IAQ 2003, Presentation 3:
Indoor Air Quality in a Photo Archive Without Climate Control.
The National Museum of Denmark has several photographic collections. The collections are scattered throughout the museum, each located within the owner department. The collections contain photographs of museum objects, excavations, expeditions etc., relevant to each department. The collection size, material, condition, and archive climate differ between the archives. This case story reports the findings of an investigation of the physical archive conditions of the negative collection of the Danish Middle Ages and Renaissance Department. In this archive all surfaces inside the room were covered with dust. The aim of the investigation was to investigate the air quality and dust load, to what degree the archive material was exposed and, finally, to find solutions to reduce or eliminate the pollution.
The collection and the archive
Fig. 1: The archive room
This collection contains approximately 60,000 photographic negatives and positives, mostly glass plates, but also cellulose acetate and polyester sheet negatives. Until 2000 the archive also contained cellulose nitrate negatives, however these have been removed and stored separately due to the flammable properties of cellulose nitrate.
The photographs are housed in paper and glassine envelopes, stored in drawers in metal cabinets. The archive is located in the Museum's attic. The room is located in a wing with the busy street Stormgade just outside, which is passed by ca. 18,000 vehicles each working day. The room itself is not designed especially for archive purposes. It has no air conditioning or mechanical ventilation, only a draughty window.
Recommendations from standards on storage conditions
In addition, a general recommendation of the ISO standards is to "Avoid abrasive particulates, and harmful air pollutants".
Other standards for paper based archival material have more specific air pollution limitations:
Methods and results
Fig. 2: Climate in archive: Temperature (red) ; Relative Humidity (blue)
The temperature varied during 2003 from 11 to 28°C, with a mean value of 20°C. The temperature was within our target value of 18°C +/- 5° for 82% of the year. The relative humidity varied between 27% and 51%, with a mean value of 39%RH. With a target value of 30-40%RH, according to ISO 18918:2000 (glass plates), the climate was within these limits for only 44% of the year 2003 (fig 3).
In other words, the yearly trend is such that the temperature will vary from an average of 15-16° during winter, up to 25-26° in summer. The RH will top at ca. 50% in summer, and fall to 30% during winter and spring. That corresponds to a Time Weighted Preservation Index (TWPI) of approx. 50 years . The preservation index will be highest in winter where the indoor climate is cool and dry, and much lower in summer where the climate is warm and humid (fig. 4).
The concentration of O3, NO2 and NOx was now measured in the archive for four months in 2003. The measurements were carried out by passive sampling, by four successive sampling periods of about one month each. The sampler type used was Analyst, as described by De Santis et al .
The result was surprising: while the I/O ratio for O3 was quite low, as expected, for three out of the four months the I/O rates for NO2 and NOx were 1 or higher, indicating that a source of nitrogen oxides was present in the archive, which drowned the contribution from the outdoor environment (fig. 5).
The area fraction covered with dust in the archive was high:
These layers are "old dust", maybe due to decades of deposition. The dust that fell on a new, clean surface (petri dish) covered 1.03% on top of a cabinet, and just 0.03% inside a drawer, after 74 days.
However, deposited particles in drawers are smaller and much more numerous, than out in the room (Fig. 6). Analysing the "old dust" layer we found, that on 1 mm3 on top of a cabinet, the average number of particles were 2902, with an average size of 130 µm2. In a drawer, the average number of particles was 9807, with an average size of just 11 µm2.
Fig. 6: Left: Dust layer from top of cabinet. Right: Dust layer from inside drawer
Investigating the dust samples by light microscopy, we identified textile fibres, skin flakes, hair, mineral wool fibres, sand grains and pollen.
Fig. 7: SEM images. Left: Dust from top of cabinet. Right: Paper fibre (wood) from inside drawer
Dust samples taken by sweeping a clean filter paper over a surface were analysed for their organic content. Analysis was carried out by GC/MS, after the samples were extracted in methylene chloride by soxhlet method.
If a dehumidifier is to run properly, the room should be made more airtight. The window must therefore be replaced with a more tight construction. This will also reduce dust from entering from outdoors.
This refers especially to the silicates, soot, pollen and NaCl found in the dust on the cabinets and in the window recess.
We recommend that the archive must undergo a major cleaning, and that a regular cleaning routine is introduced thereafter. In order to remove the dirt layer which has accumulated on the old envelopes, those should be renewed. The new housing materials should fulfil the appropriate ISO standard  .
If the high nitrogen oxide levels are indeed due to a NOx reservoir in the dust layer, this is another argument for a total cleanup of the archive room.
However, the high I/O ratio of nitrogen oxides must be investigated. Except for the month of May, the measurements indicate that a major source of nitrogen oxides is present within the archive. It would be natural to suspect that cellulose nitrate sheets still are present within the archive. However, this is very unlikely, as all of the archive drawers were searched especially for nitrate a few years ago. Another natural source of nitrogen oxides is combustion, again in this case that is very unlikely. Instead we suggest, that what we see is a sink effect of the likely high emission of nitrogen oxides when nitrate negatives were present, now held by surface reactions in the large amount of fluffy dust on top of the cabinets. Why the indoor NO2 and NOx concentration suddenly drops during the month of May we cannot explain - maybe the window has been opened by an archivist, thus increasing the air exchange rate.
Notes and References
 TWPI is a way to express the "preservation quality" of a archive or store room. It describes the chemical decay rate for organic materials, based on the combined effect of temperature and relative humidity of the surrounding environment. The unit - years - correspond to the time it will take for a noticeably degree of chemical deterioration to occur. The concept has evolved from measurements of acid release by cellulose acetate during accelerated aging tests. In short: when evaluating storage location from climate measurements, the higher TWPI the better.
 Schmidt, Kemp, Bronée, Fenger (2002): "Airborne dust in a museum environment". IAP Copenhagen 2001, 4th meeting of the Indoor Air Pollution Working Group, The National Museum of Denmark, November 8th-9th 2001. http://iaq.dk/iap/iap2001/2001_20.htm
 Ryhl-Svendsen, Padfield, Smith, De Santi (2003): "The indoor climate in historic buildings without mechanical ventilation systems". Healthy Buildings 2003. Preprints: Singapore December 7-11, 2003.
 De Santis, Bellagotti, Vichi, Allegrini (2003): "Diffusive Sampling as a Tool for the Evaluation of Indoor Air Quality in the MIMIC Project". Indoor Air Quality in Museums and Historic Properties (IAQ 2003), 5th meeting of the Indoor Air Pollution Working Group, Norwich, April 28th-29th 2003. http://iaq.dk/iap/iaq2003/2003_10.htm
 Data from the Agency of Environmental Protection in Copenhagen: air quality station at corner of HC Andersens Boulevard and Stormgade: http://www.miljoe.kk.dk/13CF0215-B825-4AB7-BB93-D632AC1C66F0.W5Doc
 BVDA Environmental Gel Lifters. Art.no. B-17000. Company P-B Miljø, Enebaervej 7, DK-8850 Bjerringbro, Denmark
 ImageJ software: http://rsb.info.nih.gov/ij/
 ISO 18902:2001 Imaging materials - Processed photographic films, plates, and papers - Filing enclosures and storage containers. International Organization for Standardization, Geneve.
Author to whom correspondence may be addressed:
Karen Brynjolf Pedersen
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© November 2003