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Article

A Comprehensive Study of a Winter Haze Episode over the Area around Bohai Bay in Northeast China: Insights from Meteorological Elements Observations of Boundary Layer

by
Boshi Kang
1,2,
Chong Liu
3,4,
Chuanhai Miao
2,*,
Tiening Zhang
5,
Zonghao Li
2,
Chang Hou
2,
Hongshuo Li
2,
Chenrui Li
6,
Yu Zheng
4 and
Huizheng Che
4
1
The Institute of Atmospheric Environment, China Meteorological Administration, Shenyang 110000, China
2
Liaoning Meteorological Equipment Support Center, Shenyang 110000, China
3
Earth System Modeling and Prediction Centre, China Meteorological Administration, Beijing 100081, China
4
State Key Laboratory of Severe Weather, Institute of Atmospheric Composition and Environmental Meteorology, Chinese Academy of Meteorological Sciences, Beijing 100081, China
5
Liaoning Weather Modification Office, Shenyang 110000, China
6
Lanzhou Central Meteorological Observatory, Lanzhou 730020, China
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(9), 5424; https://doi.org/10.3390/su14095424
Submission received: 28 March 2022 / Revised: 21 April 2022 / Accepted: 28 April 2022 / Published: 30 April 2022
(This article belongs to the Special Issue The Application of Remote Sensing in Sustainable Air Quality Monitoring)
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Abstract

:
Based on wind profile radar observations, along with high-frequency wave radar data, meteorological data, and air quality monitoring data, we studied a haze episode in Panjin—a coastal city around Bohai Bay in Northeast China—that occurred from 8 to 13 February 2020. The results show that this persistent pollution event was dominated by PM10 and PM2.5 and their mass concentrations were both ~120 μg/m3 in the mature stage. In the early stage, the southerly sea breeze of ~4.5 m/s brought a large amount of moist air from the sea, which provided sufficient water vapor for the condensation and nucleation of pollutants, and thus accelerated the formation of haze. In the whole haze process, a weak updraft first appeared in the boundary layer, according to the vertical profile, contributing to the collision and growth of particulate matter. Vertical turbulence was barely observed in the mature stage, with the haze layer reaching 900 m in its peak, suggesting stable stratification conditions of the atmospheric boundary layer. The explosive growth of pollutant concentrations was about 10 h later than the formation of the stable stratification condition of the boundary layer. The potential source areas of air pollutants were identified by the WRF-FLEXPART model, which showed the significant contribution of local emissions and the transport effect of sea breeze. This study provides insights into the formation mechanism of haze pollution in this area, but the data observed in this campaign are also valuable for numerical modeling.

