Role of Carbonaceous Aerosols in Catalyzing Sulfate Formation

The persistent and fast formation of sulfate is a primary factor driving the explosive growth of fine particles and exacerbating China’s severe haze development. However, the underlying mechanism for the persistent production of sulfate remains highly uncertain. Here, we demonstrate that soot is not only a major component of the particulate matter but also a natural carbocatalyst to activate molecular O₂ and catalyze the oxidation of SO₂ to sulfate under ambient conditions. Moreover, high relative humidity, typically occurring in severe haze events, can greatly accelerate the catalytic cycle by reducing the reaction barriers, leading to faster sulfate production. The formation pathway of sulfate catalyzed by carbonaceous soot aerosols uses the ubiquitous O₂ as the ultimate oxidant and can proceed at night when photochemistry is reduced. The high relative humidity during haze episodes can further promote the soot-catalyzed sulfate-producing process. Therefore, this study reveals a missing and widespread source for the persistent sulfate haze formation in the open atmosphere, particularly under highly polluted conditions characterized by high concentrations of both SO₂ and particulate carbon, and is helpful to the development of more efficient policies to mitigate and control haze pollution

Laboratory Study on the Hygroscopic Behavior of External and Internal C₂–C₄ Dicarboxylic Acid–NaCl Mixtures

Atmospheric aerosol is usually found to be a mixture of various inorganic and organic components in field measurements, whereas the effect of this mixing state on the hygroscopicity of aerosol particles has remained unknown. In this study, the hygroscopic behavior of mixtures of C₂–C₄ dicarboxylic acids and NaCl was investigated. For both externally and internally mixed malonic acid–NaCl and succinic acid–NaCl particles, correlation between water content and chemical composition was observed and the water content of these mixtures at relative humidity (RH) above 80% can be well predicted by the Zdanovskii–Stokes–Robinson (ZSR) method. In contrast, a nonlinear relation between the total water content of the mixtures and the water content of each chemical composition separately was found for oxalic acid–NaCl mixtures. Compared to the values predicted by the ZSR method, the dissolution of oxalic acid in external mixtures resulted in an increase in the total water content, whereas the formation of less hygroscopic disodium oxalate in internal mixtures led to a significant decrease in the total water content. Furthermore, we found that the hygroscopicity of the sodium dicarboxylate plays a critical role in determining the aqueous chemistry of dicarboxylic acid–NaCl mixtures during the humidifying and dehumidifying process. It was also found that the hydration of oxalic acid and the deliquescence of NaCl did not change in external oxalic acid–NaCl mixtures. The deliquescence relative humidity (DRHs) for both malonic acid and NaCl decreased in both external and internal mixtures. These results could help in understanding the conversion processes of dicarboxylic acids to dicarboxylate salts, as well as the substitution of Cl by oxalate in the atmosphere. It was demonstrated that the effect of coexisting components on the hygroscopic behavior of mixed aerosols should not be neglected

The Effects of Mn²⁺ Precursors on the Structure and Ozone Decomposition Activity of Cryptomelane-Type Manganese Oxide (OMS-2) Catalysts

The effects of Mn²⁺ precursors on the structure and ozone decomposition activity of cryptomelane-type manganese oxide (OMS-2) catalysts were investigated under high-humidity conditions. The OMS-2 catalysts were synthesized using a hydrothermal approach. Characterization of OMS-2 was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ physical adsorption, Raman spectroscopy, X-ray absorption fine structure (XAFS), H₂ temperature-programmed reduction (H₂-TPR), and inductively coupled plasma (ICP) spectroscopy. The OMS-2-Ac synthesized using MnAc₂ as a Mn²⁺ precursor showed the best catalytic activity for ozone decomposition (∼80%) under RH = 90% and space velocity of 600000 h^–1 and is a promising catalyst for purifying waste gases containing ozone under high-humidity conditions. Acetate groups could prevent the aggregation of manganese oxide particles, which may introduce more crystalline defects. On the basis of the characterization results, it is supposed that the greater surface area and higher amount of Mn³⁺ are the main factors that contribute to the excellent performance of OMS-2-Ac. This study can improve our understanding of ozone decomposition on OMS-2 catalysts and serve as a guide in using OMS-2 for ozone removal

Heterogeneous Kinetics of <i>cis</i>-Pinonic Acid with Hydroxyl Radical under Different Environmental Conditions

To understand the atmospheric fate of secondary organic aerosol (SOA), heterogeneous degradation behaviors of a specific tracer derived from α-pinene–<i>cis</i>-pinonic acid (CPA), initiated by hydroxyl radicals (OH), were investigated under different environmental conditions using a flow reactor. The second-order rate constant (<i>k</i>₂) of the CPA–OH reaction was determined to be (6.17 ± 1.07) × 10^–12 cm³·molecule^–1·s^–1 at 25 °C and 40% relative humidity (RH). Higher temperature promoted this reaction, while relative humidity had a little inhibiting effect on it. The atmospheric lifetime of CPA varied from 2.1 to 3.3 days under different environmental conditions. Infrared spectrometry (IR), density functional theory (DFT) calculation and gas chromatography coupled mass spectrometry (GC–MS) results indicated that the oxidation products should be ascribed to poly­(carboxylic acid)­s. This study shows that the heterogeneous degradation of CPA initiated by OH radical is appreciable, and the concentrations of CPA measured in field measurements may underestimate the corresponding precursors of SOA

Nature of Ag Species on Ag/γ-Al₂O₃: A Combined Experimental and Theoretical Study

