Background: Particulate matter, microorganisms in air and environmental conditions present a potential risk to museum collections. There are also limited studies of simultaneous measurements of airborne particles and microorganisms inside museums and the effects of seasonal variations. Therefore, extensive indoor/outdoor measurements of particulate matter mass/number concentrations and viable, cultivable microbial load were performed in two museums and a library in Greece for a period of 2 years at selected time intervals. The culture heritage collections are located at coastal (Historical Museum of Crete in Heraklion), urban (Criminology Museum of the University of Athens) and mountainous (Neophytos Doukas Library in Zagori) environments and their collections consist mainly of organic materials. Measurements of inhalable particulate mass (PM 10 , PM 2.5 , PM 1) and viable, cultivable airborne microorganism concentrations (heterotrophic bacteria, cellulose metabolizing bacteria, acid producing bacteria and mesophilic fungi) in air were performed. Results and conclusions: The indoor PM 10 and microbial concentrations were higher than the outdoor levels showing the influence of the indoor sources, such as the presence of people and indoor activities, as well as, anthropogenic outdoor sources, and natural emissions. Elevated PM 1 particle number concentrations were also encountered in the Historical Museum of Crete in Heraklion and the Criminology Museum of the University of Athens due to the high anthropogenic emissions of the urban areas. The lowest concentrations of viable, cultivable airborne microorganisms were measured in the Historical Museum of Crete at the coastal site, which encounters also well controlled microclimatic conditions. In comparison to the other two naturally ventilated sites, the highest concentrations of viable, cultivable airborne fungi were measured in the Neophytos Doukas Library at the mountainous site, whereas the highest concentrations of viable, cultivable airborne heterotrophic bacteria were measured in the Criminology Museum of the University of Athens at an urban site, where mummified tissues and dry specimens are exhibited. The closed showcases of the two museums and the library could only protect the exhibits from viable, cultivable airborne fungi, but not from specific categories of bacteria. Acid producing bacteria in the Historical Museum of Crete, cellulose metabolizing bacteria in the Neophytos Doukas Library, and opportunistic pathogenic heterotrophic bacteria in the Criminology Museum of the University of Athens showed to be enriched inside the closed showcases.
The most common way followed for the determination of degradation mechanisms of organic materials is the application of physiochemical methods after accelerated aging. In recent years, there has been a remarkable research activity towards the development of alternative decay determination methods in organic materials based on statistics. We first present a survey of European research projects in this area together with summaries of their results. Second, we describe the ongoing project entitled 'Investigation of the environmental factor effects on organic materials constituting the natural and cultural heritage' in which statistics plays a crucial role. In particular, we present a statistical methodology that is based on a designed experimental and inferential protocol which will guide the research throughout the project. By providing basic statistical and design concepts, we present guidelines to design statistical protocols that are necessary for scientifically sound quantitative experiments.
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