Chemically and size-resolved particulate matter dry deposition on stone and surrogate surfaces inside and outside the low emission zone of Milan: application of a newly developed “Deposition Box”

Abstract

The collection of atmospheric particles on not-filtering substrates via dry deposition, and the subsequent study of the particle-induced material decay, is trivial due to the high number of variables simultaneously acting on the investigated surface. This work reports seasonally resolved data of chemical composition and size distribution of particulate matter deposed on stone and surrogate surfaces obtained using a new method, especially developed at this purpose. A "Deposition Box" was designed allowing the particulate matter dry deposition to occur selectively removing, at the same time, variables that can mask the effect of airborne particles on material decay. A pitched roof avoided rainfall and wind variability; a standardised gentle air exchange rate ensured a continuous "sampling" of ambient air leaving unchanged the sampled particle size distribution and, at the same time, leaving quite calm condition inside the box, allowing the deposition to occur. Thus, the "Deposition Box" represents an affordable tool that can be used complementary to traditional exposure systems. With this system, several exposure campaigns, involving investigated stone materials (ISMs) (Carrara Marble, Botticino limestone, Noto calcarenite and Granite) and surrogate (Quartz, PTFE, and Aluminium) substrates, have been performed in two different sites placed in Milan (Italy) inside and outside the low emission zone. Deposition rates (30-90 μg cm month) showed significant differences between sites and seasons, becoming less evident considering long-period exposures due to a positive feedback on the deposition induced by the deposited particles. Similarly, different stone substrates influenced the deposition rates too. The collected deposits have been observed with optical and scanning electron microscopes and analysed by ion chromatography. Ion deposition rates were similar in the two sites during winter, whereas it was greater outside the low emission zone during summer and considering the long-period exposure. The dimensional distribution of the collected deposits showed a significant presence of fine particles in agreement with deposition rate of the ionic fraction. The obtained results allowed to point out the role of the fine particles fraction and the importance of making seasonal studies.

Study and Characterization of Environmental Deposition on Marble and Surrogate Substrates at a Monumental Heritage Site

“…In terms of PM deposition rates (DR, calculated as µg/cm 2 month −1 ), the values obtained in the present study for quartz filters are in agreement with those obtained for marble surfaces in a study recently carried out in Milan [17]: on average 68.9 µg/cm 2 month −1 for site 1 and 54.1 µg/cm 2 month −1 for site 2 against values in the range of about 50-70 µg/cm 2 month −1 measured in Milan for Carrara marble and quartz filters as surrogate surfaces [17] during the same period of the first exposure test (2014-2015).…”

“…Such process was identified as an important decay mechanism of the façade in the past [33] and can be favored by the specific exposure conditions [2]. Furthermore, the higher sulphate/nitrate ratio found for the marble surfaces with respect to quartz filters is in accordance with what already observed in a previous study [17]. The overall characterization results indicate that the deposits have a significant potential for deterioration of the stone surfaces.…”

“…Moreover, considering the specific issue of soiling of the architectural surfaces, deposition rate cannot be estimated only from ambient concentration of pollutants [13] as the inherent features of the substrates, their orientation and the microclimatic aspect are key factors governing the phenomenon. For all these reasons, site exposure tests represent a widely exploited approach to study the response of stone substrates to environmental pressure in actual exposure conditions [10,11,[14][15][16][17].…”

On the Synergy between Elemental Carbon and Inorganic Ions in the Determination of the Electrical Conductance Properties of Deposited Aerosols: Implications for Energy Applications

“…In this case too, the signal of the eluent was decreased with a chemical suppressor (Dionex PTFE filters were chosen because they are among the most common membranes for aerosol collection, thanks to their low blank values for ions they are a suitable matrix for ion chromatography analysis [76] (Section 2.2); in addition, previous studies [8,18,19,77] demonstrated that hydrophobic supports are the most suitable for aerosol-water interaction measurements (e.g., via conductance measurements). In addition, their hydrophobicity makes them a good surrogate [66] for hydrophobic surfaces, e.g., epoxy-based composites that constitute PCBs and circuit component encapsulates [78] and for glass/ceramic insulator material, making them a good candidate for the present study. Quartz fiber filters were used to determined elemental and organic carbon as detailed in Section 2.2.…”

“…At this purpose, aerosol samples were collected on PTFE (Teflon) in different environments (urban and rural site), in Northern Italy (Po Valley). The investigated sites are located in the Po Valley, a hotspot for atmospheric pollution [65] where the dry aerosol deposition rate ranges from 30 to 70 µg cm −2 month −1 [66] making the aerosol a potential dangerous material for energy application. Moreover, the two urban and rural sites were chosen as affected by different EC and ionic content [67].…”