Abstract
Abstract. 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 compact-sized 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 ng m−3 for a time resolution of 30 min. With simple upgrades these limits can be brought down by another factor of ~ 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 m a.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.
Highlights
Over the last decades, ongoing research efforts have solidified the knowledge base about the significant role aerosols play in Earth’s ecosystem (Gu et al, 2003; Mercado et al, 2009; Mahowald, 2011) and climate (Lohmann and Feichter, 2005; Forster et al, 2007; Carslaw et al, 2010)
The lower detection limits of the ToF-ACSM allow for the operation at higher time resolutions while achieving detection limits needed for ambient sampling
We present the ToF-ACSM, a new aerosol mass spectrometer optimised for long-term, stable, semi-autonomous environmental monitoring applications
Summary
Over the last decades, ongoing research efforts have solidified the knowledge base about the significant role aerosols play in Earth’s ecosystem (Gu et al, 2003; Mercado et al, 2009; Mahowald, 2011) and climate (Lohmann and Feichter, 2005; Forster et al, 2007; Carslaw et al, 2010). To assess and address these issues a large number of air quality monitoring endeavours are needed Essential to this are instruments capable of gathering in situ information about the chemical properties and composition of the ambient particles on a long-term basis. Besides the individual scientific output of every instrument, the unique databases produced with the ACSM by such monitoring networks comprise a combination of chemical information, high time resolution, longterm measurements, and more, like the ability to measure semivolatile nitrate and organics without filter artefacts or offline analysis This provides invaluable opportunities for the modelling community. We discuss the operation, testing, and initial deployment of a ToF-ACSM for a period of > 10 months at the high altitude research station, the Jungfraujoch (JFJ, 3580 m a.s.l.), in the Swiss Alps This deployment demonstrated the instrument stability, sensitivity, and enabled quantitative comparison with other aerosol mass spectrometers and particle instruments
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