ACROSS_LISA_RambForest_ToFCIMS-count_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.

Results are reported here as the product ions divided by the sum of the reagent ion signals (ion ratio).