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Bitter compounds widely exist in foods and have an important impact on food flavor. The major bitter compounds in foods include amino acids, peptides, polyphenols, alkaloids, and inorganic salts. Bitterness is perceived through binding between bitter compounds and the specific sites of the 25 human bitter taste receptors (hTAS2Rs), which further activates the downstream signal pathway mediated by G protein, converting chemical signals into electrical signals and transmitting them to the brain. Some foods with strong bitterness taste are not well accepted by consumers, so appropriately reducing bitterness in foods can improve consumers’ preference. At present, there are two main methods to reduce the perception of food bitterness: 1) masking bitterness by polymerization/complexation or flavor interaction, and 2) removing bitterness by reducing the content of bitter compounds or changing their structure. In this paper, the bitter compounds in foods, the analytical methods for them, the mechanism of bitterness perception and the methods used to reduce bitterness perception are reviewed in an effort to provide theoretical guidance for food bitterness regulation.

Traffic problems in China's river–valley-type cities are prominent. In order to solve these traffic problems, this paper presents four aspects of motorists' terrain spatial perception according to the characteristics of river–valley-type cities. Based on the structural equation model (SEM), four-dimensional terrain spatial perception is reduced by second-order confirmatory factor analysis. The SEM–Logit model was constructed to analyze the influences of individual socioeconomic attributes, objective built-environment attributes, travel characteristics, and terrain spatial perception on Park and Ride (P&R) use behavior, as well as the moderating effects of terrain spatial perception. The results show that the four latent variables can explain the terrain spatial perception of motorists in river–valley-type cities well. Objective built environments and motorists' subjective terrain spatial perception have significant impacts on the use of P&R facilities in river–valley-type cities. The terrain spatial perception of motorists in a river–valley-type city moderates the impact of work–residence distance, road slope, river crossing demand, group travel, departure time, and the time saved on P&R use behavior. The research results can provide some reference for solving traffic problems in river–valley-type cities. [ABSTRACT FROM AUTHOR]

In order to investigate the variations of cloud and aerosol vertical profiles over the Tibetan Plateau (TP) in winter, we performed ground-based lidar observations in Lhasa, a city on the TP, from November 2021 to January 2022. The profiles of extinction coefficient, depolarization ratio, and signal-to-noise ratio (SNR) were retrieved using the atmospheric echo signals collected by the lidar. Clouds were identified by the range-correction echo signals and classified into water clouds, mixed clouds, horizontally oriented ice crystal clouds (HOICC), and ice clouds by the depolarization ratio and the hourly temperature from the European Centre for Medium-Range Weather Forecasts Reanalysis version 5 (ERA5). The clouds mainly appeared at a height of 3~5 km from 14:00–22:00 Beijing Time throughout the field campaign. The height and frequency (~30%) for cloud appearance were significantly lower than that reported in previous studies in summer. The cloud categories were dominated by mixed clouds and ice clouds during the observation period. The proportions of ice clouds gradually increased with increasing heights. After eliminating profiles influenced by clouds, the aerosol extinction coefficient and depolarization ratio were obtained, and the atmospheric boundary layer height (ABLH) was calculated. The aerosol extinction coefficient decreased with increasing height in the ABLH, and there were no obvious changes for the aerosol extinction coefficient above the ABL. The aerosol extinction coefficients near the Earth's surface presented two peaks, appearing in the morning and evening, respectively. The high aerosols at the surface in the morning continually spread upward for 4–5 h and finally reached an altitude of 1 km with the development of ABLH. In addition, the depolarization ratio of aerosols decreased slowly with increasing altitudes. There was no obvious diurnal variation for depolarization ratios, indicating partly that the source of aerosols did not change significantly. These results are beneficial in understanding the evolution of cloud and aerosol vertical profiles over the TP. [ABSTRACT FROM AUTHOR]

Chen et al. (2022) analyzed the event of rapid nocturnal O 3 enhancement (NOE) observed on 31 July 2021 at the surface level in the North China Plain and proposed transport of substantial stratosphere ozone to the surface by Typhoon In-fa followed by downdraft of shallow convection as the mechanism of the NOE event. The analysis seems to be valid from the viewpoint of atmospheric physics. This comment revisits the NOE phenomenon on the basis of the China National Environmental Monitoring Center (CNEMC) network data used in Chen et al. (2022), together with the CNEMC data from Zibo (ZB) and O 3 , NO x , PAN (peroxyacetic nitric anhydride), and VOC (volatile organic compound) data from the Zibo supersite operated by the China Research Academy of Environmental Sciences (CRAES). We found (a) O x (O 3 + NO 2) levels during the NOE period approaching those of O 3 during 14:00–17:00 LT, (b) levels of PAN and the relationship between O 3 and PAN consistent with dominance of chemical and physical processes within the boundary layer, and (c) estimated photochemical ages of air mass shorter than 1 d and showing no drastic increases during the NOE. We argue that the NOE was not caused by typhoon-induced stratospheric intrusion but originated from fresh photochemical production in the lower troposphere. Our argument is well supported by the analysis of atmospheric transport as well as ground-based remote sensing data. [ABSTRACT FROM AUTHOR]

