Alternate Mid-Point Terrestrial Acidification Characterization Factors Considering Acid Strength (Pages: 1-8)

Anders S. G. Andrae

Huawei Technologies Sweden AB, Skalholtsgatan 9, 16494 Kista, Sweden





Current life cycle mid-point impact assessment practice uses several different mid-point indicators for terrestrial acidification (TA). More than a few methods use a mid-point category indicator of mole proton equivalents. The present research shows that the current mid-point TA indicators – the proton equivalents methods – are not precise as the acid strength is not considered. First the inventory result for one million tonnes solid steel manufacturing output is calculated based on literature. Then the acidifying compounds – which can form acids – are identified. Then the following are proposed: formed acids, the number of protons formed, mole protons per gram acidifying compound and eventually the product of the acidity constant of acids formed and mole protons per gram acidifying compound. After, three different mid-point TA indicators are multiplied with the inventory result: i) the proton equivalents method excluding carbon dioxide, ii) the proton equivalents method including carbon dioxide, and finally iii) the proton equivalents/acidity constant method including carbon dioxide. The results show that the present acid strength based mid-point indicator for TA improves the understanding and can act as a sensitivity check of state-of-the-art mid-point TA results. Carbon dioxide emitted to air is insignificantly contributing to mid-point TA indicator results which are based on proton release and acid strength. Hydrogen chloride emitted to air is one of the main contributors to mid-point TA indicator results which are based on proton release and acid strength.

By using the acid strength as basis for the TA mid-point indicator, a more universal method for comparing the TA potential for gases is achieved. The next step is to clarify how acidity constant based mid-point TA indicators work with normalization of acidification such as distance to target methods and environmental cost accounting methods.

Keywords: Acids, Acidity constant, Hydrogen chloride, Hydrogen fluoride, Life cycle mid-point impact assessment, Mid-point indicator, Soil acidification.