Concentration Of Transition Metal Ions Research Articles

Valorization of battery manufacturing wastewater: Recovery of high-value metal ions through reaction-enhanced membrane cascade

Leveraging the latent value within battery manufacturing wastewater holds considerable potential for promoting the sustainability of the water-energy nexus. This study presents an efficient method for recovering transition metal ions (Ni2+, Co2+, Cu2+, and Cd2+) from highly saline battery wastewater (Na+, Li+, K+, or Mg2+). Our approach involves the effective utilization of a reaction-enhanced membrane cascade (REMC), comprising a meticulously orchestrated series of selective complexation-decomplexation steps involving polyethyleneimine (PEI) and various transition metal ions. This strategic intervention effectively segregates transition metal ions from salt ions during the fractionation process using an ultrafiltration membrane in a diafiltration process, overcoming osmotic pressure limitations. The ensuing concentration step via nanofiltration achieves an impressive 99 % yield and an extraordinary 215-fold concentration of transition metal ions (>99.8 % purity). The proposed method was validated with 16 different ion pairs to demonstrate its versatility, offering a pragmatic pathway for recycling various transition metal ions from industrial wastewater.

Effect of Mashing-in pH on the Biochemical Composition and Staling Properties of the Sweet Wort

Mashing is a decisive brewing step, affecting wort quality. Critical mashing parameters include time, temperature, pH, mash density and oxygen uptake. While the pH-dependent biochemical changes during mashing have been researched, the oxidative processes remain unclear. This work explores the impact of pH conditions during mashing on the biochemical composition and oxidative properties of wort. In laboratory trials, mashing was conducted at different mashing-in pH (4.5, 5.0, 5.2, 5.4, 6.0). The sweet worts were analyzed for extract, fermentable sugars, limit dextrins, amino acids, soluble proteins, polyphenols, color, aldehydes, transition metals, reducing potential, and rate of radical formation. Differences were found in enzymatic activities (particularly proteolysis), color, aldehydes, transition metal ions, the rate of radical formation and the rate of oxygen consumption. Notably, when adjusting the pH at mashing-in, the obtained wort tends to gravitate toward the pH of the unadjusted wort, underscoring its buffering capacity. This was reflected by similar properties of the produced worts, indicating pH playing a lesser role during mashing compared to time/temperature. However, under extreme acidified conditions (pH 4.5 at mashing-in), the produced wort markedly deviates. An intriguing negative correlation between the reducing potential and the content of transition metal ions with the rate of radical formation is discussed.

Crystal growth and cation order of Ni3−xCoxB2O6 oxyborates

A series of single crystals of Ni3−xCoxB2O6 compounds with the kotoite structure and with different concentrations of transition metal ions (x = 0; 0.19; 0.6; 0.93 and 2) were obtained.

Fe2+-driven Mo(IV)/Mo(VI) redox-catalyzed PMS degradation of RhB

Molybdenum disulfide (MoS2) can activate peroxymonosulfate (PMS) to degrade organic pollutants, but due to the continuous consumption of Mo(IV) during the reaction and the slow conversion of Mo(VI) to Mo(IV), the severe shortage of Mo(IV) regeneration will cause a large loss of catalyst, thus increasing the operation cost. In this study, different transition metal ions were introduced directly into the reaction system. The effects of conditions such as light, initial pH, transition metal ion concentration and PMS dose on the degradation effect of rhodamine B were investigated. The coupling mechanism was proposed based on the free radical scavenging reaction. The experimental results showed that the different transition metals activated PMS in the order of Co2+> Fe2+> Cu2+> Mn2+> Zn2+> Ni2+. In the Fe2+/MoS2/PMS/light system, the Fe2+ concentration ranging from 0.05 mM to 0.2 mM was proportional to the activation PMS efficiency. Free radical burst experiments suggested that ·OH and SO4−· were the main reactive radicals that effectively promoted the degradation of pollutants. Humic acid had an inhibitory effect on the removal of RhB from the MoS2/Fe2+/PMS/light system. Fe2+ completed its own redox cycle (Fe3+/Fe2+) while continuously catalyzing the conversion of Mo species (Mo(VI)/Mo(IV)) in 5 cycles.

