Radiocarbon isotope technique as a powerful tool in tracking anthropogenic emissions of carbonaceous air pollutants and greenhouse gases: A review

Reduction in Organic Aerosol from Coal Combustion is Partially Offset by Enhanced Secondary Formation during the Beijing Coal Burning Ban

A coal ban policy in northern China during winter 2017 enforced a switch from coal to gas or electricity for residential heating, providing a unique opportunity to study the effect of reduced coal combustion emissions on organic aerosol (OA). This study explores OA composition, sources, and atmospheric transformations in Beijing before and during the coal ban using online aerosol chemical speciation monitor (ACSM) and offline 14C measurements. Four primary factors (hydrocarbon-like, cooking, biomass burning, coal combustion OA) and one secondary factor (oxygenated OA, OOA) were resolved from ACSM. In response to the coal ban, OA concentrations generally decreased, but coal combustion OA decreased most strongly, consistent with the decreased fossil carbon contributions to OA (67 ± 3% before vs 55 ± 4% during the ban). Concurrently, the OOA fraction increased from 45 to 72%, due to a larger decrease in concentrations of primary OA (POA; 59-88%) compared to OOA (34%), highlighting the enhanced secondary aerosol formation during the coal ban period. This aligns with the 14C evidence of higher water-soluble carbon in fossil OA (which has mostly secondary sources). During the coal ban period, Ox concentrations doubled and were positively correlated with the OOA fraction, highlighting strong photochemical OA production. The results show that the reduction of POA from stringent clean air actions is partially offset by enhanced secondary OA formation.

Insight into radionuclide 235U deposition in multiple-environmental media in Muztagh Ata Glacier Basin of the eastern Pamirs

This study concerns the 235U/238U ratios in environmental samples collected in the Pamir region (Central Asia). Cryoconite (a supra-glacial sediment), soil and river water were sampled in the Muztagh Ata Glacier Basin, a secondary basin belonging to Gaizi River watershed. The aim of the research is to assess the impact of anthropic nuclear activities in such a remote area, being the 235U/238U ratio highly sensitive to anthropogenic disturbances. Results indicate that the 235U/238U atomic ratio in the region ranges from 0.007256 to 0.007263, with an average of 0.007259 ± 0.000002. Such values are slightly higher than the natural isotopic reference (0.007256), suggesting a modest enrichment of 235U. This is related to the input of uranium with an anthropogenically modified isotopic signature. The 235U/238U ratios are higher in cryoconite compared to that of surface soil/sediment and river water, reflecting differences in the release, transmission and retention of 235U across various environmental media in the Pamir region. The variability of the isotopic ratio was also explored in relation to some key geographic parameters and compared with data from a wider geographic context. The altitude distribution of the 235U/238U ratio indicates that the deposition of 235U in the Muztagh Ata area primarily results from upper atmospheric deposition sources of the global fallout of radionuclides, which were probably released by historical human nuclear activities of global range, but without clear evidence of local uranium contamination. A conceptual model for interpretation of the 235U/238U ratios and profile distribution in eastern Pamir is provided. Comparative analysis of the 235U/238U ratios in our samples and in samples from other locations in the northern hemisphere shows that the level in the environment of the Muztagh Glacier area is cleaner, with subtle enriched uranium and not contaminated by depleted uranium. Therefore, this work is of importance in providing a complete view on the migration, dispersion, and removal of radionuclide 235U in the atmosphere and cryospheric glacier watershed of the remote Pamir region, thus offering new insights into the distribution and behavior of radionuclides in the Pamir.