1. Introduction

Haze has frequently been observed in eastern China in recent years due to enhanced anthropogenic emissions along with economic growth, which largely contribute to the expanding urbanization, industrialization, and the explosive growth of vehicles [1,2,3,4,5,6]. Many studies have been conducted on the formation and influence of haze episodes in eastern China via ground-based observations, satellite remote sensing, and numerical simulations, resulting in a comprehensive knowledge of haze pollution [6,7,8,9,10,11,12,13]. In general, there are two main factors that determine the haze process: aerosol emission intensity and atmospheric diffusion condition. Although the air quality has significantly improved due to the ecological environment protection and sustainable development policy, haze is still a main environmental pollution event in urban cities, especially during the winter when stable synoptic conditions are present [14,15,16,17,18]. Therefore, the meteorological elements observations of boundary layer and their variations related to the haze formation mechanism still need to be further investigated. There are many factors affecting haze formation; the wind field is one of the most important meteorological parameters because it determines the incoming and outgoing direction of pollutants as well as the ability of dilution and diffusion [19,20,21,22,23,24].
Among many wind detection instruments, the wind profile radar is widely used in current studies because of the high temporal and spatial resolution of its observations. The data can depict the wind field in real time and play an important role in retrieving the vertical motion of atmospheric winds and improving the accuracy of short-term predictions [25,26,27]. In addition, wind profile radars can continuously and automatically observe, in near-real-time, the atmospheric horizontal wind, vertical airflow, atmospheric refractive index structure constant, and other meteorological elements at high spatial and temporal resolutions, with respect to the atmospheric three-dimensional wind field [28,29,30]. Therefore, this type of instrument is important in the meteorological analysis of pollution and rainfall forecasts. As for its application in environmental research, a number of campaigns focused on haze pollution have been conducted in the North China Plain and Fen-Wei Plain, but in the northeast part of China, the related studies are still very few [31,32].
Northeastern (NE) China has undergone rapid economic development and urbanization since the late twentieth century, and the enlarged anthropogenic emissions have led to serious environmental pollution, such as haze, in this aera [33,34]. In addition, the transport effect of land and sea breeze from Bohai Bay makes the atmospheric environment changeable and special when compared to other regions in China, indicating that the formation mechanism of haze there still needs to be further investigated [35,36]. Furthermore, previous studies have proved that air pollutants could have a significant influence on the ecosystem, especially agriculture. For example, the tropospheric ozone could have considerable influence on net ecosystem production, and combined with black carbon, the increased emission could directly induce reductions in wheat and rice yields [37,38]. NE China is also among the most important grain-producing areas with different surface types, including plains, hills, and wetlands; therefore, air pollution research in NE China has vital practical significance in agriculture and environmental governance [39]. So far, many studies have been presented by researchers focused on haze episodes via ground-based and satellite-based observation, field sampling, and numerical modeling, which have increased the understanding of aerosol climate and environmental effects in this region [40,41,42,43]. However, there have been relatively few studies on the formation mechanism of haze and its relationship with the variation in boundary layer structure and the transport effect of land and sea breeze based on wind profile radar over this coastal area in Northeast China.
Consequently, the study presented in this paper focused on a heavy haze event that occurred in this region (specifically, in the city of Panjin) from 8 to 13 February 2020. With comprehensive application of wind field data, sea wave field data, meteorological data, and environmental monitoring data, the characteristics of the wind field and boundary layer structure during this haze episode are discussed in detail, including the variations in the meteorological elements, and the thickness and intensity of the atmospheric inversion layer. This work not only enhances knowledge of the formation mechanism of haze pollution in this coastal region of Northeast China, but could also aid in the protection and governance of the regional ecological environment of the areas surrounding Bohai Bay.

2. Data and Methods

2.1. Site Description

The observed site (Figure 1) is located at the national basic meteorological station of Panshan County, Panjin City (41.27° N, 122.04° E), Liaoning province, facing the sea to the south. The area has a warm, temperate, continental, semi-humid monsoon climate with a mean annual temperature of 8.9 °C to 9.2 °C and annual precipitation of 634 to 651 mm. Panjin is the main production area of rice, with a rice planting history of more than 60 years. The rice planting area accounts for 85% of the total cultivated land in Panjin, which is an important commodity grain base and rice export base in Liaoning Province [44,45]. In addition, the largest wetland nature reserve in China, Liaohe Estuary National Nature Reserve, is located in the southern part of Panjin, which has the largest red beach in the world.

2.2. Wind Profile Radar

A TWP-16 tropospheric wind profile radar was deployed in Panjin to obtain the distribution characteristics of the wind field during this haze process. The TWP-16 wind profile radar system collects, processes, and transmits data every six minutes. In each two-minute period, the radar first measures in the upper 50 altitude layers (high mode) in the first minute, and then switches to the lower 41 altitude layers (low mode) in the next minute. Only low-mode detection data, including horizontal and vertical wind fields, were used in this study because of the haze generating in the boundary layer [26]. A regression algorithm was written to invert the horizontal wind field, vertical wind field, reflectivity structure constant, and signal-to-noise (SNR) ratio.

2.3. High-Frequency Ground Wave Radar

High-frequency ground wave radar can detect and locate the sea surface environment and a moving target beyond the horizon. The working principle is related to the characteristics of energy attenuation when vertically polarized high-frequency electromagnetic waves propagate over the coastal water surface. When the high-frequency electromagnetic waves propagate along the coastal surface, the electromagnetic waves interact with the sea water, and the target object on the sea surface and are scattered. The back-scattered echo is analyzed and processed by the special receiver to obtain the state information on the sea surface [46,47].

