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Deserts play an important role in the climate system, which is closely associated with the emission and transport of dust aerosols. Based on the intensive observation experiment in the Taklimakan Desert, the potential physical processes between the deep convective boundary layer (CBL) and dust emission are revealed in this study. Deep CBL enables the formation of clouds in the late afternoon, leading to significant cooling of surface. Large‐scale buoyant coherent structures thereby transform into the mechanical coherent structures confined near the surface. The responses promote the earlier occurrence of low‐level jet (LLJ) than in cloudless conditions, which allows the downward transport of LLJ momentum and substantially increases surface wind. Therefore, dust emission is initiated by strong wind at dusk and lasts for several hours. The results are useful to predict dust emissions and improve our understanding of distinctive boundary‐layer processes in desert regions. Plain Language Summary: Desert is a key component of regional/global climate system, which is closely associated with the emission and transport of dust aerosols. A better understanding of dust emission mechanisms and their interaction with atmospheric physical processes is of great significance for improving numerical weather and climate models. This study investigates possible physical mechanisms of the dust emission related to deep atmosphere boundary layer, based on the field experiment in the Taklimakan Desert. It is found that the formation of late‐afternoon clouds and the occurrence of wind maxima at 400–600 m are crucial during the processes. Initially, the formation of clouds is enabled by deep atmosphere boundary layer that developed in the late afternoon. After cloud formation, surface becomes cooling, and then the upper part of the boundary layer is gradually released from the surface frictional restraint, which promotes the development of wind maxima at 400–600 m. As the momentum of the wind maxima is transported downwards, surface wind substantially increases, which systematically blows dust particles up. Consequently, dust emission happens at dusk in desert regions. Key Points: Deep convective boundary layer enables the lifting condensation of moisture and the formation of boundary‐layer clouds in desert regionsThe emergence of late‐afternoon clouds strengthens the surface cooling and thus advances the development of low‐level jetDownward momentum transfer from low‐level jet to near‐surface wind is crucial to initiate dust emission at dusk [ABSTRACT FROM AUTHOR]

Vertical exchange between the atmospheric boundary layer (ABL) and free troposphere (FT) is a key link in coupling the earth's surface and upper atmosphere. This process is usually quantified by numerical simulations, while its reliability is not well assessed until now. Using space‐time intensified ABL observations, we evaluate the ABL‐FT air mass exchange flux derived from the Weather Research and Forecast (WRF) model. A six‐site sounding experiment is conducted in the North China Plain during the wintertime of 2019. The measured data is processed to provide enough information to derive the vertical exchange flux corresponding to the model‐based result, so that a systematic comparison is conducted. Three physical processes involved in ABL‐FT vertical exchange are quantitatively evaluated, that is, temporal variation of ABL height, advection across the inclined ABL top, and vertical motion at the ABL‐FT interface. Results show that the model‐based and observation‐based fluxes are generally agreed in temporal evolution (R = 0.67, p < 0.01), both characterized by 4–6 days periodicity and diurnal cycle. Their relative mean error was about 45% during the whole study period, mainly stemming from the vertical motion term and the advection crossing term. The model inaccuracy in representing these relevant processes at the ABL top is largely responsible for the discrepancy. Besides, the difference may also be attributed to the observational uncertainty (∼22%) that is caused by the measurement's difficulties in determining ABL spatial variation and acquiring vertical velocity. Through this study, the credibility and limitation of the WRF model in deriving ABL‐FT exchange flux are quantified. Plain Language Summary: The vertical exchange between the atmospheric boundary layer (ABL) and free troposphere (FT) plays a crucial role in atmospheric matter transport and energy flow, affecting weather systems, atmospheric chemistry, air pollution and climate change. This process is usually quantified by numerical simulation. This work aims to evaluate the reliability of the air exchange flux derived from a meteorological model, using comprehensive observation data in 1 month. The result shows that the model‐based exchange flux can reproduce the temporal evolution of the observation‐based exchange flux, including 4–6 days periodicity and diurnal variation. The overall relative difference between simulated and observed fluxes is about 45% during the whole study period. A more detailed comparison of each component term is conducted to investigate the causes of the discrepancy. We found that the difference is partly attributed to the model inaccuracy in representing the ABL top spatial variation and the vertical velocity at this layer. Additionally, a 22% uncertainty in observation‐based flux introduced by the relevant data processing is also an important reason. The evaluation result provides a quantitative reference to understand the biases in the meteorological model and their impact on ABL‐FT vertical exchange simulation study. Key Points: The air exchange flux between the boundary layer and free troposphere is reproduced by the WRF model with synoptic and diurnal variationsThe model‐derived exchange flux deviates from observation‐derived flux with a relative difference of 45%The deviation is mainly attributed to simulation‐observation differences in vertical motion and spatial gradient at the boundary layer top [ABSTRACT FROM AUTHOR]

This study develops a quantitative climatology of water vapour exchange between the atmospheric boundary layer (ABL) and free troposphere (FT) over eastern China. The exchange flux is estimated for January, April, July and October over 7 years based on a water vapour budget equation using simulated meteorological data. The spatiotemporal characteristics and occurrence mechanism of ABL–FT water vapour exchange and its relationship with the El Niño–Southern Oscillation (ENSO) are revealed: (1) the vertical exchange flux varies regionally and seasonally, with downward transport to maintain ABL moisture during winter and autumn in the northern region and persistent output to humidify the FT in the southern region, particularly in summer. Additionally, the vertical exchange flux is also topographic dependent. (2) The vertical motion at the ABL top, which is produced by the dynamic forcing of the terrain on synoptic winds, is the dominant mechanism for the water vapour vertical exchange over the long-term average. The evolution of the vertical exchange flux within 1 d scale is driven by the ABL diurnal cycle. (3) The interannual variation of water vapour vertical exchange is correlated with ENSO. A triple antiphase distribution with negative–positive–negative anomalies from north to south exists in La Niña years (and vice versa in El Niño years), which corresponds to the spatial pattern of anomalous precipitation. This phenomenon is mainly due to the alteration of vertical velocity and water vapour content at the ABL top varying with ENSO phases. These results provide new insight into understanding the atmospheric water cycle. [ABSTRACT FROM AUTHOR]

