Japan’s urban methane study shows data gaps and mitigation opportunities

By Mark Lunt and Mina Berkow  

• The first study of its kind in Japan discovered Osaka’s urban emissions several times higher than official inventories report.  
• Up to 75% of Osaka’s street-level methane emissions came from man-made sources such as natural gas used in restaurants and buildings, revealing an overlooked but promising opportunity to cut climate pollution and save energy.   

When talking about emissions of methane along the oil and gas supply chain, we usually think about oil and gas fields. Indeed, methane released during extraction via venting, flaring and leaks are significant global sources, and tackling emissions there often offers the fastest and most economically feasible solutions.  

However, the story doesn’t end upstream. To minimize detrimental climate impacts and energy waste from methane leaks, we also need to act where the gas is delivered and used — and that requires reliable, actionable data.   

A new study in Japan, a major gas consumer and importer, examines this issue. For the first time, scientists have investigated methane emissions in urban areas in Japan’s third most populous city, Osaka, with the findings published in early October in Atmospheric Chemistry and Physics.   

 The first look at urban methane emission in Japan   

Conducted by scientists at Japan’s Osaka Metropolitan University and National Institute of Environmental Studies with support from the Environmental Defense Fund, the study investigated the extent of methane emissions from natural gas leaks in the Osaka metropolitan area, one of Japan’s largest urban centers, and where it was coming from, providing a foundation for targeted interventions and further research.  

Typically, urban methane sources fall into two major types: natural gas emissions from distribution pipelines or end-use, versus biogenic sources from solid or liquid waste.   

The findings were notable: Osaka’s methane emissions are estimated to be several times higher than reported in official inventories, revealing previously unaccounted emissions from urban natural gas use. Moreover, between 47-75% of the methane emissions detected at street level could be traced back to natural gas sources at end use, highlighting an untapped mitigation opportunity.   

Enhancing measurement uncovering small but widespread leaks  

What made this study novel was its use of two complementary methods to monitor methane in the city. Researchers combined data from a stationary tower, which measured emissions drifting in from upwind areas, with mobile monitoring on the ground. To reach even the narrowest streets of urban Osaka, they mounted sensors on a car and a bike that cycled more than 1100 kilometers. By measuring both methane and ethane (a marker of natural gas), they could pinpoint which emissions were linked to gas leaks.   

The results present a mixed message. On the positive side, unlike similar studies in Europe and the U.S., which often detect major leaks from city gas pipelines, the Osaka study findings suggest the local city gas companies have been effective at controlling large distribution pipeline leaks, offering lessons for other cities struggling with this issue.   

At the same time, researchers found widespread small leaks across the metropolitan area, detecting natural gas leaks at a rate of one source every five kilometers — higher than many European cities. While each leak may seem minor, together they add up to significant emissions in a city of 2.7 million people. Evidence from both tower and mobile data points to end-use sources, such as restaurants, indicating that Osaka will need targeted strategies to effectively cut emissions.  

Stronger data, smarter policies  

The implications of this research stretch well beyond Osaka. Firstly, real-world, science-based measurements offer a much-needed complement to current inventories by capturing emissions that would otherwise go unnoticed.   

Secondly, expanding monitoring from upstream supply chains into urban areas enables regulators to detect and reduce emissions, uncover hidden sources and better target mitigation solutions. It shows that countries like Japan, with very little domestic production, have a chance to reduce methane emissions in consumption at home.  

Third, the results also show that gas-consuming and importing countries like Japan have a pivotal role in global methane reduction by improving methane data transparency. Japan can share best practices with suppliers and peers across the Asia-Pacific region.   

EDF, together with OMU and NIES, are continuing to refine measurement methods and improve the understanding and tracking of methane emissions, to better inform policy development and design.