Chemical discrimination of the particulate and gas phases of miniCAST exhausts using a two-filter collection method

Abstract

Abstract. Combustion of hydrocarbons produces both particulate and gas phase emissions responsible for major impacts on atmospheric chemistry and human health. Ascertaining the impact of these emissions, especially on human health, is not straightforward because of our relatively poor knowledge of how chemical compounds are partitioned between the particle and gas phases. Accordingly, we propose to couple a two-filter sampling method with a multi-technique analytical approach to fully characterize the particulate and gas phase compositions of combustion by-products. The two-filter sampling method is designed to retain particulate matter (elemental carbon possibly covered in a surface layer of adsorbed molecules) on a first quartz fiber filter while letting the gas phase pass through, and then trap the most volatile components on a second black carbon-covered filter. All samples thus collected are subsequently subjected to a multi-technique analytical protocol involving two-step laser mass spectrometry (L2MS), secondary ion mass spectrometry (SIMS), and micro-Raman spectroscopy. Using the combination of this two-filter sampling/multi-technique approach in conjunction with advanced statistical methods we are able to unravel distinct surface chemical compositions of aerosols generated with different set points of a miniCAST burner. Specifically, we successfully discriminate samples by their volatile, semi-volatile and non-volatile polycyclic aromatic hydrocarbon (PAH) contents and reveal how subtle changes in combustion parameters affect particle surface chemistry.

Ice Nucleation Activities of Carbon-Bearing Materials in Deposition Mode: From Graphite to Airplane Soot Surrogates

“…Consequently, we characterized the nature of the organics making up the samples' surfaces using mass spectrometry techniques. Our surface analyses clearly highlighted that the 'organic content' referred to in bulk analyses 53,56,84 can be identified as being a mixture of PAHs. However, it is also clear that different features appear for the two CAST soot type of samples (Figure 8), where…”

“…The surface chemical composition of soot samples was probed by two mass spectrometry techniques: two-step laser mass spectrometry (L2MS) and secondary ion mass spectrometry (SIMS). 55,56 The custom-built L2MS apparatus has been described in detail elsewhere. 57−60 Briefly, the collimated (2 mm diameter) beam of a Nd:YAG laser (Continuum Minilite II, 5 ns, 532 nm, 10 Hz) irradiates the surface of the sample, placed under vacuum (10 −8 mbar) on a cryogenic stage.…”

“…The surface chemical composition of soot samples was probed by two mass spectrometry techniques: two-step laser mass spectrometry (L2MS) and secondary ion mass spectrometry (SIMS). , The custom-built L2MS apparatus has been described in detail elsewhere. − Briefly, the collimated (2 mm diameter) beam of a Nd:YAG laser (Continuum Minilite II, 5 ns, 532 nm, 10 Hz) irradiates the surface of the sample, placed under vacuum (10 –8 mbar) on a cryogenic stage. Neutral species in the desorption plume are then ionized by an orthogonal delayed UV beam coming from either a Nd:YAG laser (Continuum Powerlite 8010, 6 ns, 266 nm, 10 Hz) for the resonant two-photon ionization of most of the aromatic species or a 118 nm (10.5 eV) home-built coherent source in order to enable the single photon ionization of most of the condensable species, including aliphatic compounds .…”

“…Mass Spectrometry (SIMS). [55][56] The custom-built L2MS apparatus has been described in detail elsewhere. [57][58][59][60] Briefly, the collimated (2 mm diameter) beam of a Nd:YAG laser (Continuum Minilite II, 5 ns, 532 nm, 10 Hz) irradiates the surface of the sample, placed under vacuum (10 -8 mbar) on a cryogenic stage.…”

Perspectives for regulating 10 nm particle number emissions based on novel measurement methodologies

“…The CS efficiency was assessed by measuring the volatile organic fraction. An original two-filter system (Ngo et al, 2020) was developed to sample simultaneously the gas phase and the particulate matter from the exhaust, yet on separate substrates. Mass spectrometry analyses showed that the catalytic stripper effectively removed the organic content regardless of the phase (gas or particles), as demonstrated by a drastic reduction (more than one order of magnitude) of the recorded total ion count.…”