Ambient Air Analysis Intercomparison with Vocus PTR-TOF

TOFWERK and its partner Aerodyne Research, have recently deployed a Vocus PTR-TOF 2R to the CESAR observatory in the Netherlands to participate in an ACTRIS intensive PTR-MS intercomparison.

ACTRIS Campaign

ACTRIS (Aerosols, Clouds and Trace gases Research Infrastructure) is a plan to combine the efforts of European researchers in order to develop and share high-quality observations of trace gases, aerosols and clouds.

The aim of this two week campaign was to assess and compare best practices for background subtraction and PTR-MS calibration to improve the accuracy of measurements and the precision of critical atmospheric VOCs. The Vocus PTR-TOF 2R performed with 11 other PTR-MS at the CESAR observatory, eight of which also utilized TOFWERK TOF mass analyzers.

The ACTRIS campaign took place at the CESAR observatory in the Netherlands. 12 PTR-MS measured VOCs in ambient air for two weeks, sampling from a shared 10-meter sampling line.

The ACTRIS campaign took place at the CESAR observatory in the Netherlands. 12 PTR-MS measured VOCs in ambient air for two weeks, sampling from a shared 10-meter sampling line.

Vocus PTR-TOF 2R

The VOCUS 2R made continual 2 Hz measurements (2 mass spectra per second) for the whole two weeks, sampling ambient air from a communal 10 meter sampling line.

Running entirely on its own, the instrument carried out automatic calibrations each hour with a certified gas standard, and one minute automatic background measurements every 30 minutes. Illustrated below is an example of a 2 Hz xylene time series. The inset shows the high frequency response and accuracy as a result of the high sensitivity of the Vocus.

Example time series of ambient xylene concentrations recorded with the PTR-TOF 2R at 2 Hz. The inset demonstrates the precision and fast response during a period when concentrations were between 150 and 350 pptv

Example time series of ambient xylene concentrations recorded with the PTR-TOF 2R at 2 Hz. The inset demonstrates the precision and fast response during a period when concentrations were between 150 and 350 pptv.

Clear Spectral Identification at Unparalleled Speed

The high sensitivity of this instrument combined with its high mass resolving power (~12,000 as tuned during this campaign) enables clear spectral identification at an unrivalled speed.

The following example demonstrates high resolution identification and separation at 105 Th. The data unambiguously reveals five distinct ions which would be challenging to assign and measure without this high degree of resolving power.

The Vocus 2R is able to resolve many ions at each nominal mass. As an example, data at mass/charge 105 Th show 5 distinct ions. Unique time series are reported for each of these ions.

The Vocus 2R is able to resolve many ions at each nominal mass. As an example, data at mass/charge 105 Th show 5 distinct ions. Unique time series are reported for each of these ions.

TOFWERK and Aerodyne kindly thank Professor Rupert Holzinger at Utrecht University for planning this intercomparison and for the invitation to participate.

This information has been sourced, reviewed and adapted from materials provided by TOFWERK.

For more information on this source, please visit TOFWERK.

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