Augmenting electrochemical performance of nickel-rich NMC for lithium-ion batteries by combining material synthesis modification and redistribution of transition metal ion concentration

Modification of synthesis approach and material surface are well known to be elegant straightforward routes to augment the electrochemical performance of cathode materials for lithium-ion batteries. In this study, we combined the co-precipitation method modification and surface modification of material by redistributing the transitions metal ions content to synthesis nickel-rich NMC (Li1.0Ni0.8Mn0.1Co0.1O2, NMC811 M). The pristine NMC811, and NMC811 M both exhibit high energy storage capacity with initial discharge specific capacity up to approximately 220 mAh g−1 at a current density of 10 mA g−1. The achieved results also indicate that, the NMC811 M with transition metal ion content redistribution is of better capacity retention than the pristine NMC811, it maintains approximately 73% of its original capacity after 100 cycles corresponding to a specific capacity of 153 mAh g−1. This work provides a simple but effective approach dedicated to significantly enhancing the electrochemical performance of nickel-rich NMC, and thus paves a way towards high performance battery electrodes.

Photochemical vapor generation of Zinc and Gallium

Photochemical vapor generation (PVG) of Zinc (Zn) and Gallium (Ga) was firstly reported in this study. The main parameters influencing PVG of Zn and Ga were investigated with inductively coupled plasma mass spectrometry (ICP-MS), such as the type and concentration of low molecular weight organic acids (LMWOAs), the concentration of transition metal ions and their synergistic effects, the wavelength and time of UV irradiation, and pH of sample solution. Formic acid (FA) and Cu2+ were required for the generation of volatile species of Zn and Ga. In addition, the effects of interfering ions on the PVG of Zn and Ga were investigated. Good precisions with 2.3% and 2.7% were obtained under the selected conditions for replicate measurement of 200 ng mL−1 Zn and Ga standard solution (n = 7), respectively. The limits of detection (LOD, 3σ, n = 11) were calculated to be 8.8 ng mL−1 and 0.77 ng mL−1 for Zn and Ga with PVG-ICP-MS measurement, respectively. Carbonyl compounds were speculated to be formed in this study. Moreover, nanoparticles containing Cu, Zn or Ga were found in liquid solution after UV irradiation, which may be useful for investigating the formation of natural nanoparticles in environment as well as the isotope fractionation of Zn and Ga in photochemical processes.

New Insight on the Formation of 2-Aminoacetophenone in White Wines

This study aimed to improve the understanding of 2-aminoacetophenone (2-AAP) formation in white wines, a compound responsible for atypical ageing (ATA) associated with a rapid loss of white wine fruity aroma and to the development of unpleasant odors. Two surveys performed in 139 white wines from Central Europe investigated the varietal effect on wine tendency to form 2-AAP during ageing. The role of some antioxidants and important transition metal ions present in wine (Fe, Cu and Mn) in the formation of 2-AAP was also investigated. The surveys highlighted that Muscat and Riesling wines showed significantly higher concentrations of 2-AAP than Chardonnay and some other regional varieties found in Central Europe such as Grüner Veltliner, Welschriesling and Zelen. The origin of such varietal effects could not be related to the level of any 2-AAP precursor. On the other hand, some of the important wine matrix effects were highlighted. A certain variability in capacity of different antioxidants to limit 2-AAP formation was observed. Supplementations of commercial tannins in wines tended to be more efficient than glutathione in preserving wines from the formation of 2-AAP. Transition metal ions significantly impacted 2-AAP synthesis through complex interactions. Generally, Fe and Mn tended to promote formation of 2-AAP, while the presence of Cu limited it. The higher concentration of transition metal ions significantly improved the efficiency of antioxidants to reduce 2-AAP formation. Further studies investigating the origin of varietal effects and the complex matrix effects involving metal ions and antioxidants in 2-AAP production are warranted.

