Development & Validation of ToF-ACSM

In this project, funded by the Swiss Kommission für Technologie und Innovation (KTI), a new instrument for monitoring aerosol composition, the time-of-flight aerosol chemical speciation monitor (ToF-ACSM, see scheme in Fig. 1) was developed and validated in cooperation with TOFWERK AG (Thun, CH). The ToF-ACSM combines precision state-of-the-art time-of-flight mass spectrometry with stability, reliability, and easy handling, which are necessities for long-term monitoring operations on the scale of months to years. Based on Aerodyne aerosol mass spectrometer (AMS) technology, the ToF-ACSM provides continuous online measurements of chemical composition and mass of non-refractory submicron aerosol particles. In contrast to the larger AMS, the compactsized and lower-priced ToF-ACSM does not feature particle sizing, similar to the widely-used quadrupole-ACSM (Q-ACSM). Compared to the Q-ACSM, the ToF-ACSM features a better mass resolution of M/ΔM = 600 and better detection limits on the order of < 30 ngm^-3 for a time resolution of 30 min. This allows for operation at higher time resolutions and in low concentration environments.

Intercomparisons with Q-ACSM, C-ToF-AMS, nephelometer and scanning mobility particle sizer (SMPS) measurements were performed during a first long-term deployment (> 1 year) at a low-concentrations site (Jungfraujoch mountain ridge (3580 m a.s.l.) in the Swiss Alps) probing the instruments precision and stability. Godd agreements could be achieved (see Fig. 2).

Low detection limits of 182 ngm-3 for ammonium, 198 ngm^-3 for organics, 18 ngm^-3 for sulphate, 21 ngm^-3 for nitrate, and 11 ngm^-3 for chloride were determined. For a comparison with other instruments detection limits cf. Tab. 1

Additionally, the mass resolution of the ToFACSM was determined to be sufficient for basic mass defect resolved peak fitting of the recorded spectra, providing a data stream not accessible to the Q-ACSM. This allows for quantification of certain hydrocarbon and oxygenated fragments (e.g. C3H7⁺ and C2H3O⁺, both occurring at m/Q = 43 Th), as well as improving inorganic/organic separation.

KTI (Kommission für Technologie und Innovation) Projekt No. 13203.1 PFFLM-NM

Journal Articles

A technical paper about the ToF-ACSM was published in AMT. A second publication about the findings of the long term deployment of the ToF-ACSM at the high altitude site is in preparation.

The ToF-ACSM: a portable aerosol chemical speciation monitor with TOFMS detection, R. Fröhlich, M. J. Cubison, J. G. Slowik, N. Bukowiecki, A. S. H. Prévôt, U. Baltensperger, J. Schneider, J. R. Kimmel, M. Gonin, U. Rohner, D. R. Worsnop, and J. T. Jayne, Atmos. Meas. Tech. 6, 3225-3241 (2013)

Conference Contributions

* Year-round, on-line mass spectrometric PM1 measurements at the high altitude station Jungfraujoch (CH), Roman Fröhlich, Jay G. Slowik, André S. H. Prévôt and Urs Baltensperger, International Aerosol Conference (IAC), August 28 - September 2, 2014, Busan, Republic of Korea

* Q-ACSM on the Jungfraujoch 13.06.12-14.11.12, Roman Fröhlich, Jay Slowik, André Prévôt and Urs Baltensperger, ACTRIS ACSM meeting side-by-side with 14th EMEP Task Force on Measurements and Modelling (TFMM), May 05-06, 2013, Zagreb, Croatia

* Year-round measurement of pm1 chemical composition in the Swiss Alps using a Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM), Roman Fröhlich, Michael Cubison, Jay Slowik, André Prévôt, Urs Baltensperger, Urs Rohner, Marc Gonin, Joel Kimmel, Douglas Worsnop and John Jayne, European Aerosol Conference (EAC), September 02-06, 2013, Prague, Czech Republic, rewarded with a Poster Award

* A novel compact aerosol mass spectrometer - the ToF-ACSM: Instrument performance and first field deployment, Roman Fröhlich, Michael Cubison, Jay Slowik, André Prévôt, Urs Baltensperger, Urs Rohner, Marc Gonin, Joel Kimmel, Douglas Worsnop and John Jayne, European Aerosol Conference (EAC), September 02-06, 2012, Granada, Spain