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Abstract
Abstract. Different types of pollution boundary layer structures form via the coupling of different synoptic systems and local mesoscale circulation in the boundary layer; this coupling contributes toward the formation and continuation of haze pollution. In this study, we objectively classify the 32 heavy haze pollution events using integrated meteorological and environmental data and ERA-Interim analysis data based on the rotated empirical orthogonal function method. The thermodynamic and dynamic structures of the boundary layer for different pollution weather types are synthesized, and the corresponding three-dimensional boundary layer conceptual models for haze pollution are constructed. The results show that four weather types mainly influence haze pollution events in the Beijing area: (a) type 1 – southerly transport, (b) type 2 – easterly convergence, (c) type 3 – sinking compression, and (d) type 4 – local accumulation. The explained variances in the four pollution weather types are 43.69 % (type 1), 33.68 % (type 2), 16.51 % (type 3), and 3.92 % (type 4). In persistent haze pollution events, type 1 and type 2 surpass 80 % on the first and second days, while the other types are present alternately in later stages. The atmospheric structures of type 1, type 2, and type 3 have typical baroclinic characteristics at mid–high latitudes, indicating that the accumulation and transport of pollutants in the boundary layer are affected by coupled structures in synoptic-scale systems and local circulation. The atmospheric structure of type 4 has typical barotropic characteristics, indicating that the accumulation and transport of pollutants is primarily affected by local circulation. In type 1, southerly winds with a specific thickness and intensity prevail in the boundary layer, which is favorable for the accumulation of pollutants in plain areas along the Yan and Taihang Mountains, whereas haze pollution levels in other areas are relatively low. Due to the interaction between weak easterly winds and the western mountains, pollutants accumulate mainly in the plain areas along the Taihang Mountains in type 2. The atmospheric vertical structure is not conducive to upward pollutant diffusion. In type 3, the heights of the inversion and boundary layers are the lowest due to a weak sinking motion while relative humidity is the highest among the four types. The atmosphere has a small capacity for pollutant dispersion and is favorable to particulate matter hygroscopic growth; as a result, type 3 has the highest PM2.5 concentration. In type 4, the boundary layer is the highest among the four types, the relative humidity is the lowest, and the PM2.5 concentration is relatively lower under the influence of local mountain–plain winds. Different weather types will shape significantly different structures of the pollution boundary layer. The findings of this study allow us to understand the inherent difference among heavy pollution boundary layers; in addition, they reveal the formation mechanism of haze pollution from an integrated synoptic-scale and boundary layer structure perspective. We also provide scientific support for the scientific reduction of emissions and air quality prediction in the Beijing–Tianjin–Hebei region of China.
Highlights
Over the past 40 years, rapid industrialization and urbanization have caused serious haze pollution problems in China, especially in the North China Plain (NCP)
Pollution weather types were classified by the rotated empirical orthogonal function (REOF) method to analyze the differences in the structures of the pollution boundary layer
Most areas in North China do not have strong weather systems, and the average wind speed in the boundary layer is smaller, which is favorable to the formation and maintenance of the local circulation considering the topography in the Beijing area (Fig. 1i)
Summary
Over the past 40 years, rapid industrialization and urbanization have caused serious haze pollution problems in China, especially in the North China Plain (NCP). The reduction in sea ice can lead to the weakening of the Rossby wave activity south of 40◦ N, rendering the lower layer colder and resulting in a reduced moisture content, a stable atmosphere, weaker wind speeds, and an increased chance of heavy haze pollution (Wang et al, 2015b; Chen et al, 2015). Their study indicated that transport resulting from the cold front had a significant impact on PM2.5 levels in Shanghai, whereas persistent server pollution events were more closely related to weak pressure before high All these studies presented a good view of air pollution formation influenced by weather system and planetary boundary layer structure with the objective synoptic classification method. To formulate optimized emission reduction strategies, we must master the main control factors that affect the haze pollution diffusion conditions in Beijing under different weather and boundary layer conditions.
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