This study develops a quantitative climatology of water vapor exchange between the atmospheric boundary layer (ABL) and free troposphere (FT) over Eastern China. The exchange flux is estimated for January, April, July, and October over 7 years (2011 and 2014–2019) based on a water vapor budget equation using simulated meteorological data. The spatial pattern of the ABL-FT water vapor exchange flux is closely related to the topographic distribution. The seasonal variation shows that the water vapor exchange in the northern region is downward in January and October with the flux being 37 %–72 % of the surface evaporation to maintain the ABL moisture, while it is weak upward in April and July; the southern region presents persistently water vapor output from the ABL to the FT, with the ratio of exchange flux to surface evaporation increasing from 10 % in January and October to 60 %–80 % in April and July. Three physical processes determine the total water vapor exchange, among which the ABL diurnal variation drives large magnitude exchange flux within the one-day cycle, but for the net monthly mean flux, the vertical motion at the ABL top is the main contributor. The anomaly of water vapor exchange in ENSO years illustrates triple antiphase distribution: strengthening in the middle area and weakening in the north and south zones of Eastern China in La Niña year, and vice versa in El Niño year. It agrees with the spatial pattern of anomalous precipitation, implying the crucial role of ABL-FT water vapor exchange in atmospheric water cycle. [ABSTRACT FROM AUTHOR]

Turbulence intermittency driven by submeso motions limits the progress of turbulence theory. Field observations from the Horqin Atmospheric Boundary‐Layer and Environment Experimental Station, China were used to investigate turbulence intermittency. An automated algorithm to Separate and reconstruct Submeso and Turbulent motions (SST) was improved for more accurately extraction and quantitative characterization of submeso motions. The existing intermittency intensity indexes, the local intermittency strength of turbulence (LIST) and intermittency strength (IS), which are based on kinetic energy only, are revised by considering the potential energy of submeso and turbulent motions to quantify intermittency intensity more comprehensively. The analysis of eight cases revealed that turbulent intermittency events are characterized by quiescent (pulsation, material, and energy transportation are weak) and burst (pulsation, material, and energy transportation fluctuate violently) periods. The conversion of both the kinetic and potential energy of submeso to turbulent motion contributes to the transition from quiescent to burst periods. The transition always occurs after ∆TE$$ \Delta \mathrm{TE} $$ <0 (the total energy difference between the submeso motion and turbulence), followed by a significant increase in ∆TE$$ \Delta \mathrm{TE} $$. Atmospheric stability decreases during the transition from quiescent to burst periods in most cases. In a totally intermittent night, the burst periods take up most of the material and energy transport, and the amount transported is not smaller than that during a totally turbulent night. The weaker the intermittency at night, the greater the capacity of turbulent transport. A comparison of five types of turbulence intermittency intensity indexes highlights the consistency and advantages between LIST (IS) and indexes in the literature. Finally, we found that turbulent intermittency events tended to occur more easily in the atmospheric boundary layer (ABL) with small winds (U < 2 m s−1) or stable stratification (Rib > 1), although they can also occur in ABL with unstable stratification and in the non‐stationary state of the day–night transition. [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]

A field campaign was carried out in the North China Plain (NCP) spanning 4 years and formed a dataset of more than 2,700 planetary boundary layer (PBL) sounding samples (872 in summer and 1,841 in winter). Based on these data, fundamental aspects of the PBL climatology over this region were investigated. First, the ensemble mean features of the PBL were revealed. The maximum PBL height in the daytime reaches 1,079 versus 786 m (summer vs. winter, hereafter the same), while about 200 m at nighttime. The bulk mean temperature and specific humidity across the PBL in summer are significantly higher than those in winter (24.0 vs. −0.5°C; 8.9 vs. 1.7 g⋅kg−1, respectively). Mean wind speed within the PBL keeps almost the same in winter and summer (4.5 m⋅s−1) but with a seasonal difference in wind direction (southerly vs. northwesterly). Second, significant diurnal variations within/above the PBL were quantified. Day‐night temperature contrast is largest near the ground (7.9 vs. 5.1°C), and it decreases with height to almost a constant above the PBL. Diurnal variation amplitude of specific humidity is about 1.0 versus 0.3 g⋅kg−1. Diurnal variation of winds also supports the extended influence of the earth surface across the PBL. Third, the local influence on the PBL over the NCP is also presented. PBL height is higher in the plain centre; temperature is lower in coast than inland; winds in the PBL are strongly modulated by local or mesoscale circulations including the plain wind and sea breeze; low‐level jets are common at summer night over the central and eastern parts of the NCP. Analysis reveals possible energy and water vapour exchange across the PBL, and additional heating mechanism above the PBL (e.g., solar radiation absorption). [ABSTRACT FROM AUTHOR]

Primary work on the planetary boundary layer (PBL) climatic features and associated air pollution in Beijing was carried out based on a 40-year dataset. The main results are identified as follows. The annual mean PBL height was 906 m (1455 m in daytime and 357 m in nighttime). Within the PBL, the average potential temperature, specific humidity, and wind speed were 287.3 K, 5.1 g kg−1, and 6.5 m s−1. Significant seasonal variations were observed in the PBL variables, leading to distinct pollutant diffusion conditions. The PM2.5 concentrations varied seasonally, with a high value in winter (97 µg m−3) and a low value in summer (74 µg m−3). The summertime PM2.5 was closely related to the local emission intensity (R = 0.79) and declined with a reduction in the emission intensity, while the winter PM2.5 showed large interannual variabilities and trends, relying more on the PBL conditions. A comparison of polluted and clean winters was performed, revealing that polluted winters were associated with a warmer layer above the PBL that inhibited the development of the PBL (933 m vs. 1283 m, daily maximum height for polluted vs. clean winters) and led to a humid (1.4 g kg−1 vs. 0.8 g kg−1) and weak wind (5.8 m s−1 vs. 8.2 m s−1) layer within the PBL. In terms of synoptic impacts, the warm advection above the PBL (0.07 K h−1) and subsidence heating (0.21 K h−1) near the top of the PBL contributed to the occurrence of a stable and polluted PBL. [ABSTRACT FROM AUTHOR]

