One of the approaches to meet Canada’s Greenhouse gas (GHG) reduction goal is to set emission mitigation plans in mega cities. The Greater Toronto Area (GTA), is the largest mega city in Canada with a population of over 6 million.  To set a mitigation plan, it’s important to first quantify GHG emissions in the city by preparing an emission inventory. The next step is to monitor GHG levels in the atmosphere on a regular basis to verify the current emission inventory estimates and observe any trends that might follow specific mitigation policies. In this study, we developed a bottom-up methane (CH4) emission inventory with a high spatial resolution for the GTA that complements the existing CO2 emission inventory. We set up a network of portable Fourier Transform Spectrometers (FTS), EM27/SUNs, in four locations within the GTA to continuously measure total column mixing ratios of CO2, CH4 and CO. We use the enhancement ratios of CH4/CO2 and CH4/CO to estimate CH4 emissions from the GTA.