Atmospheric observations of CO2, 14CO2 and O2 concentrations to capture fossil fuel CO2 emissions from the Greater Tokyo Area

The Grater Tokyo Area is the most populated (38 million) metropolitan area in the world. To capture fossil fuel carbon dioxide (CO₂) emissions from the Grater Tokyo Area, we performed ground-based atmospheric observations for measuring concentrations of CO₂, radiocarbon in CO₂ (¹⁴CO₂), oxygen (O₂) and carbon monoxide (CO) at Tokyo Skytree (TST, with high altitude (250m) inlet) and Yoyogi (YYG, turbulentCO₂ flux measurement site located in resident area) in Tokyo and at National Institute for Environmental Studies (NIES, suburb/rural area) in Ibaraki, Japan. The ¹⁴CO₂ measurement was used for separating the fossil fuel CO₂ emissions from the biotic emissions. Results from ¹⁴CO₂ measurements showed that a ratio of fossil fuel-derived CO₂ to the variation of CO₂ concentrations was 71% in average for winter both at TST and YYG but varied from 44% to 92%, indicating significant contribution of biotic CO₂ in Tokyo. The O₂:CO₂ exchange ratio (oxidation ratio, OR) was used for the partitioning of CO₂ into emissions from gas fuels and gasoline. We observed larger OR in winter than in summer (due to both wintertime increases of fossil fuel combustion and summertime terrestrial biospheric activities) at TST and YYG and larger OR in the morning and late evening in winter due to increase of gas fuel combustion at YYG. We showed that the O₂ concentrations might be also used as a proxy for continuous monitoring of fossil fuel CO₂ content by assuming typical ratio of gas fuels and gasoline combustions. The presenter will introduce the related projects including development of building/road-scale dynamic CO₂ mapping and grid-based CO₂ emission inventory with high special resolution in Tokyo.