Supporting Methane Mitigation Efforts by Improving Urban-scale Methane Emission Estimates in Melbourne, Australia. Part 2: Developing the methane observation network for the Melbourne region
Authors: Ramirez Gamboa Jhonathan , Loh Zoe , Stavert Ann , Krummel Paul , Shahrokhi Nasimeh , Trudinger Cathy , Caldow Christopher , Spencer Darren , Roulston Christopher 
Published: February 2023

Methane (CH4) is the second greatest contributor to climate forcing after carbon dioxide (CO2). &#160;Methane has a considerably shorter atmospheric lifetime compared to CO2 (12 yr c.f. 300-1000 yr) but a higher warming potential in the atmosphere (GWP100yr 28, (IPCC, 2014)). Most anthropogenic emissions come from landfills, wastewater treatment plants, leaks in the fossil fuel supply chain and ruminant livestock. &#160;The reduction of anthropogenic methane emissions is key to maintaining the feasibility of the Paris Agreement. The Global Methane Pledge launched at COP26 aims to reduce methane emissions by 30% relative to 2020 by 2030. Urban areas are an ideal target to reduce methane emissions given that they account for around 20% of the total emissions whilst they occupy only 3% of the land surface. Urban methane mitigations plans are proven to have a high impact reducing GHG emissions and bringing co-benefits in public health through improvements in air quality.Australia is a signatory to both the Paris Agreement and the Global Methane Pledge and have an important potential emission reduction in urban areas. Melbourne is the second most populous city in Australia with over 5 million people (around 1/5 of Australia&#8217;s population) and it is projected to become the most populated by 2050. A recent study attempted to improve methane emission inventories for Melbourne using an inversion system, global emission data and atmospheric measurements (Shahrokhi , 2022).&#160; Their results showed that current emission datasets do not accurately represent the spatial distribution and total estimates of methane emissions over Melbourne. Hence, an improved emission inventory is required for Melbourne. This will reduce the uncertainty and limitations of current methane emission estimates and support the formulation of effective emissions mitigation plans. Essential to this is the expansion of the Melbourne urban observational network, which is currently too sparse to accurately detect emissions. Here we present our preliminary progress on the development of a comprehensive methane observation network. This project aims to combine different measurement techniques to achieve a better representation of methane mole fraction variability in the Melbourne region, to inform inverse modelling estimates of emissions. We use a combination of mobile and stationary ground observations in key parts of the city to better capture and represent methane emissions. Future work includes the comparison of high precision analysers with low-cost sensors, improvement of source attribution by measurements of methane isotopes and other tracers, and the use of &#8220;AirCore&#8221; technology to obtain vertical methane profiles.&#160;ReferencesIPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.Shahrokhi, N. 2022. Regional Methane Inversion for Melbourne, Australia, using in-situ measurements. Online poster [accessed 10 Jan 2022]. Available from: https://agu2022fallmeeting-agu.ipostersessions.com/default.aspx?s=2F-7B-00-39-98-DC-28-09-C3-90-81-25-D7-44-E2-D2