Introduction

The lowest layer of the atmosphere, the boundary layer, is directly affected by the earth's surface. The surface is the source of thermally and mechanically generated turbulence, which quickly mixes gases within the boundary layer. Nearly all important atmospheric trace gases are either deposited to or emitted from the surface. Some gases emitted from the surface are precursors of other trace gases formed in the atmospheric boundary layer.

Trace gas concentrations near the surface may be biased by nearby emission and deposition and therefore may not be representative of the entire boundary layer. A more accurate description of the general chemistry of the well-mixed boundary layer requires measurements aloft from tall towers (>200 m), aircraft, or tethered-balloon sampling platforms. Most towers allow the deployment of instrumentation to 60 m or without highly restrictive weight, size, and power requirements. While useful for characterizing the exchanges between the surface and the surface layer, most towers have a relatively small sampling footprint and may not be representative of the landscape-level phenomena. Aircraft platforms have the advantage that sampling may occur throughout the boundary layer, over an extended area, and with a variety of instruments. Aircraft sampling, however, is expensive, has limited temporal resolution, and is complicated by scheduling, flight hours, and aircraft configuration decisions. Also, it is not possible to sample different levels of an air column simultaneously from one aircraft.

Tethered-balloon sampling is, by contrast, relatively inexpensive, portable, characterizes the boundary layer with a footprint on...