Measurements of delays of gas-phase compounds in a wide variety of tubing materials due to gas–wall interactions
Abstract. Losses of gas-phase compounds or delays on their transfer through tubing are
important for atmospheric measurements and also provide a method to
characterize and quantify gas–surface interactions. Here we expand recent
results by comparing different types of Teflon and other polymer tubing, as
well as glass, uncoated and coated stainless steel and aluminum, and other
tubing materials by measuring the response to step increases and decreases
in organic compound concentrations. All polymeric tubings showed absorptive
partitioning behavior with no dependence on humidity or concentration, with
PFA Teflon tubing performing best in our tests. Glass and uncoated and
coated metal tubing showed very different phenomenology due to adsorptive
partitioning to a finite number of surface sites. Strong dependencies on
compound concentration, mixture composition, functional groups, humidity,
and memory effects were observed for glass and uncoated and coated metals,
which (except for Silonite-coated stainless steel) also always caused longer
delays than Teflon for the compounds and concentrations tested. Delays for
glass and uncoated and coated metal tubing were exacerbated at low relative
humidity but reduced for RH >20  %. We find that conductive PFA
and Silonite tubing perform best among the materials tested for gas-plus-particle sampling lines, combining reduced gas-phase delays with good
particle transmission.