An air sampling tube is provided that provides superior air flow, strength, and manufacturability and couples to an air sampling sensor housing. The sidewall of the tubular section has an axially extending groove. To facilitate installation and inspection, an air sampling tube is provided with a starter cap. An end cap prevents air flow through the distal end of the tube. An air sampling tube is provided that assures proper axial positioning of tubular section apertures through resort to a coupler with a rotationally asymmetric joining element. A modular kit is provided that allows for custom installation without resort to cutting or forming operations in the field.