Recent six-year atmospheric CO2 concentration at the summit of Mt. Fuji observed by a battery-powered CO2 measurement system

We developed a battery-operated carbon dioxide (CO2) measurement system and successfully observed atmospheric CO2 concentrations at the summit of Mt. Fuji (3776 m a.s.l.) in Japan throughout the year since 2009, in spite of no power supply and severe low temperature over 10 months of a year. The observational results from 2009 to 2015 showed that CO2 concentration at Mt. Fuji in summer and in winter was about 2–10 ppm lower and 2–12 ppm higher than at the Mauna Loa observatory (MLO), respectively. These episodic low concentrations at Mt. Fuji in summer have been cited as evidence that air masses originate from Siberia or China, which are affected by terrestrial CO2 uptakes. The relatively higher concentrations in winter were observed by air masses originated from China or Southeast Asia. The difference in monthly average CO2 concentration between Mt. Fuji and MLO appeared to increase from 2009 to 2015. Interannual variability and growth rate of CO2 concentration were similar both at Mt. Fuji and MLO, 13 ppm increase from 2009 to 2015, but the annual average concentration at Mt. Fuji was about 1 ppm higher than at MLO. Monthly averaged CO2 concentration at Mt. Fuji exceeded 400 ppm in April 2013. Recent CO2 concentration in 2015 at Mt. Fuji was about 62 ppm higher than the previous record measured in 1980. To evaluate a regional representative of our measurement data, CO2 values observed at Mt. Fuji were compared with airborne observations. They showed very good agreement with each other, indicating that Mt. Fuji was a representative site at which to monitor CO2 concentration in the mid-latitude Asian region.