The Greater Toronto Area (GTA, pop. 6.4 million) is the populous city in Canada, thus accurately quantifying GHG emissions from the GTA is an important step towards meeting Canada’s commitments to reduce its Greenhouse gas emissions. Mitigation of methane (CH4) emissions is of particular importance when setting the country’s policy measures to meet the GHG reduction goal since it can be economically advantageous. In this study, a methane emission inventory with a high spatial resolution was prepared using individual facility reports gathered for each municipality in the GTA. Measurements using portable Fourier Transform Spectrometers (FTS), are then used to monitor CH4 levels in the GTA continuously. Four FTS instruments were installed in different locations in the city in line with the most frequent wind directions based on historical observations. High peak events were investigated and with measurements of tracer concentrations and wind data, the emissions from the city were estimated. At the end, we investigated how the results could be used to improve the existing emission inventory.