The Sources and Impacts of Reduced Nitrogen in the Atmosphere

众所周知，人类对地球氮循环的改变是对代表我们安全运行空间的行星边界的最戏剧性的破坏之一。为了养活地球上所有的人类，我们依靠化肥氮来种植作物，并通过饲养动物来生产更多的食物。这些对氮循环的扰动会对空气质量、气候强迫、臭氧消耗、酸沉降、生态系统生产力、养分沥滤和富营养化产生影响。2021年，世界卫生组织收紧了对环境颗粒物暴露的指引，以更好地保护公众健康。越来越多的人认识到，农业排放主要由氨分子驱动，是世界各地空气中大量细颗粒物的原因，减少50%或更多可以挽救数十万人的生命，相关的经济效益达数十亿美元。然而，像这样的估计依赖于高度不确定的排放清单，这些清单往往被发现是有偏见的，损害了我们准确量化问题并制定保护公共健康而不威胁粮食安全的解决方案的能力。更好地了解氨的来源对于管理一氧化二氮造成的平流层臭氧消耗和气候强迫也可能很重要。 氨不仅对大气中颗粒物的总质量有贡献，它沿着一个类似的分子家族，称为胺，也改变了新颗粒物形成的速度。这些新粒子可以长得足够大，最终成为云滴形成的种子。在大气中非常干净的部分，例如北极，海洋上空或山顶，新粒子形成速度的微小变化可能会对云覆盖产生巨大影响。由于云是气候系统的重要组成部分，因此了解改变其丰度的成分对于预测未来变化非常重要。由于大气中清洁的部分也可能是工业化前大气的很好的类似物，它们也可能帮助我们了解颗粒和云在过去如何影响气候，这是我们理解地球气候敏感性的一个主要不确定性。 为了更好地量化还原氮化合物（氨和胺），并评估它们在影响气候强迫和空气质量的过程中的作用，我们将1）开发技术来量化空气和水中有机酸和胺的痕量水平2）确定有机酸和胺以及氨在偏远环境中新颗粒形成和生长中的作用3）限制氨的区域排放及其对气候和管理驱动因素的依赖4）量化氨和有机酸在寒冷的城市和农村环境中颗粒物污染中的作用

Human changes to Earth's nitrogen cycle are known to be one of the most dramatic disruptions to the planetary boundaries that represent our safe operating space. In order to feed all the humans on the planet, we rely on fertilizer nitrogen for our crops, and produce even more by raising animals to eat. These perturbations to the nitrogen cycle have consequences for air quality, climate forcing, ozone depletion, acid deposition, ecosystem productivity, nutrient leaching, and eutrophication. In 2021, the World Health Organization tightened its guidelines on the exposure to ambient particulate matter, in an attempt to better protect public health. There is an increasing recognition that agricultural emissions, driven largely by the molecule ammonia, are responsible for a significant amount of fine particulate matter in the air around the world and that reductions of 50% or more could save hundreds of thousands of lives, with associated economic benefits in the billions of dollars. However, estimates like these rely on highly uncertain emissions inventories, which are often found to be biased, compromising our ability to accurately quantify the problem and develop solutions that protect public health without threatening food security. A better understanding of the sources of ammonia may also be important for managing stratospheric ozone depletion and climate forcing caused by nitrous oxide. Ammonia does not just contribute to the total mass of particles in the atmosphere, it, along with a similar family of molecules called amines, also changes the rate at which new particles are formed. These new particles can grow large enough that they eventually act as seeds for cloud droplets to form on. In very clean parts of the atmosphere, for example in the Arctic, over the ocean, or at the tops of mountains, small changes in the rate of new particle formation can have big impacts on cloud cover. Because clouds are an important part of the climate system, understanding the ingredients that change their abundance is important for predicting future changes. And since clean parts of the atmosphere might also be good analogues for the pre-industrial atmosphere, they might also help us understand how particles and clouds impacted climate in the past, which is a major uncertainty in our understanding of Earth's climate sensitivity. To better quantify reduced nitrogen compounds (ammonia and amines) in the atmosphere and to evaluate their roles in processes that impact climate forcing and air quality, we will 1)Develop techniques to quantify trace levels of organic acids and amines in air and water 2)Determine the role of organic acids and amines and ammonia in new particle formation and growth in remote environments 3)Constrain regional emissions of ammonia and their dependence on climate and management drivers 4)Quantify the role of ammonia and organic acids in particle pollution in cold urban and rural environments