Articles | Volume 16, issue 13
Research article
08 Jul 2016
Research article |  | 08 Jul 2016

Eddy covariance measurements of the net turbulent methane flux in the city centre – results of 2-year campaign in Łódź, Poland

Włodzimierz Pawlak and Krzysztof Fortuniak

Abstract. To investigate temporal variability of methane (CH4) fluxes in an urban environment, air–surface exchange fluxes of CH4 were continuously measured using eddy covariance techniques at a city-centre site in Łódź, Poland, from July 2013 to August 2015. In the immediate vicinity of the measurement site, potential methane sources include vehicle traffic, dense sewerage infrastructure and natural gas networks. Sensible and latent heat fluxes have also been measured since 2000 and carbon dioxide fluxes since 2007 at this site. Upward CH4 fluxes dominated during the measurement period, indicating that the city centre is a net source of CH4 to the troposphere. The highest monthly fluxes were observed in winter (2.0 to 2.7 g m−2 month−1) and the lowest in summer (0.8 to 1.0 g m−2 month−1). Fluxes on working days were around 6 % higher than on weekends. The cumulative flux indicates that the city centre emitted a net quantity of nearly 18 g m−2 of CH4 in 2014. Stable values of the FCO2∕ FCH4 ratio in months (minimum 2.41 × 10−3, maximum 5.3 × 10−3) and the lack of a clear annual course suggest comparable magnitude of both fluxes.

Short summary
Methane, like carbon dioxide, is a greenhouse gas and changes in its concentration in the atmosphere significantly affects the Earth's climate. The most important natural source of this gas to the atmosphere is wetlands, but it is known that urban areas may emit significant amounts of greenhouse gases. The aim of the study was the analysis of temporal variability of the process of exchange of methane between the centre of Łódź, Poland, and the atmosphere.
Final-revised paper