2.4. WRF-FLEXPART Model

To reveal the potential source area of air pollutants, a backward simulation using WRF-FLEXPART was used to better reflect the potential source area distribution for a given site. In this study, the 27 × 27 km grid data provided by WRF were used as the initial field of the FLEXPART model. The simulation period was from 08:00 on 6 February to 08:00 on 12 February. The vertical direction was divided into 5 layers of 10, 100, 750, 1500, and 3000 m, and 03:00 on 10 February to 18:00 on 11 February was used as the initial field of the FLEXPART model. The particle release time period was from 03:00 on 10 February to 18:00 on 11 February, and a part of Panjin (41.265°–41.275° N, 122.035°–122.045° E; hereafter referred to as the local area), with a height of 10 m above the ground, was taken as the particle release area. A total of 200,000 particles were released continuously, and the particles were uniformly distributed across the release area and time period. The model output was the residence time (also known as the sensitivity coefficient or imprint function) in units of ps·kg, which represents the residence time of a unit mass of gas at a horizontal grid point with a horizontal grid point resolution of 0.05° × 0.05° and a time resolution of 1 h.

2.5. Determination of Haze-Top Height and Intensity

The inhomogeneous structure of the atmospheric refractive index caused by turbulent motion in the atmosphere’s scattering of electromagnetic radar waves is the basis of the radar detection of objects. Theoretically, the radar reflectance η is the sum of the backscattering cross-sections’ per-unit volume in the inertial sub-region of locally uniform isotropic turbulence:
η = 0.39 C n 2 λ − 1 3
where λ is the wavelength of the incident electromagnetic field, and C n 2 is the refractive index structure constant. Doviak (1984), based on data measured in the winter half-year in Colorado, USA, concluded that the change in the C n 2 median value with height (presented as H in Equation (2)) could be expressed by the following formula [48]:
C n 2 = 3.9 × 10 − 15 e − H 2000
The strength of the turbulent scattering echo signal is directly related to the C n 2 value. The radar meteorological scattering equation (Keeler equation) describing atmospheric turbulence scattering is
P r = α 2 P t A e ∆ r 4 π r 2 η
where Pt is the transmitting power, Ae is the effective area of the antenna, r is the distance, Δr is the range resolution, α is the transmission efficiency of the feeder, and η is the reflectivity. Substituting Equation (1) into the formula gives
P r = 0.39 C n 2 λ − 1 3 α 2 P t A e ∆ r 4 π r 2
In this study, the detection target is the pollutants in the atmospheric boundary layer, which are directly related to the radar echo power. Therefore, the value of C n 2 can reflect the range of pollutant accumulation, and then the height and thickness of the haze body can be obtained.

3. Results and Discussion

3.1. Haze Episode

From 8 to 13 February 2020, a large-scale and long-lasting air pollution process occurred in Liaoning Province, with Panjin City the most affected, characterized by deteriorating air quality and reduced visibility and leading to two outbreaks of haze pollution. To facilitate discussion of its evolutionary characteristics, the pollution episode was divided into four stages, as shown in Table 1.
As shown in Figure 2 and Figure 3, the average air quality index (AQI) was below 100 and the horizontal visibility was 10,000 m before 9 February. Combined with the upper-atmosphere situation at 500 hPa (Figure 4), Panjin was at the back end of the low-pressure trough and controlled by a weak downdraft. The atmospheric relative humidity rose steadily, indicating that there was externally transported water vapor to Panjin, which provided a good reaction environment for the condensational growth of pollutant particles. At about 12:00 on 9 February, the PM2.5 and PM10 exploded up to a concentration of 110 μg/m3, and the AQI rose to 159, suggesting a moderate air pollution episode. Visibility sharply decreased from 1800 m to 173 m. After that, it reduced to a minimum of 89 m until the evening in the mature stage. At this time, the mass concentrations of PM2.5 and PM10 were both 120 μg/m3, which means this haze process was co-dominated by particulate matter of these sizes. The severe haze process lasted until 02:00 on 11 February, during which times the minimum visibility decreased to 73 m. Although the visibility increased slightly to 500 m in some periods, it nevertheless had serious effects on human activities such as transportation. Then, the atmospheric temperature rose slowly, precipitation occurred in some areas, and the concentrations of pollutants gradually decreased because of the combined effect of dry and wet deposition, resulting in better atmospheric diffusion conditions and visibility reaching 30 km [49,50].

