Việc lựa chọn loại tác động và các chỉ số thể loại và các mô hình có thể ổ đĩa tập hợp các dữ liệu kiểm kê. Ví dụ, người ta có thể chọn để đánh giá khoáng sản chỉ có dự trữ được dự đoán bị cạn kiệt trong vòng 100 năm, hoặc một số khung thời gian hợp lý khác. | linkage between the inventory results and effects in the environment. Others . habitat modification are known to play a critical role in environmental impacts of products . agricultural products but are difficult to model quantitatively. Life cycle impact assessment practice is moving more and more toward using sophisticated fate and transport models to evaluate indicators of environmental impacts. The choice of impact categories and category indicators and models can drive the collection of inventory data. For example one might choose to evaluate only minerals whose reserves are predicted to be depleted within 100 years or some other reasonable time frame. This would eliminate the need to gather data on such materials as bauxite clay or iron ore and would decrease the cost of inventory collection and management. To date no standardized listing of impact categories to be used in LCA has been established but several categories are employed in common practice as shown in Table 5. The Classification Step. Inventory data need to be classified into the relevant impact categories for modeling. Some emissions have influence on more than one environmental mechanism and must be classified into more than one category. The classic example oif this is oxides of nitrogen or NOx which acts as catalyst in the formation of ground-level ozone smog but also is a source of acid precipitation. These substances must be characterized into both categories. One form of NOx nitrous oxide N2O is also active as a greenhouse gas. The classification rules for any LCIA must be clearly reported so that readers of a study understand what exactly was done to the inventory data. The Characterization Step The goal of life cycle impact assessment is to convert collected inventory inputs and outputs into indicators for each category aggregates can be system-wide by life cycle stage or by unit operation . Table 5 Typical Impact Categories 1. Stratospheric ozone depletion 2. Global warming 3. .
