Search

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.

Solar irradiance is one important element in conventional meteorology observations. Long-term observations of solar radiation by using China-made wide-band pyranometers have been carried out. However, the performance of instrumental systems is not sufficiently evaluated or analyzed, especially in the polar regions where harsh condition and large seasonal variations of solar elevation causes dramatic variation of surface solar irradiance. To fill this gap, the performance of the domestically made solar radiation observation systems at Zhongshan Station, Antarctica in 2017, including global solar radiation (GSR), direct solar radiation (DIR) and the diffuse solar radiation (DIF) measurements, is evaluated. The averaged nighttime thermal offsets of two domestic FS-6A pyranometers, respectively for GSR and DIF observations, are both less than 3 W·m-2, and their temporal variations are highly consistent. Compared with CM21 or CM22 pyranometer that reach the requirement of the second-class standard and are globally deployed, the additional heating effect of the auxiliary ventilation heater of FS-6A pyranometers significantly reduces the inherently physically-based correlation coefficient between the night thermal offset and the net longwave radiation, and the absolute values of FS-6A thermal offset significantly increase but are within 5 W·m-2 under higher wind speeds (noless than 15 m·s-1). The temporal variations of solar DIF irradiances from two FS-6A pyranometers are highly consistent under cloudy overcast condition, and their solar irradiance values are systemically lower (about -6 W·m-2 or -1%) than that of CM22 as the solar DIF irradiance is about 500 W·m-2 from CM22. However, the absolute (relative) difference is respectively lower than 2.6 W·m-2 (4.0%) as the solar zenith angle (θ) is less than 86 °. The GSR close examination suggests that the ratio of FS-6A GSR absolute difference from the sum of horizontally projected DIR and DIF meeting the requirement of threshold value (less than 2% or 15 W·m-2 with θ≤ 80°) proposed by the baseline surface radiation network (BSRN) is more than 80%. But only 44% samples meet the requirement of the BSRN threshold value (less than 3.5% or 20 W·m-2 with θ> 80°) when the four-quadrant tracking solar disk model is applied in operation. Under cloud-free condition, the measurements of GSR, DIR and DIF from the domestically made instruments are well comparable with the simulations from the parameterized solar radiation model that has been extensively applied in middle-low latitudes, and the correlation coefficients between the simulations and observations are more than 0.95. However, the observations are significantly higher than the simulations as the solar irradiance increases. The results suggest that China domestically made solar radiation observation system is fully qualified for the routine observation in polar regions.

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]

A comparative analysis is presented on surface solar ultraviolet B (UVB) band and ultraviolet A (UVA) irradiance measured by 3 UV broadband pyranometers: FSUVA(315-400 nm), FSUVB(280-315 nm) provided by Jiangsu Radio Scientific Institute Co. LTD (CJRSI), American Yankee UVB(280-320 nm), and Brewer ozone spectrophotometer, placed at Zhongshan Station, Antarctica. Using data of Brewer ozone spectrophotometer in 2017 as a reference, results show that, for UVB(280-315 nm) irradiance, the error of FSUVB is averagely (55±75)% but its irradiance is lower during the "ozone hole" period, indicating that domestic made FSUVB broadband radiometer is less sensitive to the ozone layer thinning. Furthermore, the irradiance relative error of FSUVB shows a certain upward trend with the increase of total atmospheric ozone, indicating an over-measured UVB irradiance by the FSUVB pyranometer in regions with normal ozone concentration, such as the area of middle-low latitudes including China. As a contrast, the error of Yankee UVB (280-320 nm) is averagely (-31±22)% lower than that of Brewer measured, however, the relative error and total ozone variation are unrelated. The under-measured UVB irradiance from the Yankee UVB pyranometer is attributed to the system calibration error. Since Brewer spectral UV measurement is limited within 286.5-363 nm, a so-called UV correction factor, on the basis of empirical ratio of spectral irradiance at the wavelength longer than 363 nm to the Brewer measured irradiance at 363 nm, is applied to make up Brewer spectral irradiance gap of 363.5-400 nm with wavelength resolution of 0.5 nm for constructing Brewer entire spectral UVA (315-400 nm) irradiance. The error of FSUVA is averagely (23±59)% when Brewer UVA irradiance is used as the reference. With tropospheric Ultraviolet visible (TUV) radiation model calculations under cloud-free and the sun zenith angle (SZA)less than 80° as references, irradiance errors measured by FSUVB, Yankee UVB and FSUVA are (30±37)%, (-22±19)% and (27±6.4)%, respectively, in 197 cases, while the average of differences between Brewer and TUV calculations are respectively (3.4±8.5)% in UVB band of 286.5-315 nm, (2.9±6.8)% in UVB band of 286.5-320 nm and (3.4±4.5)% in UVA band of 315-400 nm, proving the method of Brewer UVA correction factor is rational. Again, only the relative error of FSUVB measurements referenced to TUV calculations displays an evident increasing trend with the growth of total ozone. Mechanisms of over-measured solar irradiances from both domestic made broad-band UV pyranometers are not fully identified. Calibration methods needed to be improved with consideration of variable SZA and total ozone. In addition, the stray light at longer wavelengths should have a significant influences on the pyranometer's performances and this stray light need to be eliminated in further instrument improvement. For FSUVB, its less sensitiveness to the solar UVB irradiance during the period of "ozone hole" still needs to be resolved.

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]

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 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]

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]