3.2. Horizontal Wind Field

The horizontal wind field is one of the important meteorological factors affecting the accumulation or diffusion of air pollutants [51,52]. We present the profile of the horizontal wind field during this haze episode in Figure 5. It can be seen that on 8 February (Figure 5a), during the generation stage of the haze process, westerly and northerly winds alternately controlled the boundary layer below 750 m, and the wind speed was very low. Meanwhile, the surface layer was in a calm and stable state, which accelerated the accumulation of air pollutants. During the daytime, there was cold advection of 9.2 m/s at the layer from 750 m to 1500 m, contributing to the stable stratification of the atmosphere and the accumulation of air pollution [53,54]. At night, the cold advection rotated counterclockwise with height, destroying the inversion layer top and facilitating the uplift of air pollutants to the upper layer. However, the weak cold advection could not eliminate the whole inversion layer, and the mass concentration of PM2.5 rose from 90 μg/m3 to 111 μg/m3, and that of PM10 rose from 100 μg/m3 to 119 μg/m3 (Figure 3).
Variable sea breeze has a significant impact on the atmospheric conditions of Panjin City due to its unique geographical location. On 9 February, according to the flow field, wind field, and wave field product data from the high-frequency ground wave radar (Figure 6), the wind field of the sea near the mainland was mainly southwesterly (4.5 m/s), with a wave height of 1.3 m under the counterclockwise atmospheric general circulation. From 04:00 to 11:00 on 9 February, southwesterly airflow at 15 m/s from the ocean prevailed, dominating the layer below 750 m. Westerly and southwesterly winds dominated the height range from 750 m to 1000 m. The warm and moist air from the sea surface accelerated the process of condensation and nucleation of air pollutants. From 11:00 (Figure 5b), the wind speed of the layer below 500 m decreased to 1 m/s, and the wind direction at the surface presented a weak clockwise circulation, resulting in air subsidence, which was conducive to the accumulation of air pollutants. As a result, the atmosphere returned to a stable state and the haze process developed to a mature stage, which lasted until 15:00 on 10 February (Figure 5c). In this stage, PM2.5 and PM10 showed explosive growth to 123 μg/m3, and visibility decreased to the minimum of 87 m. As shown in Figure 5d, after 02:00 on 11 February, strong advection of 15.2 m/s dominated by prevailing southwest winds appeared in the layer from 600 m to 1200 m. Consequently, the wind speed near the ground gradually increased, and the maximum at the height of 500 m was 10 m/s, suggesting better conditions for diffusion. The wind speed of the layer above 500 m gradually increased to 20 m/s and the wind field spread to the height of 2000 m, breaking the stable stratification in the surface to 500 m layer. Influenced by the strong advection, the horizontal and vertical diffusion of air pollutants was promoted, and the haze process entered into the dissipation stage. After 17:00, the boundary layer was dominated by southwesterly winds with a maximum wind speed of 18.2 m/s. As a result, the PM2.5 concentration rapidly decreased to 44 μg/m3, and the visibility increased to 10 km.

3.3. Vertical Wind Field

Figure 7 shows the time series of the vertical velocity during this haze period, in which the positive velocity represents the downdraft and the negative velocity represents the updraft. In the early stage of the haze process on 8 February (Figure 5a), there was a weak downdraft of less than 1 m/s below 1500 m, suggesting poor atmospheric diffusion ability. In Figure 5b, it can be seen that after 21:00 on 8 February, along with the decrease in the nighttime boundary layer height, the accumulation of pollutants was rapidly enhanced with the AQI increasing from 115 to 145 [55,56], causing the decreasing visibility (10 km to 500 m) and the formation of haze pollution (Figure 3). On the morning of 9 February, influenced by the transpiration effect of sea surface wind and the evaporation effect caused by increasing temperature (Figure 2), an updraft of 2 m/s appeared at the height of 500 m. In fact, the slight vertical turbulence did not disturb the stable atmospheric stratification, but facilitated the collision and growth of smaller particles (liquid drops) into larger scales [57]. As a result, the weak updraft raised the air pollutants, spreading them to the upper layer, and the haze developed into the mature stage. The vertical wind speed in the atmospheric boundary layer was 0 m/s at 10:00 when the visibility decreased to 100 m (Figure 3). After 11:00 on 9 February, the boundary layer was in a static and stable state for a long time, demonstrating no obvious vertical air flow from the ground surface to 2000 m, although a weak downdraft of 0.8 m/s was observed between 05:30 and 18:00 on 10 February. The stable inversion stratification lasted until 03:00 on 11 February, when an updraft of 3.8 m/s appeared at 900 m, revealing that the thick haze layer was gradually disintegrated from the top downwards.
During the whole haze process, the vertical wind speed over Panjin City was relatively low, with an average of 0.6 m/s, and the development and mature stages were dominated by weak downdrafts of 1 m/s; this was conducive to the accumulation of pollutants and the maintenance of the inversion layer. In the dissipation stage, an updraft of 3 m/s appeared at the top of the haze layer, which favored diffusion of the atmospheric pollutants.

