Oxygen and sulfur mass-independent isotopic signatures in black crusts: the complementary negative ∆<sup>33</sup>S-reservoir of sulfate aerosols?

Abstract

<p><strong>Abstract.</strong> To better understand the formation and the oxidation pathways leading to gypsum-forming “black crusts” and investigate their bearing on the whole atmospheric SO<sub>2</sub> cycle, we measured the oxygen (δ<sup>17</sup>O, δ<sup>18</sup>O and ∆<sup>17</sup>O) and sulfur (δ<sup>33</sup>S, δ<sup>34</sup>S, δ<sup>36</sup>S, ∆<sup>33</sup>S and ∆<sup>36</sup>S) isotopic compositions of black crust sulfates sampled on carbonate building stones along a NW-SE cross-section in the Parisian basin. The δ<sup>18</sup>O and δ<sup>34</sup>S, ranging between 7.5 and 16.7 ± 0.5 ‰ (n = 27, 2σ) and between −2.6 and 13.9 ± 0.2 ‰ respectively, show anthropogenic SO<sub>2</sub> as the main sulfur source (from 2 to 81 %, in average ~30 %) with host-rock sulfates making the complement. This is supported by ∆<sup>17</sup>O-values (up to 2.6 ‰, in average ~0.86 ‰), requiring > 60 % of atmospheric sulfates in black crusts. Both negative ∆<sup>33</sup>S-∆<sup>36</sup>S-values between −0.34 and 0.00 ± 0.01 ‰ and between −0.7 and −0.2 ± 0.2 ‰ respectively were measured in black crusts sulfates, that is typical of a magnetic isotope effect that would occur during the SO<sub>2</sub> oxidation on the building stone, leading to <sup>33</sup>S-depletion in black crust sulfates and subsequent <sup>33</sup>S-enrichment in residual SO<sub>2</sub>. Given that sulfate aerosols have mostly ∆<sup>33</sup>S > 0 ‰ and no processes can yet explain this enrichment, resulting in a non-consistent S-budget, black crust sulfates could well represent the complementary negative ∆<sup>33</sup>S-reservoir of the sulfate aerosols solving the atmospheric SO<sub>2</sub> budget.</p>

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

“…The similarity between the isotopic values (especially the δ 34 S) from Sicilian black crusts (this study) and those from other cities in Europe (Longinelli & Bartelloni, 1978;Buzek & Šrámek, 1985;Pye & Schiavon, 1989;Torfs et al, 1997;Siedel, 2000;Klemm & Siedel, 2002;Přikryl et al, 2004;Vallet et al, 2006;Kloppmann et al, 2011;Genot et al, 2020) suggests that similar sulphur sources contribute to the formation of their black crusts. This study thus confirms that in large urban areas, the black crust formation mostly results from anthropogenic sulphur emissions (Winkler, 1966;Massey, 1999;Bugini et al, 2000;Cardell-Fernández et al, 2002;Charola & Ware, 2002;Lefèvre & Ausset, 2002;Holynska et al, 2004;Přikryl et al, 2004;Barca et al, 2011;Kramar et al, 2011;Farkas et al, 2018;La Russa et al, 2018;Genot et al, 2020). More interestingly, the present work broadens the study of black crusts to different and various atmospheric environments (urban, coastal, rural and volcanic areas), and show that anthropogenic emissions still J o u r n a l P r e -p r o o f Genot et al (2020).…”

“…Following previous studies of natural sulphate-containing samples such as aerosols, rainwaters, ice cores or volcanic deposits Lee et al, 2001a;Romero et al, 2003;Jenkins et al, 2006;Mather et al, 2006;Sofen et al, 2011;Alexander et al, 2012;Martin, 2018). Genot et al (2020) reported recently on the first oxygen and sulphur multi-isotopic composition measurements of sulphate from black crust (δ 18 ) that are inherited from the ozone molecule precursor. When a sulphur gas (e.g.…”

“…"Black Crusts" are micrometric to centimetric thick black layers observed on the surface of buildings, monument walls or sculptures (Figure 1). They represent one of the main studied cause of carbonate stone deterioration and cultural heritage damage in urban environments (Winkler, 1966;Longinelli & Bartelloni, 1978;Del Monte et al, 1981;Camuffo et al, 1982;Camuffo et al, 1983;Haneef et al, 1992;Sabbioni, 1995;Torfs et al, 1997;Ausset et al, 1999;Massey, 1999;Ausset & Lefevre, 2000;Bugini et al, 2000;Cardell-Fernández et al, 2002;Charola & Ware, 2002;Vallet et al, 2006;Lefèvre et al, 2007;Montana et al, 2008;Fronteau et al, 2010;Török et al, 2010;Barca et al, 2011;Kloppmann et al, 2011;Kramar et al, 2011;Livingston, 2012;Montana et al, 2012;Ruffolo et al, 2015;Steiger, 2016;Bonazza & Sabbioni, 2016;Comite et al, 2017;Pozo-Antonio et al, 2017;La Russa et al, 2018Farkas et al, 2018;Genot et al, 2020). In present-day polluted urban areas, black crusts are mostly found on surfaces partly shielded from rainfall, but still humid (Camuffo et al, 1982;Camuffo et al, 1983, Massey, 1999.…”

“…The only investigation into the origin of sulphate in black crusts using a multi-isotopic oxygen and sulphur approach was conducted by Genot et al (2020). Black crusts were sampled in the Parisian Basin (France) according to a NW-SE cross-section, covering from rather suburban to more polluted environments in the heart of the Paris megapolis.…”

“…Unexpected MIF isotopic compositions (Δ 17 O up to 2.56‰, -0.34‰ <Δ 33 S< 0‰ and Δ 36 S ~ -0.4‰) were measured. Based on O isotopes and δ 34 S, Genot et al (2020) proposed that sulphate from Parisian black crusts mostly originate from the oxidation of anthropogenic sulphur gases by H 2 O 2 . Furthermore, they also suggested that a magnetic isotope effect during the formation of black crust sulphate might be responsible for the very unusual S-MIF signature.…”