ACROSS_LISA_RambForest_ToFCIMS-calib_L2

Measurements were made with a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) from Aerodyne Research, Inc. It was configured with a nitrate inlet (borrowed from ICARE) to which a mixture of nitric acid in air was exposed to X-rays to generate reagent ions (primarily NO3(-) and NO3(HNO3)(-)). The reagent ions are then exposed to ambient air and react with strong acids (such as sulfuric acid) and cluster with highly oxygenated molecules (HOMs).

The instrument was positioned in a room at the top of the 40-meter tower at the Rambouillet forest supersite.

Ambient air was directly drawn into the inlet at a flow rate of approximately 8 liters per minute through a 1-meter long, ¾ inch outer diameter, and 0.61-inch inner diameter stainless-steel tube.

Automatic background zeroing : every 3 hours for a duration of 10 min, using an oil-free air compressor (Vevor model 550-9l) that channels ambient air through a HC trap.

Data processing and peak identification software :Tofware v3.2.5 / Igor Pro v8.04 64-bit.
Missing data are indicated with “-99999.99”.
Data average : 10-min
Mass resolution :~ 3700, Mass accuracy: <10 ppm.

Calibration was performed in the laboratory by introducing a known amount of gas-phase H2SO4, assuming it exhibits the same ionization kinetic rate constant and comparable transmission efficiency as HOMs.

Concentrations of products are reported here by multiplying the product ions divided by the sum of the reagent ion signals with the calibration coefficient of 4.22E+09 molecules.cm-3.ncps-1.