AMS - Aerosol Mass Spectrometry
Aerosol Mass Spectrometers (AMS) are used to learn about the composition of atmospheric aerosols with a high temporal resolution. This information can be acquired size-class-resolved. Typically, the concentrations of Sulfate, Nitrate, and Ammonium, as well as the sum of organics in the particle phase are determined. The organic fraction can be split into separate classes of different origin (primary emission, secondary formation) and different ageing conditions (oxidation state) via the use of statistical methods.
Our AMS’s feature an aerodynamic lens to focus the aerosol particles into a narrow particle beam. The particle beam passes through a differentially pumped particle-time-of-flight chamber. At the end of this chamber, a vaporizer converts the particles to the gas phase. With Electron Ionization (EI), ions are generated from the vapor mixture formed that way. These ions are then analyzed by means of a mass spectrometer. The determination of particle-time-of-flight which is size-dependant allows for the assignation of composition to particle size.
The “Aerosols” section operates three Aerosol Mass Spectrometers manufactured by Aerodyne Research Inc.. One of these AMS is equipped with a low-resolution but high-sensitivity Quadrupole Mass Spectrometer. The two other AMS are equipped with a high-resolution time-of-flight mass spectrometer (ToF-MS) built by Tofwerk AG. With the ToF-MS, mass spectra can be acquired with sufficiently high resolution to determine the elemental composition of organic fragments containing C, O, H, and N.
The AMS are used in process studies at atmospheric simulation chambers (SAPHIR, JPAC) and in field studies (EUCAARI, PEGASOS). In cooperation with Aerodyne Research Inc., the Heterogeneous Reactions Group has adapted a high-resolution ToF-AMS for measurements on a Zeppelin NT airship. Future measurements with this instrument will enable to determine height-resolved particle composition in the entire planetary boundary layer.