Abstract. Sulfates present in urban aerosols collected worldwide usually exhibit significant non-zero Δ33S signatures (from −0.6 ‰ to 0.5 ‰) whose origin still remains unclear. To better address this issue, we recorded the seasonal variations of the multiple sulfur isotope compositions of PM10 aerosols collected over the year 2013 at five stations within the Montreal Island (Canada), each characterized by distinct types and levels of pollution. The δ34S-values (n= 155) vary from 2.0 ‰ to 11.3 ‰ (±0.2 ‰, 2σ), the Δ33S-values from −0.080 ‰ to 0.341 ‰ (±0.01 ‰, 2σ) and the Δ36S-values from −1.082 ‰ to 1.751 ‰ (±0.2 ‰, 2σ). Our study evidences a seasonality for both the δ34S and Δ33S, which can be observed either when considering all monitoring stations or, to a lesser degree, when considering them individually. Among them, the monitoring station located at the most western end of the island, upstream of local emissions, yields the lowest mean δ34S coupled to the highest mean Δ33S-values. The Δ33S-values are higher during both summer and winter, and are < 0.1 ‰ during both spring and autumn. As these higher Δ33S-values are measured in “upstream” aerosols, we conclude that the mechanism responsible for these highly positive S-MIF also occurs outside and not within the city, at odds with common assumptions. While the origin of such variability in the Δ33S-values of urban aerosols (i.e. −0.6 ‰ to 0.5 ‰) is still subject to debate, we suggest that oxidation by Criegee radicals and/or photooxidation of atmospheric SO2 in the presence of mineral dust may play a role in generating such large ranges of S-MIF.

No abstract

The analysis of the three S-isotope ratios on the SF6 molecule using the so-called conventional fluorination method and dual-inlet ion ratio mass spectrometry is reliable for sample sizes down to ~20 nanomoles. Despite being close to the theoretical limits for maintaining the viscous flow regime of gas in the capillary, errors were not limited by counting statistics, but probably relate to sample gas purification. Copyright © 2016 John Wiley & Sons, Ltd.

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Sulfates present in urban aerosols collected worldwide usually exhibit significant non-zero &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S signatures (from &amp;#8722;0.6 to 0.5&amp;#8201;&amp;#8240;) whose origin still remains unclear. To better address this issue, we recorded the seasonal variations of the multiple sulfur isotope compositions of PM&lt;sub&gt;10&lt;/sub&gt; aerosols collected over the year 2013 at five stations within the Montreal Island (Canada), each characterized by distinct types and levels of pollution. The &amp;#948;&lt;sup&gt;34&lt;/sup&gt;S-values (n&amp;#8201;=&amp;#8201;155) vary from 2.0 to 11.3&amp;#8201;&amp;#8240; (&amp;#177; 0.2&amp;#8201;&amp;#8240;, 2&amp;#963;), the &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S-values from &amp;#8722;0.080 to 0.341&amp;#8201;&amp;#8240; (&amp;#177; 0.01&amp;#8201;&amp;#8240;, 2&amp;#963;) and the &amp;#916;&lt;sup&gt;36&lt;/sup&gt;S-values from &amp;#8722;1.082 to 1.751&amp;#8201;&amp;#8240; (&amp;#177; 0.2&amp;#8201;&amp;#8240;, 2&amp;#963;). Our study evidences a seasonality for both the &amp;#948;&lt;sup&gt;34&lt;/sup&gt;S and &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S, which can be observed either when considering all monitoring stations or, to a lesser degree, when considering them individually. Among them, the monitoring station located at the most western end of the island, upstream of local emissions, yields the lowest mean &amp;#948;&lt;sup&gt;34&lt;/sup&gt;S coupled to the highest mean &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S-values. The &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S-values are higher during both summer and winter, and are &lt;&amp;#8201;0.1&amp;#8201;&amp;#8240; during both spring and autumn. As these higher &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S-values are measured in &quot;upstream&quot; aerosols, we conclude that the mechanism responsible for these highly positive S-MIF also occurs outside and not within the city, at odds with common assumptions. While the origin of such variability in the &amp;#916;&lt;sup&gt;33&lt;/sup&gt;S-values of urban aerosols (i.e. &amp;#8722;0.6 to 0.5&amp;#8201;&amp;#8240;) is still subject to debate, we suggest that oxidation by Criegee radicals and/or photooxidation of atmospheric SO&lt;sub&gt;2&lt;/sub&gt; in presence of mineral dust may play a role in generating such large ranges of S-MIF.&lt;/p&gt;

Abstract. To better understand the formation and the oxidation pathways leading to gypsum-forming “black crusts” and investigate their bearing on the whole atmospheric SO2 cycle, we measured the oxygen (δ17O, δ18O, and Δ17O) and sulfur (δ33S, δ34S, δ36S, Δ33S, and Δ36S) isotopic compositions of black crust sulfates sampled on carbonate building stones along a NW–SE cross section in the Parisian basin. The δ18O and δ34S values, ranging between 7.5 ‰ and 16.7±0.5 ‰ (n=27, 2σ) and between −2.66 ‰ and 13.99±0.20 ‰, respectively, show anthropogenic SO2 as the main sulfur source (from ∼2 % to 81 %, average ∼30 %) with host-rock sulfates making the complement. This is supported by Δ17O values (up to 2.6 ‰, on average ∼0.86 ‰), requiring > 60 % of atmospheric sulfates in black crusts. Negative Δ33S and Δ36S values between −0.34 ‰ and 0.00±0.01 ‰ and between −0.76 ‰ and -0.22±0.20 ‰, respectively, were measured in black crust sulfates, which is typical of a magnetic isotope effect that would occur during the SO2 oxidation on the building stone, leading to 33S depletion in black crust sulfates and subsequent 33S enrichment in residual SO2. Except for a few samples, sulfate aerosols mostly have Δ33S values > 0 ‰, and no processes can yet explain this enrichment, resulting in an inconsistent S budget: black crust sulfates could well represent the complementary negative Δ33S reservoir of the sulfate aerosols, thus solving the atmospheric SO2 budget.

