Assessment of UK methane sources using tower based and mobile measurements.

甲烷由于其正辐射强迫效应而导致气候变化，是英国仅次于二氧化碳的第二大温室气体。近年来的主要排放源是肠道发酵、垃圾填埋和配气系统泄漏。虽然所有主要甲烷来源的排放量都有所下降，自1990年以来总体减少了60%，但英国甲烷排放量的大小仍然存在不确定性，导致对未来甲烷水平及其辐射强迫效应的模型预测存在不确定性。在英国，国家大气排放清单(NAEI；Brown等人，2017年)给出了使用自下而上方法计算的空间和部门分类排放量。自上而下的方法使用大气测量来确定城市规模和点源排放，可以评估自下而上排放清单的准确性，并提供关键信息，帮助改进自下而上的核算方法。该项目将使用最先进的仪器和复杂的数据分析技术来评估伦敦市中心和英国各地各种点源的排放量。最初，Aerodyne可调谐红外激光直接吸收光谱仪(Tildas)QCL-能够以10赫兹的时间分辨率测量甲烷和乙烷的双机箱仪器-将安装在伦敦市中心BT塔顶部的实验室中。这些测量结合快速垂直风速，将被用来利用涡旋协方差技术计算CH4和C2H6的通量(Helfter等人，2016年)。这提供了一种直接测量物种排放量的方法，该足迹通常距离伦敦塔3-5公里，覆盖伦敦市中心的大部分地区。将进行为期12个月的测量，以便对每日、每周和季节性周期进行调查，并与排放清单进行比较。以前对该塔甲烷通量的测量显示，库存中的甲烷排放量被严重低估(2倍)，潜在原因是气体供应网络的泄漏率存在误差。添加C2H6流量将提供更多关于甲烷流量来源的信息，因为甲烷/乙烷比非常依赖于来源。此外，Tildas仪器将安装在约克大学WACL空气采样平台(WASP)，这是一辆配备空气采样设备、全球定位系统和气象设备的日产面包车(Wagner等人，2021年)。它能够运行仪器长达8小时的移动测量。它将用于测量来自一系列点源(如填埋场、农场和气体分配设施)的甲烷、乙烷、NOx、二氧化碳、二氧化硫和臭氧，这些点源将根据它们在NAEI中的估计排放量进行选择。甲烷与其他物种的比率将用于来源识别，基于高斯扩散方程和程序的扩散模拟将用于排放量计算(Yacovitch等人，2015年)。结果将与NAEI中的点源估计进行比较，该估计与伦敦的测量结果相结合，将提供对英国一系列甲烷来源的库存表现的评估。

Methane contributes to climate change due to its positive radiative forcing effect, and is the second most significant greenhouse gas in the UK after CO2. The major emitting sources in recent years are enteric fermentation, landfilling of wastes, and leakage from the gas distribution system. Whilst emissions from all major methane sources have declined, contributing to an overall reduction of 60% since 1990, there are still uncertainties in the magnitude of methane emissions in the UK, leading to uncertainties in model predictions of future methane levels and hence its radiative forcing effect. In the UK, spatially and sectorally disaggregated emissions calculated using a bottom-up methodology are given in the National Atmospheric Emissions Inventory (NAEI; Brown et al., 2017). Top-down methods that use atmospheric measurements to determine city-scale and point source emissions can assess the accuracy of bottom-up emission inventories and provide crucial information to help improve bottom-up accounting methods.This project will use state of the art instrumentation and sophisticated data analysis techniques to assess the magnitude of emissions from the city centre of London and various point sources around the UK. Initially an Aerodyne Tunable IR Laser Direct Absorption Spectroscopy (TILDAS) QCL-Dual chassis instrument capable of measuring methane and ethane at a time resolution of 10Hz, will be installed in a laboratory at the top of the BT tower in central London. These measurements, combined with fast vertical wind speed, will be used to calculate fluxes of CH4 and C2H6 using the eddy covariance technique (Helfter et al., 2016). This provides a direct measurement of the emission rate of the species from a 'footprint' that is typically 3-5 km from the tower, covering much of central London. Measurements will be made for a period of 12 months, allowing daily, weekly and seasonal cycles to be investigated and compared to the emission inventory. Previous measurements of methane fluxes at the tower showed a significant (factor of 2) underestimation of CH4 emissions in the inventory, with a potential reason being errors in leakage rates from the gas supply network. The addition of C2H6 fluxes will provide more information as to the source of the methane flux, as the methane / ethane ratio is very dependent on the source.In addition, the TILDAS instrument will be installed in the University of York WACL Air Sampling Platform (WASP), which is a Nissan van equipped with air sampling equipment, GPS and meteorology equipment (Wagner et al., 2021). It is capable of running the instrumentation for up to 8 hours of mobile measurements. It will be used to measure methane, ethane, NOx, CO2, SO2 and O3 from a series of point sources (e.g. land-fill sites, farms and gas distribution facilities), which will be selected according to their estimated emission in the NAEI. Ratios of methane to other species will be used for source identification and dispersion modelling, based on the Gaussian dispersion equations and procedures, will be used for emission rate calculations (Yacovitch et al., 2015). Results will be compared to the point sources estimates in the NAEI, which, combined with the London measurements will provide an assessment of the inventories performance for a range of methane sources in the UK.