ABSTRACT
Atmospheric measurements of CO2 and O2/N2 mixing ratios have been important for quantifying the source–sink distribution of CO2 at global and sub-hemispheric scales, using a globally distributed network of atmospheric observations derived from fewer than 100 stations. At the local scale direct flux measurements by the eddy covariance technique constrain the net ecosystem exchange (NEE) to within 20%, comparable to the uncertainty estimated from inverse models. It is fair to say that ecosystem measurement sites generally sample growing forests that are not surprisingly sequestering carbon. Rather than inferring the regional flux from concentration measurements, it is also possible to measure directly the exchange of scalar quantities such as CO2 and temperature from a moving platform. The airborne fluxes and the tower measurements both contain information about the anthropogenic emissions. CO is emitted with CO2 during combustion processes like fossil fuel and biomass burning.