3.4. Structural Variation Characteristics of the Pollution Layer

The SNR is the ratio of echo signal to noise received by the radar, which is positively correlated with echo power. Wind profile radars are adept at further improving the SNR through signal processing technologies, such as coherent accumulation, so as to meet the demand for weak signal detection capability. When there are fog drops, rain drops, or ice crystals in the atmosphere, the SNR is stronger than that in clear sky. Therefore, the SNR can reflect the thickness of the haze layer, reflect the changes in atmospheric state, such as light precipitation and cold air, and have certain reference significance for the analysis of pollutant concentrations [58,59].
As shown in Figure 8, in the haze generation stage, the SNR below 700 m did not exceed 35 dB, indicating that the concentration of particles and droplets in the atmosphere was not high. During the development stage and mature stage, there was an SNR bright band from 300 m to 1200 m, and the central area was as high as 45 dB. Through accessing relevant meteorological data, there was no precipitation in the mature and stable period of this thick haze process, indicating that the high concentrations of pollution particles and droplets accumulated in the upper layer of the atmosphere in this period. The haze-top layer reached its maximum of 1200 m, indicating that the haze-body layer expanded and developed strongly.

3.5. Structural Variation Characteristics of the Boundary Layer

C n 2 (the refractive index structure constant) can be regarded as the intensity echo of the wind profile radar RHI (high sweep) in different time periods, and is used to describe the backscattering ability of clear-air atmospheric turbulence to electromagnetic waves [60]. In combination with Equation (4), it can be seen that by exploring the spatial difference of the C n 2 numerical distribution, this can be used to invert the intensity distribution of turbulence in the upper atmosphere. The intensity of turbulence inside the boundary layer is relatively strong, while above the inversion layer, it is relatively weak. C n 2 has a large step near the top of the boundary layer, so the height of the boundary layer can be determined from the time series of the vertical profile of C n 2 [61]. Because of the small magnitude, C n 2 was replaced with lg C n 2 as the analytical target (Figure 9).
In the early period of the development stage of the haze process, due to the weak atmospheric turbulence activity at night,   C n 2 was very weak, and at about 500 m, it reached the order of 10−13. In the mature stage, the C n 2 values increased significantly from 500 m to 1200 m with the arrival of the day, reaching a maximum of 10−8, and the turbulence activity increased significantly. The weak updraft promoted the collision of particulate matter and water vapor (Figure 7) and accelerated the formation of haze. On the other hand, the top of the boundary layer rose slowly, and the accumulation of haze particles developed in the upper air. The increase in the PM10 and PM2.5 concentrations also promoted the development of turbulent motion. The C n 2 value below 1500 m reached 10–11 and remained above that number, indicating the stability of the boundary layer structure. The increase in C n 2 was consistent with the timing of the explosive increase in the haze particle concentration, as reflected by the AQI value in Figure 2.

