A study of atmospheric properties and their impact on the use of the Nocturnal Boundary Layer budget technique for trace gas measurement

While most micrometeorological measurement techniques are only suitable for windy conditions, the Nocturnal Boundary Layer Technique can be used to measure trace gas flux during calm, clear nights as the nighttime stability enables gas emitted at the ground to accumulate. The difference between two measurements over the whole depth of this layer is believed to integrate emissions from a large area representative of, in this study, an agricultural farm. A tethersonde and infrared gas analyzer attached to a blimp carrying a bag sampling system monitored atmospheric variables for each ascent during two summer field campaigns. A mini-SODAR was installed in the field to obtain the wind flowfield. Strong accumulation was observed under low level jets suggesting that this feature acts as a good lid for trace gases. An average background vertical motion different from zero seemed to have more influence on gas propagation than did intermittent turbulence. On at least one night, a density current created by the nearby St-Lawrence River was observed to influence measurements.