ABSTRACT
Many studies have been conducted on the environmental impacts of combustion generated aerosols. Due to their complex composition and morphology, their chemical reactivity is not well understood and new developments of analysis methods are needed. We report the first demonstration of in-flight X-ray based characterizations of freshly emitted soot particles, which is of paramount importance for understanding the role of one of the main anthropogenic particulate contributors to global climate change. Soot particles, produced by a burner for several air-to-fuel ratios, were injected through an aerodynamic lens, focusing them to a region where they interacted with synchrotron radiation. X-ray photoelectron spectroscopy and carbon K-edge near-edge X-ray absorption spectroscopy were performed and compared to those obtained for supported samples. A good agreement is found between these samples, although slight oxidation is observed for supported samples. Our experiments demonstrate that NEXAFS characterization of supported samples provides relevant information on soot composition, with limited effects of contamination or ageing under ambient storage conditions. The highly surface sensitive XPS experiments of airborne soot indicate that the oxidation is different at the surface as compared to the bulk probed by NEXAFS. We also report changes in soot's work function obtained at different combustion conditions.
ABSTRACT
Experimental results are reported on the resuspension of particles deposited on polymer samples representative of glove boxes used in the nuclear industry, under thermal degradation. A parametric study was carried out on the effects of heat flux, air flow rate, fuel type and particle size distribution. Small-scale experiments were conducted on 10 cm × 10 cm PolyMethyl MethAcrylate (PMMA) and PolyCarbonate (PC) samples covered with aluminium oxide particles with physical geometric diameters of 0.7 and 3.6 µm. It was observed for both polymer (fuel) samples that heat flux has no effect on the airborne release fraction (ARF), whereas particle size is a significant parameter. In the case of the PMMA sample, ARF values for 0.7 and 3.6 µm diameter particles range from 12.2% (± 6.2%) to 2.1% (± 0.6%), respectively, whereas the respective values for the PC sample range from 3.2% (± 0.8%) to 6.9% (± 3.9%). As the particle diameter increases, a significant decrease in particle release is observed for the PMMA sample, whereas an increase is observed for the PC sample. Furthermore, a peak airborne release rate is observed during the first instants of PMMA exposure to thermal stress. An empirical relationship has been proposed between the duration of this peak release and the external heat flux.
Subject(s)
Polymers/chemistry , Aerosols , Air , Air Pollutants , Air Pollution , Aluminum Oxide/chemistry , Environmental Monitoring/methods , Equipment Design , Hot Temperature , Kinetics , Particle Size , Polycarboxylate Cement/chemistry , Polymethyl Methacrylate/chemistryABSTRACT
The dispersion and chemical transformation of nitrogen oxides have been studied in an urban atmosphere. In this work, nitric oxide is considered as being emitted from the ground. It is mixed with ambient ozone with which it reacts to produce nitrogen dioxide. Numerical integration of the transport equation of each species is carried out in the boundary layer, allowing for the effects of dipersion, macro- and micromixing and chemistry. The results show that the influence of turbulence on chemical reactions is important close to the emission zone. It is also found that the NO/NO2 conversion is low in this region and that it grows with increasing distances.
Subject(s)
Air Pollutants/analysis , Nitric Oxide/chemistry , Nitrogen Dioxide/chemistry , Ozone/chemistry , Atmosphere , Models, Chemical , Nitric Oxide/analysis , Nitrogen Dioxide/analysis , Urban HealthABSTRACT
Tunable diode laser spectroscopy was used to study a 1-D low pressure flame; CO and H(2)O concentration profiles along the flame axis were recorded. These results are compared to previous measurements by mass spectrometry. Three different methods are checked to infer temperature from observed spectra, and the results are compared with measurements by UV absorption spectroscopy on the OH radical.