This study estimates long‐term PM2.5 exchange flux between the atmospheric boundary layer (ABL) and free troposphere (FT) in the North China Plain. The effect of PM2.5 long‐range transport (LRT) on air quality in downwind regions is also assessed. The PM2.5 exchange fluxes are calculated based on a mass budget method with data from WRF‐Chem simulations, during wintertime months (November, December, and January) in 2014, 2016, and 2017 (represent moderate, heavier, and less polluted years). The overall PM2.5 exchange exhibits clear topographical correlation and diurnal variation. The plain area is characterized by a considerable upward flux of −0.13 μg m−2 s−1 (in a 3‐year average), acting as an effective source for LRT. ABL height variation contributes significantly to the diurnal cycle of PM2.5 vertical exchange. Over the mountainside and ridge areas, the PM2.5 exchange flux is downward and its diurnal variation is weak, due to the dominant cross‐mountain descent flows. Four LRT patterns in the FT are identified, that is, eastward, southward, recirculation, and local stagnation. They can affect air quality in Northeast China, Yangtze River Delta, South Korea, and Japan. Indicating with averages and standard deviations, the PM2.5 concentration increases (relative contribution) for these four target regions over the 3‐year winter period are respectively 5.5 ± 4.8 μg m−3 (12.6 ± 10.9%), 4.6 ± 4.5 μg m−3 (8.4 ± 6.4%), 4.4 ± 3.9 μg m−3 (5.2 ± 4.4%), and 1.6 ± 0.9 μg m−3 (2.6 ± 1.6%). While the maximum impacts can be 36.7 μg m−3 (59%), 31.1 μg m−3 (41%), 25.7 μg m−3 (30%), and 7.2 μg m−3 (13%), respectively. Plain Language Summary: The PM2.5 exchange between the boundary layer and the free troposphere is a key process directly affecting air pollution transport and influence scale. This study estimates the PM2.5 vertical exchange flux over the North China Plain (NCP) during wintertime in 2014, 2016, and 2017, and quantifies the impact of the subsequent long‐range transport on air quality in downstream areas. The long‐term average PM2.5 exchange flux is closely related to the topographic distribution and has diurnal variation characteristics. The plain area is characterized by considerable PM2.5 vertical outflow, allowing the pollutants to be transported long distances in the free troposphere. There are four transport patterns with the main affected areas being the Yangtze River Delta, Northeast China, South Korea, and Japan, as well as the NCP itself. PM2.5 concentration increases due to the long‐range transport for these areas are quantified. These results provide a more solid understanding of atmospheric transport and large‐scale air pollution. Key Points: PM2.5 vertical exchange flux over the North China Plain is characterized by topographical distribution and diurnal variationThe plain area provides an effective PM2.5 source for long‐range transport in the free troposphere with a seasonal average upward flux of −0.13 μg m−2 s−1Four long‐range transport patterns are identified and PM2.5 concentration contributions to downstream regions are quantified [ABSTRACT FROM AUTHOR]

This study reveals mesoscale planetary boundary layer (PBL) structures under various pollution categories during autumn and winter in the North China Plain (NCP). The role of the atmospheric internal boundaries (AIBs, referring to the discontinuity of meteorological conditions in the lateral direction) in regulating PBL structures and shaping the PM 2.5 pollution patterns is emphasized. The Weather Research and Forecast (WRF) model is used to display the three-dimensional meteorological fields, and its performance is evaluated by surface observations and intensive soundings. The evaluation demonstrates that the model reasonably captures the mesoscale processes and the corresponding PBL structures. Based on the reliable simulations, three typical pollution cases are analyzed. Case 1 and case 2 represent the two main modes of the wind shear category pollution, which is featured with airflow convergence line/zone as AIB, and thus is dominated by dynamical effect. Case 1 presents the west–southwest wind shear mode associated with a trough convergence belt. The convergent airflow layer is comparable to the vertical scale of the PBL, allowing PM 2.5 transport to form a high pollution area. Case 2 exhibits another mode with south–north wind shear. A "lying Y-shaped" convergence zone is formed with a thickness of about 3000 m, extending beyond the PBL. It defines a clear edge between the southern polluted air mass and the clean air in the north. Case 3 represents the topographic obstruction category, which is characterized by a cold-air damming AIB in front of the mountains. The PBL at the foothills is thermally stable and dynamically stagnant due to the capping inversion and the convergent winds. It is in sharp contrast to the well-mixed/ventilated PBL in the southern plains, especially in the afternoon. At night, this meteorological discontinuity becomes less pronounced. The diurnal variation of the PBL thermal and dynamical structure causes the pollutants to concentrate at the foot of the mountains during the daytime and locally accumulate throughout the entire plain in the evening. These results provide a more complete mesoscale view of the PBL structure and highlight its spatial heterogeneity, which promotes the understanding of air pollution at the regional scale. [ABSTRACT FROM AUTHOR]

