Characteristics of urban street level methane emissions in Bucharest, Romania

Romania has a complex geological history resulting in a very hydrocarbon rich region that is heavily exploited and utilised. Romania’s Fourth Biennial Report under the UNFCCC states that methane (CH₄) emissions have decreased by 61% between 1989 and 2017, which is a result of decreases in fugitive fossil fuel and livestock emissions. Although there is a decreasing trend of CH₄ levels in most of Europe, we still see an overall increase in atmospheric CH₄ concentrations. As atmospheric CH₄ continues to increase and the mitigation of greenhouse gases becomes more of a concern, it is important to address CH₄ emissions from large cities.  Here we ask the question: What are the major sources of urban methane emissions in Romania’s city capital, Bucharest? Together, street level continuous measurements of CH₄ and ethane (C₂H₆), and δ¹³C-CH₄ & δ²H-CH₄ of high concentration plumes assist in the identification of emissions, both for major point sources and small leaks from the natural gas distribution system.

 

Urban focused surveys were conducted in Bucharest during August of 2019. Three continuously-measuring instruments were used, including an LGR Ultraportable CH₄/C₂H₆ analyzer, allowing for the separation of natural gas leaks from other source category emissions. CH₄ and C₂H₆ have been mapped to find locations of elevated mixing ratios above background. Air samples were collected from an inlet on the vehicle bumper (60 cm above ground) that is connected to a bag pump, filling 3L Flexfoil bags.  Samples were then analyzed for δ¹³C-CH₄ & δ²H-CH₄ using an IsoPrime Trace Gas continuous flow gas chromatograph isotope ratio mass spectrometer (CF GC-IRMS) at Royal Holloway, University of London and a Thermo Fisher Delta Plus XP, at Utrecht University. Background baselines of CH₄ and isotopic ratios were statistically determined while traveling and distinguished from the various plumes of high concentrations. Point source signatures were then calculated using Keeling plot analysis. C₂:C₁ ratios from specific emissions types were compared with the correlated δ¹³C_CH4 values.

 

Detailed urban methane mapping and the use of high precision isotopic source signature measurements provide an efficient approach to identifying and sourcing small gas leaks in urban cities. These results will be useful in future government regulation of greenhouse gas emissions in urban areas as the EU continues to work on the reduction of greenhouse gases.