NASA - National Aeronautics and Space Administration

Iodide Ion ToF (Time-of-Flight) CIMS (Chemical Ionization Mass Spectrometer)

Principle of the Measurement

Chemical ionization mass spectrometric detection of gas phase organic and inorganic analytes via I- adduct formation

Species Measured

Reactive nitrogen species: HNO3 (nitric acid), HONO (nitrous acid), HO2NO2 (peroxynitric acid), N2O5 (dinitrogen pentoxide), HNCO (isocyanic acid) 
Halogen Species: ClNO2, HCl, HBr, HOBr, HOCl, Cl2, Br2 
Low to intermediate volatility organic species

Time Response

Instrumental response <1 sec, Field response is limited by inlet surface affinity for a particular species

Detection Limit

Precision on 1s data various by species

Accuracy

(15% + 1 pptv) for N2O5
(20% + 1 pptv) for ClNO2
(30% + 15 pptv) for HONO
(25% + 10 pptv) for HO2NO2
(15% + 15 pptv) for HNO3
(20% + 5 pptv) for HNCO
(20% + 15 pptv) for HCOOH
(30% + 1 pptv) for halogenated species

Manufacturer

TOFWERK/Aerodyne Research Inc. (modified)

Principle: The CU aircraft Extractive Electrospray Time-of-Flight Mass Spectrometer (EESI-TOFMS) detects the chemical composition of submicron particulate matter by simultaneous dissolution of the aerosol and soft ionization of its molecular components in an electrospray, followed by detection using time-of-flight mass spectrometry. When operated with positive ion polarity analytes are detected intact as adducts with sodium ions. When operated with negative ion polarity analytes are detected as deprotonated anions.

Aircraft Operation: Operated with positive or negative ion polarity, depending on mission goals.

Pressure-controlled EESI region with a maximum sampling altitude of 23 kft. Sensitivity can be increased for boundary layer  sampling by increasing the pressure of the electrospray region.

Calibrated relative to AMS on flight days, and confirmed with absolute calibrations on maintenance days

1s time resolution with 15s background measurements every 4 min.

Data Products: 

Positive ion polarity EESI(+): C6H10O5 calibrated as levoglucosan and C6H5NO4 calibrated as nitrocatechol

Negative ion polarity EESI(-): C6H5NO4 calibrated as nitrocatechol
Additional species under development. Species of interest for specific campaigns can be tested and calibrated for.

Detection Limits (1s):

C6H10O5 as levoglucosan: 200 ng sm^-3

C6H5NO4 as nitrocatechol: 20ng sm^-3 EESI(-), 400 ng sm^-3 EESI(+)