Aerosol Time-of-Flight Mass Spectrometer ATOFMS
An ideal aerosol mass spectrometer should be capable of determining the size of an individual aerosol particle in situ, and provide a quantitative measure of each of its molecular constituents in real time. This is a difficult task because atmospheric particles range in size from less than 10 nm to greater than 10 μm. In addition, the molecular constituents are often mixtures that can include sea salt, soot, heavy metals, mineral dust, and a large number of different organic molecules.
The ability to detect individual particles is important in atmospheric studies where it is essential to know whether particles are uniform mixtures of many constituents (internally mixed), or whether the aerosol is a heterogeneous mixture of various types of particles (externally mixed). Quantitative aerosol chemical data in high time resolution is crucial to acquire atmospheric mass budgets, to perform source apportionment studies as well as to understand atmospheric chemistry in general. Finally, great benefits accrue if such instruments are portable so that they can be transported to various locations for field experiments.
One of the main instrument in our group used for chemical analysis is an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS, TSI Model 3800). The instrument determines aerodynamic size and chemical composition of single particles in near real-time. It uses an aerodynamic sizing technique to measure particle size, and it uses time-of-flight mass spectrometry to determine the chemical composition of particles. Particles are drawn into the instrument from ambient air, sized, and - due to the bipolar design of the mass spectrometer - a positive and a negative ion spectrum are acquired from each particle. The main differences compared to the Aerodyne aerosol mass spectrometer, which is widely used in the field of aerosol mass spectrometry, are the capability of the ATOFMS to analyze individual particles and refractory materials such as sodium chloride, elemental carbon and mineral dust constituents. This fits into our major group research interests as particle types containing those components often show distinct ice and cloud condensation nuclei characteristics.
The instrument has been extensively deployed in the laboratory and in the field, e.g. during the external page Arctic Summer Cloud Ocean Study ASCOS (Sierau et al., 2014), at the external page high Alpine research station Jungfraujoch, and at the external page Leipzig Aerosol Cloud Interaction Chamber LACIS (Sullivan et al., 2010). The role of individual biological particles and soil dusts as IN was studied at the external page AIDA chamber in Karlsruhe. The ATOFMS was also used to obtain in situ chemical information on the Saharan dust aerosol during the external page CALIMA 2014 campaign, which was carried out at the external page Izaña Atmospheric Research Center on Tenerife, Spain.
Movie of ATOFMS as already in use
References:
Sierau, B., Chang, R. Y.-W. , Leck, C., Paatero, J., and Lohmann, U., Single-particle characterization of the high-Arctic summertime aerosol, Atmos. Chem. Phys., 14, 7409-7430, 2014, external page doi:10.5194/acp-14-7409-2014.
Sullivan, R.C., Petters, M.D., DeMott, P.J., Kreidenweis, S.M., Wex, H., Niedermeier, D., Hartmann, S., Clauss, T., Stratmann, F., Reitz, P., Schneider, J., Sierau, B., Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation, Atmospheric Chemistry and Physics, 10, 11471-11487, 2010, external page doi:10.5194/acp-10-11471-2010.