Search

Black carbon aerosols absorb radiation and their absorptive strength is influenced by particle mixing structures and coating compositions. Liquid-liquid phase separation can move black carbon to organic particle coatings which affects absorptive capacity, but it is unclear which conditions favour this redistribution. Here we combine field observations, laboratory experiments, and transmission electron microscopy to demonstrate that liquid-liquid phase separation redistributes black carbon from inorganic particle cores to organic coatings under a wide range of relative humidity. We find that the ratio of organic coating thickness to black carbon size influences the redistribution. When the ratio is lower than 0.12, over 90% of black carbon is inside inorganic salt cores. However, when the ratio exceeds 0.24, most black carbon is redistributed to organic coatings, due to a change in its affinity for inorganic and organic phases. Using an optical calculation model, we estimate that black carbon redistribution reduces the absorption enhancement effect by 28–34%. We suggest that climate models assuming a core-shell particle structure probably overestimate radiative absorption of black carbon aerosols by approximately 18%.

Black carbon (BC) exerts profound impacts on air quality and climate because of its high-absorption cross section over a broad band of solar spectrum. Non-BC materials coated on BC could alter the mixing state of BC particles and can considerably enhance its mass absorption coefficient. Quantification of this absorption enhancement remains a challenge due to incomplete understanding of the complex physical and chemical properties related to mixing states. In this paper, we summarize the recent progress in measurement and modeling studies on the BC mixing state and their effects on optical properties. Laboratory and field-based observations have shown that the transformation of a mixing state from a highly fractal nature to a more compact shape exhibits a decrease in electric mobility diameter but an increase in fractal dimension and effective density. Meanwhile, the transition behavior is also obviously influenced by emission source which can determine the components of BC mixtures. Based on the empirically determined parameters, accurate numerical modeling shows great capability on calculating BC optical properties. However, considering the significant uncertainties related to BC microphysical properties, proper parameterization considering realistic BC aggregates and coating fraction can help to understand the progress from an externally to internally mixed state.

Sub-type source profiles for atmospheric fine particle (PM2.5) were still scare in China, which limited the accurate source identification of it. Fugitive dust (including road dust, soil dust, resuspended dust, and construction dust, etc.) was one type of the most important contributors to PM2.5 and its associated toxic metals held potential threaten to human health. The chemical compositions, sources, and health risks of sub-type fugitive dust deserved an investigation for further accurate control of particles and alleviating human health risks. A total of sixty-five fugitive dust samples were collected in Suzhou, a fast-developing city in southern China, including eleven sub-types of road dust (overpass, main street, collector street, and ordinary street), soil dust (farmland and tree lawn), resuspended dust (site types were corresponding to those of road dust), and construction dust (large construction sites). Chemical analysis of water-soluble ions, elements, and carbonaceous components was carried out to establish the sub-type source profiles of PM2.5 for fugitive dust. Results showed that crustal elements were the most abundant components of fugitive dust, and soil dust was less polluted by anthropogenic activities. High contents of OC and low contents of EC were found in all the eleven types of dust. Equivalent ratios of anions and cations indicated that the fugitive dust was obviously alkaline. The contents of OC and EC in the four types of road dust were higher than those in other types of dust, while there existed differences among the sub-types of road dust. The NO3-/SO42- ratios (0.03-0.09) implied that coal-burning and motor vehicle emission co-existed in Suzhou. Coefficient divergence (CD) values of eleven sub-type source profiles showed that there were certain differences among them, which suggested the possibility of sub-type source identification. Cluster analysis indicated the heavy metals in fugitive dust were mainly from crustal materials, metallurgical manufacturing, vehicle emissions, and industrial activities. The enrichment degree of heavy metals for the four types of road dust was also inconsistent. Heavy metals in road dust and soil dust posed a non-carcinogenic risk to children through direct ingestion, and the non-carcinogenic risk of direct intake of heavy metals was much higher than that of respiratory and skin contact. It was found that the accumulative health risks of heavy metals were higher in densely populated areas, traffic intensive areas, and industrial areas through the spatial analysis. This study firstly discussed the chemical compositions of PM2.5 for eleven sub-types of fugitive dust in a Chinese city and assessed the accumulative health risks of heavy metals, which could be a demonstration for further related researches.

The result of Aethalometer model to black carbon (BC) source apportionment is highly determined by the absorption Ångström exponent (α) of aerosols from fossil fuel combustion (αff) and wood burning (αwb). A method using hourly measured potassium to calculate the αff and αwb values was developed in this study. Results showed that the optimal αff and αwb were 1.09 and 1.79 for the whole dataset. The optimal α values in the diurnal resolution were also calculated with αff and αwb varied in 1.02 –1.19 and 1.71–1.90, respectively. Using the dynamic α values, the Pearson correlation coefficient between BC and potassium from wood burning substantially improved compared to the results derived from the fixed α values. The method developed in this study is expected to provide more reasonable BC source identification results, which are helpful for air quality, climate, and human health modeling studies.

