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

甲烷由于其积极的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、垃圾填埋和气体分配系统泄漏。虽然所有主要甲烷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 et al.，2017年）。自上而下的方法，使用大气测量，以确定城市规模和点源排放量可以评估自下而上的排放清单的准确性，并提供重要的信息，以帮助改善自下而上的核算方法。该项目将使用最先进的仪器和先进的数据分析技术，以评估排放量的大小从伦敦市中心和英国各地的各种点源。最初，能够以10 Hz的时间分辨率测量甲烷和乙烷的Aerodyne可调谐红外激光直接吸收光谱（TILDAS）QCL-双底盘仪器将安装在伦敦市中心BT塔顶部的实验室中。这些测量结果与快速垂直风速相结合，将用于使用涡动协方差技术计算CH 4和C2 H6的通量（Helfter等人，2016）。这提供了一个直接测量的排放率的物种从“足迹”，通常是3-5公里的塔，覆盖了大部分的伦敦中心。将进行为期12个月的测量，以便对每日、每周和季节的周期进行调查，并与排放清单进行比较。以前在塔甲烷通量的测量显示了显着的（系数2）低估的甲烷排放量的清单，与一个潜在的原因是错误的泄漏率从天然气供应网络。C2 H6通量的增加将提供更多关于甲烷通量的来源的信息，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）中，该平台是一辆配备有空气采样设备、GPS和气象设备的日产货车（瓦格纳等人，2021年）。它能够运行长达8小时的移动的测量仪器。它将被用来测量甲烷，乙烷，氮氧化物，二氧化碳，二氧化硫和臭氧从一系列的点源（如填埋场，农场和天然气分销设施），这将是根据其在NAEI估计排放选择。甲烷与其他物种的比率将用于源识别，基于高斯扩散方程和程序的扩散建模将用于排放率计算（Yacovitch等人，2015）。结果将比较点源估计在NAEI，其中，结合伦敦的测量将提供一个评估的库存性能为一系列的甲烷来源在英国。

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.