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

We present a new instrument for monitoring aerosol composition, the time-of-flight aerosol chemical speciation monitor (ToF-ACSM), combining 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 (QACSM). Compared to the Q-ACSM, the ToF-ACSM features a better mass resolution of M 1 M/Lambda M = 600 and better detection limits on the order of < 30 ng m(-3) for a time resolution of 30 min. With simple upgrades these limits can be brought down by another factor of similar to 8. This allows for operation at higher time resolutions and in low concentration environments. The associated software packages (single packages for integrated operation and calibration and analysis) provide a high degree of automation and remote access, minimising the need for trained 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 (> 10 months) on the Jungfraujoch mountain ridge (3580 ma.s.l.) in the Swiss Alps, agree quantitatively. Additionally, the mass resolution of the ToF-ACSM is 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.