The influence of transition metal ions on the oxidation of kraft pulp using hydrogen peroxide under mildly acidic conditions

Abstract Oxidation of kraft pulp using hydrogen peroxide under mild acidic conditions can be applied in order to obtain new functionality of the fibres, in the form of carbonyl groups. The hydrogen peroxide concentration must, however, be higher than consumed by the oxidation reactions meaning that the liquid must be recirculated to fully utilize the hydrogen peroxide. This paper investigates the consequences of recirculation of the oxidation liquor. It was found that recirculation results in an accumulation of ions of transition metals (copper, iron and manganese) in the oxidation liquor. The transition metal ions are known for catalytic decomposition of hydrogen peroxide, producing radicals which may react with carbohydrates, forming carbonyl groups as well as causing carbohydrate degradation. This was confirmed through the recirculation of oxidation liquor as well as through controlled addition of transition metals. At high transition metal ion concentration the reactions were fast and a severe degradation of carbohydrates was observed, accompanied by a rapid hydrogen peroxide consumption. The consequence of this, in an industrial context, is that the concentration of metal ions must be carefully controlled in order to add functionality to the cellulose without causing excessive degradation of carbohydrates or consumption of hydrogen peroxide.

Concentrations of Transition Metal Ions in Rat Lungs after Tobacco Smoke Exposure and Treatment with His-Leu Dipeptide.

Tobacco smoking is deleterious to the lungs because it exposes them to many toxic substances. These include transition metal ions, such as cadmium. However, there is a lack of information about the influence of endogenous metal-binding peptides, such as His-Leu (HL), on the lung distribution of transition metals in smokers. To address this, we administered HL subcutaneously to rats exposed to tobacco smoke for six weeks, then we measured the concentrations of transition metal ions in the lungs. We found that exposure to tobacco smoke elevates the concentrations of Cd(II) and Cu(II). Administration of the HL peptide, whose elevation is a consequence of angiotensin receptor blocker anti-hypertension therapy, increases the concentration of Fe in the lungs of rats exposed to smoke. These findings suggest that smoking is a risk factor for patients receiving angiotensin receptor blockers to treat hypertension.

Lithium-Rich Layered Oxide with a Porous Prism Architecture for High-Performance Cathode Materials of Lithium-Ion Batteries

Lithium-rich layered oxides are among the most promising cathode materials for high-energy-density lithium-ion batteries (LIBs). Besides the composition and structure, the morphology of Li-rich layered materials also has significant effects on their electrochemical performance. In this work, a porous prism architecture of Li1.2Mn0.54Ni0.13Co0.13O2 materials is constructed via a coprecipitation solvothermal method and subsequent heat treatment. Appropriate concentrations of transition metal ions and oxalic acid as the precipitant used in synthesis govern the growth of the porous prism structure. When employed as a cathode material for LIBs, the optimized material achieves a high initial discharge capacity of 295.3 mAh g–1 at 0.1C and excellent rate capability of 150.6 mAh g–1 even at 5.0C. These outstanding performances can be attributed to the synergistic effect of the porous morphology and one-dimensional prism architecture. In particular, the porous morphology promotes the intercalation and extraction of Li+ while the prism architecture is associated with the observed superior structural stability. This architecture opens a promising avenue for the development of high-performance cathode materials in LIBs.

