On using an aerosol thermodynamic model to calculate aerosol acidity of coarse particles.

Thermodynamic modeling is still the most widely used method to characterize aerosol acidity, a critical physicochemical property of atmospheric aerosols. However, it remains unclear whether gas-aerosol partitioning should be incorporated when thermodynamic models are employed to estimate the acidity of coarse particles. In this work, field measurements were conducted at a coastal city in northern China across three seasons, and covered wide ranges of temperature, relative humidity and NH3 concentrations. We examined the performance of different modes of ISORROPIA-II (a widely used aerosol thermodynamic model) in estimating aerosol acidity of coarse and fine particles. The M0 mode, which incorporates gas-phase data and runs the model in the forward mode, provided reasonable estimation of aerosol acidity for coarse and fine particles. Compared to M0, the M1 mode, which runs the model in the forward mode but does not include gas-phase data, may capture the general trend of aerosol acidity but underestimates pH for both coarse and fine particles; M2, which runs the model in the reverse mode, results in large errors in estimated aerosol pH for both coarse and fine particles and should not be used for aerosol acidity calculations. However, M1 significantly underestimates liquid water contents for both fine and coarse particles, while M2 provides reliable estimation of liquid water contents. In summary, our work highlights the importance of incorporating gas-aerosol partitioning when estimating coarse particle acidity, and thus may help improve our understanding of acidity of coarse particles.

Controls for phytolith accumulation in Moso bamboo leaves across China.

Phytoliths are amorphous silica formed gradually in plant tissue, which have great potential to mitigate climate change due to their resistance to decomposition and their ability to occlude organic carbon. The accumulation of phytoliths is regulated by multiple factors. However, the factors controlling its accumulation remain unclear. Here, we investigated phytolith content in Moso bamboo leaves of different ages collected from 110 sampling sites of their main distribution regions across China. The controls for phytolith accumulation were studied by correlation and random forest analyses. Our results showed that phytolith content is leaf age-dependent (16-month-old leaf >4-month-old leaf >3-month-old leaf). Phytolith accumulation rate in Moso bamboo leaves is significantly correlated with mean monthly temperature (MMT) and mean monthly precipitation (MMP). About 67.1 % of the variance of the phytolith accumulation rate could be explained by multiple environmental factors, mainly MMT and MMP. Therefore, we conclude that the weather is the major driver that regulates the phytolith accumulation rate. Our study provides a unique dataset for estimating phytolith production rate and the potential carbon sequestration of phytolith through climatic factors.

Heterogeneous reaction of NO2 with feldspar, three clay minerals and Arizona Test Dust.

Heterogeneous reaction of NO2 with mineral dust aerosol may play important roles in troposphere chemistry, and has been investigated by a number of laboratory studies. However, the influence of mineralogy on this reaction has not been well understood, and its impact on aerosol hygroscopicity is not yet clear. This work investigated heterogeneous reactions of NO2 (∼10 ppmv) with K-feldspar, illite, kaolinite, montmorillonite and Arizona Test Dust (ATD) at room temperature as a function of relative humidity (<1% to 80%) and reaction time (up to 24 hr). Heterogeneous reactivity towards NO2 was low for illite, kaolinite, montmorillonite and ATD, and uptake coefficients of NO2, γ(NO2), were determined to be around or smaller than 1×10-8; K-feldspar exhibited higher reactivity towards NO2, and CaCO3 is most reactive among the nine mineral dust samples considered in this and previous work. After heterogeneous reaction with NO2 for 24 hr, increase in hygroscopicity was nearly insignificant for illite, kaolinite and montmorillonite, and small but significant for K-feldspar; in addition, large increase in hygroscopicity was observed for ATD, although the increase in hygroscopicity was still smaller than CaCO3.

Enhancement of phytolith-occluded carbon accumulation of Moso bamboo response to temperatures elevation and different fertilization.

