Heterogeneous Nitrate Production Mechanisms in Intense Haze Events in the North China Plain

Abstract Studies of wintertime air quality in the North China Plain (NCP) show that particulate-nitrate pollution persists despite rapid reduction in NOx emissions. This intriguing NOx-nitrate relationship may originate from non-linear nitrate-formation chemistry, but it is unclear which feedback mechanisms dominate in NCP. In this study, we re-interpret the wintertime observations of 17O excess of nitrate (∆17O(NO3−)) in Beijing using the GEOS-Chem (GC) chemical transport model to estimate the importance of various nitrate-production pathways and how their contributions change with the intensity of haze events. We also analyze the relationships between other metrics of NOy chemistry and [PM2.5] in observations and model simulations. We find that the model on average has a negative bias of −0.9‰ and −3617O(NO3−) and [Ox,major] (≡ [O3] + [NO2] + [p-NO3−]), respectively, while overestimating the nitrogen oxidation ratio ([NO3−]/([NO3−] + [NO2])) by +0.12 in intense haze. The discrepancies become larger in more intense haze. We attribute the model biases to an overestimate of NO2-uptake on aerosols and an underestimate in wintertime O3 concentrations. Our findings highlight a need to address uncertainties related to heterogeneous chemistry of NO2 in air-quality models. The combined assessment of observations and model results suggest that N2O5 uptake in aerosols and clouds is the dominant nitrate-production pathway in wintertime Beijing, but its rate is limited by ozone under high-NOx-high-PM2.5 conditions. Nitrate production rates may continue to increase as long as [O3] increases despite reduction in [NOx], creating a negative feedback that reduces the effectiveness of air pollution mitigation

Photocatalytic Degradation of Deoxynivalenol Using Cerium Doped Titanium Dioxide under Ultraviolet Light Irradiation

Deoxynivalenol (DON) is a major mycotoxin with high toxicity that often contaminates grains, foods and feeds. The traditional approaches for DON removal are difficult to meet industry and agriculture demands due to the high stability of the DON molecule. Therefore, there is an urgent need to develop green and effective strategies for DON degradation. In this study, a batch of photocatalytic nanomaterials of cerium (Ce) doped titanium dioxide (TiO2) were successfully prepared by sol-gel method. The catalysts were systematically characterized by XRD, HRTEM, FT-IR, UV-Vis and XPS. The catalyst 0.5Ce-TiO2 showed superior photocatalytic activity for DON degradation in aqueous solution under ultraviolet light irradiation, better than that of traditional photocatalyst pure TiO2, and 96% DON with initial concentration of 5.0 mg/L could be degraded in 4 h. In addition, the two possible degradation intermediate products C5H8O3 and C17H18O6 were identified, the photocatalytic degradation mechanism and degradation pathway were studied. The results indicate that Ce doped TiO2 photocatalyst can be used to reduce DON effectively

Occurrence and Risk Assessment of Dietary Exposure to Deoxynivalenol in Wheat-Based Products Based Different Wheat-Producing Area for the Inhabitants in Shanghai, China

Deoxynivalenol (DON) is one of the major mycotoxins that contaminate cereals. In this study, we determined the DON level in wheat-based products from Chinese five main production areas collected in Shanghai and calculated the daily intake of DON for inhabitants using the point evaluation and the probabilistic evaluation based on Monte Carlo simulation. The results showed the positive rates of DON in the products were higher than 80.0%, with the concentrations ranging from 41.8 to 1110 µg/kg. The estimated mean daily intakes of DON for 7- to 10-year-old children and adults groups were below 1 µg/kg bw/day, the provisional maximum tolerable daily intake (PMTDI) set by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), suggesting no health risks for the consumers. However, the 99th percentiles of dietary DON exposures for children and adults exceeded the PMTDI, indicating adverse health effects might occur if the two groups intake highly contaminated wheat-based products. The potential health risks for the two groups exposed to DON in the wheat-based products from the Middle and Lower Yangtze Valley (MLYV) were higher than those from the other areas in China

