A case study of CO₂, CO and particles content evolution in the suburban atmospheric boundary layer using a 2-μm doppler DIAL, a 1-μm backscatter lidar and an array of in-situ sensors

A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the mesoscale evolution of the daily cycle of CO₂ and related tracers in the atmospheric boundary layer (ABL) and its relation to ABL dynamics and nearby natural and anthropogenic sources and sinks. A 2-μm heterodyne Doppler differential absorption lidar, which combines measurements of, (1) structure of the atmosphere, (2) radial velocity, and (3) CO₂ differential absorption was a particularly unique element of the observational array. We analyse the differences in the diurnal cycle of CO, CO₂, lidar reflectivity (a proxy for aerosol content) and H₂O using the lidar, airborne measurements in the free troposphere and ground-based measurements made at two sites located few kilometres apart. We demonstrate that vertical mixing dominates the early morning drawdown of CO and aerosol content trapped in the former nocturnal layer but not the H₂O and CO₂ mixing ratio variations. Surface fluxes, vertical mixing and advection all contribute to the ABL CO₂ mixing ratio decrease during the morning transition, with the relative importance depending on the rate and timing of ABL rise. We also show evidence that when the ABL is stable, small-scale (0.1-km vertical and 1-km horizontal) gradients of CO₂ and CO are large. The results illustrate the complexity of inferring surface fluxes of CO₂ from atmospheric budgets in the stable boundary layer.