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; To better understand the formation and the oxidation pathways leading to gypsum-forming &amp;#8220;black crusts&amp;#8221; and investigate their bearing on the whole atmospheric SO&lt;sub&gt;2&lt;/sub&gt; cycle, we measured the oxygen (&amp;#948;&lt;sup&gt;17&lt;/sup&gt;O, &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#8710;&lt;sup&gt;17&lt;/sup&gt;O) and sulfur (&amp;#948;&lt;sup&gt;33&lt;/sup&gt;S, &amp;#948;&lt;sup&gt;34&lt;/sup&gt;S, &amp;#948;&lt;sup&gt;36&lt;/sup&gt;S, &amp;#8710;&lt;sup&gt;33&lt;/sup&gt;S and &amp;#8710;&lt;sup&gt;36&lt;/sup&gt;S) isotopic compositions of black crust sulfates sampled on carbonate building stones along a NW-SE cross-section in the Parisian basin. The &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;34&lt;/sup&gt;S, ranging between 7.5 and 16.7&amp;#8201;&amp;#177;&amp;#8201;0.5&amp;#8201;&amp;#8240; (n&amp;#8201;=&amp;#8201;27, 2&amp;#963;) and between &amp;#8722;2.6 and 13.9&amp;#8201;&amp;#177;&amp;#8201;0.2&amp;#8201;&amp;#8240; respectively, show anthropogenic SO&lt;sub&gt;2&lt;/sub&gt; as the main sulfur source (from 2 to 81&amp;#8201;%, in average ~30&amp;#8201;%) with host-rock sulfates making the complement. This is supported by &amp;#8710;&lt;sup&gt;17&lt;/sup&gt;O-values (up to 2.6&amp;#8201;&amp;#8240;, in average ~0.86&amp;#8201;&amp;#8240;), requiring &gt;&amp;#8201;60&amp;#8201;% of atmospheric sulfates in black crusts. Both negative &amp;#8710;&lt;sup&gt;33&lt;/sup&gt;S-&amp;#8710;&lt;sup&gt;36&lt;/sup&gt;S-values between &amp;#8722;0.34 and 0.00&amp;#8201;&amp;#177;&amp;#8201;0.01&amp;#8201;&amp;#8240; and between &amp;#8722;0.7 and &amp;#8722;0.2&amp;#8201;&amp;#177;&amp;#8201;0.2&amp;#8201;&amp;#8240; respectively were measured in black crusts sulfates, that is typical of a magnetic isotope effect that would occur during the SO&lt;sub&gt;2&lt;/sub&gt; oxidation on the building stone, leading to &lt;sup&gt;33&lt;/sup&gt;S-depletion in black crust sulfates and subsequent &lt;sup&gt;33&lt;/sup&gt;S-enrichment in residual SO&lt;sub&gt;2&lt;/sub&gt;. Given that sulfate aerosols have mostly &amp;#8710;&lt;sup&gt;33&lt;/sup&gt;S&amp;#8201;&gt;&amp;#8201;0&amp;#8201;&amp;#8240; and no processes can yet explain this enrichment, resulting in a non-consistent S-budget, black crust sulfates could well represent the complementary negative &amp;#8710;&lt;sup&gt;33&lt;/sup&gt;S-reservoir of the sulfate aerosols solving the atmospheric SO&lt;sub&gt;2&lt;/sub&gt; budget.&lt;/p&gt;

Oceans play a key role in the global mercury (Hg) cycle, but studies on Hg isotopes in seawater are rare due to the extremely low Hg concentration and the lack of a good preconcentration method. Here, we introduce a new coprecipitation method for separating and preconcentrating Hg from seawater for accurate isotope measurement. The coprecipitation was achieved by sequential addition of 0.5 mL of 0.5 M CuSO 4 , 1 mL of 0.5 M Na 2 S, and 1 mL of 0.5 M CuSO 4 reagents, which allowed for quantitatively precipitating Hg from up to 10 L of seawater. The protocol was validated by testing synthetic solutions with varying Hg and iodide (I − ) concentrations and by comparing the reaction times of various reagents added. The method resulted in a quantitative recovery of 98 ± 12% (n = 32, two standard deviations, 2 SD) and a relatively low procedure blank (103 pg of Hg, n = 8). The precipitates were filtrated and analyzed for Hg isotopes. Repeated measurements of synthetic seawaters spiked with certificated standard materials (NIST 3133 and 3177) using the entire method gave identical Hg isotope ratios with near-quantitative Hg recovery, indicating no isotope fractionation during preconcentration. A total of six nearshore seawater samples from the Yellow Sea and the Bohai Sea (China) were analyzed using the coprecipitation method. The data showed a large fractionation of Hg isotopes and revealed the possible impact of both atmospheric and anthropogenic inputs to the coastal seawater Hg budget, implying the potential application of this method in studying marine Hg systematics and global Hg cycling.

No abstract