3.6. Source Identification

The WRF-FLEXPART model was used in this study to explore the potential source regions of air pollution in this haze episode. This model has been used in many previous studies, and has been proven to be a reliable method to reveal the transportation pathways of air pollution, the potential source areas, and their contributions [62,63].
Figure 10 shows the average residence times in four layers from 10 m to 1500 m during this episode. It can be seen that the air pollutants in the near-surface layer (from 10 m to 100 m) were mainly from the local area, with a few contributions from the south and west areas. This agreed with the observations of the wind profile radar, which indicated that the horizontal surface wind speed was very low from the generation to mature stage (mostly < 10 m/s). A dominant southwest transportation pathway was found in the layers of 750 m and 1500 m, suggesting a water vapor transported from the sea. As mentioned above in the discussion of Figure 5, during the development stage, an increasing southerly wind (~20 m/s) was observed from 01:00 to 09:00 on 9 February. This may explain the sharp increase in relative humidity from 70% to 95% from 9 to 10 February. Consequently, the process of secondary particle generation was greatly enhanced due to the humid environment, and the maximum PM2.5 (~123 μg/m3) was measured on 10 February.
The emissions from resident heating are significantly increased from November to February in North China, and consist of large amounts of sulfate and nitrate [64,65,66]. The hygroscopic growth process of these particles could be greatly enhanced due to the stable weather conditions and humid environment [1,55,67]. Therefore, considering the results and discussion above, the accumulation of local emissions from anthropogenic activities and weak transportation of humid air mass from see breeze should be regarded as the important contributors inducing this haze pollution over Panjin.

4. Conclusions

A haze pollution event occurred in Panjin City (coastal Northeast China) from 8 to 12 February 2020. We performed a comprehensive study based on wind profile radar observations, along with high-frequency wave radar data, meteorological data, and air quality monitoring data, to explore the formation mechanism of haze and its relationship with the variation in boundary layer structure and the transport effect of land and sea breeze over this area around Bohai Bay in Northeast China.
According to the horizontal wind field data of the wind profile radar and wave field data of the high-frequency ground wave radar, there was a 4.5 m/s−1 southerly sea breeze bringing a lot of wet air over the sea in the early stage of the haze development, which provided a rich water vapor environment for the condensation of pollutants and accelerated the formation of thick haze.
The vertical wind field profile of the wind profile radar showed that in the development stage of haze, weak updrafts appeared in the boundary layer, which were conducive to the collision and growth of pollutant particles. In the mature stage, the boundary layer was stable with weak vertical turbulent movement.
The SNR showed the distribution of particles and droplets in the atmosphere and reflected the thickness of the haze layer. The top of the continuous fog and haze process reached up to 1200 m, with a large impact range. The SNR of the central region was as high as 45 dB, and the haze deeply developed. The turbulence distribution in the upper atmosphere was studied by using the refractive index structure constant, C n 2 . At night, C n 2 reached the order of 10−13 and the turbulence activity was weak, which was conducive to the accumulation of pollutants. During the day, C n 2 reached 10−8, and increased turbulence accelerated the formation of haze.
The results of the WRF-FLEXPART model showed that the water vapor transport from the sea during the haze development stage may have increased the relative humidity, which facilitated the process of secondary particle generation, significantly contributing to this haze episode.
In this study, we explored a haze episode mainly by comprehensively analyzing wind profile radar data, combined with high-frequency wave radar data and meteorological data. However, the mechanism that promoted the haze development via the influence of water vapor transport still needs to be further verified in a modeling study. In addition, it should be noted that in order to achieve a clear mechanism for haze formation over this coastal region, the exact dominate pollutant and its source should be investigated via field sampling and modeling analysis in further study.

