Search

Taking China's air quality management during the 13th 5-Year Plan (2016–2020) as a case, this study empirically examines the impact of mandatory policy target set by the higher-level government on the performance of lower-level government in achieving the target. The results show that there is an inverted U-shaped relationship between environmental target value and target completion rate. In addition, the inverted U-shaped relationship is moderated by local economic growth rate. Specifically, economic growth impairs the positive effect of environmental target value on environmental performance before the turning point but alleviating the negative effect after the turning point. Moreover, higher-level attention can strengthen the target setting effect for local governments. Therefore, a successful target-based performance management system needs the reasonable design for the target difficulty and coordination of conflicting targets. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) is troubled by severe haze pollution and the evolution of haze pollution is closely related to the atmospheric boundary layer (ABL). However, experimental and theoretical studies on the physical-chemical processes of the ABL in the NCP are lacking, with many scientific problems to be addressed. To solve these problems, the Comprehensive Observation on the Atmospheric boundary layer Three-dimensional Structure (COATS) during haze pollution was carried out in the NCP from 2016 to 2020. The COATS experiment adopted a "point-line-surface" spatial layout, obtaining both spatial-temporal profiles of the meteorological and environmental elements in the ABL and the turbulent transport data of fine particulate matter (PM2.5) in winter and summer. The research achievements are as follows. The spatial-temporal distribution characteristics of the ABL structure and PM2.5 concentrations in the NCP were determined. The typical thermal structure of persistent heavy haze events and the pollutant removal mechanism by low-level jets were revealed. It was determined that the spatial structure of the ABL adjusted by the Taihang Mountains is responsible for the heterogeneous distribution of haze pollution in the NCP, and that mountain-induced vertical circulations can promote the formation of elevated pollution layers. The restraints of the atmospheric internal boundaries on horizontal diffusion of pollutants were emphasized. The contribution of the ABL to haze pollution in winter and summer was qualitatively compared and quantitatively estimated. The turbulent transport nature behind the relationship between the atmospheric boundary layer height (ABLH) and surface PM2.5 concentrations was analyzed. The concept of "aerosol accumulation layer" was defined, and the applicability of the material method in determining ABLH was clarified. A measurement system for obtaining the turbulent flux of PM2.5 concentrations was developed, and the turbulence characteristics of PM2.5 concentrations were demonstrated. The COATS experiment is of great theoretical significance for thoroughly understanding the physical mechanisms of the ABL during haze pollution and filling the knowledge gap on the impacts of the ABL three-dimensional structure on haze pollution. The results of this study are conducive to the improvement and development of ABL parameterization schemes and serve as a scientific basis for formulating regional pollution prevention and control measures. [ABSTRACT FROM AUTHOR]

Low-level temperature inversions play crucial roles in inhibiting vertical exchange of energy and mass, and may lead to air pollutants accumulation. The climatological study of them provides a fundamental overview of the static stability of atmosphere and is indispensable for air pollution controls. Based on high-vertical-resolution radiosondes at 00 and 12 UTC during 2011–2018, this work comprehensively examined the spatial and temporal variability of three characteristics (occurrences, strengths, and depths) of low-level inversions in China. Results revealed that inversions are prevalent (more than 80% of the observation records) over Eastern China. The northern part of Eastern China is dominated by the thick strong surface-based inversions with median thickness and strength of 200 m and 3 K, while the southern part by thin weak elevated ones of 80 m and 0.8 K. Tibetan Plateau experiences rare inversions (less than 50% of the time) which tend to be strong thick surface-based inversions with median depth and intensity of 170 m and 4 K. Inversion depths and strengths are positively correlated. The three properties of inversions present remarkable seasonal variations. Generally, inversions are strongest, thickest, and most frequent in winter and least so in summer, with median intensity and depth ranging from 0.3 K and 80 m to 5 K and 220 m. This paper also analyzed the monthly variations of inversions of four representative stations (Harbin, Urumqi, Beijing, and Chongqing) in details. These four cities are known for frequent severe air pollution events. The quantitative investigations of inversions may play a significant role in atmospheric environmental management. [ABSTRACT FROM AUTHOR]