Isotopic constraints on heterogeneous sulphate production in Beijing haze

Discerning mechanisms of sulfate formation during fine-particle pollution (referred to as haze hereafter) in Beijing is important for understanding the rapid evolution of haze and for developing cost-effective air pollution mitigation strategies. Here we present the first observations of the oxygen-17 excess of PM2.5 sulfate (Δ17O(SO42−)) collected in Beijing haze from October 2014 to January 2015, to constrain possible sulfate formation pathways. Throughout the sampling campaign, the 12h-averaged PM2.5 concentrations ranged from 16 to 323 μg m−3 with a mean of (141 ± 88 (1σ)) μg m−3, with SO42− representing 8–25 % of PM2.5 mass. The observed Δ17O(SO42−) varied from 0.1 ‰ to 1.6 ‰ with a mean of (0.9 ± 0.3) ‰.Δ17O(SO42−)increased with PM2.5 levels in October 2014 while the opposite trends were observed in November 2014 to January 2015. Heterogeneous sulfate production rate (Phet) on aerosols was estimated to enhance with PM2.5 levels, generally dominating sulfate formation during haze days when cloud liquid water content (LWC) was low. When LWC was high, however, in-cloud reactions would dominate haze sulfate formation with a fractional contribution up to 68 %. For the specific mechanisms of heterogeneous oxidation of SO2, chemical reaction kinetics calculations suggest S(IV) (= SO2•H2O + HSO3− + SO32−) oxidation by H2O2 in aerosol water accounted for 5–13 % of Phet. The relative importance of heterogeneous sulfate production by other mechanisms was constrained by our observed Δ17O(SO42−). Heterogeneous sulfate production via S(IV) oxidation by O3 was estimated to contribute 21–22 % of Phet on average. Heterogeneous sulfate production pathways that result in zero-Δ17O(SO42−), such as S(IV) oxidation by NO2 in aerosol water and/or by O2 on acidic microdroplets via a radical chain mechanism, contributed the remain 66–73 % of Phet. The assumption about the thermodynamic state of aerosols (stable or metastable) was found to significantly influence the calculated aerosol pH (7.6 ± 0.1 or 4.7 ± 1.1, respectively), and thus influence the relative importance of heterogeneous sulfate production via S(IV) oxidation by NO2 and by O2 on acidic microdroplets. Our calculation suggests sulfate formation via NO2 oxidation can be the dominant pathway in aerosols at high pH-conditions calculated assuming stable state while S(IV) oxidation by O2 on acidic microdroplets can be the dominant pathway providing that highly acidic aerosols (pH ≤ 3) exist. Our results also illustrate the utility of Δ17O(SO42−) for quantifying sulfate formation pathways and its inclusion in models may improve our understanding of rapid sulfate formation during haze events

Flavonoid Compound Icariin Activates Hypoxia Inducible Factor-1α in Chondrocytes and Promotes Articular Cartilage Repair.

