Study on the quality change of crown pear during storage

Using the high-quality Crown Pear as the subject of experimental research, an analysis of the changes in the quality of Crown Pears during a storage period is conducted to provide a theoretical basis for the development of the pear cold storage industry. The study utilizes a handheld digital refractometer, texture analyzer, colorimeter, T-type thermocouple, and electronic balance to explore six aspects of Crown Pears: soluble solids content, hardness, color difference, freezing point, drying loss, and taste. The results reveal the following changes in pear quality during different storage periods within one cycle: the content of soluble solids in Crown Pears initially increases and then decreases during the storage period; hardness decreases with increasing storage time; the external appearance of pears gradually darkens; and drying loss increases with storage time. During the cold storage process of Crown Pears, the optimal temperature setting for the cold storage should be maintained at -1°C to 0.5°C. The flavor of Crown Pears is not optimal during the early stage of storage. The storage time for Crown Pears should be within four months

Effects of hydrodynamic cavitation on physicochemical structure and emulsifying properties of tilapia (Oreochromis niloticus) myofibrillar protein

The purpose of this research was to explore the different hydrodynamic cavitation (HC) times (0, 5, 10, 15, 20 min; power 550 W, pressure 0.14 MPa) on the emulsifying properties of tilapia myofibrillar protein (TMP). Results of pH, particle size, turbidity, solubility, surface hydrophobicity, and reactive sulfhydryl (SH) group indicated that HC changed the structure of TMP, as confirmed by the findings of intrinsic fluorescence and circular dichroism (CD) spectra. Furthermore, HC increased the emulsifying activity index (EAI) significantly (P < 0.05) and changed the emulsifying stability index (ESI), droplet size, and rheology of TMP emulsions. Notably, compared with control group, the 10-min HC significantly decreased particle size and turbidity but increased solubility (P < 0.05), resulting in accelerated diffusion of TMP in the emulsion. The prepared TMP emulsion showed the highest ESI (from 71.28 ± 5.50 to 91.73 ± 5.56 min), the smallest droplet size (from 2,754 ± 110 to 2,138 ± 182 nm) and the best rheological properties, as demonstrated by the microstructure photographs. Overall, by showing the effect of HC in improving the emulsifying properties of TMP, the study demonstrated HC as a potential technique for meat protein processing

Influence of photochemical loss of volatile organic compounds on understanding ozone formation mechanism

Volatile organic compounds (VOCs) tend to be consumed by atmospheric oxidants, resulting in substantial photochemical loss during transport. An observation-based model was used to evaluate the influence of photochemical loss of VOCs on the sensitivity regime and mechanisms of ozone formation. Our results showed that a VOC-limited regime based on observed VOC concentrations shifted to a transition regime with a photochemical initial concentration of VOCs (PIC-VOCs) in the morning. The net ozone formation rate was underestimated by 3 ppbh(-1) (similar to 36 ppb d(-1)) based on the measured VOCs when compared with the PIC-VOCs. The relative contribution of the RO2 path to ozone production based on the PIC-VOCs accordingly increased by 13.4 %; in particular, the contribution of alkene-derived RO(2 )increased by approximately 10.2 %. In addition, the OH-HO2 radical cycle was obviously accelerated by highly reactive alkenes after accounting for photochemical loss of VOCs. The contribution of local photochemistry might be underestimated for both local and regional ozone pollution if consumed VOCs are not accounted for, and policymaking on ozone pollution prevention should focus on VOCs with a high reactivity.Peer reviewe

A New Type of Quartz Smog Chamber : Design and Characterization

Publisher Copyright: ©Since the 1960s, many indoor and outdoor smog chambers have been developed worldwide. However, most of them are made of Teflon films, which have relatively high background contaminations due to the wall effect. We developed the world's first medium-size quartz chamber (10 m(3)), which is jointed with 32 pieces of 5 mm thick polished quartz glasses and a stainless-steel frame. Characterizations show that this chamber exhibits excellent performance in terms of relative humidity (RH) (2-80%) and temperature (15-30 +/- 1 degrees C) control, mixing efficiency of the reactants (6-8 min), light transmittance (>90% above 290 nm), and wall loss of pollutants. The wall loss rates of the gas-phase pollutants are on the order of 10(-4) min(-1) at 298 K under dry conditions. It is 0.08 h(-1) for 100-500 nm particles, significantly lower than those of Teflon chambers. The photolysis rate of NO2 (J(NO2)) is automatically adjustable to simulate the diurnal variation of solar irradiation from 0 to 0.40 min(-1). The inner surface of the chamber can be repeatedly washed with deionized water, resulting in low background contaminations. Both experiments (toluene-NOx and alpha-pinene-ozone systems) and box model demonstrate that this new quartz chamber can provide high-quality data for investigating SOA and O-3 formation in the atmosphere.Peer reviewe