An intensive atmospheric boundary layer (ABL) experiment was conducted simultaneously at six stations arranged in a cross shape on the North China Plain (NCP) from 26 November to 26 December 2019. The impacts of the regional ABL structure on heavy haze pollution and the relationship between the ABL height and aerosol accumulation layer (AAL) depth were discussed. Bouts of downdrafts generate a persistent descending elevated inversion layer, helping the maintenance and exacerbation of haze pollution. Continuous weak wind layers contribute to the pollutants accumulation, and low-level jets promote the removal of air pollutants. The unique landform conditions of the NCP are reflected in its regional ABL structure and further affect the spatial distribution of haze pollution. Due to the drainage flow and strong downdrafts, the western stations near the mountains have a colder surface and warmer upper air masses, resulting in a more stable stratification and worse diffusion conditions; these stations also experience a thicker weak wind layer caused by increased friction. Thus, the spatial distribution of haze is heavier in the west and lighter in the east. The convective boundary layer (CBL) height declines evidently during haze episodes, usually lower than 560 m. Furthermore, as the vertical distribution of aerosols is mainly influenced by daytime thermal turbulence and maintained at night, it is appropriate to determine the CBL height using the AAL depth. However, the AAL depth is not consistent with the stable boundary layer height due to the influence of the residual layer at night. [ABSTRACT FROM AUTHOR]

Interactions between the spatiotemporal distribution of pollutants and the structure of the atmospheric boundary layer were studied using data obtained by GPS (Global Positioning System) sounding balloons in an intensive observation period from December 2018 to January 2019 at the Dezhou experimental station in the North China Plain. Under haze weather conditions, negligible variation or a slight increase in temperature, higher relative humidity (RH) and lower wind speed with uncertain wind direction are common characteristics. The concentration distribution of particulate matter ≤2.5 μm ( PM 2.5 ) has a close relationship with the inversion layer, which contributes to the accumulation of PM 2.5 in the lower atmosphere. The reduction of pollutants suspended in the upper layer during haze periods is closely related to low-level jets and intermittent turbulence. Higher RH values are also favourable for the formation of heavy haze, and the value of PM 2.5 increases with an increase in humidity. During hazy days, the heat fluxes and turbulent kinetic energy (TKE) are much smaller than those during clear days. The values of the average maxima of net radiation, sensible heat flux, and latent heat flux are 154, 76, and 15 W / m 2 , respectively, and the value of TKE is approximately 0.67 m 2 / s 2 . The decrease in atmospheric boundary layer height (ABLH) is caused by weaker turbulent transfer during haze episodes. The ABLH is approximately 400 m during the daytime and 240 m at night. The power function relationship is shown by a negative correlation between the ABLH and surface PM 2.5 concentration in the convective boundary layer. • PM 2.5 concentration profiles were collected by GPS sounding balloons in winter. • The influence of the ABL structure on PM 2.5 distribution is explained. • The scavenging effect of low-level jets on PM 2.5 in the upper layer is confirmed. • Heavily polluted layers were discovered at high altitudes and explained. [ABSTRACT FROM AUTHOR]