BackgroundYellow nutsedge is a unique plant species that can accumulate up to 35% oil of tuber dry weight, perhaps the highest level observed in the tuber tissues of plant kingdom. To gain insight into the molecular mechanism that leads to high oil accumulation in yellow nutsedge, gene expression profiles of oil production pathways involved carbon metabolism, fatty acid synthesis, triacylglycerol synthesis, and triacylglycerol storage during tuber development were compared with purple nutsedge, the closest relative of yellow nutsedge that is poor in oil accumulation.ResultsCompared with purple nutsedge, high oil accumulation in yellow nutsedge was associated with significant up-regulation of specific key enzymes of plastidial RubisCO bypass as well as malate and pyruvate metabolism, almost all fatty acid synthesis enzymes, and seed-like oil-body proteins. However, overall transcripts for carbon metabolism toward carbon precursor for fatty acid synthesis were comparable and for triacylglycerol synthesis were similar in both species. Two seed-like master transcription factors ABI3 and WRI1 were found to display similar transcript patterns but were expressed at 6.5- and 14.3-fold higher levels in yellow nutsedge than in purple nutsedge, respectively. A weighted gene co-expression network analysis revealed thatABI3was in strong transcriptional coordination withWRI1and other key oil-related genes.ConclusionsThese results implied that pyruvate availability and fatty acid synthesis in plastid, along with triacylglycerol storage in oil bodies, rather than triacylglycerol synthesis in endoplasmic reticulum, are the major factors responsible for high oil production in tuber of yellow nutsedge, and ABI3 most likely plays a critical role in regulating oil accumulation. This study is of significance with regard to understanding the molecular mechanism controlling carbon partitioning toward oil production in oil-rich tuber and provides a valuable reference for enhancing oil accumulation in non-seed tissues of crops through genetic breeding or metabolic engineering.

Light-absorbing carbonaceous aerosols (LACs), including black carbon and light-absorbing organic carbon (brown carbon, BrC), have an important role in the Earth system via heating the atmosphere, dimming the surface, modifying the dynamics, reducing snow/ice albedo, and exerting positive radiative forcing. The lifecycle of LACs, from emission to atmospheric evolution further to deposition, is key to their overall climate impacts and uncertainties in determining their hygroscopic and optical properties, atmospheric burden, interactions with clouds, and deposition on the snowpack. At present, direct observations constraining some key processes during the lifecycle of LACs (e.g., interactions between LACs and hydrometeors) are rather limited. Large inconsistencies between directly measured LAC properties and those used for model evaluations also exist. Modern models are starting to incorporate detailed aerosol microphysics to evaluate transformation rates of water solubility, chemical composition, optical properties, and phases of LACs, which have shown improved model performance. However, process-level understanding and modeling are still poor particularly for BrC, and yet to be sufficiently assessed due to lack of global-scale direct measurements. Appropriate treatments of size- and composition-resolved processes that influence both LAC microphysics and aerosol–cloud interactions are expected to advance the quantification of aerosol light absorption and climate impacts in the Earth system. This review summarizes recent advances and up-to-date knowledge on key processes during the lifecycle of LACs, highlighting the essential issues where measurements and modeling need improvement.

Atmospheric black carbon makes an important but poorly quantified contribution to the warming of the global atmosphere. Laboratory and modelling studies have shown that the addition of non-black carbon materials to black carbon particles may enhance the particles’ light absorption by 50 to 60% by refracting and reflecting light. Real world experimental evidence for this ‘lensing’ effect is scant and conflicting, showing that absorption enhancements can be less than 5% or as large as 140%. Here we present simultaneous quantifications of the composition and optical properties of individual atmospheric black carbon particles. We show that particles with a mass ratio of non-black carbon to black carbon of less than 1.5, which is typical of fresh traffic sources, are best represented as having no absorption enhancement. In contrast, black carbon particles with a ratio greater than 3, which is typical of biomass burning emissions, are best described assuming optical lensing leading to an absorption enhancement. We introduce a generalised hybrid model approach for estimating scattering and absorption enhancements based on laboratory and atmospheric observations. We conclude that the occurrence of the absorption enhancement of black carbon particles is determined by the particles’ mass ratio of non-black carbon to black carbon.

Heterogeneous cellular networks (HCNs) will be the typical network structure for future mobile networks. Relay nodes (RNs), as one type of low power nodes in the HCNs, can be deployed to increase cell coverage and improve cell-edge user throughput. Since RNs may be densely deployed in hot traffic zones, the co-channel interference (CCI) is more serious and complex than that in the conventional homogeneous networks. In this paper, we propose an interference coordination oriented user association scheme in cellular relay networks for CCI coordination. Firstly, we define a relay interference matrix (RIM), which is used to decrease the interference-related information feedback overhead. Then we define a function named as interference duration density (IDD), which indicates the interference probability from a RN to a user equipment in both the time and frequency domains. Specifically, based on RIM and IDD, the proposed user association scheme can reduce the probability of the CCI from interfering RNs by adjusting the number of users associated with such interfering RNs. By doing so, the CCI among RNs can be mitigated and the system performance is improved. The proposed scheme can be applied to both the frequency reuse of RNs and the frequency sharing of RNs in one cell. In the simulation, we verify the effectiveness of the defined RIM. Then we evaluate the performance of the proposed scheme in terms of relay link user throughput, spectrum efficiency and user fairness.