Long-term observations of CO2 mole fraction by commercial airliner and its application to validate urban emission inventories

For evaluating implementation of the Paris Agreement, it is an increasingly urgent task to validate emission inventories in urban areas, which account for about 70% of global total anthropogenic CO2 emissions. Umezawa et al. (2020) have analyzed vertical atmospheric CO2 mole fraction data obtained onboard commercial aircraft in proximity to 36 airports worldwide and found that the magnitude of CO2 variability near the ground (~1 km altitude) at an airport was correlated with the intensity of CO2 emissions from a nearby city. Here we further investigate the inter-annual relationship between the magnitude of CO2 variability observed over Narita International Airport (35.8°N, 140.4°E), Japan, and the strength of CO2 emission inventories around Tokyo for 2006–2019. At an altitude of 1 km, the CO2 variability is clearly correlated with the interannual CO2 emission changes around Tokyo, associated with the Japanese economy and energy mix (e.g., Lehman shock in 2008, increased renewable energy supplies after 2013). The results indicate commercial aircraft data in the lower troposphere can be useful for validating changes in urban CO2 emissions. We also estimate the annual CO2 emissions in 2020/2021 using the observed CO2 variability in the years and the relationship between the CO2 variability and annual CO2 emissions derived for 2006–2019. We find that the annual CO2 emissions in 2020 (during the COVID-19 pandemic) is clearly dropped down compared with previous years.

This study is performed as part of the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project.