Page 238 - Materials Chemistry, Second Edition
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224                                               R.K. Rosenbaum et al.

            respectively, affecting groundwater via percolation and surface water via runoff and
            leaching processes, and of ammonia emitted to air and deposited on land nearby.
            Oxides of nitrogen may be emitted from incineration processes. Point sources in the
            form of wastewater treatment plants for households (e.g. from polyphosphates in
            detergents) and industry as well as fish farming are important sources of phosphorus
            and nitrates. Apart from man-made emissions, natural sources include leaching and
            runoff of nitrogen and phosphates. The natural addition of nutrients to terrestrial
            areas is believed to consist mainly of atmospheric deposition of oxides of nitrogen
            and ammonia while some natural plant species also possess the ability to fixate
            atmospheric nitrogen.
              Emissions of organic materials can lead to oxygen consumption by bacteria
            degrading this organic matter and thus contributing to oxygen depletion similarly to
            what is observed as a result of the nutrient enrichment of lakes and coastal waters.
            However, this is a primary effect and is strictly speaking not part of the nutrient
            enrichment mechanism. Therefore, emissions of BOD (biological oxygen demand—
            substances which consume oxygen on degradation) or COD (chemical oxygen
            demand) may additionally be characterised by some LCIA methods considering
            oxygen depletion (hypoxia) in water as a common midpoint for both mechanisms.
            Most LCIA methods are currently based on the N/P ratio and typically do not
            classify BOD or COD as contributing to nutrient enrichment and thus eutrophica-
            tion. In large parts of the industrialised world organic matter emissions are only of
            local significance in watercourses and for occasional emissions of untreated effluent.



            10.9.4 Existing Characterisation Models


            The essential evolutions during the last decade were related to improved fate
            modelling, distinguishing P-limited (freshwater) and N-limited (marine) ecosys-
            tems, introduction of a midpoint effect factor in the more recent methods, and
            characterisation  models  becoming  global  and  spatially  more  detailed.
            Midpoint LCIA methods usually propose units in P- and N-equivalents such as kg
                         3

            P-eq or kg PO 4 -eq and kg N-eq or kg NO 3 -eq. For endpoint characterisation
                                                                       2
            most models use Potentially Disappeared Fraction of species (PDF) in [m years],
            except LIME which uses Net Primary Productivity (NPP) loss. For further details
            see Chap. 40 and Hauschild and Huijbregts (2015).


            10.10   Photochemical Ozone Formation


            This impact category appears under a number of different names in the various
            LCIA methods: (tropospheric) ozone formation, photochemical ozone formation or
            creation, photo oxidant formation, photosmog or summer smog. There are minor
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