Photocatalytic degradation of methyl orange in the presence of transition metals (Mn, Ni, Co) modified TiO2 coatings formed by plasma electrolytic oxidation

The effect of selected transition metals (Mn, Ni, Co) modified TiO2 coatings formed by plasma electrolytic oxidation of titanium on their surface morphology, phase and chemical composition, optical absorption, and photocatalytic degradation of methyl orange (MO) was investigated. Coatings were formed in an alkaline electrolyte with varying concentrations of MnO, NiO, or Co3O4 powders. The morphology, thickness and phase structure of all formed coatings are nearly identical and independent of the content of transition metal ions embedded in TiO2. The X-ray diffraction and X-ray photoelectron spectroscopy results indicated that anatase TiO2 coatings were loaded with MnO, NiO, or Co3O4 from electrolytes. When up to 2.0 g/L of MnO, NiO, or Co3O4 is added to the electrolyte, the photocatalytic activity (PA) of the forming coatings is higher than for pure TiO2. The coatings formed in electrolyte with the addition of 0.75 g/L MnO, 1.5 g/L NiO, or 2.0 g/L Co3O4 had the highest PA. Increased PA is associated with a decrease in photogenerated electron/hole recombination rate, according to UV–Vis diffuse reflectance spectroscopy and photoluminescence measurements.

Effects of Transition Metal Ions on the Colour of Blue-Green Beryl

This study reports the effects of transition metal ions on the colour of blue-green beryl. Industrial cameras were used to measure colour in the CIELAB colour space. X-ray fluorescence (XRF), X-ray diffraction (XRD), infrared spectroscopy (IR), and ultraviolet-visible (UV–vis) spectroscopy were used for characterization. The d–d transition of Fe3+ with sixfold coordination, the O2−→Fe3+ charge transfer, and the charge transition of binuclear metal M–M complexes formed by [Fe2(OH)4]2+ in the channel caused a yellow tone, whereas the charge transfer of Fe2+/Fe3+ with sixfold coordination caused a blue-green tone. The chroma of blue-green beryl was negatively correlated with the ratio of Cs+Mn to Fe contents. The lightness of blue-green beryl was negatively correlated with the total content of transition metal ions.

Fenton-magnetic based therapy by dual-chemodrug-loaded magnetic hydroxyapatite against colon cancer

Fenton-based therapy is emerging as an effective and selective strategy against cancer. However, a low concentration of transition metal ions, insufficient endogenous H2O2, and a high level of antioxidant activity within the cancer cells have hindered the therapeutic efficacy of this strategy. To address these issues, in this study, the Fenton reagent (magnetic hydroxyapatite, mHAP) was accompanied with chemotherapy drugs (cisplatin (CDDP) and methotrexate (MTX)) and static magnetic field (SMF), in such a way to be a pH-, redox-, and magnetic-responsive nanoplatform. In vitro and in vivo experiments revealed higher toxicity of the final construct, MTX.CDDP@mHAP, toward colon cancer cells, as compared with that of free drugs. The most effective antitumor activity was observed as MTX.CDDP@mHAP-treated tumor cells were exposed to SMF (0.9 T) and no noticeable damage was observed in the normal cells and tissues. Active targeting by MTX and magnetic targeting by mHAP under magnetic field increased the tumor selectivity and enhanced the tumor site accumulation and cellular uptake of MTX.CDDP@mHAPs. The released iron ions within the cancer cells trigger the Fenton reaction while the release of chemotherapy drugs, reduction of intracellular glutathione, and application of SMF aggravated the Fenton reaction, subsequently leading to the generation of reactive oxygen species (ROS) and induction of apoptosis. Therefore, Fenton magnetic-based therapy-mediated by MTX.CDDP@mHAP could be considered as a promising strategy against colon cancer with high therapeutic efficiency and biosafety.