The deep convective boundary layer (CBL) in the Taklimakan Desert plays an important role in the climate system in East Asia. Based on the observation experiment and large‐eddy simulation, turbulent mechanisms for its formation were revealed in this study. This explained why the daily maximum CBL depth was independent of surface heating. In the late‐morning, there was a weak temperature inversion and a near‐neutral residual layer (RL) above the CBL. With the development of the CBL, stronger convection could penetrate the RL and even overshoot the top of the RL. The distinctive boundary‐layer process entrained free‐tropospheric air to warm the RL and then promoted the entrainment of the warmed air in the RL into the CBL. This extra energy supply effectively contributed to the growth of the CBL. With further positive feedback between the CBL and RL depths, a deeper CBL would form in consecutive fair‐weather conditions. Plain Language Summary: The atmospheric boundary layer controls the exchange of momentum, heat, and mass between the land surface and the free atmosphere. Contrary to the typical 1,000–2,000 m over land, the convective boundary layer (CBL) in the Taklimakan Desert can reach 5,000 m. By coupling with the Tibetan Plateau, the deep CBL becomes a key component of the climate system in East Asia. Traditionally, it is considered that intense surface heating is the primary reason for its formation, but our correlation analysis shows that surface heating can only maintain a CBL of ∼1,800 m. To understand the potential physical processes, we further modeled the development of the deep CBL and found that the presences of weak temperature inversion and near‐neutral residual layer (RL) above the CBL are crucial. The distinctive vertical structure leads to a unique boundary‐layer process, which entrains warm air from the higher level into the RL and further promotes the warmed air in the RL to be entrained into the CBL. The special energy supply is key to the formation of deep CBL. The results are helpful to understand the land‐atmosphere interactions under climate change and improve the numerical weather prediction in northern China and even East Asia. Key Points: The convective boundary layer (CBL) in the Taklimakan Desert commonly developed to 3,000 m and even reached over 5,000 m in summerStrongly penetrative convection could overshoot the top of near‐neutral residual layer (RL) and entrain free‐tropospheric air into the RLThe warmed RL strengthened the entrainment heating, which supplied extra energy for the further development of deep CBL [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]

Persistent severe haze pollution seldom happens in summer in Beijing. In this study, a persistent severe haze pollution event, defined as daily PM2.5 concentration higher than 150 μg m−3 on 5 consecutive days, was observed in Beijing from 26 to 30 in July 2010. It was not caused by crop residue burning during the harvest period. Weak pressure systems dominated at surface and implicated weak advection. Regional weak southerly winds with speeds of 2–3 m s−1 consistently brought pollutants from southern large-emission regions to Beijing. Surface convergence resulted from northerly winds prevailing in northern regions induced pollutants remaining in Beijing, which contributed to the maximum daily PM2.5 concentration on 26 in July. A continental high-pressure system persisted in the northwest of Beijing at 500 hPa, which led to significant sinking motion. Elevated inversion was found in the form of subsidence inversion, and this was confirmed by a skew T-logp diagram and vertical velocity analysis. It is much different from the vertical boundary layer structure in wintertime pollution period that surface-based inversion dominates. The subsidence inversion was an extremely stable layer with an average depth of hundred meters and strength of 1.4 °C. The capping effect of the inversion layer at low altitude of average 720 m limited vertical diffusion of pollutants and trapped them in a shallow layer, and thus, extremely high concentration of PM2.5 remained. WRF-Chem model simulation demonstrated that about 70% of PM2.5 was transported to Beijing from its southern regions. [ABSTRACT FROM AUTHOR]

Variation of the turbulence barrier effect caused by the turbulence intermittency have a strong impact on the vertical distribution and variation of pollutants, which limits the accuracy of pollution process simulation. Turbulence observation data from the five layers of the 255 m meteorological tower in Tianjin during two severe haze pollution periods were used to discuss energy changes during the enhancement and break of the turbulence barrier. Results showed that a sharp decrease in turbulence kinetic energy contributed to barrier enhancement and the kinetic energy transfer from sub-mesoscale motion to turbulence triggered the barrier break. The barrier break point tends to occur after Δ KE < 0 (the kinetic energy difference between turbulence and sub-mesoscale motion), subsequently followed by a significant increase in Δ KE. Due to the significant reduction in wind speed during severe haze pollution, type-B intermittency events occurred more frequently and existed at five heights. Type-A intermittency events were more likely to occur at the heights of 40 and 80 m, and type-C intermittency events were more likely to occur at heights above 80 m. Wind speed thresholds at different heights (2.5 m s−1 for 40 m, 4 m s−1 for 80 m, 4 m s−1 for 120 m, 4 m s−1 for 160 m, 4.5 m s−1 for 200 m) can be used to determine whether turbulent barrier effects occurred. This study provides an important research basis for solving the theoretical problem of the stable boundary layer that currently limits the accurate prediction of severe haze pollution processes. [Display omitted] • The sharp decrease of turbulence kinetic energy contributes to barrier enhancement. • Energy transition from sub-mesoscale to turbulent motion triggers barrier break. • Barrier break point tends to occur after Δ KE < 0 following significant increase. • Type-B intermittency occurs more frequently and exists at all levels in haze events. • Wind speed thresholds for whether turbulence barrier effect occur was determined. [ABSTRACT FROM AUTHOR]

Heavy haze pollution events are closely related to the turbulent structure of the stable boundary layer (SBL). SBL can be divided into two regimes, weak(coupled) and strong(decoupled). The weak SBL conforms to the classical turbulent theory and couples with the surface and different heights, whereas the strong SBL does not conform and decouples. However, the thresholds between coupled and decoupled SBL have not been determined in haze pollution events. Five levels of turbulence observation data from two severe haze pollution cases observed at the 255 m meteorological tower in Tianjin were employed to address this dilemma. The first case was analyzed in detail, and the second case was used for verification. The occurrence frequency of SBL was approximately 50% during the two haze pollution cases. The wind speed thresholds distinguishing coupled and decoupled SBL are: 2.5 m s−1 at 40 m, 4.0 m s−1 at 80 m, and 5.0 m s−1 at 120 m. The decoupled SBLs accounted for >70% of SBLs in haze pollution events. The turbulent structures notably differed between coupled and decoupled SBL events. In a decoupled SBL, the scalar concentration at different heights was substantially higher, the strength and occurrence frequency of sub-mesoscale motion were larger, and turbulent barrier effects occurred. Moreover, there was an inverse gradient transport and a smaller spatiotemporal scale of turbulent eddies. Therefore, there was a weaker turbulent kinetic energy, flux, and turbulent correlation across the layers in the decoupled SBL. The results reveal the failure of Monin-Obukhov similarity theory and traditional turbulent energy spectrum theory in a decoupled SBL. Wind speed thresholds can be widely used in the severe haze pollution simulation. The results of this study also indicate that decoupled SBL requires further study and attention in haze pollution events to improve the accuracy of pollutant concentration forecasting. • U threshold for coupled and decoupled SBL was determined and related with height. • Decoupled SBLs account for >70% of SBLs in observed haze pollution events. • Weaker(stronger) turbulent transfer (barrier effect) occurred in decoupled SBL. • Weaker turbulent correlations across layers were observed in decoupled SBL. [ABSTRACT FROM AUTHOR]

