A Comprehensive Coupled Model for Tropospheric Halogen Chemistry: Evaluation of Impacts on Tropospheric Ozone, Hydroxyl Radical (OH), and Mercury

气体排放的命运取决于我们大气的氧化能力，它控制着臭氧(一种标准污染物和短暂的温室气体)、活性汞(一种有毒污染物)和甲烷(一种温室气体)的产生。观察表明，来自自然和人为来源的卤素(氯、溴和碘)也可以作为氧化剂发挥关键作用，这改变了传统的认为羟基自由基是主要氧化剂的观点。然而，这些过程没有包括在当前的模型中，限制了它们预测未来影响的能力。这项拟议的研究将开发一个具有这种新的卤素化学的全球尺度大气化学模型，该模型将通过观测进行评估，以便能够进行适当的验证和不确定性量化的预测。该提案涉及卤素自由基光化学在对流层臭氧(一种短暂的温室气体)、羟基自由基(主要氧化剂)和有毒污染物汞的产生中的作用，这一点是不确定的，但可能非常重要。这项研究将了解导致关键大气氧化剂和污染物观测结果与限制我们预测未来变化能力的模型模拟之间存在显著差异的基本机制。为实现这一目标，它将利用科学界GEOS-Chem模式框架内现有的实验室测量，实施耦合卤素(氯-溴-I)化学光化学机制，并通过目前可用的(包括美国国家科学基金会资助的空中实地活动)大气组成随纬度、经度、海拔和季节变化的大型数据集(来自飞机、地面和空间)对其进行评估。这一全面的模型-测量集成将用于关键地诊断卤素自由基对臭氧、羟基自由基和汞的具体特征，量化不确定性并确定差距，从而使人们能够重新理解卤素自由基对对流层化学的作用，以便更好地量化(1)臭氧的辐射强迫，(2)控制臭氧影响空气质量、氧化能力和甲烷寿命的因素，以及(3)汞对生态系统的影响。

The fate of gaseous emissions is determined by the oxidative capacity of our atmosphere that controls the production of ozone (a criteria pollutant and short lived greenhouse gas), reactive mercury (a toxic pollutant) and the lifetime of methane (a greenhouse gas). The conventional view that hydroxyl radical is the dominant oxidant has been altered by observations that show that halogens (chlorine, bromine and iodine) from natural and anthropogenic sources could also play an critical role as oxidants. However, these processes are not included in current models limiting their ability to predict future impacts. The proposed research will develop a global scale atmospheric chemistry model with this new halogen chemistry that will be evaluated with observations to enable predictions with proper validation and uncertainty quantification.The proposal addresses the role of halogen radical photochemistry on the production of tropospheric ozone (a short lived greenhouse gas), the hydroxyl radical (the major oxidant) and the toxic pollutant Mercury that is uncertain but potentially very important. The research will understand the fundamental mechanisms that cause the outstanding disagreements between observations of key atmospheric oxidants and pollutants and model simulations that limit our ability to predict future changes. To achieve this it will implement a coupled halogen (Cl-Br-I) chemistry photochemical mechanism using existing laboratory measurements within the state-of-the science community GEOS-Chem model framework and evaluate it by the large data sets (from aircraft, ground and space) of atmospheric composition as a function of latitude, longitude, altitude and season that are now available (including from NSF funded airborne field campaigns). This comprehensive model-measurements integration will be used to critically diagnose specific signatures of halogen radicals on ozone, hydroxyl radical and mercury, quantify uncertainties and identify gaps that will enable a new understanding of the role of halogen radicals on tropospheric chemistry to better quantify (1) radiative forcing by ozone, (2) the factors controlling ozone affecting air quality, oxidative capacity and methane lifetime and (3) the impacts of mercury on ecosystems.