Short name:
EESI-TOF (EESI-MS)

Full name:
Extractive Electrospray Ionization (Time-of-Flight) Mass Spectrometer

What is being measured:
Particle-phase chemical speciation (molecular-level)

Sampling Protocol:
Online

Manufacturer:
Aerodyne Research, Inc (Spectrometer), Aerodyne/Tofwerk EESI interface

Model:
NA

Instrument year :
2011 (Mass Spec), 2018 (EESI interface)

Data recording software:
TofDaq

Data analysis software:
Tofware

Raw data time resolution:
1 sec

Analysis data averaging:
None

Detection limit:
Ion-specific, ~1-100 ng/m3

Sensitivity to temperature (and correction method, if applicable): :
None observed

Sensitivity to relative humidity (and correction method, if applicable): :
Insensitive

Sampling method:
Direct aerosol sampling

Sample preparation method:
None

Sample residence time (chamber to instrument) (seconds):
0.5

Length of tubing (cm):
250

Instrument flow rate:
1 lpm (inlet flowrate: 3.8 lpm)

Tubing inner diameter:
0.38 cm

Tubing material:
Stainless Steel

Chemical identification method:
Elemental formula and selective ionization and well-characterized chemical system

Data analysis method:
Standard Tofware high-resolution peak fitting

Quantification method:
Not needed for Liu et al 2019 experiments, since relative changes only required for experimental design.

Calibration method:
Data are reported in ions/s since since individual species were not directly calibrated and can vary by 1-2 orders of magnitude (https://amt.copernicus.org/articles/14/6955/2021/amt-14-6955-2021.html). However, the instrument was periodically calibrated with levoglucosan and sucrose particles to track instrument sensitivity. During the experiments reported in the ICARUS database for Liu et al. 2019, sensitivity to levoglucosan was ~100-200 ions/s per ug/m3 and sensitivity to sucrose was ~one-third that of levoglucosan, on average.

Calibration drift estimate:
High (on the order of hours)

Calibration schedule:
As Needed

Uncertainty estimation method:
Not required because relative signal response used for analysis.

Known interferences:
None known

Link to supplemental information:
Manuscript describing the EESI-ToF: Lopez-Hilfiker, F. D., Pospisilova, V., Huang, W., Kalberer, M., Mohr, C., Stefenelli, G., Thornton, J. A., Baltensperger, U., Prevot, A. S. H., and Slowik, J. G.: An extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) for online measurement of atmospheric aerosol particles, Atmos. Meas. Tech., 12, 4867–4886, https://doi.org/10.5194/amt-12-4867-2019, 2019.

Additional notes:
For the Liu et al. 2019 study: The primary spray was generated from a solution of water–acetonitrile 1:1 mixture containing 100 ppm (by weight) sodium iodide (NaI). The collisions between particles and highly charged spray droplets dissolve particulate analytes, resulting in the formation of gas-phase ions (typically Na+ adducts). The background of the measured compounds was determined by passing the ambient sample through a HEPA air filter, demonstrating an effective time response of ~6 s. Data analysis was conducted using DHN measurements for the five available seeded experiments (Supplementary Table 2 in Liu et al. 2019) and THNs for the sucrose experiment. THNs were only measured at reliable signal-to-noise ratios for the sucrose-seeded EESI experiment after more extensive instrument tuning.

Measurement uncertainty:
Accuracy uncertainty unknown since not calibrated.

Measurement units:
ions/s (Hz). See notes on "calibration method"