The Method

CHARON PTR-TOFMS is an on-line analytical technique that characterizes the molecular composition of sub-µm organic particles on a chemical composition level at a one-minute time-resolution. The CHARON particle inlet consists of a honeycomb activated charcoal denuder that efficiently adsorbs organic gases and transmits particles, a high-pressure aerodynamic lens system that collimates and extracts sub-µm particles, and a thermo-desorber that evaporates non-refractory organic particulate matter at moderate temperatures of 100-160°C and reduced pressures of a few mbar.

These organics are subsequently analyzed as gas-phase analytes with one of IONICON’s high-resolution PTR-TOFMS instruments. By coupling the CHARON inlet to a PTR-TOFMS, the VOC inlet remains fully operational. An automated valve system allows for scheduled switching between gas- and particle-phase measurements as well as zeroing of the particle inlet.

Benefits

CHARON PTR-TOFMS is a designated on-line and real-time particle analyzer. There is no need for off-line particle pre-concentration e.g. by collection/desorption on surfaces. Analytical artefacts, which may result by reactions on such collection surfaces or thermal degradation at high desorption temperatures and residence times, are efficiently reduced. In addition, the CHARON particle inlet significantly extends the range of by PTR-MS measurable compounds from gas-phase volatile and intermediate volatile organics (VOC and IVOC) to particle-phase intermediate, semi and low volatile organic compounds (IVOC, SVOC and LVOC, respectively). Therefore, the PTR-MS technology allows for the detection of almost the full range of atmospheric organic carbon with one single instrument. The controlled chemical ionization at reduced pressures and defined reaction energies of a PTR-MS drift tube impede the formation of ionic artefacts (e.g. clusters of organics) that might be falsely attributed. Ionization typically proceeds at collision rates that are well predictable (+/- 30%). Fragmentation due to ionization is typically low; between 60% - 100% of the organic mass concentrations can be directly calculated without the need of any additional corrections.
With its high temporal resolution and the high degree of conserved chemical composition information, CHARON PTR-TOFMS is thus the perfect analytical technique to identify and quantitatively follow atmospheric particulate tracer compounds like levoglucosan and polycyclic aromatic hydrocarbons. One-minute resolved data of hundreds of identified chemical compositions boost the quality of source apportionment (e.g. by positive matrix factorization; PMF) to an unseen level.

Taking CHARON PTR-TOF to the Sky. At the Frontier of Airborne Research aboard NASA’s Flying Laboratory.

Using the opportunity provided by NASA’s Student Airborne Research Program (SARP) Ionicon gave wings to the newly developed CHARON aerosol inlet. In cooperation with the University of Oslo, the Ionicon team combined CHARON and a custom-built PTR-TOF 4000 instrument.

Airworthiness requires withstanding of heavy G-forces, coping with pressure changes and most importantly being fail safe. Therefore, unique modifications to CHARON have been made and thoroughly tested before getting airborne and install the system in the DC-8 Flying Laboratory, ready for the first airborne measurements.

Flying within the boundary layer over the Central Valley in California or through wildfire plumes, pushed the instrument to its limits. CHARON performed admirably under these demanding conditions and gathered promising data from anthropogenic and biogenic emissions sources.