Cities are responsible for more than 70% of the global total greenhouse gas (GHG) emissions. Ability to monitor GHG emissions from cities is an important capability to develop in order to support climate mitigation activities in response to the Paris Agreement. The science community has examined the data collected from different platforms, such as ground-based, aircraft and satellites, to establish a science-based monitoring capability. A study by an international team, published in Scientific Reports, examined the data collected by commercial airliners and showed the potential of the aircraft data to contribute to the global GHG emission monitoring.

The CONTRAIL (Comprehensive Observation Network for TRace gases by AIrLiners) program is Japan’s unique aircraft observation project. Since 2005, the CONTRAIL team has achieved high-precision atmospheric CO2 measurements using instruments onboard Japan Airlines’ (JAL) commercial airliners. “Following the aircraft measurements conducted between Tokyo and Australia that I initiated in 1993, and had maintained during my entire career, the CONTRAIL program continuously expanded its global network and has provided numerous data to understand the carbon budget of this planet,” stated Hidekazu Matsueda, co-author of the study and researcher at the Meteorological Research Institute, Japan.

Recently, the team analyzed thousands of vertical ascending and descending measurements over airports and characterized CO2 variations over 34 major cities worldwide for the first time. Airports are often located in the proximity of large cities to ensure convenient access. The CONTRAIL aircraft fly up and down over Narita International Airport many times nearly on a daily basis (7,692 times in total during 2005-2016) and are able to obtain atmospheric chemical signature of the Greater Tokyo Area (~several tens km away). With similar geographical locations of major airport relative to large urban centers, the research team examined the data collected around global airports in order to retrieve urban CO2 emission signatures from the data. “We analyzed millions of observational data collected at and around the Tokyo Narita Airport and found clear CO2 enhancements when the wind comes from the Greater Tokyo Area,” Taku Umezawa, leading author of the study and researcher at the National Insititute for Enviromental Studies, Japan, said. “That was also the case globally for other airports, such as Moscow, Paris, Beijing, Osaka, Shanghai, Mexico City, Sydney, and others.”

Read more at National Institute for Environmental Studies