The accumulation of phytolith-occluded carbon (PhytOC) in Moso bamboo could be a novel long-term carbon sequestration strategy. The objective of this study was to investigate the effects of temperature change and different fertilization on PhytOC accumulation. The pot experiment was established with different fertilization (including control (CK), nitrogen fertilizers (N), silicon fertilizers (Si), and a combination of nitrogen and silicon (NSi)) under high- and low-temperature. Despite the different fertilization, the PhytOC accumulation of the high-temperature group increases by 45.3% on average compared with the low-temperature group, suggesting higher temperature is greatly beneficial to the PhytOC accumulation. Fertilization significantly increases the accumulation of PhytOC (increased by 80.7% and 48.4% on average for the low- and high-temperature group, respectively) compared with CK. However, the N treatment increased both Moso bamboo biomass and PhytOC accumulation. The difference in the accumulation of PhytOC in Si and NSi was insignificant, indicating the combination of N and Si didn't bring extra benefit to PhytOC accumulation compared to Si fertilizer alone. These results indicated the application of nitrogen fertilizer is a practical and effective method for enhancing long-term carbon sequestration for Moso bamboo. Based on our study, we conclude that global warming poses a positive effect on promoting the long-term carbon sequestration of Moso bamboo.

Mass fractions, solubility, speciation and isotopic compositions of iron in coal and municipal waste fly ash.

Deposition of anthropogenic aerosols may contribute significantly to dissolved Fe in the open ocean, affecting marine primary production and biogeochemical cycles; however, fractional solubility of Fe is not well understood for anthropogenic aerosols. This work investigated mass fractions, solubility, speciation and isotopic compositions of Fe in coal and municipal waste fly ash. Compared to desert dust (3.1 ± 1.1%), the average mass fraction of Fe was higher in coal fly ash (6.2 ± 2.7%) and lower in municipal waste fly ash (2.6 ± 0.4%), and the average Fe/Al ratios were rather similar for the three types of particles. Municipal waste fly ash showed highest Fe solubility (1.98 ± 0.43%) in acetate buffer (pH: 4.3), followed by desert dust (0.43 ± 0.30%) and coal fly ash (0.24 ± 0.28%), suggesting that not all the anthropogenic aerosols showed higher Fe solubility than desert dust. For the samples examined in our work, amorphous Fe appeared to be an important controlling factor for Fe solubility, which was not correlated with particle size or BET surface area. Compared to desert dust (-0.05‰ to 0.21‰), coal and municipal waste fly ash showed similar or even higher δ56Fe values for total Fe (range: 0.05‰ to 0.75‰), implying that the presence of coal or municipal waste fly ash may not be able to explain significantly smaller δ56Fe values reported for total Fe in ambient aerosols affected by anthropogenic sources.

In situ transient Laue x-ray diffraction during high strain-rate tension.

In situ transient synchrotron Laue x-ray diffraction based on high-energy and broadband x rays under high strain-rate tensile loading was developed at a superconducting wiggler beamline at the Beijing Synchrotron Radiation Facility. A split-Hopkinson tensile bar is utilized to realize this dynamic loading condition, while the transient Laue x-ray diffraction captures the transient internal structure of monocrystalline materials. Plastic deformation of a monocrystalline nickel specimen was investigated to prove the ability of this instrumentation in the characterization of a dynamic response of monocrystalline materials during a high strain-rate impact process with 5 µs time resolution.

A survey of chloramphenicol residues in aquatic products of Shenzhen, South China.

Food safety is a top priority of concern for consumers. To promote growth, as well as to treat diseases which occur in aquaculture, antibiotics, even banned veterinary antibiotics, are widely used. This survey investigated the levels of chloramphenicol (CAP) by LC-MS/MS in 291 aquatic samples (all the products in this survey were local sales, exported products were not included), including shellfish, shrimp and fish, from Shenzhen, South China. The CAP concentrations in these samples (based on wet weight) were: shellfish (

Silicon fertilizer and biochar effects on plant and soil PhytOC concentration and soil PhytOC stability and fractionation in subtropical bamboo plantations.

