Carbon Balance Analysis of Artificial Soil Materials from the Perspective of Life Cycle Assessment

  This study focuses on artificial soil materials, which constitute the largest component of green roofs, and aims to compare and analyze the carbon balance of each material from a life cycle assessment perspective. The analyzed artificial soil materials comprise perlite, bottom ash, zeolite, vermiculite, peat moss, cocopeat, humus, carbonized rice hull, biochar, and bark.   Initially, the carbon emissions of these 11 artificial soil materials were examined, spanning raw material collection, manufacturing, processing, packaging, and transportation. The data utilized comes from both domestic and foreign Life Cycle Inventory (LCI) databases. For materials not present in these databases, estimates were derived based on the values of materials sharing similar production and manufacturing processes.   Subsequently, the study calculated the carbon balance during the use phase by measuring carbon emissions from the soil to the atmosphere upon application to rooftop planters. Monitoring took place on the roof of the Korea Institute of Civil Engineering and Building Technology (KICT) from September 2022 to September 2023. Measurements were conducted at regular intervals in three replicates of 11 soil material experiments using an EGM-5 portable CO2 gas analyzer. Additionally, Total Carbon (TC) analysis was conducted to assess carbon storage in the soil.   Perlite and vermiculite, with energy-intensive manufacturing processes but minimal organic matter in the soil, emitted low carbon. Conversely, humus and bark, requiring less energy in manufacturing but containing high organic matter, emitted more carbon into the atmosphere. For peat moss and cocopeat, although manufacturing processes generated little carbon, significant emissions occurred during transportation due to their importation, coupled with notable carbon emissions from organic matter in the soil.   This study emphasizes the significance of careful material selection when formulating artificial soil for rooftop greening. Even if soil carbon emissions are low, materials with substantial carbon generation during production may undermine carbon neutrality from a life cycle assessment perspective.