Multi O- and S-isotopes as tracers of black crusts formation under volcanic and non-volcanic atmospheric conditions in Sicily (Italy)

A multi-analytical approach for the identification of pollutant sources on black crust samples: Stable isotope ratio of carbon, sulphur, and oxygen

This study is focused on the identification of pollutant sources on black crust (BC) samples from the Monumental Cemetery of Milan (Italy), through a multi-analytical approach based on the determination of stable isotope ratios of carbon, sulphur, and oxygen. Six black crust samples, mainly developed on marble sculptures over a time span of 100-150 years, were analysed. For the first time, δ13C was measured for BC samples: δ13C values of the pulverized samples (from -1.2 to +1.3 ‰) are very close to the values obtained from the carbonate matrix, whereas after the removal of the matrix through acidification, δ13C values of BC samples from Milan range from -27.2 to -22.1 ‰, with no significant variation between samples with different ratios of organic carbon to elemental carbon. In sum, the δ13C values obtained for all BC samples fall within the range of anthropogenic emissions such as vehicle traffic, coal combustion and industrial emissions. δ34S and δ18O values of sulphate from BC samples range from -6.3 to +7.0 ‰ and from +7.6 to +10.5 ‰, respectively. Coupling the analysis of the oxygen isotope ratio with that of sulphur enables a more precise identification of the origin of sulphates: the observed isotopic composition falls in the range typical for anthropogenic emission of sulphur dioxide. Overall, in this study, C, S and O isotopes were combined for the first time to assess pollutant sources on black crust samples: this multi-stable isotope approach allowed to show that the BC formation on monuments from the Monumental Cemetery of Milan mostly results from anthropogenic emissions from fossil fuels combustion by road vehicles and factories, as well as domestic heating.

Multiple Sulfur Isotopic Evidence for Sulfate Formation in Haze Pollution

The mechanism of sulfate formation during winter haze events in North China remains largely elusive. In this study, the multiple sulfur isotopic composition of sulfate in different grain-size aerosol fractions collected seasonally from sampling sites in rural, suburban, urban, industrial, and coastal areas of North China are used to constrain the mechanism of SO2 oxidation at different levels of air pollution. The Δ33S values of sulfate in aerosols show an obvious seasonal variation, except for those samples collected in the rural area. The positive Δ33S signatures (0‰ < Δ33S < 0.439‰) observed on clean days are mainly influenced by tropospheric SO2 oxidation and stratospheric SO2 photolysis. The negative Δ33S signatures (-0.236‰ < Δ33S < ∼0‰) observed during winter haze events (PM2.5 > 200 μg/m3) are mainly attributed to SO2 oxidation by H2O2 and transition metal ion catalysis (TMI) in the troposphere. These results reveal that both the H2O2 and TMI pathways play critical roles in sulfate formation during haze events in North China. Additionally, these new data provide evidence that the tropospheric oxidation of SO2 can produce significant negative Δ33S values in sulfate aerosols.

Multi-analytical study of the medieval wall paintings from the rupestrian church Grotta del Crocifisso at Lentini (eastern Sicily): new evidence of the use of woad (Isatis tinctoria)

This study presents the results of the examination and characterisation of the wall paintings that decorate the rupestrian church named Grotta del Crocifisso, which is located in the territory of Lentini (eastern Sicily, few tens of kilometres from Catania and Syracuse). The earliest mural paintings in the church date back to the twelfth century AD. A multi-analytical approach was adopted for the characterisation of stone materials, secondary degradation products, and pigments. For this purpose, the following techniques were used: reflected light microscopy (RLM), polarised light microscopy on thin sections (PLM), X-ray powder diffraction (XRPD), mercury intrusion porosimetry (MIP), portable X-ray fluorescence (p-XRF), scanning electron microscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy (RS). The lithic substrate and the plaster's coating layers were thoroughly characterised from compositional and textural points of view, and the use of locally available raw materials was established. Similarly, the newly formed crystalline phases produced by alteration processes of the original materials were recognised. The red, yellow, brown, and green pigments were easily identified by p-XRF and SEM-EDS. The use of "earth pigments" widely available in the surrounding area (various types of ochre) was thus highlighted. The recognition of the dark blue pigment created some additional issues in its identification, making further diagnostic methods necessary. In fact, the use of the most common mineral pigments was categorically excluded by both p-XRF and SEM-EDS, since no chromophore metallic elements were highlighted with the exception of trace amounts of iron. A combination of detailed microscopic observations together with the application of FTIR and RS supported the use of an organic pigment obtained from the maceration of woad (Isatis tinctoria). The green pigment is the result of a mixture between woad and yellow ochre. Woad is even today easily available in Sicily, and some additional experimental tests were carried out on Isatis tinctoria that had been freshly collected in the area (treated with traditional procedures). Over the past centuries, woad was widely used for dyeing fabrics, but its practice for wall paintings has only been sporadically proven. The identification reported in this case study could be considered a novelty at least in the Sicilian panorama.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12520-022-01656-6.

Study on the mechanism of the black crust formation on the ancient marble sculptures and the effect of pollution in Beijing area

In Beijing area, the precious stone objects often suffer from the black crusts on the specific parts of the objects, in order to understand the forming mechanism of the black crusts, samples from the stone sculptures in Beijing Stone Carving Art Museum, ZHIHUA Temple and Museum of Western Zhou Yandu Relics were taken and studied. Nondestructive measurement was carried out firstly to acquire main elements of the samples by portable X-ray spectrum (pXRF). Morphology and microstructure of typical black crust samples were examined by ultra-depth of field microscope (UDFM) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). Compositions of black crusts and body rocks were evaluated with X-ray diffraction (XRD), Raman spectra and mapping. Inductively coupled plasma optical emission spectrometry (ICP-OES) and pyrolysis-gas chromatography/mass spectrometry (Py-GCMS) were used to identify the major pollution sources leading to the black crusts.

Through this study, the composition of the black crusts was revealed. Different gypsum crystals and carbonaceous species were found. Pollutant elements analysis and pyrolysis products provide indicators of the pollution sources. As consequence of strong photochemical oxidation processes and the high temperature from June to September in Beijing, more acid rain precursors can be formed. Frequent sulphation process occurs on the CaCO₃/CaMg(CO₃)₂ surface. Combining morphology results and atmospheric data, the formation of black crusts in Beijing can be deduced.