Measurement locations
To perform the air quality risk assessment, related to the preventive conservation of the objects in the National military museum and the Tismana monastery, air quality measurements were carried out over a 3 months period, from July to October in the year 2012, in locations of interest at the two sites. The measurements were performed in locations with significant objects on exhibit or in store, and which were expected to offer different degrees of protection against external and internally emitted air pollutants.
The measurements in the National military museum were performed in three rooms and inside a protective enclosure in each room: (1a) In the warehouse for foreign uniforms, and (1b) in a melamine fibreboard storage wardrobe in the warehouse; (2a) in the probative objects storage room, and (2b) in a wooden historic storage chest in the storage room; and (3a) in a contemporary history room in the main museum building, and (3b) in a display showcase in this room. Figure 1 shows five of the six locations. A photo of the measurement samplers located outside of the wooden chest in the probative objects storage room was not available.
Cultural heritage objects on exhibit or in store at these locations were woollen blankets, silk dresses, different types of military uniforms made from wool and cotton, swords, medals, military decorations, rifles, a binocular, a military casket, and different types of weapons and metals. The majority of the objects were composite objects consisting of inorganic and organic materials, some with specific coatings. Figure 1 shows some of the objects.
In the Tismana monastery, (Fig. 2) the measurements were performed in an icons and textile storeroom and in a book store room, and just outside of the rooms in a corridor. Figure 2 shows the Tismana monastery, and its iconostasis. Photos of the exact measurement locations were not available.
Measurement methods
A Memori risk evaluation can be based either on measurements with generic dosimeters and/or on parameter measurements of the considered photo-oxidizing (NO2 and O3) and acidic (acetic and formic acid) pollutant gases. Memori was developed with the use of Memori-EWO (PPO) (Early Warning Organic (Polyphenylenoxide)) synthetic polymer dosimeters to measure photo-oxidizing impact, and a specially designed sensitive glass dosimeter (GSD) to measure acidic impact [6]. The translucent dosimeter materials react with the atmosphere and become more opaque due to exposure in the heritage locations.
When dosimeters are used for the air quality measurements, the results are reported as change in light absorption due to the exposures, as “delta absorption values”, for the relevant wavelengths in the ultraviolet (the Memori-EWO) and the infrared (the GSD) region. This change observed in the dosimeter material due to the exposure, corresponds with the air pollution load and thus with the risk. In The EU-Propaint project [9, 23] dose-response equations were developed, which correlated the values for the influencing environmental parameters and the dosimeter responses, based on statistical treatment of a large database of measurements. In the indoor museum locations, the concentrations in air of NO2 and O3 (“traffic pollutants”), and the uv (ultraviolet)-light exposure were found to influence the EWO response at rates depending on the temperature, whereas the concentration in air of acetic acid was found to influence to GSD response.
It was a major task in the EU-Memori project to further correlate the dosimeter response with the expected impact on different cultural heritage materials [6], for the application in risk assessment, as reported below. The dose-response equations from the EU-Propaint project and additional available information about the sensitivity of cultural heritage materials to photo-oxidizing and acidic air pollutants, was the basic information used for this assessment. As a strong statistical correlation was found between the GSD response and the measured concentration of acetic acid indoor in museums [23], the GSD absorption values reported by default in Memori evaluations, can also be approximated by calculation from measured concentration values of acetic acid. The applied correlation equation is [23]:
$${\text{GSD}}\left( {\text{app}} \right) \, = \, 0. 2\cdot \,\left[ {{\text{HAc}} + {\text{FA}}} \right]/ 1000$$
(1)
where GSD (app) = Approximated Memori-GSD value (absorption units). [HAc+FA] = the sum of measured concentrations of acetic and formic acids (µg/m3). This equation was used for the reporting in this work of the acidic effects as GSD values, or the concentration values of acetic plus formic acid are reported. Similarly, a dose-response equation for the influence of NO2 and O3 on the EWO dosimeter has been developed [23]. Thus, the photo-oxidizing impact can optionally be reported as EWO values calculated from measured concentration values of NO2 and O3, or as the concentration values of NO2 and O3. Some further considerations related to the application of either dosimeter or parameter measurements, and their conversion by Eq. (1) are discussed in the “Discussion” chapter.
For the measurement in the National military museum and the Tismana monastery, Memori-EWO (PPO) dosimeters were used to measure the photo-oxidizing effect and passive pollution badge samplers [35] for acetic and formic acids were used to measure the acidic effect (Fig. 1).
The Memori-EWO dosimeter is a small piece of quartz glass, of dimension 1.5 ∙ 0.7 ∙ 0.1 cm. A thin synthetic organic polymer film is spin coated on the glass surface. The glass piece is mounted in an aluminium holder (Fig. 3). The dosimeter should be exposed for 3 months in the indoor atmosphere. The results measurements can be performed in a purpose built small portable instrument [6] or with a laboratory uv/visible spectrophotometer. The detection limit has been found to be equivalent to approximately 4 μg/m3 NO2 + O3 [32].
The results evaluation of the dosimeters is calibrated for a typical museum indoor temperature of 20 °C and relative humidity (RH) of 50%. The dosimeter is normally mounted in upright position. The holder then gives some sheltering against dust deposition. In indoor cultural heritage locations, the effect of dust during the recommended 3 months exposure has been found to be low. The explanatory power of the dose-response equation, which does not include dust impact, was about R2 = 0.7 [23]. If the presence of dust is high or the dosimeter is exposed in horizontal position, lying down, dust can however accumulate on the dosimeter and affect the response.
In an indoor situation with a temperature (T) significantly different from 20 °C or RH significantly different from 50%, or with much dust, the dosimeter will respond to these factors and measure a higher risk value, and/or the object sensitivity may be different from that applied for the Memori traffic light evaluation (see below). The materials damage risk assessment was not calibrated towards these impacts. Thus, the occurrence and influence of such variations in environmental factors (T, RH and dust) on the dosimeter response, and on the risk evaluation, must be evaluated separately.
The acetic and formic acids were measured with passive pollution badge samplers. The gases diffuse though the net into the badge sampler (Fig. 3) and are absorbed from the air on an alkaline filter located at its base. Subsequent laboratory analysis gave the values for the concentrations of the acids in air. The detection limit has been found to be 0.5 µg/m3 [23].
The Memori assessment includes a “traffic light evaluation” of the measurement results, with indication of risk for degradation of 22 cultural heritage materials. The risk is described as the probable time before observable damage occurs and conservation is needed, with: “red” = within 3 years, “yellow” = from 3 to 30 years, and “green” = more than 30 years. General risk levels for cultural heritage, given as response values from measurements with the EWO and GSD, which are unrelated to the MEMORI “traffic light evaluation”, exist from pre MEMORI work. For the EWO these are described as different typical European indoor museum environments [23, 28]. For the GSD they are based on overall evaluation of results from dosimeter development and application [36]. These GSD levels can be approximated as acetic plus formic acid concentrations by Eq. (1).