Abstract We examined two low‐temperature hydrothermal deposits rich in Fe‐Si‐Mn collected from the recently discovered hydrothermal fields at the Southwest Indian Ridge using mineralogical, geochemical, and molecular biological techniques. The mineralogical and geochemical analyses indicated that the low‐temperature hydrothermal fields would provide a warm and chemical species‐rich habitat for chemosynthetic‐based hydrothermal ecosystems. Analyses of 16S rRNA sequences showed that ζ‐Proteobacteria, Pseudoalteromonas , Leptothrix , and Pseudomonas were potential Fe and Mn oxidizers in the low‐temperature hydrothermal environments, but they were not present in equal abundance among the subniches. Some potential Fe and Mn reducers were also recovered; they were more commonly found in the exterior black Fe‐Mn oxides. The difference between the exterior black Fe‐Mn oxides and the interior Opal‐A could be related to differences in in situ physicochemical conditions. We also identified microbial players that may participate in sulfur (S) geochemical cycling in these low‐temperature hydrothermal environments via analyses of 16S rRNA sequences and the aprA functional gene. The results indicated that members of γ‐Proteobacteria and α‐Proteobacteria were involved in the S oxidation process, while members of δ‐Proteobacteria, Nitrospirae, Firmicutes, and Archaea might participate in the S reduction process. Fe, Mn, and S oxidizers and reducers might actively participate in hydrothermal biogeochemical processes, which could influence the transfer of chemical species and the formation of biogenic minerals.
Abstract. As major chemical components of airborne fine particulate matter (PM2.5), organic carbon (OC) and elemental carbon (EC) have vital impacts on air quality, climate change, and human health. Because OC and EC are closely associated with fuel combustion, it is helpful for the scientific community and policymakers assessing the efficacy of air pollution control measures to study the impact of control measures and regional transport on OC and EC levels. In this study, hourly mass concentrations of OC and EC associated with PM2.5 were semi-continuously measured from March 2013 to February 2018. The results showed that annual mean OC and EC concentrations declined from 14.0 to 7.7 µg m−3 and from 4.0 to 2.6 µg m−3, respectively, from March 2013 to February 2018. In combination with the data of OC and EC in previous studies, an obvious decreasing trend in OC and EC concentrations was found, which was caused by clean energy policies and effective air pollution control measures. However, no obvious change in the ratios of OC and EC to the PM2.5 mass (on average, 0.164 and 0.049, respectively) was recorded, suggesting that inorganic ions still contributed a lot to PM2.5. Based on the seasonal variations in OC and EC, it appeared that higher OC and EC concentrations were still observed in the winter months, with the exception of winter of 2017–2018. Traffic policies executed in Beijing resulted in nighttime peaks of OC and EC, caused by heavy-duty vehicles and heavy-duty diesel vehicles being permitted to operate from 00:00 to 06:00 (China standard time, UTC+8, for all times throughout the paper). In addition, the fact that there was no traffic restriction in weekends led to higher concentrations on weekends compared to weekdays. Significant correlations between OC and EC were observed throughout the study period, suggesting that OC and EC originated from common emission sources, such as exhaust of vehicles and fuel combustion. OC and EC levels increased with enhanced SO2, CO, and NOx concentrations while the O3 and OC levels were enhanced simultaneously when O3 concentrations were higher than 50 µg m−3. Non-parametric wind regression analysis was performed to examine the sources of OC and EC in the Beijing area. It was found that there were distinct hot spots in the northeast wind sector at wind speeds of approximately 0–6 km h−1, as well as diffuse signals in the southwestern wind sectors. Source areas further away from Beijing were assessed by potential source contribution function (PSCF) analysis. A high-potential source area was precisely pinpointed, which was located in the northwestern and southern areas of Beijing in 2017 instead of solely in the southern areas of Beijing in 2013. This work shows that improvement of the air quality in Beijing benefits from strict control measures; however, joint prevention and control of regional air pollution in the regions is needed for further improving the air quality. The results provide a reference for controlling air pollution caused by rapid economic development in developing countries.
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