Influence of Incense-Derived Soot on the Photooxidative Aging Behavior of Palm-Leaf Manuscript Substrates

Palm-leaf manuscripts are an important category of organic cultural heritage and frequently exhibit soot deposition associated with long-term incense burning in temples and religious archives. However, the influence of soot contamination on the deterioration of lignocellulosic manuscripts remains insufficiently understood due to the slow progression of natural aging processes. In this study, accelerated UV aging was employed as a laboratory model to investigate the effects of Tibetan incense-derived soot on the degradation behavior of palm-leaf manuscript substrates. Soot-contaminated and pristine samples were characterized using spectroscopic, microscopic, physicochemical, and mechanical analyses. Under the accelerated UV-aging conditions employed, soot-contaminated samples exhibited more pronounced changes than pristine samples, including alterations in lignocellulosic functional groups, increased surface oxidation and oxidized carbon species, acidification, increased hydrophilicity, microstructural changes, and mechanical weakening. Although the accelerated UV-aging protocol does not reproduce the spectral characteristics of museum or temple lighting, it provides a controlled framework for examining soot-associated photooxidative processes under enhanced irradiation conditions. The photochemical evolution of incense-derived soot, together with the altered aging behavior of soot-contaminated palm-leaf substrates, is consistent with a soot-assisted photooxidative degradation pathway at the material interface. These findings provide mechanistic insight into pollutant-assisted degradation of palm-leaf manuscript substrates and highlight the importance of controlling soot accumulation in preventive conservation.