A novel method has been employed to measure carbon dioxide profiles through the atmospheric boundary layer and lower troposphere using an ultralight and light aircraft. A series of three field campaigns conducted near the WLEF radio tower near Park Falls, Wisconsin have produced data on the seasonal variation and rectifier effect of CO₂ concentration in and above the boundary layer.

A powered parachute (PPC) ultralight aircraft was used to profile over a mixed forest in north central Wisconsin. During periods of higher winds a Cessna 182 was used as the sampling aircraft. Both platforms produced profiles from the surface to over 3000 m and back to the surface in under 1 hour of flight time. Rapid turn-around time for both aircraft allowed up to 8 flights to be made during daylight hours.

The same instrumentation was flown on both aircraft, and could be transferred between them in under one hour. A pair of bag samplers was used to collect 12 air samples during each flight, and allow one sampler to be flown while the other was analyzed on the ground. Analyses were made at the surface using a Li-Cor 6262 infrared gas analyzer (IRGA) in differential mode with a known reference gas supplied from a gas cylinder. In addition to the bag sampler, all flights included a basic meteorological payload and GPS sensor. Most flights also included a UV ozone instrument to measure O₃ concentration, and on some flights, mostly during the later campaigns, a second IRGA was flown to obtain continuous measurements of CO₂.

Differences in CO₂ concentrations across the boundary layer were observed in many of the flights over WLEF. The May campaign seemed to show that CO₂ concentrations were lower within the boundary layer, while the trip in October showed that CO₂ concentrations tend to be higher in the boundary layer. This result is logical, as May is the start of the growing season for Wisconsin, a time when photosynthesis is extracting CO₂ from the surroundings faster than respiration is producing CO₂. Subsequently, the campaign in October was performed soon after the end of the Wisconsin growing season. Photosynthesis slowed, and respiration caused increased CO₂ concentrations.

Because we were able to detect the growth of the boundary layer from multiple PPC or Cessna flights, we could use the changing CO₂ concentrations within and above the boundary layer, and determine surface fluxes of CO₂. Surface fluxes were also inferred from a nearby 400 m tower equipped with Li-Cor IRGAs and Campbell Scientific sonic anemometers, using both turbulent and storage fluxes. The two methods of surface flux calculations showed a great deal of agreement.