| Ammonia（NH3）is the most important alkaline gas in the atmospheric environment,and play an important role in the formation of atmospheric fine particulate matter(PM2.5)pollution,due to it easily reacts with acidic gases to form ammonium aerosols（NH4+）.China’s pollution is serious in the world,Therefore,it is very important to accurately identify and quantify the main sources of atmospheric NH3 to reduce PM2.5 concentration and protect public health in China.Since the main sources of atmospheric NH3 have unique stable nitrogen isotope fingerprints,the traceability based on stable nitrogen isotope analysis is considered to be one of the most reliable techniques for the current atmospheric NH3 source analysis.These studies have basically clarified the contribution of key sources（e.g.,agricultural emissions）to the atmospheric NH3 in the region and pointed out that non-agricultural activities such as motor vehicle exhaust may also have an important impact on NH3 in the urban atmosphere.The Pearl River Delta（PRD）is one of the most densely urbanized and developed regions in China,yet its PM2.5 concentrations are gradually hit a plateau in recent years,while the contribution of NH4+aerosols to PM2.5 is generally showing an increasing trend.Therefore,this thesis uses stable nitrogen isotopes as a key technical tool to collect PM2.5 samples at different heights of Canton Tower atmospheric environment monitoring stations,analyzes the vertical and seasonal variation characteristics of PM2.5 and NH4+aerosol concentrations in Guangzhou urban area,and quantifies the source contribution of key emission sources to NH4+aerosol in Guangzhou urban area and the potential influence of the Bayesian isotope mixing model.factors,and the specific findings are as follows.（1）PM2.5 concentrations have obvious vertical distribution characteristics,specifically decreasing with increasing height,but the annual average concentrations of NH4+aerosols do not differ significantly in vertical height.In terms of seasonal variations,the NH4+aerosol concentrations in autumn and winter are 2.5 and 2.4 times higher than those in summer,respectively,indicating that the secondary ion NH4+pollution of atmospheric PM2.5 is more serious in Guangzhou in autumn and winter.（2）The annual mean value of NH4+aerosol stable nitrogen isotope(δ15N-NH4+)is 11.9‰,of which the maximum value is 27.7‰and the minimum value is-16.7‰;in the vertical profile,the annual mean value ofδ15N-NH4+decreases with increasing altitude,but there are differences in the seasonal changes ofδ15N-NH4+in different altitude layers,indicating that the source of NH4+aerosol varies with The source of NH4+aerosol at the ground station is presumed to be more closely related to non-agricultural sources such as motor vehicle exhaust;at 488 m height,the variation ofδ15N-NH4+is closely related to the incoming direction of air masses.（3）Bayesian isotope mixing model was used to quantify the source contribution of NH3 to the Guangzhou,and it was found that non-agricultural activities（e.g.,motor vehicle exhaust）were the most significant contributors to atmospheric NH3 in Guangzhou,with the most significant contribution from fossil fuel combustion emissions,with an annual average contribution of nearly 60%.In contrast to the changes in agricultural emissions,the changes in NH3 from agricultural and non-agricultural activities are closely related to the incoming direction of air masses,reflecting the influence of local emissions and transport of pollutants from surrounding regions.Theδ15N-NH4+source apportionment results were compared with the"bottom-up"emission inventory,and it was found that the non-agricultural NH3 sources in the PRD region might be seriously underestimated by the current emission inventory. |
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