Efficient solar-driven CO2-to-fuel conversion via Ni/MgAlO x @SiO2 nanocomposites at low temperature

Solar-driven CO2-to-fuel conversion assisted by another major greenhouse gas CH4 is promising to concurrently tackle energy shortage and global warming problems. However, current techniques still suffer from drawbacks of low efficiency, poor stability, and low selectivity. Here, a novel nanocomposite composed of interconnected Ni/MgAlO x nanoflakes grown on SiO2 particles with excellent spatial confinement of active sites is proposed for direct solar-driven CO2-to-fuel conversion. An ultrahigh light-to-fuel efficiency up to 35.7%, high production rates of H2 (136.6 mmol min-1g- 1) and CO (148.2 mmol min-1g-1), excellent selectivity (H2/CO ratio of 0.92), and good stability are reported simultaneously. These outstanding performances are attributed to strong metal-support interactions, improved CO2 absorption and activation, and decreased apparent activation energy under direct light illumination. MgAlO x @SiO2 support helps to lower the activation energy of CH* oxidation to CHO* and improve the dissociation of CH4 to CH3* as confirmed by DFT calculations. Moreover, the lattice oxygen of MgAlO x participates in the reaction and contributes to the removal of carbon deposition. This work provides promising routes for the conversion of greenhouse gasses into industrially valuable syngas with high efficiency, high selectivity, and benign sustainability.

Unraveling the Spatio-Temporal Relationship between Ecosystem Services and Socioeconomic Development in Dabie Mountain Area over the Last 10 years

The Dabie Mountain area is a typical poverty-stricken area in China. It is of great significance to evaluate the ecosystem service value and its impact mechanism toward optimizing the ecological structure and coordinating ecological protection and economic development. This study determined the ecosystem service value coefficient and calculated the ecosystem service value (ESV) according to the regional economic development in the past ten years, and the ESV was spatialized based on NPP, which is closely related to ecological function. The temporal and spatial variation of ESV was then analyzed, and an RDE index was proposed to describe its response to land cover change. Further, the relationship between ESV and several parameters that reflect socioeconomic development was researched and analyzed. The results show that the total ESV in the study area first decreased and then increased, with an overall increase of CNY 3.895 billion. Among the land cover types, forest land had the greatest impact, contributing more than 70%. In the ecosystem service functions, the contribution of regulation function exceeded 50%. ESV was found to be sensitive to land cover change. On average, every 1 km2 change leads to an ESV change of about CNY 1 million. Socioeconomic-related parameters were negatively correlated with ESV, among which the correlation with per capita disposable income was the weakest, indicating that there was no obvious contradiction between human well-being and ESV. Therefore, a path for harmonious symbiotic development can be found between man and nature.

Dual-carbon isotope constraints on source apportionment of black carbon in the megacity Guangzhou of the Pearl River Delta region, China for 2018 autumn season

Black carbon (BC) aerosol negatively affects air quality and contributes to climate warming globally. However, little is known about the relative contributions of different source control measures to BC reduction owing to the lack of powerful source-diagnostic tools. We combine the fingerprints of dual-carbon isotope using an optimized Bayesian Markov chain Monte Carlo (MCMC) scheme and for the first time to study the key sources of BC in megacity Guangzhou of the Pearl River Delta (PRD) region, China in 2018 autumn season. The MCMC model-derived source apportionment of BC shows that the dominant contributor is petroleum combustion (39%), followed by coal combustion (34%) and biomass burning (27%). It should be noted that the BC source pattern is highly sensitive to the variations of air masses transported with an enhanced contribution of fossil source from the eastern area, suggesting the important impact of regional atmospheric transportation on the BC source profile in the PRD region. Also, we further found that fossil fuel combustion BC contributed 84% to the total BC reduction during 2013-2018. The response of PM_2.5 concentration to the ¹⁴C-derived BC source apportionment is successfully fitted (r = 0.90) and the results predicted that it would take ∼6 years to reach the WHO PM_2.5 guideline value (10 μg m^-3) for the PRD region if the emission control measures keep same as they are at present. Taken together, our findings suggest that dual-carbon isotope is a powerful tool in constraining the source apportionment of BC for the evaluations of air pollution control and carbon emission measures.