Interpreting Pavement LCA Results
As output, the Pavement LCA produces a detailed life cycle inventory for an entered design. It also generates a set of summary impact indicators in graphical and tabular form based on US EPA’s Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (the US Environmental Protection Agency’s TRACI - Tool for the Reduction and Assessment of Chemical and other environmental Impacts) life cycle impact indicator methodology (2007 version). The software supports characterization measures based on mid-point impact estimation methods, including the following:
- total primary energy
- non-renewable primary energy
- fossil fuel consumption
- acidification potential
- aquatic eutrophication potential
- global warming potential
- human health criteria air-mobile
- ozone depletion
- smog
- solid waste
This section briefly describes the environmental measures used to summarize the environmental assessment results provided by the Pavement LCA.
Total Primary Energy
Total Primary Energy Consumption is reported in mega-joules (MJ) at the bottom of the Energy Consumption absolute value table as well as the Detailed and Condensed Summary Mesure tables. Embodied primary energy includes all energy, direct and indirect, used to transform or transport raw materials into products and buildings, including inherent energy contained in raw or feedstock materials that are also used as common energy sources. (For example, natural gas used as a raw material in the production of various plastic (polymer) resins.) In addition, the Impact Estimator captures the indirect energy use associated with processing, transporting, converting and delivering fuel and energy. If the user inputs Operating Energy Consumption, it will also be included in Total Primary Energy.
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Non-Renewable Primary Energy
Non-Renewable Energy is a subtotal of Total Primary Energy, by energy type, that includes all fossil fuel energies and nuclear energy.
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Fossil Fuel Consumption
Fossil Fuel Consumption is reported in mega-joules (MJ). Embodied Fossil Fuel Consumption includes all energy, direct and indirect, used to transform or transport raw materials into products and roadways, including inherent energy contained in raw or feedstock materials that are also used as common energy sources. (For example, natural gas used as a raw material in the production of various plastic (polymer) resins.) In addition, the Pavement LCA captures the indirect energy use associated with processing, transporting, converting and delivering fuel and energy plus the operating energy.
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Acidification Potential (AP)
Acidification is a more regional rather than global impact effecting human health when high concentrations of NOx and SO2 are attained. The AP of an air or water emission is calculated on the basis of its H+ equivalence effect on a mass basis.
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Aquatic Eutrophication Potential
Eutrophication is the fertilization of surface waters by nutrients that were previously scarce. When a previously scarce or limiting nutrient is added to a water body it leads to the proliferation of aquatic photosynthetic plant life. This may lead to a chain of further consequences ranging from foul odours to the death of fish. The calculated result is expressed on an equivalent mass of nitrogen (N) basis.
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Global Warming Potential (GWP)
Global warming potential is a reference measure. The methodology and science behind the GWP calculation can be considered one of the most accepted LCIA categories. GWP will be expressed on an equivalency basis relative to CO2 – in kg or tonnes CO2 equivalent.
Carbon dioxide is the common reference standard for global warming or greenhouse gas effects. All other greenhouse gases are referred to as having a "CO2 equivalence effect" which is simply a multiple of the greenhouse potential (heat trapping capability) of carbon dioxide. This effect has a time horizon due to the atmospheric reactivity or stability of the various contributing gases over time.
As yet, no consensus has been reached among policy makers about the most appropriate time horizon for greenhouse gas calculations. The International Panel on Climate Change100-year time horizon figures have been used here as a basis for the equivalence index:
CO2 Equivalent kg = CO2 kg + (CH4 kg x 23) + (N2O kg x 300)
While greenhouse gas emissions are largely a function of energy combustion, some products also emit greenhouse gases during the processing of raw materials. Process emissions often go unaccounted for due to the complexity associated with modelling manufacturing process stages. One example where process CO2 emissions are significant is in the production of cement (calcination of limestone). Because the Pavement LCA uses data developed by a detailed life cycle modelling approach, all relevant process emissions of greenhouse gases are included in the resultant global warming potential index.
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Human Health (HH) Criteria Air-Mobile
Particulate matter of various sizes (PM10 and PM2.5) have a considerable impact on human health. The EPA has identified "particulates" (from diesel fuel combustion) as the number one cause of human health deterioration due to its impact on the human respiratory system – asthma, bronchitis, acute pulmonary disease, etc. It should be mentioned that particulates are an important environmental output of plywood product production and need to be traced and addressed. The Institute used TRACI’s "Human Health Particulates from Mobile Sources" characterization factor, on an equivalent PM2.5 basis, in our final set of impact indicators.
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Ozone Depletion Potential (ODP)
Stratospheric ozone depletion potential accounts for impacts related to the reduction of the protective ozone layer within the stratosphere caused by emissions of ozone depleting substances (CFCs, HFCs, and halons). The ozone depletion potential of each of the contributing substances is characterized relative to CFC-11, with the final impact indicator indicating mass (e.g., kg) of equivalent CFC-11.
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Photochemical Ozone Formation Potential (Smog)
Under certain climatic conditions, air emissions from industry and transportation can be trapped at ground level where, in the presence of sunlight, they produce photochemical smog, a symptom of photochemical ozone creation potential (POCP). While ozone is not emitted directly, it is a product of interactions of volatile organic compounds (VOCs) and nitrogen oxides (NOx). The “smog” indicator is expressed on a mass of equivalent NOx basis.
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Solid Waste
Solid waste is reported on a mass basis in kilograms and is generally self-explanatory. No attempt has been made to further characterize emissions to land as either hazardous or non-hazardous.
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Note: Solid Waste will be retired in version 4.0 or version 4.1.