The use of exogenous silicon (Si) amendments, such as Si fertilizers and biochar, can effectively increase crop Si uptake and the formation of phytoliths, which are siliceous substances that are abundant in numerous plant species. Phytolith-occluded carbon (C) (PhytOC) accumulation in soil plays an important role in long-term soil organic C (SOC) storage. Nevertheless, the effects of both Si fertilizer and biochar application on PhytOC sequestration in forest plant-soil systems have not been studied. We investigated the impact of Si fertilizer and biochar applications on 1) the PhytOC pool size, the solubility of plant and soil phytoliths, and soil PhytOC in soil physical fractions (light (LFOM) and heavy fractions of organic matter (HFOM)) in Moso bamboo (Phyllostachys pubescens) forests; and 2) the relationships among plant and soil PhytOC concentrations and soil properties. We used a factorial design with three Si fertilizer application rates: 0 (S0), 225 (S1) and 450 (S2) kg Si ha-1, and two biochar application rates: 0 (B0) and 10 (B1) t ha-1. The concentrations of PhytOC in the bamboo plants and topsoil (0-10 cm) increased with increasing Si fertilizer addition, regardless of biochar application. Biochar addition increased the soil PhytOC pool size, as well as the LFOM- and HFOM-PhytOC fractions, regardless of Si fertilizer application. The Si fertilizer application increased or had no effect on soil phytolith solubility with or without biochar application, respectively. Soil PhytOC was correlated with the concentration of soil organic nitrogen (R2 = 0.32), SOC (R2 = 0.51), pH (R2 = 0.28), and available Si (R2 = 0.23). Furthermore, Si fertilizer application increased plant and soil PhytOC by increasing soil available Si. Moreover, biochar application increased soil PhytOC concentration in LFOM-PhytOC and the unstable fraction of PhytOC. We conclude that Si fertilizer and biochar application promoted PhytOC sequestration in the plant-soil system and changed its distribution in physical fractions in the Moso bamboo plantation in subtropical China.

Colorimetric determination of uranyl (UO22+) in seawater via DNAzyme-modulated photosensitization.

Various DNA-modulated photosensitization schemes have been reported for various applications, but DNAzyme has not yet been included. Here, we found the DNAzyme with metal ion as cofactor could also be efficient in modulation of photosensitization process. The UO22+-specific DNAzyme can switch between double strand DNA (dsDNA) and single strand DNA (ssDNA) upon UO22+ cleavage, which can regulate the photosensitization process of SYBR Green I. Coupling with photosensitization-induced chromogenic reaction (TMB oxidation), a simple colorimetric sensor for UO22+ was developed accordingly. To increase the visual resolution of the proposed assay, a background color was supplied. Compared with the previous DNAzyme-based UO22+ sensors, the proposed assay featured label-free and simple. Besides, the tolerance for high salinity of this assay is appealing. The proposed assay offered a detection limit of 0.08 µg/L with UV-vis detection and 0.5 µg/L with the naked eye. With the proposed colorimetric assay, UO22+ levels in the range of 0.7-1.2 µg/L (2.9-5.0 nM) were identified in high salinity seawater samples, with spike-recoveries ranging from 93% to 104%.

Photosensitization of Molecular Oxygen on Graphene Oxide for Ultrasensitive Signal Amplification.

H2 O2 and horseradish peroxidase (HRP) are commonly used together in bioassays. HRP is required to accelerate the reaction between a chromogenic substrate (e.g., 3,3',5,5'-tetramethylbenzidine, TMB) and H2 O2 , and thus amplifies the signal. Herein, molecular oxygen for enzyme-free and H2 O2 -free oxidation is explored, still using the same colorimetric reaction. Restricted by spin selection rules, the ground-state triplet oxygen needs to be converted to the singlet state to oxidize TMB. Phloxine B (PB) is used as the photosensitizer because of its excellent performance and safety. Under green light irradiation, each PB has a turnover of approximately 51 TMB molecules in 20 min, making PB a "molecular enzyme mimic" for signal amplification. With its small size, multiple PB molecules are loaded on a graphene oxide nanosheet to design a modified enzyme-linked immunosorbance (ELISA) assay (termed photosensitization immunosorbent assay, PISA), improving the 1:1 enzyme/target ratio to n:1. PISA is more sensitive for carcinoembryonic antigen than a commercial ELISA kit, and successfully measures the antigen in the serum of multiple cancer patients. This simple and green method of oxidation coupled with the small size of the photosensitizer and graphene oxide may enable many other applications in biosensor development, smart materials, and energy harvesting.

Photocatalytic oxidation of TMB with the double stranded DNA-SYBR Green I complex for label-free and universal colorimetric bioassay.

We report here the newly discovered photocatalytic activity of the dsDNA-SYBR Green I (SG) complex, which can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) under light irradiation corresponding to the excitation of the dsDNA-SG complex. The most appealing feature of the photocatalytic system here is that it can be obtained using random DNA sequences that can form a duplex. Considering the universality of the photooxidase, a label-free and universal platform was proposed for highly sensitive visual bioassays.