The New Baseline Surface Radiation (NBSR) system was established at the Shangdianzi (SDZ) regional Global Atmosphere Watch (GAW) station in 2013 to observe nine broadband radiation components, i.e. the global, direct, diffuse, and upwelling shortwave irradiance (GSWI, DSWI, DifSWI, and UpSWI); the photosynthetically active radiation (PAR); the ultraviolet irradiance (UVAI and UVBI); and the down- and upwelling longwave irradiance (DnLWI and UpLWI). To test the 1 min raw radiometric data, a Hybrid Algorithm for Radiation Data Quality Control (HARDQC) is presented in this study based on well-established methods, together with the solar irradiance dataset and the spectral features of the instrument bands. Subsequently, a NBSR dataset, which consists of radiation data at multiple timescales (i.e. 1 min, hourly, daily, monthly, monthly average hourly, and monthly average daily) over 2013–2022, is established and evaluated. Results show that more than 98.7 % of all radiation components passed the physical possibility test. The percentages of those that passed the extremely rare test are greater than 98.6 % for all radiation components except for the DnLWI (97.1 %). The percentages of those that passed the comparison test are greater than 83.3 % (GSWI), 78.3 % (DSWI), 81.7 % (DifSWI), 93.1 % (UpSWI), 88.9 % (PAR), 95.6 % (UVAI), 96.3 % (UVBI), 99.8 % (DnLWI), and 99.7 % (UpLWI), respectively. Due to data logger faults, removal of the instruments for calibration, and lightning strikes, some apparent data gaps in the upwelling radiation components (January 2015–August 2017) and all radiation components (December 2018; July to September 2021) were detected. Despite the existence of a few imperfections in the NBSR dataset, it is still reliable to apply it in many fields such as the validation of satellite products and numerical models, the investigation of relationships between radiation and atmospheric composition, and the detection of changes in the surface fluxes. The dataset described in this paper is available at 10.1594/PANGAEA.963330 (Quan et al., 2023b). [ABSTRACT FROM AUTHOR]

Direct catalytic conversion of methane to liquid oxygenates under mild conditions remains a challenge due to high bond energy of symmetric CH4. Isolated Rh atoms were supported on hydrophobic fluorine modified TS-1 (FTS-1). Single-atom Rh on FTS-1 catalyst was characterized with Ac-HAADF/STEM and CO adsorption FTIR. The aerobic selective conversion of methane to oxygenates was carried out in a fixed bed continuous flow reactor upon co-feeding CO and H2O at 423 K under relative low pressure (42.3 kPa CH4, 21.1 kPa CO, 10.6 kPa O2, 0.476 MPa H2O). Hydrophobic Rh/FTS-1 catalyst exhibits higher activity (151.9 molproducts/(molmetalh)) than the activity (36.4 molproducts/(molmetalh)) over hydrophilic Rh-ZSM-5 (Si/Al = 15) under such reaction conditions. Hydrophobicity of different catalysts were compared by water adsorption test. The catalytic activity of F modified TS-1 supported single-atom Rh (Rh/FTS-1) is higher than that of unmodified Rh/TS-1 which is due to its higher Lewis acidity as shown by pyridine adsorption FTIR and NH3-TPD. [ABSTRACT FROM AUTHOR]

We review the 2017 Antarctic ozone hole, making use of various meteorological reanalyses, and in-situ, satellite and ground-based measurements of ozone and related trace gases, and ground-based measurements of ultraviolet radiation. The 2017 ozone hole was associated with relatively high-ozone concentrations over the Antarctic region compared to other years, and our analysis ranked it in the smallest 25% of observed ozone holes in terms of size. The severity of stratospheric ozone loss was comparable with that which occurred in 2002 (when the stratospheric vortex exhibited an unprecedented major warming) and most years prior to 1989 (which were early in the development of the ozone hole). Disturbances to the polar vortex in August and September that were associated with intervals of anomalous planetary wave activity resulted in significant erosion of the polar vortex and the mitigation of the overall level of ozone depletion. The enhanced wave activity was favoured by below-average westerly winds at high southern latitudes during winter, and the prevailing easterly phase of the quasi-biennial oscillation (QBO). Using proxy information on the chemical make-up of the polar vortex based on the analysis of nitrous oxide and the likely influence of the QBO, we suggest that the concentration of inorganic chlorine, which plays a key role in ozone loss, was likely similar to that in 2014 and 2016, when the ozone hole was larger than that in 2017. Finally, we found that the overall severity of Antarctic ozone loss in 2017 was largely dictated by the timing of the disturbances to the polar vortex rather than interannual variability in the level of inorganic chlorine.

Chen et al. (2022) analyzed the event of rapid nocturnal O3 enhancement (NOE) observed on 31 July 2021 at surface level in the North China Plain and proposed transport of substantial stratosphere ozone to the surface by Typhoon In-fa followed by downdraft of shallow convection as the mechanism of the NOE event. The analysis seems to be valid in the view-point of atmospheric physics. This comment revisits the NOE phenomenon on the basis of the China National Environmental Monitoring Center (CNEMC) network data ever used in Chen et al. (2022), together with the CNEMC data from Zibo (ZB), and O3, NOx, PAN and VOCs data from the Zibo supersite operated by China Research Academy of Environmental Sciences (CRAES). We found (a) Ox (O3+NO2) levels during the NOE period approaching to those of O3 during 14:00–17:00 LT; (b) the relationship between O3 and PAN (peroxyacetic nitric anhydride) consistent with dominance of chemical and physical processes within the boundary layer, and (c) estimated photochemical ages of air mass being shorter than one day and showing no drastic increases during the NOE. We argue that the NOE was not caused by typhoon-induced stratospheric intrusion but originated from fresh photochemical production in the lower troposphere. [ABSTRACT FROM AUTHOR]