The influence of relative humidity on the heterogeneous oxidation of sulfur dioxide by ozone on calcium carbonate particles

A Method to Reduce the Occurrence of Egg Translucency and Its Effect on Bacterial Invasion

Translucent egg consumption is low due to consumer acceptance and quality concerns, which is a problem that egg producers need to address. This study was performed to evaluate the reasons for the high occurrence of egg translucency in summer, as well as whether the addition of mono-dicalcium phosphate (MDCP) to the diet can relieve eggshell translucency and whether eggshell translucency is associated with the risk of bacterial invasion. A total of 72 laying hens that were 36 weeks old were randomly divided into control (CON) and MDCP groups and fed in the same environment. Results showed that the number of translucent eggs increases in July and August as the temperature and humidity increase. Compared with the CON group, in July, August, and October, the translucent egg grade (TEG) of the MDCP group was lower than that of the CON group (p < 0.05). TEG was correlated with mastoid space height (MSH), width (MSW), and area (MSA) (correlation coefficients 0.63, 0.59, and 0.68, respectively, p ≤ 0.05). There was no significant difference in the invasion rate of E. coli between translucent and non-translucent egg groups (47.2% vs. 39.33%), and translucent area and non-translucent area (13.49% vs. 15.08%). In conclusion, our results show that dietary MDCP may alleviate eggshell translucency and that eggshell translucency would not increase the probability of E. coli cross-shell penetration rate.

Mineralogy and phase transition mechanisms of atmospheric mineral particles: Migration paths, sources, and volatile organic compounds

Inorganic mineral particles play an important role in the formation of atmospheric aerosols in the Sichuan Basin. Atmospheric haze formation is accompanied by the phase transition of mineral particles under high humidity and stable climatic conditions. Backward trajectory analysis was used in this study to determine the migration trajectory of atmospheric mineral particles. Furthermore, Positive matrix factorization (PMF) was used to analyze the sources of atmospheric mineral particles. The phase transition mechanisms of atmospheric mineral particles were studied using ion chromatography, inductively coupled plasma emission spectrometry, total organic carbon analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive spectrometry, and grand canonical Monte Carlo methods. Three migration and phase transition paths were identified for the mineral particles. Sources of atmospheric mineral particles included combustion, vehicle emissions, industrial emissions, agricultural sources, and mineral dust. The main mineral phases in atmospheric particles, calcite and dolomite, were transformed into gypsum, and muscovite may be transformed into kaolinite. The phase transition of mineral particles seriously affects the formation of aerosols and worsens haze. Typically, along the Nanchong-Suining-Neijiang-Zigong-Yibin path, calcite is converted into gypsum under the influence of man-made inorganic pollution gases, which worsen the haze conditions and cause slight air pollution for 3-5 days. However, along the Guangyuan-Mianyang-Deyang-Chengdu-Meishan-Ya'an path, anthropogenic volatile organic compounds (VOCs) hindered gypsum formation from dolomite. Furthermore, dolomite and VOCs formed stable adsorption systems (system energies from -0.41 to -4.76 eV, long bonds from 0.20 to 0.24 nm). The adsorption system of dolomite and m/p-xylene, with low system energy (-1.46 eV/-1.33 eV) and significant correlation (r² = 0.991, p < 0.01), was the main cause of haze formation. Consequently, calcite gypsification and dolomite-VOC synergism exacerbated regional haze conditions. This study provides a theoretical reference for the mechanism of aerosol formation in basin climates.

Heterogeneous reaction of SO2 on CaCO3 particles: Different impacts of NO2 and acetic acid on the sulfite and sulfate formation

Despite the heterogeneous reaction of sulfur dioxide (SO₂) on mineral dust particles significantly affects the atmospheric environment, the effect of acidic gases on the formation of sulfite and sulfate from this reaction is not particularly clear. In this work, using the in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technique, we employed a mineral dust particle model (CaCO₃) combined with NO₂ and acetic acid to investigate their effects on the heterogeneous reaction of SO₂ on CaCO₃ particles. It was found that water vapor can promote the formation of sulfite and simulated radiation can facilitate the oxidation of sulfite to sulfate. The addition of NO₂ or acetic acid to the reaction system altered the production of sulfate and sulfite accordingly. There was a synergistic effect between NO₂ and SO₂ that promoted the oxidation of sulfite to sulfate, and a competitive effect between acetic acid and SO₂ that inhibited the formation of sulfite. Moreover, light and water vapor can also affect the heterogeneous reaction of SO₂ with the coexistence of multiple gases. These findings improve our understanding of the effects of organic and inorganic gases and environmental factors on the formation of sulfite and sulfate in heterogeneous reactions.

