Development and characterization of a single particle laser ablation mass spectrometer (SPLAM) for organic aerosol studies

Abstract

Abstract. A single particle instrument has been developed for real-time analysis of organic aerosols. This instrument, named Single Particle Laser Ablation Mass Spectrometry (SPLAM), samples particles using an aerodynamic lens system for which the theoretical performances were calculated. At the outlet of this system, particle detection and sizing are realized using two continuous diode lasers operating at λ = 403 nm. Polystyrene Latex (PSL), sodium chloride (NaCl) and dioctylphtalate (DOP) particles were used to characterize and calibrate optical detection of SPLAM. The optical detection limit (DL) and detection efficiency (DE) were determined using size-selected DOP particles. The DE is ranging from 0.1 to 90 % for 100 and 350 nm DOP particles respectively and the SPLAM instrument is able to detect and size-resolve particles as small as 110–120 nm. Scattered light is detected by two photomultipliers and the detected signals are used to trigger a UV excimer laser (λ = 248 nm) used for laser desorption ionization (LDI) of individual aerosol particles. The formed ions are analyzed by a 1 m linear time-of-flight mass spectrometer in order to access to the chemical composition of individual particles. The TOF-MS detection limit for gaseous aromatic compounds was determined to be 0.85 attograms. DOP particles were also used to test the overall functioning of the instrument. The analysis of a secondary organic aerosol, formed in a smog chamber by the ozonolysis of indene, is presented as a first scientific application of the instrument. Single particle mass spectra are obtained with a global hit rate of 10 %. They are found to be very different from one particle to another, reflecting chemical differences of the analyzed particles, and most of the detected mass peaks are attributed to oxidized products of indene.