Influence of organic aerosol molecular composition on particle absorptive properties in autumn Beijing

Publisher Copyright: © 2022 Jing Cai et al.Organic aerosol (OA) is a major component of fine particulate matter (PM), affecting air quality, human health, and the climate. The absorptive and reflective behavior of OA components contributes to determining particle optical properties and thus their effects on the radiative budget of the troposphere. There is limited knowledge on the influence of the molecular composition of OA on particle optical properties in the polluted urban environment. In this study, we characterized the molecular composition of oxygenated OA collected on filter samples in the autumn of 2018 in Beijing, China, with a filter inlet for gases and aerosols coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-CIMS). Three haze episodes occurred during our sampling period with daily maximum concentrations of OA of 50, 30, and 55 μg m-3. We found that the signal intensities of dicarboxylic acids and sulfur-containing compounds increased during the two more intense haze episodes, while the relative contributions of wood-burning markers and other aromatic compounds were enhanced during the cleaner periods. We further assessed the optical properties of oxygenated OA components by combining detailed chemical composition measurements with collocated particle light absorption measurements. We show that light absorption enhancement (Eabs) of black carbon (BC) was mostly related to more oxygenated OA (e.g., dicarboxylic acids), likely formed in aqueous-phase reactions during the intense haze periods with higher relative humidity, and speculate that they might contribute to lensing effects. Aromatics and nitro-aromatics (e.g., nitrocatechol and its derivatives) were mostly related to a high light absorption coefficient (babs) consistent with light-absorbing (brown) carbon (BrC). Our results provide information on oxygenated OA components at the molecular level associated with BrC and BC particle light absorption and can serve as a basis for further studies on the effects of anthropogenic OA on radiative forcing in the urban environment.Peer reviewe

Seasonal variation in oxygenated organic molecules in urban Beijing and their contribution to secondary organic aerosol

Oxygenated organic molecules (OOMs) are crucial for atmospheric new particle formation and secondary organic aerosol (SOA) growth. Therefore, understanding their chemical composition, temporal behavior, and sources is of great importance. Previous studies on OOMs mainly focus on environments where biogenic sources are predominant, yet studies on sites with dominant anthropogenic emissions, such as megacities, have been lacking. Here, we conducted long-term measurements of OOMs, covering four seasons of the year 2019, in urban Beijing. The OOM concentration was found to be the highest in summer (1.6 x 10(8) cm(-3)), followed by autumn (7.9 x 10(7) cm(-3)), spring (5.7 x 10(7) cm(-3)) and winter (2.3 x 10(7) cm(-3)), suggesting that enhanced photo-oxidation together with the rise in temperature promote the formation of OOMs. Most OOMs contained 5 to 10 carbon atoms and 3 to 7 effective oxygen atoms (nO(eff) = nO - 2 x nN). The average nO(eff )increased with increasing atmospheric photo-oxidation capacity, which was the highest in summer and the lowest in winter and autumn. By performing a newly developed workflow, OOMs were classified into the following four types: aromatic OOMs, aliphatic OOMs, isoprene OOMs, and monoterpene OOMs. Among them, aromatic OOMs (29 %-41 %) and aliphatic OOMs (26 %-41 %) were the main contributors in all seasons, indicating that OOMs in Beijing were dominated by anthropogenic sources. The contribution of isoprene OOMs increased significantly in summer (33 %), which is much higher than those in the other three seasons (8 %-10 %). Concentrations of isoprene (0.2-5.3 x 10(7) cm(-3)) and monoterpene (1.1-8.4 x 10(6) cm(-3)) OOMs in Beijing were lower than those reported at other sites, and they possessed lower oxygen and higher nitrogen contents due to high NO, levels (9.5-38.3 ppbv - parts per billion by volume) in Beijing. With regard to the nitrogen content of the two anthropogenic OOMs, aromatic OOMs were mainly composed of CHO and CHON species, while aliphatic OOMs were dominated by CHON and CHON2 ones. Such prominent differences suggest varying formation pathways between these two OOMs. By combining the measurements and an aerosol dynamic model, we estimated that the SOA growth rate through OOM condensation could reach 0.64, 0.61, 0.41, and 0.30 mu g m(-3) h(-1) in autumn, summer, spring, and winter, respectively. Despite the similar concentrations of aromatic and aliphatic OOMs, the former had lower volatilities and, therefore, showed higher contributions (46 %-62 %) to SOA than the latter (14 %-32 %). By contrast, monoterpene OOMs and isoprene OOMs, limited by low abundances or high volatilities, had low contributions of 8 %-12 % and 3 %-5 %, respectively. Overall, our results improve the understanding of the concentration, chemical composition, seasonal variation, and potential atmospheric impacts of OOMs, which can help formulate refined restriction policy specific to SOA control in urban areas.Peer reviewe