Enhancement of the Ln3+ ratiometric nanothermometers by sensitization with transition metal ions

• The transition metal ions were used for sensitization of lanthanide ions. • This strategy enables the enhancement of the thermal LIR changes. • An increase of relative sensitivity by 300% was observed after co-doping. One of the most important parameters that affect the thermal resolution in the luminescent thermometry is the relative sensitivity of phosphor to temperature changes. Therefore various approaches to enhance its value are intensively investigated. The strategy of the relative sensitivity enhancement of the ratiometric lanthanide ions based luminescent thermometer by the sensitization with the transition metal ions is proposed in this work. It was found that by taking advantage of the temperature dependent energy transfer from transition metal ion (Mn 4+ -, Cr 3+ - and Ti 3+/4+ -) to the Tb 3+ and Eu 3+ ions in the YAG powder, the thermal variation of the Tb 3+ to Eu 3+ luminescence intensity ratio increases leading to the improvement of its thermometric properties even by 300%. Therefore, the maximal relative sensitivity increases from S R = 0.09%/°C for unco-doped powder up to S R = 0.15, 0.28, 0.30%/°C, for powders co-doped with Cr 3+ , Mn 4+ and Ti 3+/4+ , respectively. The beneficial influence of the transition metal to lanthanides energy transfer was investigated in a function of the transition metal ion concentration.

Effect of Fe3+ as an electron-transfer mediator on WO3-induced activation of peroxymonosulfate under visible light

The effect of ferric ions (Fe3+) on the degradation of organic pollutants through the photocatalytic activation of peroxymonosulfate (PMS) was investigated. In the presence of Fe3+, the degradation of 4-chlorophenol (4-CP) was significantly enhanced in the PMS/tungsten oxide (WO3) system under visible light irradiation. The enhanced degradation efficiency by Fe3+ is primarily ascribed to the role of Fe3+ as an electron-transfer mediator, as it induces a cascadal electron transfer from WO3 to Fe3+ to PMS. The production of the sulfate radical (SO4−) and its significant contribution to the degradation of 4-CP in the Fe3+/PMS/WO3 system were verified via electron paramagnetic resonance (EPR) spectroscopy and degradation experiments using radical scavengers (methanol and tert-butyl alcohol), respectively. The addition of Fe3+ to the PMS/WO3 system also significantly increased the degradation rate of other organic pollutants, such as phenol, 2,4-dimethylphenol, bisphenol A, sulfamethoxazole, sulfanilamide, and propranolol. The degradation efficiency of the Fe3+/PMS/WO3 system was largely maintained in multiple degradation cycles by the regular addition of PMS only. In addition, the Fe3+/PMS/WO3 system exhibited a higher degradation efficiency than the conventional cobaltous ion (Co2+)/PMS system at equal transition metal ion concentrations. The addition of Fe3+ for the purpose of enhancing the degradation efficiency is not restricted to the PMS activation system. This method can be applied to the activation of other oxyanions, such as peroxydisulfate (S2O82−) and bromate (BrO3−), for wastewater treatment.

Terbium-functionalized silica nanoparticles for metal ion sensing by fluorescence quenching

We describe preparation of a new luminescent material based on silica nanoparticles functionalized with terbium (Tb3+) complex of a polyamino polycarboxylic chelator, which displayed fluorescence when dispersed in aqueous and organic solvents. The functionalized material, TbL@SiO2, was firstly characterized by FTIR, UV–Vis and photoluminescent (PL) measurements. Further, it was used for various metal ions sensing as monitored by fluorescence quenching, indicating the highest decrease for iron(III), copper(II) and cobalt(II) metal ions. The calculated Stern-Volmer constants (KSV) equalled 2.21 × 105 M−1 for Fe3+, 6.81 × 105 M−1 for Cu2+ and 9.26 × 105 M−1 for Co2+, while the resulted lower detection limits reached 0.17 μM, 0.10 μM and 0.13 μM for Fe3+, Cu2+ and Co2+ respectively. In addition, the quenching mechanism was investigated through lifetime measurements which revealed a dynamic nature upon increase of the transition metal ion concentration. This was evidenced by changes in the emission lifetime (from τ0 = 1600 μs to τq = 1102 μs, thus a decrease of 31% in lifetime in presence of 8.6 μM Cu2+), most probably due to the collision interactions that affected the energy transfer of the ligand towards terbium ions.