The nature of silver species on Ag/Al₂O₃ catalysts with different silver loadings was studied by photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS) combined with theoretical calculation (DFT). On the basis of selective catalytic reduction of NO_<i>x</i> by ethanol experiments, it was found that the optimum silver content varies from 1 wt % to 2 wt %. The supported silver species are predominated by +1 oxidation state ions attached to surface oxygen atoms (Ag–O) under low silver loading of 2 wt %, which play a crucial role during the HC-SCR process. An Ag–Ag shell emerged clearly in analysis of EXAFS data when silver loading was increased to 2 wt %, which was beneficial for low-temperature activity. The theoretical models for Ag_n^δ+ species (1 ≤ <i>n</i> ≤ 4, both ions and oxidized silver clusters) on alumina were consistent with the coordination structure analysis by EXAFS. The predominant silver ions are most likely stabilized at isolated tetrahedral Al sites (Ag–O–Al_IVb) on the γ-Al₂O₃ (110) surface. However, the most reactive silver ion seems to be anchored on a tricoordinate Al_III site (Ag–O–Al_III). Density of states analysis revealed that the Ag–O–Al_III entity might be a very active silver species in terms of the hybridization of Ag, O, and Al orbitals to promote its catalytic activity

Role of NH₃ in the Heterogeneous Formation of Secondary Inorganic Aerosols on Mineral Oxides

In this work, a relationship between the role of NH₃ and the properties of mineral oxides (α-Fe₂O₃, α-Al₂O₃, CaO, and MgO) in the evolution of NO₃^–, SO₄^2–, and NH₄⁺ has been established. It was found that the promotion effect of NH₃ was more favorable for the formation of NO₃^– (or SO₄^2–) and NH₄⁺ on acidic α-Fe₂O₃ and α-Al₂O₃ due to acid–base interactions between NO₂ with NH₃ or between SO₂ and NH₃, while this effect was weaker on basic CaO and MgO possibly due to their basic nature. The acid–base interaction (NO₂/SO₂ with NH₃) overpowered the redox reaction (SO₂ with NO₂) on Fe₂O₃ owing to its unique redox chemistry. However, the opposite was found on basic CaO and MgO for the formation of SO₄^2– and NO₃^–. Under equivalent concentration conditions, the two synergistic effects did not further strengthen on Fe₂O₃, CaO and MgO due to a competition effect. In NH₃-rich situation, a synchronous increase of SO₄^2–, NO₃^–, and NH₄⁺ occurred on Fe₂O₃. On acidic Al₂O₃, the favorable adsorption of NH₃ on the surface as well as the existence of NO₂ with an oxidizing capability synergistically promoted the formation of SO₄^2–, NO₃^–, and NH₄⁺

Nanosize Effect of Al₂O₃ in Ag/Al₂O₃ Catalyst for the Selective Catalytic Oxidation of Ammonia

Ammonia (NH₃) has potentially harmful effects on human health and has recently been found to be an important factor in the formation of haze; thus, its emission control is urgent, especially during haze pollution periods. In this work, two kinds of Ag/Al₂O₃ catalysts with different Al₂O₃ particle sizes (micro-Al₂O₃ and nano-Al₂O₃) were prepared and tested for the selective catalytic oxidation of ammonia (NH₃-SCO). It was shown that Ag/nano-Al₂O₃ was much more active than Ag/micro-Al₂O₃ for NH₃-SCO in the low-temperature range. The results of characterization by BET, TEM, NH₃-TPD, XRD, H₂-TPR, UV–vis, and XAFS revealed that Ag/nano-Al₂O₃ possesses much smaller Ag particles and more metallic Ag species (Ag_NPs) and also contains abundant acid sites, which facilitate the adsorption and dissociation of NH₃, therefore resulting in much higher NH₃-SCO activity. In addition, on the basis of in situ DRIFTS, kinetic measurements, and DFT calculation results, we discovered that the NH₃-SCO reaction over Ag/nano-Al₂O₃ follows a reaction pathway we call the N₂^– mechanism

The Impact of U.S. Consumption Tax Reform on Canada

<p>(A) The reactivity of various recombinant GST-fusion proteins with mAb5B7 was confirmed using Western blot. The mutant amino acids are underlined. (B) The reactivity of various mutant full-length GapC proteins with mAb5B7 was confirmed using Western blot. The mutant amino acids are highlighted with number.</p

Identification of a Conserved Linear B-Cell Epitope of <i>Streptococcus dysgalactiae - Fig 2 </i> GapC Protein by Screening Phage-Displayed Random Peptide Library

<p>(A) The purified mAb5B7 was determined by SDS-PAGE. (B) The class of the mAb5B7 was determined to be IgG1 and κ chain using mouse mAb isotyping kit. (C) GapC^1-150 recognized by mAb5B7 was detected using Western Blot. (D) The reactivity of mAb5B7 with the recombinant GapC of <i>S. dysgalactiae</i>, <i>S. uberis</i>, <i>S. agalactiae</i> and <i>S. aureus</i> was determined by Western blot. (E) The reactivity of mAb5B7 with the whole bacteria of inactivated <i>S. dysgalactiae</i>, <i>S. agalactiae</i> and <i>S. uberis</i> was confirmed by indirect ELISA (* <i>P</i> < 0.05; ** <i>P</i> < 0.01). (F) Passive immunization of mAb5B7 against <i>S. dysgalactiae</i> infection was performed and its protective effect was determined.</p

The recombinant GapC-His-TrxA protein was expressed and purified.

<p>The fusion protein was confirmed with Western Blot using anti-His antibody and anti-GapC serum, respectively.</p