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

Abstract

Abstract. A single particle instrument was developed for real-time analysis of organic aerosol. 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 by 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 ranges 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. During optical detection, particle scattered light from the two diode lasers, is detected by two photomultipliers and the detected signals are used to trigger UV excimer laser (λ = 248 nm) used for one-step 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 × 10 −15 kg (∼4 × 10 3 molecules). DOP particles were also used to test the overall operation 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 application of the instrument. Single particle mass spectra were obtained with an effective hit rate of 8 %. Some of these mass spectra were found to be very different from one particle to another possibly reflecting chemical differences within the investigated indene SOA particles. Our study shows that an exhaustive statistical analysis, over hundreds of particles, and adapted reference mass spectra are further needed to understand the chemical meaning of single particle mass spectra of chemically complex submicrometer-sized organic aerosols.

Evaluating the influence of laser wavelength and detection stage geometry on optical detection efficiency in a single-particle mass spectrometer

“…600 nm) there is a correlation between the two curves, indicating that the low size cut-off in the sampling efficiency, in this case 350 nm, is limited by the scattering intensity of small particles. However, it is also clear that C sca function is non-monotonic and will also affect the detection efficiency of larger particles, particularly in the region 700-900 nm as suggested by Gaie-Levrel et al (2012) and Gemayel et al (2016).…”

“…The implementation of 532 nm Nd:YAG solid-state lasers with an output in the range of 50-300 mW greatly improved laser fluence and beam quality in later-generation instrument (Thomson et al, 2000;Su et al, 2004;Zelenyuk and Imre, 2005;Brands et al, 2011). Other groups have opted for newly developed laser diodes (Gaie-Levrel et al, 2012) that, while producing less output (40 mW), have shorter wavelengths (405 nm) and are relatively cheap and easy to implement. Shorter wavelengths are desirable when sampling particles whose diameter (D) is smaller than the wavelength of the incident radiation as C sca is proportional to D 6 in the Rayleigh regime.…”

The performance and the characterization of laser ablation aerosol particle time-of-flight mass spectrometry (LAAP-ToF-MS)

“…A comparison between the scattering efficiencies of LAAP-ToF-MS, the single particle laser ablation mass spectrometer (SPLAM) (Gaie-Levrel et al, 2012) and the sin-gle particle laser ablation time-of-flight mass spectrometer (SPLAT) (Zelenyuk and Imre, 2005) has been undertaken (Fig. 6).…”

“…Hence, there is a need for the development of appropriate analytical methods for on-line, time-resolved measurements of atmospheric particles. In the last decade several hyphenated laser ablation -mass spectrometry instruments have been developed (see for instance Gaie-Levrel et al (2012) with the aim of chemically characterizing aerosol particles. Murphy (2007) has reviewed the development and implementation of single particle laser mass spectrometers.…”

Exploring femtosecond laser ablation in single-particle aerosol mass spectrometry

“…Single-particle mass spectrometry (SPMS) is a powerful tool for the investigation of the size-resolved chemical composition of individual atmospheric aerosol particles in real time (Brands et al, 2011;Gaie-Levrel et al, 2012;Murphy, 2007;Murphy et al, 2006;Pratt et al, 2009;Pratt and Prather, 2012;Zelenyuk et al, 2010). Although a two-step approach separating laser ablation and laser ionization bears several advantages for identifying specific molecules (Passig et al, 2017) many instruments currently still use single-step laser desorption and ionization.…”