Resolving Atmospheric Ammonia Sources And Their Spatiotemporal Variability Based On Stable Isotopes Of Nitrogen And Hydrogen

As the most important basic gas in the atmosphere,NH3 plays an important role in atmospheric physio-chemical processes.Secondary inorganic aerosols formed by atmospheric NH3 with sulfuric and nitric acids are major constituents of atmospheric fine particulate matter(PM2.5)and are one of the precursors of haze pollution.However,there is still a lack of concern on NH3 mitigation,and the main reason for this are that the attribution of NH3 emission sources is currently obscure,which makes it difficult to develop a practicable abatement plan.At present,studies addressing the resolution of atmospheric NH3 sources generally use nitrogen stable isotope ratios of NH3(δ15N-NH3)as the single integrator(tracer)in the isotope mixing model.However,it becomes insufficient to further refine NH3 sources,especially across temporal and spatial scales.Therefore,we developed an isotope signature map of ammonia emission sources by simultaneously investigating them with the help of stable isotopes of two elements,nitrogen and hydrogen.The δ15N-NH3 value of pig farming was-25.1±6.2‰,the δD-NH3 value was 184.0±10.4‰;The δ15N-NH3 of hen farming value was-25.0±7.8‰,the δD-NH3 value was181.9±19.1‰;The δ15N-NH3 value of farmland was-27.1±4.3‰,the δD-NH3 value was149.5±13.7‰;The δ15N-NH3 value of biomass burning was-12.3±5.8‰,the δD-NH3 value was-208.2±20.0 ‰;The δ15N-NH3 value of coal combustion was-20.0±4.6‰,the δD-NH3 value was-201.5±12.4‰;The δ15N-NH3 value of thermal power was +0.15 16.8‰,the δD-NH3 value was-184.9± 15.1‰;The δ15N-NH3 value of vehicle exhaust was-1.9±7.1‰,the δD-NH3 value was-1 83.9±4.5‰;The δ15N-NH3 value of natural water bodies was-32.3±4.1‰,the δDNH3 value was-200.9±5.5‰;The δ15N-NH3 value of wastewater treatment plant was+-2.5±6.3‰,the δD-NH3 value was-1 70.8±10.3‰;The δ15N-NH3 value of human body was-33.7±3.6‰,the δD-NH3 value was-181.3± 13.4‰.Based on the emission source map,the formation mechanism of ammonia in the emission source is analyzed:in the process of NH3 released from the emission source of farms,farmland,human body and natural water body,the main isotopic fractionation process comes from the natural volatilization of NH3,and the isotopic fractionation ofthis slow process is very significant(15ε=-36±13‰,2ε:-141 ±24.5‰);NH3 in the combustion process mainly comes from ammonia escape,and the isotopic fractionation in this process is also high(15ε=-12.6±5.0‰,2ε:-104±20‰);The isotope fractionation effect of tunnel,thermal power plant and sewage plant is not significant,close to 0.Meanwhile,according to the emission source of δ15N-NH3 and δD-NH3 data,the MixSIAR model was used to resolve atmospheric NH3 sources separately for urban and rural areas.The average annual NH3 concentration in rural areas of Qingdao was 5.22±2.53μg/m3,while the NH3 concentration in urban areas was 4.67±2.54 μg/m3.,the NH3 concentration in Qingdao is higher in the rural areas,and significant seasonal differences were found between the locations,being higher during the warm season and lower during the cold season;Both nitrogen and hydrogen isotopes show significant spatiotemporal variations in Qingdao.Rural and urban areas of δ15N-NH3 and δD-NH3 values are all closer to emission sources which could cause more significant effects on them.The highest contribution to rurality during the cold season was for combustion as well as for livestock farming,with only 8.0%of the contribution from agricultural fields that were previously thought to contribute substantially in rurality;The highest contributions to rural atmospheric NH3 during the warm season were livestock and farmland;The contribution of industry and vehicles was highest in the town area during the cold season,followed by sewage treatment;Emission sources that contributed the most to the warm season in urban areas were similarly industrial vehicles and sewage treatment.Overall seasonal variations were not evident in urban areas.In the rural atmosphere,δ15N overestimates the contribution from agricultural fields but underestimates that from almost all other sources,particularly combustion and traffic and industry.In the town atmosphere,using only δ15N can also give a more accurate contribution proportion.Emission from Qingdao greatly overestimates the ammonia contribution to the atmosphere from agricultural sources,especially livestock farming,while ignoring the contribution from other sources.