Particle growth with photochemical age from new particle formation to haze in the winter of Beijing, China

Secondary aerosol formation in the aging process of primary emission is the main reason for haze pollution in eastern China. Pollution evolution with photochemical age was studied for the first time at a comprehensive field observation station during winter in Beijing. The photochemical age was used as an estimate of the time scale attributed to the aging process and was estimated from the ratio of toluene to benzene in this study. A low photochemical age indicates a fresh emission. The photochemical age of air masses during new particle formation (NPF) days was lower than that on haze days. In general, the strongest NPF events, along with a peak of the formation rate of 1.5 nm(J(1.5)) and 3 nmparticles (J(3)), were observed when the photochemical age was between 12 and 24 h while rarely took place with photochemical ages less than 12 h. When photochemical age was larger than 48 h, haze occurred and NPF was suppressed. The sources and sinks of nanoparticles had distinct relation with the photochemical age. Our results show that the condensation sink (CS) showed a valley with photochemical ages ranging from 12 to 24 h, while H2SO4 concentration showed no obvious trend with the photochemical age. The high concentrations of precursor vapours within an air mass lead to persistent nucleation with photochemical age ranging from 12 to 48 h in winter. Coincidently, the fast increase of PM2.5 mass was also observed during this range of photochemical age. Noteworthy, CS increased with the photochemical age on NPF days only, which is the likely reason for the observation that the PM2.5 mass increased faster with photochemical age on NPF days compared with other days. The evolution of particles with the photochemical age provides new insights into understanding how particles originating from NPF transform to haze pollution. (C) 2020 Elsevier B.V. All rights reserved.Peer reviewe

Rapid mass growth and enhanced light extinction of atmospheric aerosols during the heating season haze episodes in Beijing revealed by aerosol-chemistry-radiation-boundary layer interaction

Despite the numerous studies investigating haze formation mechanism in China, it is still puzzling that intensive haze episodes could form within hours directly following relatively clean periods. Haze has been suggested to be initiated by the variation of meteorological parameters and then to be substantially enhanced by aerosol-radiation-boundary layer feedback. However, knowledge on the detailed chemical processes and the driving factors for extensive aerosol mass accumulation during the feedback is still scarce. Here, the dependency of the aerosol number size distribution, mass concentration and chemical composition on the daytime mixing layer height (MLH) in urban Beijing is investigated. The size distribution and chemical composition-resolved dry aerosol light extinction is also explored. The results indicate that the aerosol mass concentration and fraction of nitrate increased dramatically when the MLH decreased from high to low conditions, corresponding to relatively clean and polluted conditions, respectively. Particles having their dry diameters in the size of similar to 400-700 nm, and especially particle-phase ammonium nitrate and liquid water, contributed greatly to visibility degradation during the winter haze periods. The dependency of aerosol composition on the MLH revealed that ammonium nitrate and aerosol water content increased the most during low MLH conditions, which may have further triggered enhanced formation of sulfate and organic aerosol via heterogeneous reactions. As a result, more sulfate, nitrate and water-soluble organics were formed, leading to an enhanced water uptake ability and increased light extinction by the aerosols. The results of this study contribute towards a more detailed understanding of the aerosol-chemistry-radiation-boundary layer feedback that is likely to be responsible for explosive aerosol mass growth events in urban Beijing.Peer reviewe

Continuous and comprehensive atmospheric observations in Beijing : a station to understand the complex urban atmospheric environment

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