The process of making ultrapure polysilicon by the Siemens process results in an unwanted secondary reaction forming oligomers and polymers containing a silicon backbone. These byproducts accumulate ...in the exhaust piping and downstream equipment used in the polysilicon manufacturing process. They become extremely dangerous when exposed to moisture, including moisture contained in ambient air, becoming intensely flammable and shock-sensitive. This flammability is retained even in an inert atmosphere. Tragically, these byproducts were involved in the deadly explosion at the Yokkaichi Plant of Mitsubishi Materials Corporation in Japan. The work presented here characterizes these byproducts in their various states and provides insights into best practices for treating piping and equipment fouled by these materials. An example of the calculation of the energy released by ignition of these materials in an industrial piece of equipment is included.
Ground‐based and airborne volatile organic compound (VOC) measurements in Los Angeles, California, and Paris, France, during the Research at the Nexus of Air Quality and Climate Change (CalNex) and ...Megacities: Emissions, Urban, Regional and Global Atmospheric Pollution and Climate Effects, and Integrated Tools for Assessment and Mitigation (MEGAPOLI) campaigns, respectively, are used to examine the spatial variability of the composition of anthropogenic VOC urban emissions and to evaluate regional emission inventories. Two independent methods that take into account the effect of chemistry were used to determine the emission ratios of anthropogenic VOCs (including anthropogenic isoprene and oxygenated VOCs) over carbon monoxide (CO) and acetylene. Emission ratios from both methods agree within ±20%, showing the reliability of our approach. Emission ratios for alkenes, alkanes, and benzene are fairly similar between Los Angeles and Paris, whereas the emission ratios for C7–C9 aromatics in Paris are higher than in Los Angeles and other French and European Union urban areas by a factor of 2–3. The results suggest that the emissions of gasoline‐powered vehicles still dominate the hydrocarbon distribution in northern mid‐latitude urban areas, which disagrees with emission inventories. However, regional characteristics like the gasoline composition could affect the composition of hydrocarbon emissions. The observed emission ratios show large discrepancies by a factor of 2–4 (alkanes and oxygenated VOC) with the ones derived from four reference emission databases. A bias in CO emissions was also evident for both megacities. Nevertheless, the difference between measurements and inventory in terms of the overall OH reactivity is, in general, lower than 40%, and the potential to form secondary organic aerosols (SOA) agrees within 30% when considering volatile organic emissions as the main SOA precursors.
Key PointsUrban VOC emission ratios are compared in two modern megacitiesGasoline‐powered vehicles emissions are still the dominant VOC urban sourceObservations/inventory differences are <40% in terms of OH‐reactvity and SOAP
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