concentrations inside and around the WWTP varied from 2.04 to 32.78 ppm. Most of the highest concentrations were found inside the WWTP; however, high concentrations were found up to 500 m from its center. The values in the urban zones were between 2.06 and 3.52 ppm, consistently higher in the area with the highest population density. Finally, considering the WWTP as a single source and according to the operational and atmospheric conditions during the studied period, the mean CH 4 emission rate from this source was 2.08E + 04 μg s −1 . The proposed sampling methodology could be applied to estimate CH 4 emission rates from fixed sources in areas with overlapping sources.