Georgia Tech Chemical Ionization Mass Spectrometer

A chemical ionization mass spectrometer (CIMS) capable of measurements in two basic configurations has been constructed for the HIAPER platform. In CIMS the target molecule is ionized via an ion-molecule reaction with a reagent ion and selectively detected with a mass spectrometer. The HIAPER CIMS is designed to operate in either negative or positive ion mode, allowing trace gases with affinities for forming either type of ions to be detected. In its most common configuration the instrument uses SF₆ gas, ionized, to react with trace gases like SO₂. producing charged reaction products that are then detected by a mass spectrometer in which the path of the molecule is determined by its mass.The standard CIMS (negative ion) mode allows measurement of nitric acid, pernitric acid and sulfur dioxide in real-time. Other species such as chlorine nitrate or dinitrogen pentoxide may be available after post-flight processing of the data by a scientist. The second (positive ion) configuration is as a proton transfer reaction - mass spectrometer (PTR-MS) and focuses on the real-time measurement of organics such as methanol, acetaldehyde, acetonitrile and acetone. Measurements are reported at 1 - 3 s time intervals and are made available in a standard data exchange format. The instrument is a routine operational instrument and is designed for unattended operation during flight.

Measurements Provided: sulfur dioxide, nitric acid, pernitric acid, and nitrous acid. Many others are possible, including an organic detection mode.

Measurement Characteristics: Contact Greg Huey or Frank Flocke for current information on the performance of this instrument.