2021年春季葫芦岛海陆风特征及对臭氧污染影响亮点文章
Sea-land breeze (SLB) circulation is a mesoscale process induced by the thermal difference between land and sea. After sunrise, the land surface is heated faster than the sea surface, which leads to a pressure gradient force and the air flow from sea to land to form a sea breeze. At night, there is a contrary thermal difference, and the air flows from land to sea to form a land breeze. SLB circulation plays an important role in the generation and transportation of air pollutants, which impacts the weather, climate, and air quality of coastal areas. Lying on the south of Liaodong Bay, Huludao is easily influenced by SLB. In recent years, regional pollution characterized by ozone (O3) and particles have become increasingly serious under the impact of chemical industry production and automobile exhaust emissions in Huludao. SLB circulation will change the temperature and humidity structure in the coastal boundary layer which determines the photochemical reaction conditions. Meanwhile, it impacts the transport of pollutants in coastal areas. Influenced by local circulation, solar radiation, precursor concentration, and other factors, the O3 concentration on SLB days is more complicated, which has important research significance. Coherent Doppler wind lidar (CDWL) has a high spatiotemporal resolution and continuous observational ability. It can obtain the complete SLB and detailed structure of the atmospheric boundary layer, which is of great significance for understanding the horizontal and vertical transport characteristics of pollutants during SLB circulation.
From March 1st to April 30th in 2021, wind profile observation was carried out with CDWL in Juehua Island, Huludao, Liaoning (120.78° E, 40.48° N). The obtained meteorological parameters include wind speed/direction and temperature in the Huludao area and O3 concentrations measured by ground-based instruments during observation. Three main factors should be considered in SLB identification: 1. large-scale background wind field; 2. temperature difference between sea and land; 3. near-surface wind direction change. We identified the SLB days during observation depending on these three conditions and the coastline direction in the Huludao area. We gathered the temporal and spatial distributions of SLB circulation in Huludao, including arrival time, prevailing speed, main direction, and the height of the sea breeze. The impact of SLB on O3 concentration was analyzed, with the ground air quality monitoring data taken into account. Weather Research and Forecasting (WRF) modeling was performed to investigate SLB and its impact on O3 concentration.
A total of 11 SLB days were identified with the data from CDWL and automatic meteorological stations in Huludao, accounting for 18% of the observation days. The results show that the sea breeze started at 08:30 averagely. During 14:00—17:00, it developed stronger, and the average speed exceeded 7.0 m·s-1. The height of the sea breeze was 0.3-0.5 km during 10:00—16:00 and reached above 0.9 km after 18:00. As the main direction was east, the sea breeze showed a tendency to deflect in a clockwise direction over time (Figs. 2, 3, and 4). The WRF model presents the sea breeze circulation in the vertical section on April 4th. Sea breeze moved to the Huludao area at 10:00, and a strong wind convergence zone formed along the coastal line at 12:00 (Fig. 5). Pollutants accumulated at the intersection of sea and land breezes and transported to the ground surface by cold air