Review of organic gaseous pollutant concentrations in indoor conservation spaces.

Gaseous organic and inorganic pollutants negatively affect cultural heritage materials, accelerating their deterioration. Although assessing their concentrations is crucial, these pollutants are rarely measured in indoor spaces housing artefacts, known as conservation spaces. This review examines 39 selected studies (1990-2023) encompassing 58 case studies in which gaseous organic pollutants were monitored in such spaces. Acetic and formic acids emerged as primary contributors to the deterioration of collections. The sites monitored, predominantly in Europe, were categorised into three scales: building scale (37 museums, 12 archives, 4 palaces, 7 worship places), room scale (exhibition rooms in 45 sites, storage rooms in 16 sites) and enclosure scale (conservation or display cases, microclimate frames, cabinets in 18 sites). Passive samplers were used more frequently than active ones, with continuous monitoring equipment being limited to total volatile organic compounds (VOCs). Across the sites, the median concentration and 95th percentile values for various pollutants were as follows: acetic acid at 68 ppb and 624 ppb; acetaldehyde at 8 ppb and 77 ppb; formic acid at 30 ppb and 227 ppb; formaldehyde at 27 ppb and 265 ppb; and total VOCs at 66 ppb and 1655 ppb. No clear correlation was found between pollutant concentrations and the use of old versus new enclosures, as both types can contribute to indoor pollution. Further research is needed to develop continuous monitoring technologies, improve active and passive sampling methods and establish standardised concentration thresholds to better preserve cultural heritage.