Field observations of the atmospheric boundary layer were made over urban and suburban terrain in the Yangtze River Delta, China. A multiresolution decomposition was applied over three different types of terrain: flat homogeneous terrain, suburban terrain and urban terrain, with results indicating that, (1) the average scale contribution of u, v, w and $$T_{v}$$ had a similar variability with length scale for all these three sites respectively, and the dimensionless length scale corresponding to the maximum sensible heat flux contribution increased with the terrain complexity; (2) the length scale corresponding to the maximal average scale contribution for vertical wind velocity $$\lambda _w $$ was directly proportional to the roughness length $$z_{0}$$ in unstable conditions; and (3) the contributions of large-scale motions led to sensible heat fluxes determined with a large-aperture scintillomter being larger than those using the eddy-covariance method for the suburban case, whereas this phenomenon was not substantial for the urban case. [ABSTRACT FROM AUTHOR]

• Flux-variance method is an effective way to indirectly obtain pressure flux. • Pressure flux convergence/divergence is partially related to larger-scale eddies. • Ejection and sweep events lead to opposite vertical gradient of pressure flux. • There's a quadratic relation between pressure flux gradient and friction velocity. • Taking pressure transport into account refines estimation of turbulent flux in CBL. Using multi-layer pressure fluctuations and other conventional turbulence observational data over a nearly flat and homogeneous dune underlying surface, the temporal and spatial characteristics of pressure flux and its profile were analyzed to illustrate the physical mechanism of pressure flux convergence/divergence and the impact of pressure transport terms on the estimation of turbulent fluxes in this study. The flux-variance (FV) method is an effective approach to indirectly obtain pressure flux through momentum flux when no fast-response observations of pressure fluctuations are available. The fitted functions are w ′ p ′ ¯ = 0.16 · (− F Z (z) · u ′ w ′ ¯ σ p σ u) and u ′ p ′ ¯ = 0.55 · (F X (z) · u ′ w ′ ¯ σ p σ w) , where F Z (z) and F X (z) are the height normalized functions for vertical and horizontal directions. Under the circumstance of pressure flux divergence (FD), the transport efficiency of pressure and contribution of larger-scale eddies to pressure flux at higher levels are greater than those at lower levels, and flows in the atmospheric surface layer (ASL) are mainly dominated by the sweep events; while the pressure flux convergence (FC) cases are exactly the opposite situations. A good quadratic function relationship was found between the vertical gradient of pressure flux and friction velocity under different atmospheric stabilities: ∂ w ′ p ′ ¯ ∂ z = 0.01 u * (16 u * − 1). Turbulence kinetic energy (TKE) and its vertical transport are greater in the FD cases than those in the FC cases. The momentum and sensible heat fluxes in the convective boundary layer (CBL) were overestimated by their common second-order diagnostic equations and Rotta model (pressure redistribution term parameterization) which neglect the diffusion terms. After adding the contribution of pressure transport terms into the diagnostic equations and Rotta model and modifying the original Rotta constants, the overestimations were well corrected and the estimated turbulent fluxes were more consistent with the observations. This work provides a novel direction and idea for the future improvement of the planetary boundary layer (PBL) parameterization schemes in many numerical weather and climate models. [ABSTRACT FROM AUTHOR]

Field observations of the atmospheric boundary layer were made over urban and suburban areas in the Yangtze River Delta, China. Sensible heat fluxes were obtained by eddy-covariance (EC) systems and large-aperture scintillometers (LASs). The results indicated that (1) the sensible heat flux obtained by LAS $$(H_\mathrm{LAS})$$ was less noisy and slightly larger than that obtained by EC $$(H_\mathrm{EC})$$ over both urban and suburban surfaces; (2) the values of $$H_\mathrm{LAS} /H_\mathrm{EC} $$ were higher when the correlation coefficient of vertical wind speed and temperature ( $$r_{wT}$$ ) was smaller. Lower values of $$r_{wT}$$ were due to low-frequency trends. The urban values of $$H_\mathrm{LAS} /H_\mathrm{EC}$$ were smaller than suburban values at low $$r_{wT} $$ values; (3) the sensible heat flux determined by LAS was improved by use of the Monin-Obukhov similarity theory of the temperature structure parameter $$(\phi _{\mathrm{CT}})$$ over urban and suburban areas, and the improvement is more significant over urban surface areas. [ABSTRACT FROM AUTHOR]