Author Contributions

Conceptualization, C.M. and H.C.; methodology, Y.Z.; validation, T.Z. and C.H.; formal analysis, Z.L.; investigation, B.K. and H.L.; data curation, C.L. (Chenrui Li); writing—original draft preparation, B.K., C.L. (Chong Liu), and Y.Z.; project administration, B.K. and Y.Z.; All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Joint Open Fund of Shenyang Institute of Atmospheric Environment and Liaoning Provincial Key Laboratory of Agrometeorological (grant No. 2019SYIAE12), the National Natural Science Foundation of China project (grant No. 42030608, 42105138, 41375146), the Basic Scientific Research Fund of Shenyang Institute of Atmospheric Environment (grant No. 2019SYIAEMS1), the Basic Research Fund of Chinese Academy of Meteorological Sciences (grant No. 451336), and the Science and Technology Development Fund of Chinese Academy of Meteorological Sciences (grant No. 2019KJ001).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Datasets used in the present study are available from the corresponding author on reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Observational site and the red square stands for its overall location in China.
Figure 1. Observational site and the red square stands for its overall location in China.
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Figure 2. Changes in AQI, particulate matter mass concentrations, temperature, and relative humidity during the haze episode.
Figure 2. Changes in AQI, particulate matter mass concentrations, temperature, and relative humidity during the haze episode.
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Figure 3. Average horizontal visibility.
Figure 3. Average horizontal visibility.
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Figure 4. Upper-atmosphere situation at 500 hPa.
Figure 4. Upper-atmosphere situation at 500 hPa.
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Figure 5. Profile of the horizontal wind field during this haze episode: (a) generation; (b) development; (c) maturity; (d) dissipation.
Figure 5. Profile of the horizontal wind field during this haze episode: (a) generation; (b) development; (c) maturity; (d) dissipation.
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Figure 6. Wind field (a), wave field (b) and flow field (c) from the high-frequency ground wave radar observation at 00:00 on 9 February 2020. The green circle and red star stand for observation sites and surrounding cities. The orange flag (a), diamond (b) and arrow (c) stand for wind field, wave height and flow velocity, respectively.
Figure 6. Wind field (a), wave field (b) and flow field (c) from the high-frequency ground wave radar observation at 00:00 on 9 February 2020. The green circle and red star stand for observation sites and surrounding cities. The orange flag (a), diamond (b) and arrow (c) stand for wind field, wave height and flow velocity, respectively.
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Figure 7. High-altitude profile of the change in radial velocity during the thick haze process: (a) generation; (b) development; (c) maturity; (d) dissipation.
Figure 7. High-altitude profile of the change in radial velocity during the thick haze process: (a) generation; (b) development; (c) maturity; (d) dissipation.
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Figure 8. Time series of variation in SNR during this haze episode.
Figure 8. Time series of variation in SNR during this haze episode.
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Figure 9. Time series of the variation in C n 2 during this haze episode.
Figure 9. Time series of the variation in C n 2 during this haze episode.
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Figure 10. Potential source area based on the WRF-FLEXPART model in the 10 m, 100 m, 750 m, and 1500 m layers.
Figure 10. Potential source area based on the WRF-FLEXPART model in the 10 m, 100 m, 750 m, and 1500 m layers.
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Table
Table 1. Four stages of the haze pollution process.
Table 1. Four stages of the haze pollution process.
StageDuration
Generation0:00–24:00 8 February
Development0:00–11:00 9 February
Maturity11:00 9 February to 02:00 11 February
Dissipation02:00 11 February to 20:00 13 February
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Kang, B.; Liu, C.; Miao, C.; Zhang, T.; Li, Z.; Hou, C.; Li, H.; Li, C.; Zheng, Y.; Che, H. A Comprehensive Study of a Winter Haze Episode over the Area around Bohai Bay in Northeast China: Insights from Meteorological Elements Observations of Boundary Layer. Sustainability 2022, 14, 5424. https://doi.org/10.3390/su14095424

AMA Style

Kang B, Liu C, Miao C, Zhang T, Li Z, Hou C, Li H, Li C, Zheng Y, Che H. A Comprehensive Study of a Winter Haze Episode over the Area around Bohai Bay in Northeast China: Insights from Meteorological Elements Observations of Boundary Layer. Sustainability. 2022; 14(9):5424. https://doi.org/10.3390/su14095424

Chicago/Turabian Style

Kang, Boshi, Chong Liu, Chuanhai Miao, Tiening Zhang, Zonghao Li, Chang Hou, Hongshuo Li, Chenrui Li, Yu Zheng, and Huizheng Che. 2022. "A Comprehensive Study of a Winter Haze Episode over the Area around Bohai Bay in Northeast China: Insights from Meteorological Elements Observations of Boundary Layer" Sustainability 14, no. 9: 5424. https://doi.org/10.3390/su14095424

APA Style

Kang, B., Liu, C., Miao, C., Zhang, T., Li, Z., Hou, C., Li, H., Li, C., Zheng, Y., & Che, H. (2022). A Comprehensive Study of a Winter Haze Episode over the Area around Bohai Bay in Northeast China: Insights from Meteorological Elements Observations of Boundary Layer. Sustainability, 14(9), 5424. https://doi.org/10.3390/su14095424

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