The Picarro instrument installed on board of MASIN was a flight-enabled Picarro L2130-i (Ser. No. HIDS2254), provided by FARLAB, University of Bergen. This particular L2130-i is a custom-made, flight-enabled modification that has an additional laser, allowing faster switching between wavelengths and thus faster measurement frequency, regulation of the flow rate through the cavity at changing ambient pressure, and a measurement cavity certified down to 200 ppmv H2O, lower than regular instruments of the same type. In addition to mixing ratio, isotope delta values and a range of internal control parameters, the instrument records ambient pressure, which allows for an alignment of the vapour isotope measurements with meteorological measurements onboard the aircraft. A backward-facing inlet was installed for vapour measurements. Inlet tubing was heated to about 60 deg C by self-regulating heat trace (Thermon Inc., USA). Less than 1 m stainless steel tubing (1/4 inch diameter) was used from the point where a T-valve allowed to draw air from either the forward or backward facing inlet line. From there, another 2.5 m of 3/8 inch stainless steel tubing with Sulfinert coating (Silcotek Inc., USA) for lower moisture retention led to a connection with a T-valve, that allowed to bypass the KNF manifold pump (N022AN.18) with a flow rate of about 5–10 lpm. During two of the flights, this valve was by mistake turned such that the pump did not flush the inlet, such that only the CRDS analyzer with a flow rate of about 40 sccm provided flow through the inlet. Less than 1 m of 1/4 inch stainless steel tubing then branched off to the analyzer, connected to an critical orifice required for low-flow mode, and protected by a check valve against reverse flow. An additional T-valve allowed for switching between flow from the inlet or from the calibration unit. These last parts of tubing had a flow rate of about 30–40 sccm, as the analyzer was operated in low-flow mode.