Articular cartilage has poor capability for repair following trauma or degenerative pathology due to avascular property, low cell density and migratory ability. Discovery of novel therapeutic approaches for articular cartilage repair remains a significant clinical need. Hypoxia is a hallmark for cartilage development and pathology. Hypoxia inducible factor-1alpha (HIF-1α) has been identified as a key mediator for chondrocytes to response to fluctuations of oxygen availability during cartilage development or repair. This suggests that HIF-1α may serve as a target for modulating chondrocyte functions. In this study, using phenotypic cellular screen assays, we identify that Icariin, an active flavonoid component from Herba Epimedii, activates HIF-1α expression in chondrocytes. We performed systemic in vitro and in vivo analysis to determine the roles of Icariin in regulation of chondrogenesis. Our results show that Icariin significantly increases hypoxia responsive element luciferase reporter activity, which is accompanied by increased accumulation and nuclear translocation of HIF-1α in murine chondrocytes. The phenotype is associated with inhibiting PHD activity through interaction between Icariin and iron ions. The upregulation of HIF-1α mRNA levels in chondrocytes persists during chondrogenic differentiation for 7 and 14 days. Icariin (10-6 M) increases the proliferation of chondrocytes or chondroprogenitors examined by MTT, BrdU incorporation or colony formation assays. Icariin enhances chondrogenic marker expression in a micromass culture including Sox9, collagen type 2 (Col2α1) and aggrecan as determined by real-time PCR and promotes extracellular matrix (ECM) synthesis indicated by Alcian blue staining. ELISA assays show dramatically increased production of aggrecan and hydroxyproline in Icariin-treated cultures at day 14 of chondrogenic differentiation as compared with the controls. Meanwhile, the expression of chondrocyte catabolic marker genes including Mmp2, Mmp9, Mmp13, Adamts4 and Adamts5 was downregulated following Icariin treatment for 14 days. In a differentiation assay using bone marrow mesenchymal stem cells (MSCs) carrying HIF-1α floxed allele, the promotive effect of Icariin on chondrogenic differentiation is largely decreased following Cre recombinase-mediated deletion of HIF-1α in MSCs as indicated by Alcian blue staining for proteoglycan synthesis. In an alginate hydrogel 3D culture system, Icariin increases Safranin O positive (SO+) cartilage area. This phenotype is accompanied by upregulation of HIF-1α, increased proliferating cell nuclear antigen positive (PCNA+) cell numbers, SOX9+ chondrogenic cell numbers, and Col2 expression in the newly formed cartilage. Coincide with the micromass culture, Icariin treatment upregulates mRNA levels of Sox9, Col2α1, aggrecan and Col10α1 in the 3D cultures. We then generated alginate hydrogel 3D complexes incorporated with Icariin. The 3D complexes were transplanted in a mouse osteochondral defect model. ICRS II histological scoring at 6 and 12 weeks post-transplantation shows that 3D complexes incorporated with Icariin significantly enhance articular cartilage repair with higher scores particularly in selected parameters including SO+ cartilage area, subchondral bone and overall assessment than that of the controls. The results suggest that Icariin may inhibit PHD activity likely through competition for cellular iron ions and therefore it may serve as an HIF-1α activator to promote articular cartilage repair through regulating chondrocyte proliferation, differentiation and integration with subchondral bone formation

Icariin increases chondrocytes proliferation.

<p>(A) MTT assay for cell viability of chondrocytes treated with or without Icariin (0 M, 10⁻⁷ M, 10⁻⁶ M, 10⁻⁵ M) for 3 days. Treated groups compared with control group, *<i>P</i> < 0.05, **<i>P</i> < 0.01, n = 3. (B) BrdU incorporation assay for chondrocytes treated with or without Icariin (0 M, 10⁻⁷ M, 10⁻⁶ M, 10⁻⁵ M) for 1 day or 3 days. Treated groups compared with control group, *<i>P</i> < 0.05; ***<i>P</i> < 0.001, n = 3. (C) Colony formation assay for chondroprogenitor cells treated with Icariin (10⁻⁷ M, 10⁻⁶ M, 10⁻⁵ M) for 24 h followed by 14 days sub-culture. (D) Quantitation of the colony numbers from (C), *<i>P</i> < 0.05, n = 3.</p

Icariin upregulates HIF-1α expression in chondrocytes by inhibiting PHDs activity through competition for iron ions.

<p>(A) The chemical formula of Icariin. (B) Hypoxia response element luciferase reporter assay in C2C12 cells treated with Icariin at indicated concentrations. (C) Western blot analysis for HIF-1α protein expression in primary culture-derived chondrocytes under normoxia or hypoxia or treated with or without Icariin (10⁻⁶ M) for 8 h. β-actin used as the loading control. (D) Detection of HIF-1α nuclear localization in Icariin (10⁻⁶ M)-treated chondrocytes by immunofluorescence staining under confocal microscope. (E, F) Chondrocytes were cultured and induced to differentiate in chondrogenic medium in the presence or absence of Icariin (10⁻⁶ M) for 7 or 14 days. HIF-1α mRNA levels were detected by real-time PCR in Icariin-treated chondrocytes compared with that of the control cells. *<i>P</i> < 0.05, **<i>P</i> < 0.01, n = 3. (G) UV-Vis spectra of the Icariin, FeSO₄ and their mixture (<i>n</i>_Icariin: <i>n</i>_FeSO4 = 3: 1, <i>C</i>_Icariin = 0.5mM) in aqueous solution after incubation at 37°C for 12 h; <i>C</i>_Icariin = 0.5mM; <i>C</i>_FeSO4 = 1mM; The inset shows the visual appearance of each species. (H) Western blot analysis for HIF-1α protein expression in chondrocytes treated with or without Icariin (10⁻⁶ M) and FeSO₄ (100 μM) for 12 h. (I) Western blot analysis for PHDs and HIF-1α protein expression in chondrocytes treated with or without Icariin (10⁻⁶ M) for 12 h. In all Figs, ICA, Icariin.</p

Deletion of HIF-1α eliminates the positive effects of Icariin on chondrocytes.