An extreme dust storm hit North China from March 14 to 16, 2021. With the enhanced observations in Beijing, the vertical dispersion of long-range transported dust was investigated from the perspective of atmospheric turbulence. A framework was developed by combining two types of turbulence intermittency parameter to distinguish intermittent or continuous turbulence; thus, the evolution of turbulence and its roles in dust dispersion were clearly illustrated on March 15, 2021. Initially, turbulence remained in the long quiescent period and turbulent exchange was suppressed significantly, which negligibly increased the dust mass concentration in the lower atmosphere, despite the dust mass being located at 300 to 800 m. Then, a short turbulence burst occurred as the cold front approached Beijing, and the elevated dust was mixed downward intensely and rapidly, leading to a sharp increase in the near-surface dust mass concentration. Finally, continuous turbulence dominated and diffused dust upward when the cold front fully occupied Beijing. Furthermore, the dissimilarity between the turbulent transport of dust and momentum-heat depends on the presence of dust sources (e.g., elevated dust mass and advection). When dust sources exist, there is efficient dust transport by large-scale turbulence, and thus the transport of dust and momentum-heat is similar. However, when there is no dust source, dust particles do not follow the air mass for small-scale turbulence and exhibit strong random movements, which confounds downgradient transport by large-scale turbulence and leads to low dust transport efficiency. In this condition, the conventional flux-gradient method is not applicable to estimate the dust flux especially by replacing the diffusion coefficient or universal function of dust mass concentration with that of momentum or heat. • A framework was developed to distinguish intermittent or continuous turbulence. • A short turbulence burst controlled the sharp increase in near-surface dust concentration. • Continuous turbulence was responsible for the dust storm dissipation. • Flux similarity between momentum, heat, and dust depends on the presence of dust sources. [ABSTRACT FROM AUTHOR]

• Loess Plateau turbulence intermittency features burst and quiescent periods. • Submeso has a significantly greater effect on quiescent than burst periods. • Energy closure during burst (quiescent) periods is 68 % (17 %) during nighttime. Turbulence intermittency is a challenge facing in the field of atmospheric boundary layer (ABL) and micrometeorology. We employed an automated algorithm for the separation and reconstruction of Sub-Mesoscale and Turbulent motions (SMT) to examine the basic characteristics of turbulence intermittency driven by sub-mesoscale motion over the complex underlying surface of the Loess Plateau. The findings revealed that sub-mesoscale motion has a significant influence on turbulence statistical parameters. We analyzed five cases and found that the turbulent intermittency events were characterized by quiescent and burst periods. During the quiescent (burst) period, the turbulent transport weakened (strengthened), turbulence fluctuations weakened (strengthened), atmospheric stability increased (decreased), and turbulent energy decreased (increased). These bursts can be triggered by energy conversion from sub-mesoscale to turbulent motion. Actual observations revealed atmospheric conditions where turbulent intermittency events are more likely to occur: wind speed U < 3.5 ms−1, wind speed gradient ΔU/ΔZ < 0.2 s −1, temperature gradient ΔT/ΔZ > -5.1 K/100 m, or bulk Richardson number Ri b > -0.1. The influence of turbulence intermittency on the classical energy non-closure issue over the Loess Plateau was explored further. The results show that the presence of sub-mesoscale motions contributed to energy closure, with an energy closure of 78 % during daytime and 36 % during nighttime. And different periods of turbulent intermittency events affected energy non-closure differently, the energy closure during the burst (quiescent) period was approximately 98 % (70 %) during daytime and 68 % (17 %) during nighttime, approaching closure and far exceeding the overall closure rate during the burst period, whereas significantly low during the quiescent period. This suggests that turbulence intermittency is a very important factor causing energy non-closure over complex underlying surfaces, especially in stable boundary layer (SBL) during nighttime. The results are highly significant for a better comprehension of turbulence intermittency and surface-atmosphere interactions over complex underlying surface. [Display omitted] [ABSTRACT FROM AUTHOR]

Under low wind speed conditions, the frequent intermittent turbulence phenomenon in the atmospheric boundary layer (ABL) greatly weakens the turbulent diffusion of pollutants to cause the heavy haze events. Turbulence may disappear at certain heights forming a laminar flow as if there is a barrier layer hindering the transmission up and down during the heavy haze periods. The turbulent data at five layers and PM 2.5 (fine particular matter with a diameter smaller than 2.5 μm) concentration at two levels were used to discuss the barrier that is called the barrier effect vividly. The results revealed that the changes in the PM 2.5 concentration at different heights corresponded excellently with the change in vertical turbulence barrier effect. This work explains the physical mechanism responsible for the accumulation of pollutants in heavy pollution events and the influence of turbulent diffusion conditions on the distribution of the PM 2.5 concentration. Unlabelled Image • Introduce turbulence barrier effect • Explain the mechanism of the rapid accumulation of PM 2.5 in heavy haze events • Explore the influence of turbulent diffusion conditions on the PM 2.5 distribution [ABSTRACT FROM AUTHOR]

To obtain the differences in the turbulence structures between the light and heavy haze pollution process, a light pollution episode (LPE) from November 3 to 72,017, and a heavy pollution episode (HPE) from December 15 to 232,016, were investigated. The weather conditions, mean meteorological fields, and turbulence structures of the two episodes were analysed. The results show that the two cases have similar weather backgrounds, and the differences in mean meteorological field are mainly related to the difference in the degree of solar radiation weakening. The turbulence during the HPE was suppressed to a greater extent in both thermal and dynamic effects. The structure of turbulence is weak and typically characterized by intermittent turbulence in the stable boundary layer. The parameter IS (Intermittent Strength) is introduced to indicate the strength of intermittency. Because of the complexity of atmospheric motion, we use the change in IS, i.e., ∆ IS, to indicate the change in the intensity of turbulent intermittency during each pollution process. In the accumulation stage, the weakening of turbulent exchange caused by the influence of sub-mesoscale motion may result in poor turbulent diffusion conditions, which should be considered because they can lead to heavy pollution events when ∆ IS > 0.1. The same conclusions were verified in an analysis of Tianjin for these two cases. Further analysis of the vertical structure of turbulence indicated that during the pollution stage of the LPE, the turbulent energy comes from the surface and is consistent with the traditional surface layer turbulent transport mechanism. Moreover, the upper layer intermittent strength is stronger than that in the lower layer, and ∆ IS < 0.1 at different heights. During the pollution stage of the HPE, the boundary layer is almost decoupled from the surface, and ∆ IS > 0.1 in all layers, which suggests that the weakening of turbulent exchange affected the vertical turbulence structure and resulted in pollutant accumulation. During the dissipation stage of both the HPE and the LPE, the low-level jets provide a turbulence source in the upper layer. The effect of sub-mesoscale motion is weak, and the turbulence component diffuses pollutants. In this stage, ∆ IS < 0.1 in all layers. The upside-down structure of the atmospheric boundary layer leads to full coupling with the ground and promotes the dissipation of pollutants during the HPE. And, the analysis of the pollution processes, from December 16, 2016 to January 8, 2017, also indicate that ∆IS > 0.1 is a feature of severe pollution. The results for these cases indicate that ∆ IS = 0.1 can be used as an indicator to characterize the turbulent exchange conditions and different levels of contamination. • To describe the differences in the turbulence structures between the light and heavy haze pollution episodes • Introduce the parameter IS to indicate the strength of turbulence intermittency. • ∆ IS = 0.1 can be used as an indicator to characterize the turbulent exchange and pollution conditions. [ABSTRACT FROM AUTHOR]