sinking at the sea breeze head simultaneously. The data from the environmental monitoring station shows that O3 concentration rose faster and had a higher peak on SLB days (Fig. 6). The surface wind speed on SLB days was lower than on non-SLB days, and the difference was more than 2 m·s-1 at the same time point (Fig. 7). Land breeze carried O3 from inland to sea at night, and the sea breeze during daytime blew pollutants back to the land, causing the cyclic accumulation of pollutants. With April 4th as an example, the O3 concentration rose faster after the sea breeze arrived at Huludao and peaked at 106 μg·m-3 (Fig. 9). The local recirculation index of horizontal wind in Huludao was only 0.049 on April 4th (Fig. 10), indicating that the transmission capacity of wind field was weak, and thus pollutants were not easy to spread.
According to the criteria at home and abroad, we identified the SLB days during spring, 2021 in Huludao with the wind data from CDWL and ground stations. In addition, we analyzed the temporal and spatial distributions of SLB circulation in Huludao, including the arrival time, prevailing speed, main direction, and the height of the sea breeze. The result shows that sea breeze forms later at a high altitude than on the surface, and the wind direction changes clockwise. The mesoscale WRF model was used to analyze the development of the sea breeze circulation on April 4th, which proved the results observed by CDWL. The O3 concentration rises faster and has a higher peak on SLB days. The study case shows that the local recirculation of horizontal wind under SLB is low, indicating that it is not conducive to the spread of pollutants. Pollutants will recirculate to the inland area after moving away from the coast during the shift of sea breeze and land breeze, which causes the cyclic accumulation of pollutants.
1 引言
海陆风(SLB)是海陆间热力性质差异引起的一种中尺度大气物理现象,在垂直空间上表现为上下方向相反的环流运动,当近地面空气从海洋流向陆地时为海风,而空气从陆地流向海洋时为陆风[1-2]。海陆风特殊的气象条件与局地环流结构对沿海地区大气污染物的输送和扩散具有重要影响[3-4]。近年来,学者们广泛关注海陆风对颗粒物和
激光雷达具有高时空分辨率,有助于获得海陆风的垂直精细结构。Nakane等[8]利用激光雷达的后向散射数据观测到了完整的海风锋,包括形状及湍流特征。Kolev等[9]利用激光雷达观测结果对黑海沿岸地区海风循环过程和昼夜演变进行了详细分析。许满满等[10]利用测风激光雷达、温度脉动仪在深圳沿海地区的观测结果,研究发现海陆风条件下湍流动能耗散率与湍流强度呈线性关系,较陆风条件,湍流在海风条件下发展得更为充分。此外,激光雷达技术已广泛应用于大气成分探测方面,利用拉曼散射激光雷达、偏振激光雷达、差分吸收激光雷达等可实现对温度、湿度、云、气溶胶、
海陆风环流会造成沿海地区污染物的循环累积,加剧空气质量的污染。林长城等[13]对福建沿海地区海陆风的观测研究表明,海陆风连续出现会导致
受到局地环流及太阳辐射、前体物浓度等多种因素的影响,海陆风期间
2 资料与方法
2.1 站点与数据
2021年3月1日至4月30日,Wind3D 6000型相干多普勒测风激光雷达(CDWL)系统架设在辽宁省葫芦岛市觉华岛西南侧(120.78° E,40.48° N),开展三维风场观测,现场照片如
表 1. Wind3D 6000型相干多普勒测风激光雷达的技术性能指标
Table 1. Technical parameters of Wind3D 6000 coherent Doppler wind lidar
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2.2 海陆风日判定
对葫芦岛地区海陆风的判定主要考虑大尺度背景风场、海陆温差、近地面风向转换3项[18]。大尺度背景风场对海陆风的形成有重要影响,判定时首先要筛选出利于海陆风生成的背景环流形势,本文利用700 hPa高空风场资料对背景风场进行限制[19]。海陆温差是海风建立的先决条件之一,不同地区采取的阈值不同,本文设定海陆风日发生时海陆温差应大于1.5 ℃,以确保较大的海陆热力差异[20-21]。近地面风向转换是海陆风的基本特征,根据葫芦岛地区海岸线走向,划分海风范围ENE~SSW、陆风范围WSW~NNE,平行于海岸线的NE和SW为沿岸流方向[22]。具体判定方法如下:
1)海风时段13:00—20:00(local standard time,LST),海风至少出现4 h;
2)陆风时段01:00—08:00(LST),陆风至少出现4 h;
3)一天内,700 hPa地转风风向改变量小于90°,风速改变量小于6
4)海陆风日
2.3 WRF模式参数配置
由美国国家大气研究中心(NCAR)和国家环境预报中心(NCEP)等机构开发的中尺度天气预报(WRF)模式是模拟城市尺度到中尺度范围气象状况的有效工具[23]。为了研究区域内海陆风的发展过程,利用WRF模式对2021年4月4日的海陆风进行模拟。模式采用三层嵌套,水平分辨率分别为27 km、9 km、3 km,垂直方向设置为34层,为更精细地模拟海风结构,将离地
表 2. WRF配置采用的物理参数化方案
Table 2. Physical parameterization scheme employed for WRF configurations
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3 分析与讨论
3.1 海陆风时空特征分析
3.1.1 基于CDWL的海风统计特征
基于CDWL水平风资料结合葫芦岛自动气象站数据,识别出2021年3月到4月期间辽宁省葫芦岛地区海陆风日11天,占观测日期的18%。

