Acute episodes of black carbon and aerosol contamination in a museum environment: Results of integrated real-time and off-line measurements
Graphical abstract
Introduction
In the last decade indoor pollution has become a hot topic in aerosol science with an increasing number of papers dealing with the monitoring, the characterization and the evaluation of human exposure and health effects in the living and working environments (Morawska and Salthammer, 2003, Morawska et al., 2013). In museum environments the question of indoor contamination and pollution is even more important for the implications on both human health and artwork conservation.
Typically, museum environmental monitoring and control are based on conventional measurements of thermo-hygrometric values and on long-time averaged measurements of atmospheric pollutants' concentration (Grøntoft et al., 2010). Thermo-hygrometric parameters are used to provide a first indication of the museum air quality and of the impact of the outdoor environment on the indoor microclimate. For this reason they are usually recorded in museums to routinely check the efficiency of the air control systems (Camuffo et al., 2001). Previous surveys report measurements of thermo-hygrometric values integrated with the characterization of gaseous pollutants, microbiological contaminants and, with a less extent, particulate matter (Camuffo et al., 2001, Daher et al., 2011, Gysels et al., 2004, Krupinska et al., 2012, Schieweck et al., 2005). Particulate matter (PM) air pollution is an emerging concern for its variable extent of risk for cultural heritage. Coarse PM deposition has long been studied for soiling of surfaces exposed outdoor (De Bock et al., 1996, Nazaroff and Cass, 1991), while fine PM is mostly charged for chemical damage (Grau-Bové and Strlič, 2013). Black carbon (BC) and ozone are also very important. Black carbon, the light-absorbing component of aerosol, is an impure form of near-elemental carbon with a graphite-like structure mostly originated by anthropogenic combustion processes and internal combustion engines (Bond et al., 2013). Black carbon is typically associated with the fine (<1 μm) particle fraction, with distinct agglomeration morphology that can be readily recognized under the scanning (SEM) or transmission electron microscope. In the past, the attention on black carbon in cultural heritage was mostly addressed to the effects of soiling and darkening of outdoor surfaces (Ghedini et al., 2006); much less is known about indoor air pollution and surface reactions prompted by deposited BC particles (Grau-Bové and Strlič, 2013). Ozone is a strong oxidant and its reactivity has a direct impact on the degradation of organic artists’ materials (Grosjean et al., 1994, Bonaduce et al., 2013). Ozone is originated outdoor and in controlled indoor environments, like museums, O3 concentration generally exhibits dependence from outdoor–indoor exchanges and can be used to estimate the extent of outdoor atmospheric pollutants infiltration (Cavicchioli et al., 2013).
Indoor pollution inside museums is mostly due to the permeation and diffusion of pollutants inside the building (Lopez-Aparicio et al., 2011). Environmental monitoring activity inside museums is generally based on long-time averaged measurements from fixed instrumentations (Camuffo et al., 1999, Daher et al., 2011, Krupinska et al., 2012). This approach tends to underestimate the processes especially in the case of acute contamination episodes. The latters, for their great intensity, both in mass and in number, and sharp localization in space and time, require high time resolution and portable measurement devices (He et al., 2004).
In this work we report on the detailed characterization of the phenomenology producing a strong contamination condition in a relevant museum painting collection in Umbria (Central Italy). The study was organized in three consecutive seasonal monitoring campaigns based on real-time measurements by portable instrumentations integrated with off-line chemical analysis of PM and gaseous pollutants. The results revealed intense air pollution episodes that would have remained totally undetected without this study, with consequences on artwork conservation and human health.
Section snippets
The sampling site
The “Galleria Nazionale dell’Umbria” extends over the second and the third floor of a XIIIth century building located in the historical centre (traffic-restricted area) of the medium sized town of Perugia (about 160.000 inhabitants) in central Italy. This historic part of the town is frequented by tourists and is served by many restaurants and pizzerias with wood-fired ovens. The museum has a medium visitor flow with the exception of occasional increases in coincidence with special events
Environmental parameters and pollution events
The full set of measurements of microclimatic, aerosol and BC temporal profiles obtained in the museum (R21 and/or R11) during the July and November 2012 campaigns, along with the corresponding outdoor time series, are reported in Fig. 1. For seek of simplicity in the plots the particles were grouped into a fine (0.28 < DP < 1.1 μm) and a coarse (1.1 < DP < 10 μm) mode. These size ranges were chosen following the instrumental size channels, and are in agreement with typical urban aerosol size
Conclusions
The analysis of a set of severe air pollution events occurred in a city museum allowed us to evaluate the impact of outdoor sources of pollutants in the indoor system, and the potential of the system itself to bear the fortuitous pollutant events. In particular, we used an analytical approach based on integrated real-time measurements by portable instrumentations with off-line chemical analysis of PM and gaseous pollutants, which allowed us to study intrusion phenomena of black carbon aerosol
Acknowledgements
This work was carried out within the research activities of the project ”Sviluppo delle attività di ricerca, valutazione e tutela conservative” of the Regione Umbria, “Progetto 1 del Primo atto integrativo all'APQ: Tutela e prevenzione dei beni culturali”. The Soprintendente per i Beni Storici, Artistici ed Etnoantropologici dell'Umbria is gratefully acknowledged for making this study possible. We thank the Regional Environmental Agency (ARPA Umbria) for providing data on outdoor levels of
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