Microclimate Behaviour Inside Archival Boxes, Books, and Paper Stacks: Buffering, Ventilation, and Pollutant Dynamics

Paper-based heritage objects are commonly stored in archival boxes, books, and paper stacks, creating confined microclimates that may differ from the surrounding environment. While room-level climate control is central to preventive conservation, object-level conditions are shaped by enclosure permeability, hygroscopic buffering, ventilation, and internal emissions. This study investigates temperature, relative humidity, air exchange, and gaseous pollutants inside archival boxes, bound books, and paper stacks under laboratory and real storage conditions. Air exchange rates were determined using CO2 tracer decay, while climates were monitored over periods from hours to one year. Chemical conditions were assessed using passive sampling of air pollutants, oxygen measurements, and dosimetric methods. The results show that boxes, books, and paper stacks behave as semi-permeable rather than sealed systems. Hygroscopic buffering attenuated short-term RH fluctuations, especially within books and paper stacks, while long-term internal conditions followed ambient trends with pronounced time lags. Restricted ventilation limited the ingress of external pollutants but could allow for internally generated gases to accumulate. Experiments using acid-sensitive indicator paper demonstrated the slow penetration of acetic acid into paper stacks. Overall, enclosure performance reflected a balance between buffering capacity, permeability, and chemical reactivity rather than airtightness alone, highlighting the importance of object-level microclimate assessment in preventive conservation.