图 2. 海陆风日海风风速与发展高度日变化。(a)风速;(b)发展高度
Fig. 2. Diurnal variation of sea breeze speed and height in the SLB days. (a) Speed; (b) height

图 3. 海陆风日海风风玫瑰图。(a)9:00—12:00;(b)13:00—16:00;(c)17:00—20:00;(d)21:00—24:00
Fig. 3. Wind rose of sea breeze in the SLB day. (a) 9:00—12:00; (b) 13:00—16:00; (c) 17:00—20:00; (d) 21:00—24:00
3.1.2 海陆风垂直结构与发展个例
利用激光雷达可以获得海风在垂直方向的精细结构。

图 4. 海陆风日测风激光雷达观测水平风。(a)2021年4月4日;(b)2021年4月14日
Fig. 4. Horizontal wind observed by wind lidar in the SLB days. (a) 2021-04-04; (b) 2021-04-14
4月4日凌晨至10:00为陆风控制阶段,初始高度接近1.3 km,08:00左右下降至0.6 km。陆风风速随高度增加而增加,0.3 km高度内不超过6
4月14日凌晨至05:00葫芦岛低空受西向陆风控制,风速不超过8
以4月4日为例,利用WRF模式分析此次海风发展过程,选取激光雷达观测位置所在经度120.78° E作葫芦岛及附近海域南北向剖面,所跨纬度范围为40.3° N~41.0° N。如

图 5. 2021年4月4日沿120.78° E的经向风(V)与温度垂直分布。(a)08:00;(b)10:00;(c)12:00;(d)14:00
Fig. 5. Temperature and V vertical distribution along 120.78° E on April 4th, 2021. (a) 08:00; (b) 10:00; (c) 12:00; (d) 14:00
3.2 海陆风对 污染的影响
3.2.1 海陆风日 浓度日变化特征
海陆风日与非海陆风日葫芦岛地区
海风登陆时,来自海洋的湿冷气流与内陆较为干热的气流相遇形成热内边界层,污染物受到其内部湍流的作用被带至地面[38],出现局地
为了区分太阳辐射与海陆风环流对

图 8. 不同天气条件下葫芦岛平均 质量浓度日变化。(a)晴天少云;(b)多云阴天
Fig. 8. Diurnal variation of the average mass concentration of in Huludao at different weather conditions. (a) Sunny; (b) cloudy
3.2.2 海陆风的局地再循环作用
污染物在空间内的传输与分布受局地天气系统(如海陆风)的影响。以海陆风日2021年4月4日为例,分析海陆风发生时局地风场对当地

图 9. 海陆风日葫芦岛地面站观测结果。(a) 质量浓度, 质量浓度,地面温度;(b)水平风
Fig. 9. Observation of Huludao ground station in the SLB day. (a) mass concentration, mass concentration, land temperature; (b) horizontal wind
局地回流描述了空间内污染被风场输送出去后再次输送回来的现象[41],局地回流指数(
式中:i(1

图 10. 海陆风日葫芦岛水平风局地回流,L为位移,S为路程
Fig. 10. Horizontal wind local recirculation of Huludao in the SLB day, L is transport distance, S is wind run
4 结论
基于相干多普勒测风激光雷达,在葫芦岛开展风场测量实验,结合地面观测数据,对海陆风时空特征及其对当地
海陆风作为一种中尺度局地环流现象对当地大气环境与污染输运有重要影响,基于观测资料与模式结果研究海陆风期间
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Article Outline
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