Currently available data suggest that most of the energy and material consumption related to the production of an integrated circuit is due to the wafer fabrication process. The complexity of wafer manufacturing, requiring hundreds of steps that vary from product to product and from facility to facility and which change every few years, has discouraged the development of material, energy, and emission inventory modules for the purpose of insertion into life cycle assessments. To address this difficulty, a flexible, process-based system for estimating material requirements, energy requirements, and emissions in wafer fabrication has been developed. The method accounts for mass and energy use atthe unit operation level. Parametric unit operation modules have been developed that can be used to predict changes in inventory as the result of changes in product design, equipment selection, or process flow. A case study of the application of the modules is given for energy consumption, but a similar methodology can be used for materials, individually or aggregated.
The size distributions of aliphatic carbon, carbonyl, and organonitrate functional groups in ambient aerosol were determined at three sites during an air quality field study conducted during August and September 2000, in Houston, Texas. Samples were collected using a Hering low-pressure impactor and were analyzed, in transmission mode, using Fourier transform infrared spectroscopy. The submicron fractions of the samples exhibited patterns seen in other urban areas. Carbonyl and organonitrate group absorbances showed maxima in the 0.05-0.26 µm and the 0.5-1.0 µm size fractions, and based on these absorbances appear to be primarily due to secondary organic aerosol. Aliphatic carbon absorbances in the submicron aerosol showed maxima in the 0.076-0.12 µm size fraction and the 0.5-1.0 µm size fraction. Weak correlation between ozone concentrations and aliphatic carbon absorbances suggest that some of these aliphatic functional groups are due to primary emissions. For the supermicron aerosol, all three functional groups exhibit maxima in the 2-4 µm size fraction. These coarse size fractions observed in Houston were not observed in similar samples collected in Los Angeles. In addition, some of the aerosol samples collected in Houston display organic functional group concentrations, especially for organonitrates, that are significantly higher than the median concentrations. Samples with very high organic functional group concentrations had molar ratios of carbonyl and organonitrate functional groups that are suggestive of either primary emissions or secondary organic aerosol formation processes that are not commonly observed in other urban areas.
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