Measurement of elemental concentration of aerosols using spark emission spectroscopy

Abstract

A coaxial microelectrode system has been used to collect and analyse the elemental composition of aerosol particles in near real-time using spark emission spectroscopy. The technique involves focused electrostatic deposition of charged aerosol particles onto the flat tip of a microelectrode, followed by introduction of spark discharge. A pulsed spark discharge was generated across the electrodes with input energy ranging from 50 to 300 mJ per pulse, resulting in the formation of controlled pulsed plasma. The particulate matter on the cathode tip is ablated and atomized by the spark plasma, resulting in atomic emissions which are subsequently recorded using a broadband optical spectrometer for element identification and quantification. The plasma characteristics were found to be very consistent and reproducible even after several thousands of spark discharges using the same electrode system. The spark plasma was characterized by measuring the excitation temperature (~7000 to 10 000 K), electron density (~10 16 cm −3 ), and evolution of spectral responses as a function of time. The system was calibrated using particles containing Pb, Si, Na and Cr. Absolute mass detection limits in the range 11 pg to 1.75 ng were obtained. Repeatability of spectral measurements varied from 2 to 15%. The technique offers key advantages over similar microplasma-based techniques such as laser-induced breakdown spectroscopy, as: (i) it does not require any laser beam optics and eliminates any need for beam alignment, (ii) pulse energy from dc power supply in SIBS system can be much higher compared to that from laser source of the same physical size, and (iii) it is quite conducive to compact, field-portable instrumentation.

Characterization of an aerosol microconcentrator for analysis using microscale optical spectroscopies

“…1 shows the schematic diagram of the corona aerosol microconcentrator (CAM) used in this study. The design of the CAM is similar to the aerosol collection systems used in earlier work in our group (Diwakar et al, 2012; Diwakar & Kulkarni, 2012; Zheng, Kulkarni, Birch, Deye, & Dionysiou, 2016). The key components of the CAM include two coaxial electrodes with their tips separated by a distance of 5 mm.…”

“…The particulate mass accumulated on the collection electrode tip of the CAM was measured using spark emission spectroscopy (SES) (Diwakar & Kulkarni, 2012; Zheng, Kulkarni, Birch, Deye, & Dionysiou, 2016). In the SES system, a high voltage pulse generator (Cascodium Inc., Andover, MA, USA) was used to produce a spark microplasma in the electrode gap to ablate the collected particulate matter from the collection electrode.…”

“…Microscopic concentration, i.e. collection of aerosol particles over a miniscule area (on the order of 1 mm 2 or less) at high number or mass density is particularly important for aerosol characterization using laser spectrometric methods, such as laser-induced breakdown, micro-Raman, and infrared spectroscopies that probe miniscule amounts of particulate samples (Diwakar, Kulkarni, & Birch, 2012; Diwakar & Kulkarni, 2012, Zheng, Kulkarni, Birch, Deye, & Dionysiou, 2016). …”

“…Recently our group has developed a corona-based aerosol microconcentration method for efficient coupling with laser or spark emission spectroscopy (Diwakar et al, 2012; Diwakar & Kulkarni, 2012, Zheng, Kulkarni, Birch, Deye, & Dionysiou, 2016). The previous studies mainly dealt with the characterization of analytical aspects of aerosol elemental measurements.…”

“…In this study, we present detailed characterization of a corona-based aerosol microconcentration technique developed previously (Diwakar and Kulkarni, 2012). The method involves two coaxial electrodes separated by a few millimeters, one held at a high electrical potential and the other grounded.…”