[A-AS01] Global Carbon Cycle Observation and Analysis

[AAS01-06] Fine-scale CO₂ variations over the Tokyo megacity observed by CONTRAIL

*Taku Umezawa¹, Hidekazu Matsueda², Toshinobu Machida¹, Yousuke Sawa², Yosuke Niwa² (1.National Institute for Environmental Studies, 2.Meteorological Research Institute)

Keywords:Megacity, CO2, Aircraft measurements

Urban areas are considered to account for ~70% of the global anthropogenic carbon emissions. Many cities now take actions to reduce their carbon emissions. However, atmospheric CO₂ measurement networks capable of verifying carbon emissions from large cities are still far from sufficient. CONTRAIL, an ongoing project to measure trace gases with instruments onboard aircraft of Japan Airlines, has obtained millions of CO₂ data over worldwide large cities since 2005. In general, we have observed increases of CO₂ concentration approaching down to the airports, indicating presence of CO₂ plume over metropolitan areas. We found vertical gradient of CO₂ concentration (i.e. difference between the free troposphere and the lowermost layer) larger for large megacities, suggesting that CO₂ plume correlates with size of the city. This infers that the CONTRAIL measurements may have potential to assess city’s carbon emission trends. In this study, we focus on detailed analysis of CO₂ distributions over Tokyo, currently the world largest megacity. Analyzing thousands of vertical profiles of CO₂ over the Narita and Haneda airports over the last 10 years, we found CO₂ levels significantly different between areas over Haneda and north and south of Narita. This likely reflects different catchments of CO₂ plumes over the respective areas.