Ammonia (NH3) in the marine atmosphere and impact on aerosols (Ref:4299)

项目背景：大气颗粒(气溶胶)是地球气候的关键，并影响空气质量。氨(NH3)是气溶胶(形成颗粒态铵，NH4+)的主要前体气体之一，也是大气中的主要碱，中和酸并促进新颗粒的形成。在过去几十年中，污染法规(例如《清洁空气法》)大大减少了欧洲和北美酸性气溶胶前体的排放，包括化石燃料燃烧排放的硫磺和氮氧化物。然而，主要由农业推动的NH3排放几乎没有减少。这导致了气溶胶酸碱度和化学成分的长期变化，但人们对此还不太了解。此外，欢迎了解天然NH3的来源。海洋NH4+可能是海洋大气中NH3的主要来源，这取决于生物地球化学、水温和水的pH。区域/全球尺度上对海-气NH3通量的估计受到以下因素的严重阻碍：a)缺乏海洋大气NH3观测，以及b)缺乏对气-水NH3交换过程的机制研究。因此，NH3在全球气候模型中没有得到很好的描述，其影响也没有得到很好的约束或忽视。项目目标和方法：预计本博士项目将结合长期的环境观测、实验室实验和地球系统模型，显著提高我们对大气NH3循环、海洋NH3排放以及NH3对气溶胶的影响的理解。鼓励学生定义博士学位的比例重点。研究问题的一些例子可能是：1.不同气团(如海洋大西洋、欧洲大陆、北极)中大气NH3和气溶胶NH4+的浓度是多少，它们是如何季节变化的？2.海-气NH3交换是否如现有理论所预测的那样(作为水温和pH的函数)，海洋是海洋大气NH3的一大来源吗？3.(海洋来源的)NH3对海洋气溶胶和云有什么影响？4.未来海洋NH3排放将如何变化，对海洋气溶胶、云和气候有什么反馈？

Project Background:Atmospheric particles (aerosols) are key to the Earth's climate and affect air quality. Ammonia (NH3) is oneof the principal precursor gases to aerosols (forming particulate ammonium, NH4+) and the primary base inthe atmosphere, neutralising acids and facilitating new particle formation. Over the last few decades,pollution regulations (e.g. Clean Air Acts) have significantly reduced the emissions of acidic aerosolprecursors in Europe and North America, including sulphur and nitrogen oxides emitted from fossil fuelcombustion. However, NH3 emissions, driven largely by agriculture, have hardly decreased. This hasresulted in long-term changes in aerosol pH and chemistry that are not well understood. Additionally, welack understanding of natural NH3 sources. Oceanic NH4+ may be a key source of NH3 to the marineatmosphere, depending on biogeochemistry, water temperature and water pH. Estimates of air-sea NH3flux on a regional/global scale are severely hampered by a) a paucity of marine atmospheric NH3observations, and b) a lack of mechanistic studies of air-water NH3 exchange processes. As a result, NH3 isnot well represented in global climate models and its impact is poorly constrained or neglected.Project Aims and Methods:It is envisaged that this PhD project will combine long-term ambient observations, laboratory experiments,and an Earth System Model to significantly improve our understandings in atmospheric NH3 cycling, oceanicNH3 emissions, and the impact of NH3 on aerosols. The student is encouraged to define the proportionalfocus of the PhD. Some examples of research questions may be:1. What are the concentrations of atmospheric NH3 and aerosol NH4+in different airmasses (e.g.marine Atlantic, mainland Europe, Arctic) and how do they vary seasonally?2. Does air-sea NH3 exchange behave as predicted according to existing theory (as a function of watertemperature and pH) and is the ocean a large source of NH3 to the marine atmosphere?3. What are the impacts of (ocean-derived) NH3 on marine aerosols and clouds?4. How will oceanic NH3 emission change in the future and what feedback may that have on marine aerosols, clouds and climate?