In this study, the integral and microscopic turbulent statistical characteristics of pressure fluctuations, applicability of the pressure gradient and pressure flux divergence to the Monin-Obukhov similarity theory (MOST), and contribution of the pressure transport term to turbulence kinetic energy (TKE) were analyzed using the turbulence observational data obtained from a field observational station over the Horqin Sandy Land in Inner Mongolia, China. The normalized standard deviations of the pressure fluctuations have no obvious relationship with the dimensionless stability parameter (z / L). The turbulent variance spectra of pressure fluctuations S p (n) follow the n −2 scaling law with a peak frequency of approximately one to two orders of magnitude lower than that of the wind speed and temperature. The spectral gap also shifts to lower frequencies, and the transition from turbulent scale to the larger scale is sharper. The normalized vertical pressure gradient (κz p ∗ ∂ p ¯ ∂ z) has no significant relationship with z / L. The non-dimensional pressure transport term (φ p = κz ρ ¯ u ∗ 3 ∂ w ' p ' ¯ ∂ z) represents the pressure flux divergence and is well related to the z / L with expressions of φ p = ± (1 − 14.5 z / L) for unstable stratifications and φ p = ± (1 + 15.0 z / L) for stable stratifications. The relative importance of pressure transport term in the TKE budget equation with respect to the shear production and buoyancy terms is larger at larger scales. The pressure transport term is averagely one order of magnitude larger than the sum of these two terms at scales above 5 min. The contribution of the pressure transport term to the TKE is non-negligible. • The pressure variance spectra follow n −2 scaling law with a peak frequency lower than that of wind speed and temperature. • The pressure flux divergence approximately satisfies the Monin-Obukhov similarity theory. • The pressure transport term in the TKE budget equation is more important at larger scales and cannot be ignored. [ABSTRACT FROM AUTHOR]

Heavy haze pollution usually occurs in winter. However, according to the enhanced atmospheric boundary layer (ABL) field experiments conducted in the North China Plain (NCP) from 17 June to 6 July 2019, heavy haze pollution may also occur in summer, although with a lower probability. Winter haze pollution is significantly affected by adverse boundary layer meteorological conditions, whereas our study shows different mechanisms of summer haze pollution from that of winter. In summer, PM 2.5 is distributed uniformly as a thick layer at a lighter pollution level; however, the PM 2.5 column content in summer exceeds that in winter, suggesting that the better air quality in summer is mainly due to improved diffusion conditions. In summer, even under haze conditions, the ABL can develop over 1000 m and has a large ventilation similar to clean periods, which indicates both favourable vertical diffusion conditions and advection capability of the summer ABL. Unlike in winter, the heavy haze pollution in summer is often caused by regional transport which is related to local circulation. To explore the influence of different scale systems on summer haze pollution, we applied the spectral analysis method to surface PM 2.5 concentrations. Strong periodicity of PM 2.5 concentrations is found in 4-9 d and 1 d, corresponding to the impacts of large-scale synoptic system changes and the ABL evolution, respectively. The influence of weather change is much stronger than that of the ABL evolution on PM 2.5 concentrations in summer. The resulting changes in PM 2.5 concentrations are approximately 45 μg/m 3 and 15 μg/m 3 , respectively. There has been a consensus on the importance of emission control in winter. And this study shows that heavy haze pollution can also occur in summer and regional joint emission control should also be emphasized in summer., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Background: Phenotypic diversity of floral organs plays an important role in plant systematic taxonomy and genetic variation studies. Previous research have focused on the direction of variation but disregarded its degree. Phenotypic variation (including directions and degrees) of 17 floral traits from wild to cultivated crabapples were explored by comparing their distributions and deviations in three different dimensions: floral organ number, size, and the shape., Results: Except for petal number, petal length / petal width, and sepal length / sepal width, the analyzed floral traits of cultivated crabapples all showed downward distributed box bodies in box plot analysis and left deviations of fitted curves in frequency distribution function analysis when compared to the wild, which revealed consistent variation directions of petaloid conversion (pistils or stamens → petals), size miniaturization (large → small), and shape narrowness (petal shape: circular → elliptic; sepal shape: triangular → lanceolate). However, only seven floral traits exhibited significant differences in box plot analysis, while all of the traits in frequency distribution function analysis were obviously offset. The variation degrees were quantitatively characterized by sizing traits > shaping traits > numbering traits and by horizontal dimensions > radial dimensions., Conclusions: Frequency distribution function analysis was more sensitive than the box plot analysis, which constructed a theoretical basis for Malus flower type breeding and would provide a new quantitative method for future evaluation of floral variation among different groups of angiosperms at large.