Identification of dust aerosols, their sources, and the effect of soil moisture in Central Asia

Selective molecular characterization of organic aerosols using in situ laser desorption ionization mass spectrometry

RATIONALE

The sources and chemical compositions of organic aerosol (OA) exert a significant influence on both regional and global atmospheric conditions, thereby having far-reaching implications on environmental chemistry. However, existing mass spectrometry (MS) methods have limitations in characterizing the detailed composition of OA due to selective ionization as well as fractionation during cold-water extraction and solid-phase extraction (SPE).

METHODS

A comprehensive MS study was conducted using aerosol samples collected on dusty, clean, and polluted days. To supplement the data obtained from electrospray ionization (ESI), a strategy for analyzing OAs collected using the quartz fiber filter directly utilizing laser desorption ionization (LDI) was employed. Additionally, the ESI method was conducted to explore suitable approaches for determining various OA compositions from samples collected on dusty, clean, and polluted days.

RESULTS

In situ LDI has the advantages of significantly reducing the sample volume, simplifying sample preparation, and overcoming the problem of overestimating sulfur-containing compounds usually encountered in ESI. It is suitable for the characterization of highly unsaturated and hydrophobic aerosols, such as brown carbon-type compounds with low volatility and high stability, which is supplementary to ESI.

CONCLUSIONS

Compared with other ionization methods, in situ LDI helps provide a complementary description of the molecular compositions of OAs, especially for analyzing OAs in polluted day samples. This method may contribute to a more comprehensive MS analysis of the elusive compositions and sources of OA in the atmosphere.

Enhanced microbial remediation of uranium tailings through red soil utilization

Seepage of uranium tailings has become a focus of attention in the uranium mining and metallurgy industry, and in-situ microbial remediation is considered an effective way to treat uranium pollution. However, this method has the drawbacks of easy biomass loss and unstable remediation effect. To overcome these issues, spare red soil around the uranium mine was used to enhance the efficiency and stability of bioremediation. Furthermore, the bioremediation mechanism was revealed by employing XRD, FTIR, XPS, and 16S rRNA. The results showed that red soil, as a barrier material, had the adsorption potential of 8.21-148.00 mg U/kg soil, but the adsorption is accompanied by the release of certain acidic and oxidative substances. During the dynamic microbial remediation, red soil was used as a cover material to neutralize acidity, provide a higher reduction potential (<-200 mV), and increase the retention rate of microbial agent (19.06 mL/d) compared to the remediation group without red soil. In the presence of red soil, the anaerobic system could maintain the uranium concentration in the solution below 0.3 mg/L for more than 70 days. Moreover, the generation of new clay minerals driven by microorganisms was more conducive to the stability of uranium tailings. Through alcohol and amino acid metabolism of microorganisms, a reducing environment with reduced valence states of multiple elements (such as S2-, Fe2+, and U4+) was formed. At the same time, the relative abundance of functional microbial communities in uranium tailings improved in presence of red soil and Desulfovirobo, Desulfocapsa, Desulfosporosinus, and other active microbial communities reconstructed the anaerobic environment. The study provides a new two-in-one solution for treatment of uranium tailings and resource utilization of red soil through in-situ microbial remediation.

Dust temporal and spatial deposition affected by climate and soil mineralogical and chemical properties in a semi-arid area

The important process of aerosol dusting is of economic, environmental and heath significance. The objective was to investigate the climatic parameters including rainfall (R), wind speed (WS), temperature (T), and relative humidity (RH), as well as soil mineralogical and chemical properties affecting dust deposition rate (DDR), in a unique and rarely studied area, the Kuhdasht watershed (456 km²) of Lorestan province, Iran. Data were collected seasonally using glass-traps inserted in ten research stations to indicate DDR seasonal and spatial variations using ARC-GIS. The spatial distribution of organic matter (OM), clay and CaCO₃, and the mineralogical properties (using diffractograms obtained by XRD) of the dust and soil samples were determined. The city had the highest DDR decreasing toward the mountains. Spring (3.28-4.18 ton/km²) and autumn (1.82-2.52 ton/km²) resulted in the highest and the least DDR, respectively. The diffractograms indicated the sources of dust were local or from out of the borders. The clay minerals (kaolinite and illite) and the evaporating minerlas (gypsum, calcite, dolomite, and halite), detected in the soil and dust samples indicated their contribution to the process of DDR. According to the regression models and the correlation coefficients, DDR was highly and significantly correlated with R (R2= 0.691), WS (0.685) and RH (0.463) indicating such parameters can importantly affect DDR in the semi-arid areas.