We did so by
estimating monthly fluxes and their uncertainty over a one - year period between June 2009 and May 2010 from 1)
observational data collected in
existing networks of surface CO2 measurement sites (GLOBALVIEWCO2 2010; extrapolated to the year 2010) and 2) both the surface observations and column - averaged dry air mole fractions of CO2 (XCO2) retrieved from GOSAT soundings.