Instrument - Nitrate-adduct Chemical Ionization Mass Spectrometer
Nitrate-CIMS (NO3- CIMS)
Nitrate-adduct Chemical Ionization Mass Spectrometer
What is being measured:
Highly-oxidized organic molecules (gas phase)
Aerodyne Research, Inc (Spectrometer), Airmodus (NO3 interface)
Data recording software:
Data analysis software:
Raw data time resolution:
Analysis data averaging:
Sensitivity to temperature (and correction method, if applicable):
Unimportant on timescale of experiment, instrument housed in temperature controlled chamber for Krechmer et al 2017, Liu et al 2019 experiments uploaded to the ICARUS database.
Sensitivity to relative humidity (and correction method, if applicable):
Possible RH-dependencies on sample air; however, RH held constant during Krechmer et al 2017, Liu et al 2019 experiments
Direct gas sampling
Sample preparation method:
Sample residence time (chamber to instrument) (seconds):
Length of tubing (cm):
Instrument flow rate:
Tubing inner diameter:
Chemical identification method:
Elemental formula and selective ionization and well-characterized chemical system
Data analysis method:
Standard Tofware high-resolution peak fitting
Not needed for Krechmer et al 2017, Liu et al 2019 experiments, since relative changes only required for experimental design.
While absolute quantification was not needed for the Krechmer et al 2017, Liu et al 2019 experiments uploaded to ICARUS using this instrument, we provide an approximate calibration method that can be applied to this data. The method is described in the two papers: http://pubs.acs.org/doi/10.1021/acs.est.5b02031, http://www.atmos-chem-phys.net/12/4117/2012/. Species posted are in ions/s (commonly referred to as Hz). For obtaining molecules/cm3, the 1 Hz measurements are to be multiplied by 1.89e10 and then divided by the total reagent ion rate (~90% of which is NO3- and NO3(HNO3)- with smaller contributions from other ions such as NO3(HNO3)2-, NO3(H2O)-). Total reagent ion rates for the Krechmer et al 2017, Liu et al 2019 experiments were 8,000-12,000 Hz. Therefore compute concentrations as: molec/cm3 = (ion rate(Hz) x 1.89e10)/10,000. This represents a lower-limit concentration as it is based on the ion-collision rate limit.
Calibration drift estimate:
Low (on the order of weeks)
Uncertainty estimation method:
Not required for applications here because relative signal used for analysis and insignificant drift over timescale of experiments in Krechmer et al 2017, Liu et al 2019 experiments.
Isomers are indistinguishable, although selective ionization can provide guidance.
Link to supplemental information:
ions/s (Hz) Also see below and also approximate conversion to absolute concentration (molec/cm3) under "calibration" field