Air quality is significantly influenced by the synoptic, regional and local meteorological conditions. This study aims at elucidating the relation between synoptic flow patterns and low visibility events of haze and fog over the North China Plain (NCP), and the contribution of synoptic flow patterns and boundary layer structure to the severe haze events over the NCP in January 2013. Nine synoptic flow types are statistically identified over the Northern China for autumn and winter of 2004–2014. The flow types with high pressure to the northeast of the NCP (NEH, type 8), weak low pressure band (L-, type 5), high pressure to the southeast (SHE, type 4), and high pressure to the north (NH, type 6) are associated with high occurrence frequencies of low visibility events (48.3%, 42.0%, 37.2%, and 36.7%). The meteorological conditions of these flow patterns reveal synergistic contribution of weak wind and high relative humidity (RH) to low visibility. Quantitative measures for dispersion conditions (recirculation, ventilation, and stagnation) suggest undesirable ventilation and frequent stagnation of the flow types 9 (EH, high pressure to the east), 4, 5, and 8. In January 2013 three regional haze episodes are identified from the distribution of visibility over the NCP, i.e., 10–16 January (EP 1), 22–24 January (EP 2), and 28 January–1 February (EP 3), which were largely associated with the flow types 5, 8, 4, and 9. Coverage of the hazy area exhibited northward expansion in the EP 2 and EP 3 when the RH increased. The abnormally high RH could be attributed to the flow type 6 (NH), which has the highest frequency of precipitation (13.7%) and RH among the nine flow types, and occurred more frequently in that month than in January 2004–2014. The simulation results indicate the evolution of the planetary boundary layer and southerly advection, which was responsible for the high RH and persistent temperature inversion that contributed to the long-lasting haze events. [ABSTRACT FROM AUTHOR]

The atmospheric boundary layer (ABL) is known for its vertical structure in affecting air pollution due to the dilution and ventilation capacity. But how this effect playing over horizontal scales is not well investigated. This study reveals the ABL structure over a sub-synoptic scale or mesoscale related to regional PM 2.5 (particulate matter with an aerodynamic diameter less than 2.5 μm) pollution in the North China Plain (NCP). A typical PM 2.5 pollution episode from December 1–4, 2017, is chosen for analysis, which is characterized by the rapid development of a vast polluted air mass along the mountainous side of the NCP extended hundreds of kilometers. In association with this episode, a shallow trough and a warm tongue at 850 hPa, with warm air advection in the upper layer and an orographic trough at the surface, provide favorable conditions for low-level warm front formation in the NCP. Surface meteorological data from 116 observatories and pollution-monitoring data recorded at 40 stations on the NCP are used to diagnose the hourly evolution of the meteorological and PM 2.5 concentration fields, based on the California Meteorological (CALMET) model and a simple interpolation scheme. In addition to the surface wind, the equivalent potential temperature (EPT) is used to analyze air-mass boundaries or fronts at the surface. The results show that a block of colder air mass is gradually confined by warmer air, driven both from the southeast by a warm front and from the northwest by the thermal effect of the mountains. Consequently, a polluted air mass develops, with sharp boundaries indicated by both the discontinuity of wind fields and a strong gradient in the EPT. Numerical simulation using the Weather Research and Forecast model reproduces the meteorological evolution at the surface, revealing a three-dimensional ABL structure during this episode. With a dome-like warm cap covering the colder polluted air mass, an abrupt drop of ABL height occurs at the cross section from outside into this zone. Strong stratification suppresses the daytime ABL height to as low as 300 m over this zone. Thus, the cold air mass is confined not only laterally but also vertically. This ABL structure persisted throughout the daytime and night, in addition to weak winds in the nearly isolated air mass, which constitutes adverse dispersion conditions. This may help to explain the simultaneous increase in PM 2.5 concentrations over a vast area of the NCP. [Display omitted] • The mesoscale ABL structure related to regional PM 2.5 pollution in the North China Plain was revealed. • The effect of synoptic and mesoscale processes on the ABL was analyzed. • Warm front and mountain thermal effect formed a cold air pile with dome-like warm cap. • PM 2.5 pollution played as a tracer to display internal boundaries of the atmosphere. [ABSTRACT FROM AUTHOR]

