¹⁵N-NH₃ of urban human excreta using end-elements,and limit the?¹⁵N-NH₃ of human excreta from urban buildings.Our approach constrains human excreta source?¹⁵N-NH₃ values?8?0)?69?⁸?6?₈4)9)))to-35.6‰_-39^-31..₈9_‰‰.The?¹⁵N?22 in total?of NH₃ in 5 kinds of straw samples were significantly different which ranged from-14.8?-11.8‰,-16.8?-14.1‰,-19.4?-15.2‰,-14.3?-12.7‰and-13.7?-12.6‰,respectively for wheat,rice,corn,leaves and branches.It is determined that the characteristic value of localized biomass burning isotope ranges from-19.4‰to-11.8‰.The results help to track the source of NH₃and the formation and transport of ammonium salts in the urban environment.