Progress in improving the properties of dissolving pulp by enzymes

Dissolving pulp consists of high purity cellulose and is widely used to as raw materials for the production of regenerated cellulose fiber, cellulose ester and cellulose ether. The characteristic of dissolving pulp affects greatly the production and processing performance of subsequent products. The α-cellulose content, hemicellulose content, pulp viscosity, ash, transition metal ion content, fiber morphology, molecular weight distribution of cellulose and the reactivity are the important properties. Because of its green, mild and high efficiency, the application of enzymes in improving the properties of dissolving pulp has a promising application prospect and has been researched significantly. In this review, the main properties of dissolving pulp are presented first, followed by a recommendation of the enzymes to improve these properties. The application and current research of cellulase and xylanase in improving the properties of dissolving pulp are emphasized. The main problems and the future research areas in improving the properties of dissolving pulp by enzymes are revealed. Finally, the technology prospects in this field are proposed.

Physical Model of Catalyst Dissolution, Platinum Band Formation, Hydrogen Peroxide Production and Chemical Degradation of Proton Exchange Membrane in Low Temperature Fuel Cells

Low temperature fuel cells with perfluorinated proton exchange membrane (LT-PEMFC) are recognized as one of the most promising technologies for clean electricity production in automotive sector. Despite significant progress in their efficiency and reliability, the degradation of fuel cells still remains an important issue, significantly hindering their wider market adoption. Degradation processes can to some extent be avoided by the use of new, more durable materials and components, but also by properly managing the fuel cell operation and thus avoiding the conditions in which the fuel cell degradation is most pronounced. Fast and reliable computational models of fuel cell operation and degradation are crucial for efficient development of such mitigation strategies.The catalyst layer and the membrane are the components recognized as being most susceptible to degradation phenomena. In the catalyst layer, high temperature, electric potential and relative humidity lead to electrochemical corrosion of carbon support and dissolution of the catalyst, most commonly being platinum or platinum-based binary alloy. Dissolved platinum, diffusing into the membrane, plays an important role in its chemical and consequent mechanical degradation. The platinum particles in the membrane serve as the catalyst for hydrogen peroxide formation from crossover fluxes of hydrogen and oxygen, while the presence of transition metal ions, such as copper or cobalt, originating from the binary catalyst dissolution, initiate the decay of hydrogen peroxide into various radical species via Fenton-like reactions [1]. The radical’s attack on the perfluorinated chains and sulphonic groups leads to a reduction of membrane conductivity, thinning of the membrane and consequent increase in its susceptibility to mechanical degradation, caused by the swelling and shrinking of the membrane due to the changes in its humidity, which can result in formation of cracks and pinholes in the membrane.To properly model the entire causal chain of chemical membrane degradation, several individual processes mentioned above need to be coupled into a unified model. To achieve this, we present a physically based spatially and temporally resolved model of fuel cell operation, providing the detailed picture of species concentration and electric potential distribution in the fuel cell [2], coupled with innovative model of hydrogen peroxide formation, diffusion and decay into reactive radicals, causing the chemical degradation of the membrane. The model describes the electrochemical dissolution of binary alloy catalyst, its diffusion into the membrane and the formation of so-called Pt band. The hydrogen peroxide production is modeled by including both its formation in the catalyst layers and inside the Pt band by consistently taking into account the cross-over fluxes of reactants and local electric potential across the membrane [3]. The rate of radical formation (.H, .OH, .OOH) via Fenton-like reactions is modeled by considering the concentration of transition metal ions, originating from electrochemical dissolution of binary alloy catalyst and their diffusion into the membrane. The chemical degradation due to reactive radical’s attack on the membrane is described by recently developed 0-D reactor approach [4].The output of the model is a detailed spatially and temporally resolved profile of chemical groups concentration in the membrane, which enables the calculation of changes in both membrane thickness and proton conductivity. The results, indicating most pronounced membrane degradation in vicinity of Pt band, are compatible with the Raman measurements of chemical group concentrations in the aged membrane [5]. Furthermore, the testing of the model on long-term degradation experiments is used to identify the optimal fuel cell operating conditions in which the durability of the fuel cell membrane is maximized.[1] Strlič M, Kolar J, Šelih VS, Kočar D, Pihlar B. A comparative study of several transition metals in fenton-like reaction systems at circum-neutral pH, Acta Chim Slov 2003;50:619–32.[2] Tavčar G, Katrašnik T. A Real Time Capable Quasi 3D System Level Model of PEM Fuel Cells, Fuel Cells 2020;20:17–32.[3] Burlatsky SF, Gummalla M, Atrazhev V V., Dmitriev D V., Kuzminyh NY, Erikhman NS. The Dynamics of Platinum Precipitation in an Ion Exchange Membrane, J Electrochem Soc 2011;158:B322.[4] Frühwirt P, Kregar A, Törring JT, Katrašnik T, Gescheidt G. Holistic approach to chemical degradation of Nafion membranes in fuel cells: modelling and predictions, Phys Chem Chem Phys 2020;22:5647–66.[5] Ohma A, Yamamoto S, Shinohara K. Membrane degradation mechanism during open-circuit voltage hold test. J Power Sources 2008;182:39–47. Figure 1

