The ToF-ACSM: a portable aerosol chemical speciation monitor with TOFMS detection

[摘要] We present a new instrument for monitoring aerosol composition, thetime-of-flight aerosol chemical speciation monitor(ToF-ACSM), combining precision state-of-the-arttime-of-flight mass spectrometry with stability, reliability, andeasy handling, which are necessities for long-term monitoringoperations on the scale of months to years. Based on Aerodyneaerosol mass spectrometer (AMS) technology, the ToF-ACSM providescontinuous online measurements of chemical composition and mass ofnon-refractory submicron aerosol particles. In contrast to thelarger AMS, the compact-sized and lower-priced ToF-ACSM does notfeature particle sizing, similar to the widely-used quadrupole-ACSM(Q-ACSM). Compared to the Q-ACSM, the ToF-ACSM features a bettermass resolution of M/ΔM = 600 and better detectionlimits on the order of < 30 ng m⁻³ for a timeresolution of 30 min. With simple upgrades these limits can bebrought down by another factor of ~ 8. This allows foroperation at higher time resolutions and in low concentrationenvironments. The associated software packages (single packages forintegrated operation and calibration and analysis) provide a highdegree of automation and remote access, minimising the need fortrained personnel on site. Intercomparisons with Q-ACSM, C-ToF-AMS,nephelometer and scanning mobility particle sizer (SMPS)measurements, performed during a first long-term deployment (> 10months) on the Jungfraujoch mountain ridge (3580 m a.s.l.) in theSwiss Alps, agree quantitatively. Additionally, the mass resolutionof the ToF-ACSM is sufficient for basic mass defect resolved peakfitting of the recorded spectra, providing a data stream notaccessible to the Q-ACSM. This allows for quantification of certainhydrocarbon and oxygenated fragments (e.g. C₃H₇⁺ andC₂H₃O⁺, both occurring at m/Q = 43 Th), as well asimproving inorganic/organic separation.

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