Isolation and identification of pigments from oyster mushrooms with black, yellow and pink caps

The genus Pleurotus, namely oyster mushroom, is widely cultivated and consumed worldwide. Cap color is an important commercial trait for oyster mushroom. Diverse color is determined by various pigment constituents. However, the pigments of oyster mushrooms are still ambiguous. In this study, we extracted and identified pigments of oyster mushroom species with black, yellow and pink cap color. The extracted pigments appearing the three color types correspondingly to the cap color, which were all identified as melanin using a panel of spectroscopic and physical/imaging techniques. Nevertheless, HPLC and elemental analysis indicated that the melanin in oyster mushrooms was actually a mixture of eumelanin and phaeomelanin. Differences in the quantities and relative proportions of eumelanin and phaeomelanin resulted in the color variation in oyster mushroom caps. Electron microscopy studies showed that the melanin units are likely located in the cell wall, as reported in other fungi. The pigments in oyster mushrooms with three different cap color were extracted and identified for the first time in this study, which provided fundamental knowledge for future studies on the mechanism of color formation in mushrooms.

Exploring dust heterogeneous chemistry over China: Insights from field observation and GEOS-Chem simulation

Dust heterogeneous chemistry plays an important role in tropospheric chemistry, but its parameterization in numerical models is often quite simplified, which hampers accurate prediction of particulate matter and its chemical component. In this study, we investigate the evolution of dust heterogeneous chemical process and its potential impacts on gaseous and aerosol components during a dust pollution episode from March 27 to April 2, 2015 over North China. Based on field measurements, the significant role of relative humidity (RH) in dust heterogeneous chemistry is found and a RH-dependent parameterization for uptake coefficients of HNO₃ and SO₂ is incorporated in GEOS-Chem to reproduce the dust heterogeneous chemical process. During the study period, observed dust sulfate (DSO4) and dust nitrate (DNIT) exhibit maximum concentrations of 9.1 and 22.8 μg m^-3 respectively, accompanied by high RH and gaseous precursor concentrations. DSO4 concentrations are positively related to RH. The observed dust sulfate oxidation ratio (DSOR) is elevated evidently with increased RH, especially when RH is higher than ~40%, implying that enhanced RH could promote heterogeneous oxidation of SO₂ to DSO4. Model simulation shows that when incorporating the RH-dependent parameterization, DNIT and DSO4 are generally well captured and the model performance of total sulfate oxidation ratio (TSOR) and total nitrate oxidation ratio (TNOR) are improved. High contribution of DNIT and DSO4 are found to be located over the regions close to source areas (>60%) and downwind regions (>40%), respectively. Sensitivity results show that SO₂ and HNO₃ reduce by 2-24 μg m^-3 and 1-18 μg m^-3 when considering dust heterogeneous impacts, thus leading to reduction in non-dust sulfate and non-dust nitrate concentrations. As a result, simulated NH₃ increases and ammonium reduces by more than 20%. Our study indicates that the contribution of heterogeneous reactions to sulfate formation is 20-30% over North China.

A new parameterization of uptake coefficients for heterogeneous reactions on multi-component atmospheric aerosols

Based on laboratory studies and field observations, a new parameterization of uptake coefficients for heterogeneous reactions on multi-component aerosols is developed in this work. The equivalent ratio (ER) of inorganic aerosol is used to establish the quantitative relationship between the heterogeneous uptake coefficients and the composition of aerosols. Incorporating the new ER-dependent scheme, the WRF-CUACE model has been applied to simulate sulfate mass concentrations during December 2017 in the Beijing-Tianjin-Hebei region and evaluate the role of aerosol chemical components played in the sulfate formation. Simulated temporal variations and magnitudes of sulfate show good agreement with the observations by using this new scheme. From clean to polluted cases, although both dominant cations and anions increase significantly, the equivalent ratio decreases gradually and is closer to unity, representing the variation of aerosol compositions, which inhibits the heterogeneous uptake of SO₂, with the uptake coefficient decreasing from 1 × 10^-4 to 5.3 × 10^-5. Based on this phenomenon, a self-limitation process for heterogeneous reactions with the increasing secondary inorganic aerosol from clean to polluted cases is proposed.

