Formation of Metal-Cyanide Complexes in Deliquescent Airborne Particles: A New Possible Sink for HCN in Urban Environments

Urban Exotic Pollution: The Harmful Environmental Footprint for Health and Historical Architecture

The study in this paper was carried out as a result of the observation of pollution phenomena and foaming effects associated with anthropogenic activities, including street cleaning activity. The processes of dust binding used in order to reduce PM10 and PM 2.5 pollution has been proven to be inefficient, and even contributing to pollution with particulate matter. Our results suggest that the use of dust binders must be integrated in a technique that includes methods of removing agglomerated particle structures resulting from the process of coagulation or flocculation. These are the conclusions of the investigations carried out by spectroscopic methods (FTIR, SEM-EDX) on samples collected from the streets of Iasi on 10 March 2021, and on samples collected from the surface of the Precinct Wall of the historical monument Golia-Iasi Monastery Ensemble (Romania). On the later samples, coloristic analysis was also performed. The alert for investigation was given by the foaming waters that were leaking on the streets. The phenomenon was observed after the streets had been washed by specialized vehicles. Analyses revealed compounds used as dust binders and coagulant type (aluminum sulfate, sodium aluminate and their derivatives, plus anti-skid chemicals such as calcium chlorine and magnesium chlorine), as well as organic compounds included in aggregate type structures, and they showed contamination of the Golia Precinct Wall. The results show that the dust binders or coagulants used as such, or embedded in various products intended for the cleaning process of streets or other outdoor public places, must be subject to regulation. Otherwise, there is a risk of adding more pollutants during an operation with the opposite purpose. The migration of these pollutants on the studied building offers an image on how both our health and all constructions and equipment exposed in the open air are affected.

Emerging investigator series: aqueous-phase processing of atmospheric aerosol influences dissolution kinetics of metal ions in an urban background site in the Po Valley

Metals are an important atmospheric aerosol component; their impacts on health and the environment depend also on their solubility, dissolution kinetics and chemical form in which they are present in the aerosol (e.g., oxidation state, inorganic salt or oxide/hydroxide, organic complex). In this study, we investigated the impact of fog processing on the solubility and dissolution of metals in PM_2.5 samples collected in an urban background site in Padova (Italy). For each sample, we determined the solubility and dissolution kinetics of 17 elements in a solution simulating fog water in the winter season in the Po Valley (pH 4.7, T 5 °C, and water content ∼0.5 g m^-3). We also determined water-soluble inorganic and organic compounds having ligand properties. We used the model E-AIM IV to calculate the aerosol liquid water (ALW) content and pH, and we used the model Visual MinteQ to determine the speciation picture of the most important elements under conditions of both deliquescent aerosol (ALW and pH calculated using E-AIM IV, ambient temperature) and simulated fog. We found that the dissolution of Al, Cu, and Fe metal ions, predicted to be largely coordinated with organic compounds under fog conditions, was either immediate or considerably faster in samples collected on days with observed fog events compared with those collected on days having drier conditions. For readily soluble elements, such as As, Cd, Cr, Sr, and Zn, such an effect was not observed. Our study highlights the importance of coordination chemistry in atmospheric aerosol and fog in determining the bioavailability of particle-bound metals.

A Membrane-based Disposable Well-Plate for Cyanide Detection Incorporating a Fluorescent Chitosan-CdTe Quantum Dot

A novel approach to building a membrane-based disposable well-plate, here applied to cyanide detection, is described. Chitosan encapsulated CdTe quantum dots with a maximum emission at 520 nm (CS-QD520) were used as fluorophores. The CS-QD520 nanoparticle was specifically quenched by copper(II), and the quenched CS-QD520 (Cu-CS-QD520) was deposited onto a glass microfiber filter (GF/B). Subsequent introduction of cyanide ion resulted in fluorescence recovery. The "signal-ON" fluorescence linearly correlated to cyanide concentrations in the range of 38.7 to 200 μM with a limit of detection of 11.6 μM. The assay was incorporated into a membrane-based well-plate format to enhance sample throughput. A three-layer paper/glass microfiber well plate design was cut using a laser cutter and assembled using a polycaprolactone (PCL) as a bonding agent in a low-cost laminator. The experimental conditions were optimized and applied to detect cyanide in drinking water with rapid, high-throughput, low-cost analysis.

Formation of metal-organic ligand complexes affects solubility of metals in airborne particles at an urban site in the Po valley

Metals in atmospheric aerosols play potentially an important role in human health and ocean primary productivity. However, the lack of knowledge about solubility and speciation of metal ions in the particles or after solubilisation in aqueous media (sea or surface waters, cloud or rain droplets, biological fluids) limits our understanding of the underlying physico-chemical processes. In this work, a wide range of metals, their soluble fractions, and inorganic/organic compounds contained in urban particulate matter (PM) from Padua (Italy) were determined. Metal solubility tests have been performed by dissolving the PM in water and in solutions simulating rain droplet composition. The water-soluble fractions of the metal ions and of the organic compounds having ligand properties have been subjected to a multivariate statistical procedure, in order to elucidate associations among the aqueous concentrations of these PM components in simulated rain droplets. In parallel, a multi-dimensional speciation calculation has been performed to identify the stoichiometry and the amount of metal-ligand complexes theoretically expected in aqueous solutions. Both approaches showed that the solubility and the aqueous speciation of metal ions were differently affected by the presence of inorganic and organic ligands in the PM. The solubility of Al, Cr, and Fe was strongly correlated to the concentrations of oxalic acid, as their oxalate complexes represented the expected dominant species in aqueous solutions. Oxalates of Al represented ∼98% of soluble Al, while oxalates of Cu represented 34-75% of the soluble Cu, and oxalates of Fe represented 76% of soluble Fe. The oxidation state of Fe can strongly impact the speciation picture. If Fe is present as Fe(II) rather than Fe(III), the amount of Cr and Cu complexed with diacids can increase from 75% to 94%, and from 32% to 53%, respectively. For other metals, the solubility depended on the formation of soluble aquo-complexes, hence with a scarce effect of the organic ligands. An iron-oxalate complex was also directly detected in aerosol sample extracts.

Direct target and non-target analysis of urban aerosol sample extracts using atmospheric pressure photoionisation high-resolution mass spectrometry

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous atmospheric pollutants of high concern for public health. In the atmosphere they undergo oxidation, mainly through reactions with ·OH and NOx to produce nitro- and oxygenated (oxy-) derivatives. In this study, we developed a new method for the detection of particle-bound PAHs, nitro-PAHs and oxy-PAHs using direct infusion into an atmospheric pressure photoionisation high-resolution mass spectrometer (APPI-HRMS). Method optimisation was done by testing different source temperatures, gas flow rates, mobile phases and dopants. Samples were extracted with methanol, concentrated by evaporation and directly infused in the APPI source after adding toluene as dopant. Acquisition was performed in both polarity modes. The method was applied to target analysis of seasonal PM_2.5 samples from an urban background site in Padua (Italy), in the Po Valley, in which a series of PAHs, nitro- and oxy-PAHs were detected. APPI-HRMS was then used for non-target analysis of seasonal PM_2.5 samples and results compared with nano-electrospray ionisation (nanoESI) HRMS. The results showed that, when samples were characterised by highly oxidised organic compounds, including S-containing compounds, like in summer samples, APPI did not bring any additional information with respect to nanoESI in negative polarity (nanoESI(-)). Conversely, for winter samples, APPI(-) could detect a series of aromatic and poly-aromatic compounds, mainly oxidised and nitrogenated aromatics, that were not otherwise detected with nanoESI.