Detection, attribution and quantification of methane emissions using mobile measurement techniques in European cities

Global actions are required to reduce Greenhouse Gas (GHG) emissions, and thus mitigate global warming. On the 4th of November 2016 the Paris agreement between 196 countries entered into force which aims to limit global warming to less than 2 °C. Methane (CH4) has a relatively short atmospheric lifetime (≈10 years) which makes it an effective mitigation target to slow down global warming on the short to medium term. The CH4 mitigations can be implemented faster and have less severe economic effects than reduction of carbon dioxide (CO2) emissions because CO2 emission is directly proportional to energy consumption. Despite the attractiveness of CH4 reduction, on the longer term also CO2 emission will need to be reduced to zero around the middle of this century to reach the goals of the Paris agreement. Among all the CH4 sources, emission mitigation in the energy sectors seems to be the most time efficient and cost effective compared to emission reduction from other sectors. CH4 emissions from the energy sector, particularly from production, storage, transportation, distribution and end-use of fossil fuels (oil, gas and coal) contribute 19% to total anthropogenic CH4 emissions in Europe. This contribution can increase to more than 60% in fossil fuel producing countries. Fossil fuel related emission have been identified as an interesting target within the CH4 reduction strategy of the EU. The emissions from these activities are mainly estimated using Emission Factors (EFs) and Activity Data (AD) in inventories. The EFs are the ratio of emission rate per activity unit, e.g. kg of CH4 emitted per amount of gas produced. The EFs are tabulated in reports from national or international agencies, and standard EFs for emission reporting have been tabulated by the Intergovernmental Panel on Climate Change (IPCC). However, the EFs can vary temporally and spatially which increases the uncertainty in the estimated emissions. To reduce the uncertainty, independent measurement campaigns are required to update or verify these EFs, some of which are outdated or are possibly affected by sampling and / or emission rate biases. Detailed information is required on where and how large the emissions are, for effective mitigation policies. This thesis was carried out within the MEMO2 (MEthane goes MObile, MEasurements and MOdelling) project, with the objective to use mobile measurement techniques to improve our understanding of CH4 emissions. The main focus was on emissions in the energy sector. In this thesis, we provide detailed results from detection, quantification and attribution of CH4 emissions from extensive measurement campaigns focusing on emissions from the gas distribution networks in cities. These measurements showed that the contribution of CH4 emissions from natural gas leaks, microbial or combustion sources are different from one city to another, thus dedicated emission mitigation policies are required for different cities