Observation of chemical components of PM2.5 and secondary inorganic aerosol formation during haze and sandy haze days in Zhengzhou, China

Mineral dust particles play an important role in the formation of secondary inorganic aerosols, which largely contribute to haze pollution in China. During this study, a haze episode (haze days) and a typical haze process mixed with sandstorm (sandy haze days) were observed in Zhengzhou with a series of high-time-resolution monitoring instruments from November 22 to December 8, 2018. Concentrations of PM10 and crustal elements clearly increased in the sandy haze days. Concentrations of gaseous pollutants, metallic elements emitted from anthropogenic sources, nitrate, and ammonium during sandy haze days were slightly lower than those during the haze days but still obviously higher than those during the non-haze days. The sulfate concentrations, the sulfate fractions in PM2.5, and the sulfur oxidation ratios significantly increased in the sandy haze days. Heterogeneous reactions dominated the conversion of SO2 during the haze and sandy haze days. Enhanced SO2 conversion during the sandy haze days may be attributed to the high concentrations of transition metal ions from the sandstorm when the values of relative humidity (RH) were in 30%–70%, and high O3 at certain time points. Gas-phase NO2 oxidation reactions were the main pathways for nitrate formation. In the sandy haze days, higher nitrogen oxidation ratio (NOR) at daytime may be associated with higher RH and lower temperature than those in the haze days, which facilitate the gas-to-particle partitioning of nitrate; higher NOR values at night may be attributed to the higher O3 concentrations, which promoted the formation of N2O5.

Measurements of HO2 uptake coefficient on aqueous (NH4)2SO4 aerosol using aerosol flow tube with LIF system

Laboratory studies of HO2 uptake coefficients, γ(HO2), were conducted at room temperature using an aerosol flow tube coupled with a laser induced fluorescence (LIF) system. The measurement was conducted with atmospherically relevant HO2 concentrations (∼1×109molecule/cm3) at 51% RH. The measured γ(HO2) onto aqueous (NH4)2SO4 aerosol was 0.001 ± 0.0007, which was consistent with the relatively low first-order loss rate of HO2 onto aqueous (NH4)2SO4 aerosol. The γ(HO2) was elevated with increase of Cu(II) concentrations in aqueous (NH4)2SO4 aerosol. The threshold of Cu(II) concentration was 10−3 mol/L for the dramatic increase of γ(HO2). It was found that γ(HO2) reached 0.1 when Cu(II) concentration in aerosol was larger than 10−3 mol/L, suggesting that γ(HO2) is very sensitive to concentration of transition metal ions in aerosol.