Importance of marine gases and particles for tropospheric chemistry

海洋覆盖了大约70%的地球表面。海洋上空大气的最低部分--海洋边界层(MBL)受到海洋喷雾气溶胶和海洋气体通量的影响，通过对流事件中的垂直混合以及锋面通道或热带东风波等大尺度混合事件与自由对流层(FT)相联系。大多数温室气体(如二氧化碳、二氧化碳、一氧化二氮、N2O)的大气寿命为数百年或数千年，但其他温室气体，特别是甲烷、CH4和对流层臭氧臭氧的寿命要短得多(分别为9年和数周)，这主要是因为它们在对流层中有化学汇。它们加起来约占全球所有温室气体辐射强迫的30%。在大多数情况下，由于NOx的低浓度，MBL是臭氧的汇；此外，大约25%的对流层CH4破坏发生在热带MBL，另外35%发生在热带海洋自由对流层，因此(热带)海洋上方的大气是大气化学的一个非常重要的区域。大气氧化能力(“自净”能力)在很大程度上由羟基自由基(OH)、臭氧及其收支和循环决定；全球大部分对流层OH都在热带地区。因此，定量了解海洋大气的组成和化学成分对于研究大气氧化能力和气候强迫是至关重要的。本项目将使用区域三维模式(WRF-CHEM)来研究海洋大气中的气象和化学过程。模型的结果将与最近在东太平洋(Torero，EqPOS)和北大西洋(佛得角大气观测站和百慕大)的实地活动的数据进行比较。通过将模型结果与现场数据进行比较，我们将能够了解模型中包含的过程、源和化学反应是否足以解释数据，或者是否需要对反应机理、排放清单或物理参数的细节进行修改和改进。一旦进行了这些改进，模型能够再现数据，我们就能够量化臭氧和有毒汞等重要化合物的寿命和预算，将我们的结果转移到其他海洋区域，并向包括地球系统模型在内的全球模型提供信息。这个项目的目的是定量描述潜在的过程，而不是简单地通过模型中的非物理调整来优化与观测数据的拟合。

The oceans cover ~70% of the Earth's surface. The lowest part of the atmosphere over the oceans, the marine boundary layer (MBL), is subject to fluxes of sea spray aerosol and gases from the ocean and is linked to the free troposphere (FT) by vertical mixing in convective events but also by large scale mixing events such as frontal passages or tropical easterly waves. Most greenhouse gases (such as carbon dioxide, CO2, nitrous oxide, N2O) have atmospheric lifetimes of hundreds or thousands of years but others, notably methane, CH4, and tropospheric ozone, O3, have much shorter lifetimes (~9 years and weeks, respectively), largely because they have chemical sinks in the troposphere. Together they account for about 30% of the global radiative forcing of all greenhouse gases. Under most conditions, the MBL acts as a sink for O3 due to the low concentrations of NOx; furthermore about 25% of the tropospheric CH4 destruction occurs in the tropical MBL and a further 35% in the tropical marine free troposphere, hence the atmosphere above the (tropical) oceans is a very important region for atmospheric chemistry. The atmospheric oxidation capacity ("self-cleansing" capacity) is to a large extent determined by the hydroxyl radical (OH), O3 and their budgets and cycling; globally most tropospheric OH is found in the tropics. Therefore a quantitative understanding of the composition and chemistry of the marine atmosphere is crucial to examine the atmospheric oxidative capacity and climate forcing.This project will use a regional three-dimensional model (WRF-Chem) to study meteorological and chemical processes in the marine atmosphere. The model results will be compared to data from recent field campaigns in the East Pacific (TORERO, EqPOS) and from the North Atlantic (Cape Verde Atmospheric Observatory and Bermuda). By comparing model results with field data we will be able to see if the processes, sources and chemical reactions that are included in the model are sufficient to explain the data or if modifications and improvements to the reaction mechanism, emissions inventories or details of physical parameterisations will have to be made. Once these improvements have been made and the model is capable of reproducing the data, we will then be able to quantify lifetimes and budgets of important compounds such as ozone and the toxic mercury and to transfer our results to other ocean regions and to inform global models including Earth System models. This project aims to quantitatively describe the underlying processes and not to simply optimise the fit to observational data by unphysical adjustments in the model.