<p>(A) Western blot analysis for HIF-1α protein expression in MSCs (HIF-1α Floxed) following treatment with Ad-GFP or Ad-Cre and treated with or without Icariin (10⁻⁶ M) for 12 h. β-actin used as the loading control. (B) Alcian blue staining for preoteoglycan synthesis in MSCs (HIF-1α floxed) following treatment with Ad-GFP or Ad-Cre and treated with or without Icariin (10⁻⁶ M) for 14 days. (C) Quantitation of the value of integral optical density (IOD) from (B). Compared with Ad-GFP-treated control group, *<i>P</i> < 0.05; n = 3. (D) BrdU incorporation assay for chondrocytes following treatment with Ad-GFP or Ad-Cre and treated with or without Icariin (10⁻⁶ M) for 48 h. Compared with Ad-GFP-treated control group, *<i>P</i> < 0.05, **<i>P</i> < 0.01; n = 3. Compared with Ad-GFP-treated ICA control group, ^##<i>P</i> < 0.01; n = 3. (E, F) Chondrocytes following treatment with Ad-GFP or Ad-Cre were cultured under normal medium in the presence or absence of Icariin (10⁻⁶ M). (E) <i>Sox9</i>, <i>Aggrecan</i> and <i>Col2α1</i> mRNA expression in chondrocytes was detected by real-time PCR. (F) <i>Adamts4</i>, <i>Mmp2</i>, and <i>Mmp9</i> mRNA expression in chondrocytes was detected by real-time PCR. Compared with Ad-GFP-treated control group,*<i>P</i> < 0.05, **<i>P</i> < 0.01; n = 3. Compared with Ad-Cre-treated control group, ^#<i>P</i> < 0.05; ^##<i>P</i> < 0.01; n = 3.</p

Icariin inhibits catabolic marker genes expression in chondrocytes.

<p>Chondrocytes were cultured and induced to differentiate in chondrogenic medium in the presence or absence of Icariin (10⁻⁶ M) for 7 (A) or 14 (B) days. <i>Mmp2</i>, <i>Mmp9</i>, <i>Mmp13</i>, <i>Adamts4</i> and <i>Adamts5</i> mRNA expression was detected by real-time PCR in Icariin treated chondrocytes compared with that of the control cells. *<i>P</i> < 0.05; **<i>P</i> < 0.01; n = 3.</p

Icariin enhances chondrogenic marker expression and cartilage matrix synthesis while the effect is limited by knockdown of HIF-1α.

<p>(A) Chondrocytes were processed for micromass culture and induced to differentiate in chondrogenic medium in the presence or absence of Icariin (10⁻⁷ M, 10⁻⁶ M, 10⁻⁵ M). The cell masses were stained with Alcian blue after 7 or 14 days culture, respectively. Note that Icariin (10⁻⁶ M) increased proteoglycan synthesis. (B) Quantitation of the value of integral optical density (IOD) from (A). Treated groups compared with control group, *<i>P</i> < 0.05; **<i>P</i> < 0.01; ***<i>P</i> < 0.01, n = 3. (C, D) ELISA assays for production of aggrecan (C) and hydroxypoline (D) in chondrocytes. Icariin treated groups versus control groups, *<i>P</i> < 0.05; **<i>P</i> < 0.01; ***<i>P</i> < 0.001, n = 3. (E, F) Chondrocytes were cultured and induced to differentiate in chondrogenic medium in the presence or absence of Icariin (10⁻⁶ M) for 7 (E) or 14 (F) days. <i>Sox9</i>, <i>Col2α1</i> and <i>Aggrecan</i> mRNA expression was detected by real-time PCR in Icariin treated chondrocytes and compared with that in the control cells. *<i>P</i> < 0.05, **<i>P</i> < 0.01; ***<i>P</i> < 0.001, n = 3.</p