Characterization of a thermal desorption mass spectrometer for freshly nucleated secondary aerosol particles
P 3.9 in Ökosysteme: Funktion und Leistungen
Secondary aerosol formation introduces new particles to the atmosphere. It is thereby relevant for the global climate by influencing the earth’s radiative balance, both directly and indirectly. Chemical reactions leading to atmospheric secondary aerosol formation are not yet fully understood. At the same time, analysing the chemical composition of freshly nucleated particles is still a challenging task.
We are developing a field portable aerosol mass spectrometer for nucleation particles with diameters smaller than 30 nm. The instrument consists of a custom-built aerosol sizing and collection unit coupled to a time-of-flight mass spectrometer (TOF-MS). The aerosol sizing and collection unit is composed of three major parts: (1) a unipolar aerosol charger; (2) a radial differential mobility analyser for particle size separation; and (3) an electrostatic precipitator where the aerosol is collected on a metal filament. After collection, the particles are thermally desorbed, and the gas sample is transferred to the TOF-MS for chemical analysis.
We will present results of preliminary measurements performed with a laminar flow reactor for calibration of the instrument. Secondary organic aerosol is produced from dark ozonolysis of alpha-pinene. Particles with diameters below 30 nm are separated from the generated polydisperse particle population, collected in the electrostatic precipitator and subsequently analysed by the TOF-MS.
To date, the major part of chemical composition measurements of particles focus on particles larger than 40 nm in diameter. The spectra measured with our instrument provide chemical information of freshly nucleated particles, extending the size range to the nucleation mode (< 30 nm).