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—Passenger aircraft based measurements of atmospheric CO2 and other trace gases

Carbon dioxide (CO2) in the atmosphere has been increasing since the beginning of the industrial age due to the rapid growth of human activities. There is now sufficient scientific evidence to show that the atmospheric CO2 increase is the main cause of the observed global warming and changing climate (IPCC, 2007). How well we can predict the future states of climate, its change and variability depends greatly therefore on how well we can predict the future levels of CO2 and other greenhouse gases in the atmosphere. The spatial and temporal variations of atmospheric CO2 contain information about the nature and characteristics of the CO2 exchange processes between the atmosphere and the land biosphere and the oceans. However, right now there is an acute shortage of observations of CO2 in the atmosphere to constrain and reduce large uncertainties in the inverse CO2 flux estimates; the severity of this shortage is particularly critical in the portion of the atmosphere above the planetary boundary layer.

Commercial airlines provide a powerful observational platform for obtaining free tropospheric CO2 systematically for long periods of time over a large geographical space. An earlier observation between Australia and Japan was carried out in 1984 and 1985 by Tohoku University, Japan, in cooperation with Japan Airlines (JAL) (Nakazawa et al., 1991). The JAL project was re-started in 1993 likewise over the western Pacific region, with the collaboration of scientific institutes in Japan, the JAL Foundation, JAL, aircraft engineering companies, and aviation regulatory agencies.

The first phase of the JAL project from 1993 to 2005 was carried out using an automated flask sampling system to obtain a long-term record of CO2 and other trace gases. The CO2 record over the western Pacific has provided valuable information on the latitudinal distribution of the atmospheric CO2 seasonal cycle and on the inter-annual variation of long-term increasing trends in the upper troposphere of both the Northern and Southern Hemispheres (Matsueda et al., 2002).

For the second phase of the JAL project (Comprehensive Observation Network for TRace gases by AIrLiner: CONTRAIL, a new Automatic air Sampling Equipment (ASE) for flask sampling and a new Continuous CO2 Measuring Equipment (CME) for in-situ CO2 measurements were installed on Boeing 747-400 and Boeing 777-200ER aircraft (Machida et al., 2008; Matsueda et al. 2008). In all, one or both of these instruments have been installed on several Boeing aircraft operated by JAL with regular flights from Japan to Australia, Europe, East, South and Southeast Asia, Hawaii, and North America, providing large spatial data coverage, particularly in the Northern Hemisphere.