Particle-Phase Photoreactions of HULIS and TMIs Establish a Strong Source of H2O2 and Particulate Sulfate in the Winter North China Plain

During haze periods in the North China Plain, extremely high NO concentrations have been observed, commonly exceeding 1 ppbv, preventing the classical gas-phase H₂O₂ formation through HO₂ recombination. Surprisingly, H₂O₂ mixing ratios of about 1 ppbv were observed repeatedly in winter 2017. Combined field observations and chamber experiments reveal a photochemical in-particle formation of H₂O₂, driven by transition metal ions (TMIs) and humic-like substances (HULIS). In chamber experiments, steady-state H₂O₂ mixing ratios of 116 ± 83 pptv were observed upon the irradiation of TMI- and HULIS-containing particles. Correspondingly, H₂O₂ formation rates of about 0.2 ppbv h^-1 during the initial irradiation periods are consistent with the H₂O₂ rates observed in the field. A novel chemical mechanism was developed explaining the in-particle H₂O₂ formation through a sequence of elementary photochemical reactions involving HULIS and TMIs. Dedicated box model studies of measurement periods with relative humidity >50% and PM_2.5 ≥ 75 μg m^-3 agree with the observed H₂O₂ concentrations and time courses. The modeling results suggest about 90% of the particulate sulfate to be produced from the SO₂ reaction with OH and HSO₃^- oxidation by H₂O₂. Overall, under high pollution, the H₂O₂-caused sulfate formation rate is above 250 ng m^-3 h^-1, contributing to the sulfate formation by more than 70%.

How Relevant Is It to Use Mineral Proxies to Mimic the Atmospheric Reactivity of Natural Dust Samples? A Reactivity Study Using SO2 as Probe Molecule

The experimental investigation of heterogeneous atmospheric processes involving mineral aerosols is extensively performed in the literature using proxy materials. In this work we questioned the validity of using proxies such as Fe2O3, FeOOH, Al2O3, MgO, CaO, TiO2, MnO2, SiO2, and CaCO3 to represent the behavior of complex mixtures of minerals, such as natural desert and volcanic dusts. Five volcanic dusts and three desert dusts were compared to a number of metal oxides, commonly used in the literature to mimic the behavior of desert dusts in the ability to form sulfites and sulfates on the surface exposed to SO2 gas. First, all samples were aged at room temperature, atmospheric pressure, under controlled experimental conditions of 175 ppm SO2 for 1 h under 30% of relative humidity. Second, they were extracted with 1% formalin and analyzed by High-Performance Liquid Chromatography (HPLC) to quantify and compare the amount of sulfites and sulfates formed on their surfaces. It was evidenced that under the experimental conditions of this study neither one selected pure oxide nor a mixture of oxides can adequately typify the behavior of complex mixtures of natural minerals. Therefore, to evaluate the real-life impact of natural dust on atmospheric processes it is of vital importance to work directly with the natural samples, both to observe the real effects of desert and volcanic dusts and to evaluate the relevancy of proposed proxies.

Inorganic composition and occult deposition of frost collected under severe polluted area in winter in the North China Plain

Frost as a kind of deposition plays an important role in the removal of atmospheric compounds. However, studies concerning frost in the atmospheric environment were rare although chemical composition in frost samples might be affected by the surrounding atmospheric environment. In this study, a total of 35 frost samples were collected by means of a homemade glass-plate frost condenser under severe polluted condition in the North China Plain (NCP) from Dec. 4, 2018 to Mar. 2, 2019. The pH values and water-soluble ions (WSI) were conducted. The extremely high concentrations of WSI were found, which reflected the severe pollution significantly affecting the level of chemical composition in frost. The major ions were Ca²⁺, SO₄^2- and HCO₃^- with averaged concentrations of 1242, 1143, 1076 μeq L^-1, respectively. These ions were at least one order of magnitude higher than the previous frost studies. HCO₃^- was one of the most abundant components in frost. Its high proportion contributed to the ionic balance and led to the alkaline characteristic of frost. SO₄^2- had the almost doubled ratio in frost compared with the concurrent PM_2.5 samples. Different from the huge diversity of chemical components in PM_2.5, the frost had similar ratio of WSI under great variety of PM_2.5 concentrations. It proved that PM_2.5 had less effect on the ratio of WSI in frost. Nutrient ions of NH₄⁺, NO₃^- and K⁺ accounted for 13.9%, 5.4% and 1.6% of the total averaged concentrations, respectively. On average, per square meter soil would receive 563 μg nitrogen and 123 μg potassium nutrient during a frost night. High occult deposition flux of ions indicated the strong scavenging effect from the frost event. In addition, the occult deposition flux of SO₄^2- was comparable to the dry deposition flux, further emphasizing frost process as a non-negligible atmospheric removal pathway of SO₄^2-.

