A chemical analyzer for charged ultrafine particles

Abstract

Abstract. New particle formation is a frequent phenomenon in the atmosphere and of major significance for the Earth's climate and human health. To date the mechanisms leading to the nucleation of particles as well as to aerosol growth are not completely understood. A lack of appropriate measurement equipment for online analysis of the chemical composition of freshly nucleated particles is one major limitation. We have developed a Chemical Analyzer for Charged Ultrafine Particles (CAChUP) capable of analyzing particles with diameters below 30 nm. A bulk of size-separated particles is collected electrostatically on a metal filament, resistively desorbed and subsequently analyzed for its molecular composition in a time of flight mass spectrometer. We report on technical details as well as characterization experiments performed with the CAChUP. Our instrument was tested in the laboratory for its detection performance as well as for its collection and desorption capabilities. The manual application of defined masses of camphene (C10H16) to the desorption filament resulted in a detection limit between 0.5 and 5 ng, and showed a linear response of the mass spectrometer. Flow tube experiments of 25 nm diameter secondary organic aerosol from ozonolysis of alpha-pinene also showed a linear relation between collection time and the mass spectrometer's signal intensity. The resulting mass spectra from the collection experiments are in good agreement with published work on particles generated by the ozonolysis of alpha-pinene. A sensitivity study shows that the current setup of CAChUP is ready for laboratory measurements and for the observation of new particle formation events in the field.

Size-resolved online chemical analysis of nanoaerosol particles: a thermal desorption differential mobility analyzer coupled to a chemical ionization time-of-flight mass spectrometer

“…Depending on the target analyte, the primary ion is chosen. Prominent examples include the proton transfer reaction technique using hydronium ions (Hansel et al, 1995;Graus et al, 2010;Breitenlechner et al, 2017),…”

An intercomparison study of four different techniques for measuring the chemical composition of nanoparticles

“…However, several analytical techniques have recently been developed in order to better advance our understanding on their chemistry. Techniques that are capable of measuring sub-30 nm particles include the Volatile Aerosol Component Analyzer (VACA) (Curtius et al, 1998), thermal desorption-chemical ionization mass spectrometry (TD-CIMS) (Voisin et al, 2003), the Nano Aerosol Mass Spectrometer (NAMS) (Wang et al, 2006), the aerosol timeof-flight mass spectrometer (Laitinen et al, 2009), the inlet for the size-resolved collection of aerosols (Phares and Collier, 2010), the Chemical Analyzer for Charged Ultrafine Particles (CAChUP) (Gonser and Held, 2013), electrostatic precipitation-electrospray ionization mass spectrometry (EP-ESI-MS) (He et al, 2015), droplet-assisted inlet ionization (DAII) (Horan et al, 2017), and online aerosol chemical characterization by the extractive electrospray ionization-ultra-high-resolution mass spectrometer (EESI-Orbitrap) (Lee et al, 2020). Single-particle analysis by mass spectrometry methods based on aerodynamics, light scattering, and laser desorption ionization are suitable for particles with larger sizes.…”