Abstract
Abstract. Heavy particulate pollution events have frequently occurred in the North China Plain over the past decades. Due to high emissions and poor dispersion conditions, issues are becoming increasingly serious during cold seasons. Although early studies have explored some potential reasons for air pollution, there are few works focusing on the effects of intermittent turbulence. This paper draws upon two typical PM2.5 (particulate matter with diameter less than 2.5 mm) pollution cases from the winter of 2016–2017. After several days of gradual accumulation, the concentration of PM2.5 near the surface reached the maximum as a combined result of strong inversion layer, stagnant wind, and high ambient humidity and then sharply decreased to a very low level within a few hours. In order to identify the strength of turbulent intermittency, an effective index, called the intermittency factor (IF), was proposed by this work. The results show that the turbulence is very weak during the cumulative stage due to the suppression by strongly stratified layers, while for the stage of dispersion, the turbulence is highly intermittent and not locally generated. The vertical structure of turbulence and wind profiles confirms the generation and downward transport of intermittent turbulence associated with low-level jets. The intermittent turbulent fluxes contribute positively to the vertical transport of particulate matter and improve the air quality near the surface. This work has demonstrated a possible mechanism of how intermittent turbulence affects the dispersion of particulate matter.
Highlights
In the winter of 2016–2017, severe air pollution events occurred in the North China Plain, affecting more than one-fifth of the total population in China (Ren et al, 2017)
Based on the concentration of PM2.5, we can divide each case into two periods: one called the cumulative stage (CS), during which the particulate matter accumulates near the surface, and the other named the transport stage (TS), representing the stage when pollutants dissipate (Zhong et al, 2017)
For Case-1, wind at lower levels mainly comes from the southeast during the CS, while the dominant wind direction turns into west when it comes to the TS
Summary
In the winter of 2016–2017, severe air pollution events occurred in the North China Plain, affecting more than one-fifth of the total population in China (Ren et al, 2017). Some works (Wang et al, 2010; Zhang et al, 2016) reveal the effects of the increasing consumption of fossil fuel and the production of secondary pollutants. J. Zheng et al, 2015; Jiang et al, 2015) are of great importance in the transport of pollutants as well. Air pollution is essentially a phenomenon of the atmospheric boundary layer (ABL) and is strongly affected by the thermodynamic and dynamic structure of the ABL (Bressi et al, 2013; Gao et al, 2016; Tang et al, 2016). Most of the works (Petäjä et al, 2016) focus on the feedback between aerosol, turbulent mixing, and the boundary layer, with little discus-
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