Mass spectrometry of freshly nucleated secondary organic aerosol from flow reactor experiments
P 2.1 in Research in its Prime: First Results of Ongoing Research
An aerosol mass spectrometer for particles with diameters below 30 nm called the Chemical Analyzer for Charged Ultrafine Particles (CAChUP) has been developed (Gonser&Held, 2013). The instrument was designed to study the chemical composition of freshly nucleated secondary aerosol particles.
CAChUP consists of a custom-built aerosol sizing and collection unit coupled to a compact time-of-flight mass spectrometer (CTOF, Tofwerk, Thun, Switzerland). The aerosol sizing and collection unit is composed of a unipolar aerosol charger with an extrinsic charging efficiency of 32 % for 20 nm particles, based on corona discharge from carbon fibres (Han et al., 2008), a compact radial differential mobility analyzer (Zhang et al., 1995) for particle size separation, and an electrostatic precipitator for aerosol collection on a high-voltage biased metal filament. After collection, the aerosol sample is thermally desorbed, and the resulting gas sample is transferred to the mass spectrometer for chemical analysis.
In flow reactor experiments, secondary organic aerosol particles (SOA) have been produced from dark ozonolysis of alpha-pinene. Particles with a diameter of 25 nm were separated from the aerosol population after the flow reactor and analyzed. The mass spectra compare well with previous measurements of larger SOA from alpha-pinene ozonolysis. The flow reactor allows adjusting the reaction time of terpenes and ozone from a few seconds up to several minutes, resulting in the formation of particles of varying sizes and ages. The main goal of these experiments is to investigate the evolution of the chemical composition of freshly formed secondary organic aerosol.
This work was funded by the Deutsche Forschungsgemeinschaft (DFG) under grant DFG HE 5214/3-1.
S. G. Gonser and A. Held, Atmos. Meas. Tech., 2013, 6, 2339-2348.
B. Han, H. J. Kim, Y. J.Kim and C. Sioutas, Aerosol Sci. Technol., 2008, 42, 793-800.
S. H. Zhang, Y. Akutsu, L. M. Russell, R. C. Flagan and J. H. Seinfeld, Aerosol Sci. Technol., 1995, 23, 357-372.