In this study, observational data from the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) in July 2008 were used to analyze the characteristics of the turbulence intermittency and its influence on the land-atmosphere turbulent transport over the complex terrain of the semi-arid region of the Loess Plateau in summer. Using the Hilbert-Huang transform (HHT), the local intermittent strength of turbulence (LIST) was calculated based on pure dynamics through an automated algorithm to characterize the turbulence intermittency in this region. But LIST misjudged the actual turbulence intermittency under the condition of weak wind and strong radiation. The thermal effects cannot be ignored in this situation and a thermodynamic intermittency correction factor LIST Thermal is suggested to modify LIST. Then a new intermittent strength index LIST Revise is proposed, which is assumed to be the weighted average of LIST and LIST Thermal according to the stability parameter z / L. LIST (LIST Thermal) is closely related to the near-surface wind-speed (sensible heat flux). Most misjudgments of LIST to turbulence intermittency are corrected, and LIST Revise is more consistent with the general diurnal variation of turbulence intermittency. There are overestimations in turbulent standard deviations and fluxes calculated by conventional eddy covariance (EC) method due to sub-mesoscale motions and turbulence intermittency, producing inaccurate quantifications of turbulent mixing and transport in the planetary boundary layer parameterization schemes. After eliminating the influence of it, the relationship between the normalized standard deviations of different meteorological variables and z / L is more consistent with the Monin-Obukhov similarity rule under stable and unstable stratification. • The thermodynamic intermittency correction factor LIST Thermal and a modified intermittency index LIST Revise are suggested. • Turbulent statistics are overestimated in the Loess Plateau due to sub-mesoscale motions and turbulence intermittency. • Relationship between reconstructed normalized standard deviations of various variables and stability parameter is improved. [ABSTRACT FROM AUTHOR]

Characteristics of wind direction, wind speed, wind shear, and height of low-level jets (LLJs) are obtained and studied using the wind profile data collected by a wind-profile radar located at Xiqing station in Tianjin from 2015 to 2016. Results on the general characteristics of LLJs show that the dominate wind direction of LLJs ranges from 180° to 270° (47%), which is also the prevailing wind direction of strong LLJs (wind speed larger than 14 m s–1). The wind speeds of LLJs are mostly lower than 14 m s−1, and the occurrence proportion of strong LLJs is only 22.8%. The occurrence height distributions of LLJs are relatively uniform throughout the year except the peak at the lower heights (500–600 m). Moreover, the seasonal and diurnal variations of LLJs are investigated, respectively, and the results show that the occurrence frequency of LLJs during warm season is larger than that during cold season, which may be due to the increasing amplitude of inertial oscillations in the boundary layer. The diurnal variation of all categories of LLJs shows a pronounced a unimodal pattern, with the peak of occurrence number appearing at around midnight. In addition, the relationship between LLJs and fog events in Tianjin is investigated based on the data obtained from the surface automatic weather station (AWS) and a 255-m atmospheric boundary layer meteorological tower, since LLJs frequently occur in foggy days (almost 50%) in Tianjin. Eleven fog events accompanied by LLJs are analyzed and statistical results show LLJ plays a critical role in fog life cycle. The effect of northerly LLJs on fog is to enhance turbulent mixing in the fog layer, which is induced by wind shear associated with northerly LLJs and propagates downward to fog layer. There is a threshold relationship between the northerly LLJs and fog development, strong LLJs lead to inversion layer collapse and fog dissipation, while weak LLJs weaken the strength of inversion and atmospheric stability, which are favorable for fog development. Therefore, for fog events accompanied by northerly LLJs, there are negative correlations between fog durations and the strength of LLJs. However, the main contribution of northerly LJJs to fog is to result in fog dissipation in Tianjin, since the duration of fog with northerly LLJs is shorter than that without LLJs. The main contribution of the southwesterly LLJs are to transport water vapor to fog area and increase the humidity in fog layer. Therefore, the southwesterly LLJs are favorable for the fog formation, development and prolong the duration of fog. • Characteristics of different categories LLJs are unique. • Fog events are closely linked to LLJs. • The effect of LLJs on fog is to enhance turbulent mixing and specific humidity. [ABSTRACT FROM AUTHOR]

Air pollution has recently become a regional problem in the North China Plain, which is heavily populated with industrialized city clusters. The local air quality is frequently affected by air pollutant transport in this region, as well as other meteorological conditions. This study aims to reveal the roles of air pollutant transport and atmospheric boundary layer variation in the development of air pollution episodes. Two cities (Dezhou and Cangzhou in Shandong and Hebei Provinces, respectively) near the centre of the North China Plain are chosen, and PM 2.5 (particulate matter with an aerodynamic diameter less than 2.5 μm) concentrations over two winters (January 2016 and December 2017 to January 2018) are evaluated. Both meteorological and air quality observational data are used to construct hourly wind and PM 2.5 concentration fields. High-quality atmospheric boundary layer soundings provide detailed information on boundary layer height and its diurnal evolution. A simple box model is employed to simulate variation in PM 2.5 levels in these two cities by using the spatial gradients and temporal variation rates in the diagnostic fields of wind and PM 2.5 concentrations. Two prominent factors affecting PM 2.5 concentration variation are identified by comparing the simulated and observed diurnal variation in PM 2.5 concentration. The first one is the entrainment of upper-layer air pollutants into the boundary layer in the morning. And the second one is the temporary accumulation of PM 2.5 during the day-to-evening period. After incorporating these two effects, the simulated PM 2.5 is comparable with the observed data. The correlation coefficients between the simulation and observation are 0.84 and 0.77 (P < 0.01) for Cangzhou and Dezhou, respectively, and the normalized mean biases are −0.04 and −0.09, respectively. The relative contributions of different processes affecting PM 2.5 concentrations during air pollution episodes are assessed with the model simulations. The percentage contributions for local emissions, deposition, horizontal advection, temporary accumulation, and boundary layer height variation are from 27% to 45%, −28% to −20%, 46% to 76%, 13% to 40%, and −6% to 22%, respectively. Local emission and regional air pollutant transport are the main causes of these episodes. Temporary accumulation of PM 2.5 during the day-to-evening period is also an important contributor to the episodes. In addition, the entrainment shows varying contributions to PM 2.5 increase with a maximum rate of 30% during the PM 2.5 pollution episodes in the North China Plain. Image 1 • A diagnostic analysis was carried out for characteristics of PM 2.5 episode in the North China Plain. • Observed concentration fields, wind fields, and atmospheric boundary layer data were applied to run a box model. • Regional transport and local source played the major roles in PM 2.5 episode formation. • Diurnal variation of atmospheric boundary layer played complicate role to the PM 2.5 episodes. [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]