FORM · Quantification of FOssil methane emissions using Radiocarbon measurements of atmospheric Methane

Quantification of FOssil methane emissions using Radiocarbon measurements of atmospheric Methane

Methane (CH4) is the second most important anthropogenic greenhouse gas (GHG) but has a lifetime much shorter than carbon dioxide (10 yrs compared to millennia). This means that mitigation strategies could have a rapid effect on global warming, making methane one of the main targets of climate policy. A sudden increase in the atmospheric CH4 concentration has been observed during the last decade but there is still no consensus on the causes of this rapid CH4 growth. This is an immense challenge to society - if CH4 sources are not clearly identified and their emissions controlled, it will be very difficult indeed to meet the goals of the United Nations Paris Agreement on Climate Change adopted in December 2015, including limiting global temperature rise “well below 2 degrees Celsius”. Several studies found that observations highly differ from the inventories estimates, especially in the attribution of the emissions to specific source sectors.. Therefore, new constraints are needed to accurately attribute emitted methane to fossil fuel sources or other anthropogenic sources or natural processes.In this context, radiocarbon (14C) is a very powerful tool as 14C measurements provide the most accurate way of identifying fossil fuel-derived methane in air. Fossil carbon is entirely depleted in 14C, having lost it all after millions of years of radioactive decay during burial underground (14C half time is 5730 years). When emitted into the atmosphere, fossil-derived methane will cause a strong decrease into the atmospheric radiocarbon ratio 14C/C (Δ14C) that can be quantified. Despite their incredible usefulness, at present there are very few published Δ14CH4 measurements, because ambient methane levels are low (~ 2 ppm) and hundreds of litres of air need to be sampled and processed to obtain enough CH4 for 14C analysis. Within the FORM project, the researcher aimed to produce new Δ14CH4 measurements to yield answers to these fundamental scientific questions: Q1) Which methane sources need to be targeted for a more effective reduction of methane emissions? Q2) How accurate are methane emissions estimates for urban environments? These scientific questions were answered by developing a portable methane sampling device for analysis of small-sized carbon samples, a key feature for ambient air samples containing typically only 2 ppm of methane.

Data: CORDIS, © European Union