Methane emission rates from water infrastructures derived from mobile surveys along the final course of the Llobregat basin

The final course of the Llobregat river (south-west of Barcelona, Spain) is surrounded by densely populated cities, industrial areas and agricultural lands. Multiple water infrastructures where anaerobic processes may be expected are present in the basin: three wastewater treatment plants, a drinking water treatment plant, several irrigation channels and a desalination plant. Other likely methane emission infrastructures as waste processing plants or gas refilling stations are present, together with natural methane potential sources as wetlands.

Multiple mobile measurements were performed during 2019 along the final course of the Llobregat basin to study the variability of methane emissions throughout the year. The surveys were carried out in different days at different times with a car equipped with a flight-ready CO2/CH4/H2O cavity ring-down spectrometer.

Emissions of different infrastructures and its variability throughout the year has been determined using a statistical approach from the georeferenced data. Local winds and plume modeling has been used to better pinpoint the sources and estimate the emissions. Finally methane concentrations and emissions variability have been related with meteorological factors as temperature or pressure. These factors, together with human-related management of the water infrastructures, may drive the methane emissions significantly far from inventory estimations.