Continuous in-situ measurements of atmospheric CH4 at the Port-de-Bouc urban-industrial station (south-east of France): a two-year analysis of CH4 spatio-temporal variability and source identification using co-emitted species.

Methane (CH4) is the second most important direct anthropogenic greenhouse gas after carbon dioxide (CO2). Its lifetime is 10 times shorter than that of CO2, and its warming potential 80 times greater over a 20-year period. Reducing methane emissions therefore represents a lever for rapid action on global warming. The Sud-PACA region (south-eastern France), classified by IPCC as a climate "hotspot", is part of these efforts to reduce CH4 emissions, with the aim of achieving carbon neutrality by 2050. To achieve this, it is essential to reduce the uncertainties of regional CH4 emissions. Although over 50% of regional methane is estimated to be emitted in the south-western part of the region, there are few CH4 measurements in this highly urbanized and industrialized area. With a view to filling this gap and better characterizing anthropogenic sources of CH4, a PICARRO G2401 CRDS analyser and meteorological station were set up in May 2021 as part of the ANR COol-AMmetropolis project at Port-de-Bouc (4324'7.056''N; 458'55.459''E), surrounded by numerous petrochemical industries. This station continuously measures CH4, CO2 and CO concentrations to study the variability of these species for the different wind sectors. The spatio-temporal variability of CH4 concentration and the identification of its sources using co-emitted species will be presented. All these data represent the first measurements of CH4 in this industrial area and will also be used to independently verify regional inventories.