ABSTRACT

This chapter describes the application of the Atmospheric Boundary Layer (ABL) equilibrium concepts to net CO2 flux over land, and authors extend these concepts to the stable isotopes of CO2 measured in the ABL. The ABL is most distinct from the free troposphere when high-pressure systems persist and large-scale subsidence pushes free-tropospheric air down onto the ABL, and ABL air diverges horizontally. The mixing ratio of scalars in the ABL is influenced by the interaction of several processes, the relative balance of which may change dramatically over the synoptic cycle or with the initiation of deep convection. CO2 and other scalars are similarly influenced by their surface fluxes and the mass flux of air from the free troposphere through the ABL. Down-drafts, associated with evaporation of precipitation into free-tropospheric air, during storms and frontal passages can replace the ABL air mass with cool, moist air and reset the concentration of other scalars to that of the free troposphere.