Competitive reactions of SO2 and acetic acid on α-Al2O3 and CaCO3 particles

Heterogeneous reactions between gaseous pollutants and mineral particles have gradually become a research hotspot in the field of atmospheric chemistry. In this paper, competitive reactions between SO₂ and acetic acid on the surface of α-Al₂O₃ and CaCO₃ particles were studied by the diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) technique in dark and dry conditions. At the same time, the temporary evolution of the integrated absorbance of acetate and sulfite was investigated to further understand the interaction of SO₂ and acetic acid on the mineral particles. On the surface of α-Al₂O₃ particles, acetate and sulfite can compete for surface-active sites, resulting in a decrease in the total amount of acetates. In dark and dry conditions, the effect of acetic acid on SO₂ cannot be obtained by the DRIFTS method. On the surface of CaCO₃ particles, SO₂ can have a competitive impact on acetic acid by grabbing active sites, leading to a slight decrease of the amount of acetates. The heterogeneous reaction of SO₂ can be impeded by coexisting acetic acid, resulting in a drastic reduction of the number of sulfites. It can be seen that the formation mechanisms of acetate and sulfite on the surface of different mineral particles in the atmosphere are different, which provides a variety of ideas and possibilities for the formation of related inorganic and organic salts in the atmosphere.

Optimization of activated palm oil sludge biochar preparation for sulphur dioxide adsorption

Palm oil sludge (POS) is an organic waste generated from the palm oil industry. POS causes environmental pollution if it is improperly disposed. In this study, the potential of activated POS biochar, as an adsorbent for the removal of SO₂ gas was tested. POS biochar was physically activated using CO₂ gas. The effects of activation preparation variables i.e. activation temperature (300-700 °C), activation time (30-150 min) and CO₂ flow rate (100-500 ml/min) were investigated using design expert version 8.0.7.1 software. Central Composite Design (CCD) was used to develop a quadratic model to correlate the operating variables with the activated biochar adsorption capacity. Analysis of variance (ANOVA) was performed to identify the significant factors on the experimental design response. The optimum preparation conditions of activated POS biochar were found to be at activation temperature of 442 °C, activation time of 63 min and CO₂ flow rate of 397 ml/min. The maximum adsorption capacity at the optimum conditions was recorded as 16.65 mg/g. The adsorption capacity increased significantly after the activation process. Characteristics of the activated POS biochar proposed that SO₂ was physically adsorbed. Furthermore, it was found that the adsorption capacity can be further enhanced by increasing the reaction temperature to 100 °C or with 15% of relative humidity in the inlet gas. The prepared adsorbents can be regenerated by thermal treatment.

Influence of relative humidity on SO2 oxidation by O3 and NO2 on the surface of TiO2 particles: Potential for formation of secondary sulfate aerosol

The heterogeneous reactions of SO₂/O₃ and SO₂/NO₂ with TiO₂ particles were studied as a function of relative humidities (RHs). An in situ microscopic Fourier transform infrared (micro-FTIR) spectrometer was used to monitor the reaction kinetics. Rapid conversion of SO₂ to sulfate occurs on the surface of TiO₂ particles in the presence of O₃ or NO₂, which is sensitive to RHs. For unreacted (fresh) particles, the uptake coefficients for SO₂ in initial stage are both obviously enhanced over four times with the increasing RH from ~4% to ~85%. Moreover, the uptake coefficient in the system of SO₂/O₃ is about 40% higher than that of SO₂/NO₂ on TiO₂ particles at the similar RH conditions. For TiO₂ after exposure to SO₂/O₃ or SO₂/NO₂ (sulfated) particles, the uptake coefficients for SO₂ in moisture absorption stage are all higher than that on fresh particles in initial stage at the similar RH, indicating rapid mixture gases adsorption with particle hygroscopic growth. The high production of the secondary sulfate for heterogeneous reaction of mixture gases on TiO₂ surface from arid region to humid region provides new insights for better understanding the severe haze under the humid condition.

The influence of temperature on the heterogeneous uptake of SO2 on hematite particles

Despite the increased awareness of heterogeneous reactions of SO₂ on mineral particles, the knowledge of how temperature influences the product species and kinetic parameters remain a crucially important part in atmospheric research. Here, we reported the formation of sulfur-containing species on hematite particles under various temperature and humidity conditions by mean of in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatography (IC). High temperature is helpful in the ionization of H₂SO₃, making sulfite compounds occupy a great share among total products. The whole reaction could be divided into three stages according to the formation rate of hydroxyl groups. High temperature brings about more activated SO₂ and then results in the increased uptake coefficients with increasing temperature in the initial reaction stage. On the contrary, moisture absorption on particles is inhibited by high temperature, leading to the decreased uptake coefficients with increasing temperature in the latter two stages. Observed enthalpy and entropy, as well as activation energy values for relevant reactions were calculated. Overall, the product specie and reaction rate vary with temperature and humidity conditions, as well as reaction stages. This work broadens the knowledge of heterogeneous reactions on mineral dust influenced by temperature, and consequently provides important opportunities for atmospheric model improvements.