Effects of turbulence structure and urbanization on the heavy haze pollution process

Abstract

In this paper, an automated algorithm, which is used to identify the spectral gap during the heavy haze pollution process, reconstruct acquired data, and obtain pure turbulence data, is developed. Comparisons of the reconstructed turbulent flux and eddy covariance (EC) flux show that there are overestimations regarding the exchange between the surface and the atmosphere during heavy haze pollution episodes. After reconstruction via the automated algorithm, pure turbulence data can be obtained. We introduce a definition to characterize the local intermittent strength of turbulence (LIST). The trend in the 15 LIST during pollution episodes shows that when pollution is more intense, the LIST is smaller, and intermittency is stronger; when pollution is weaker, the LIST is larger, and intermittency is weaker. During the heavy pollution process, air quality on an hourly scale is determined via turbulent motion. At the same time, the LIST at the city site is greater than that at the suburban site, which means that intermittency over the complex city area is weaker than that over the flat terrain area.Urbanization seems to reduce intermittency during heavy haze pollution episodes, which means that urbanization reduces the 20 degree of weakening in turbulent exchange during pollution episodes. This result is confirmed by comparing the average diurnal variations in turbulent fluxes at urban and suburban sites during polluted and clean periods. The sensible heat flux, latent heat flux, momentum flux, and turbulent kinetic energy (TKE) in urban and suburban areas are all affected when pollution occurs. Material and energy exchanges between the surface and the atmosphere are inhibited. Moreover, the impact of the pollution process on suburban areas is much greater than that on urban areas. Urbanization seems to help reduce the 25 consequences of pollution.

Assessing the pollutant evolution mechanisms of heavy pollution episodes in the Yangtze-Huaihe valley: A multiscale perspective

“…For the CS, the atmosphere presents the strong stable stratification at nighttime, which is beneficial to the accumulation of aerosol pollutants. Under the strong stable conditions, the turbulence is intermittent ( Ren et al, 2019 ; Wang et al, 2018 ), and the model has insufficient performance for turbulence, which leads to large differences in the simulation of pollutant concentration. The knowledge of the physical mechanism behind the intermittent behavior of turbulence in the stable boundary layer is still very limited, thus more observational data are needed to analyzed and better applied the model.…”

Impacts of Boundary-Layer Structure and Turbulence on the Variations of PM2.5 During Fog–Haze Episodes

“…Turbulent intermittency is driven by non-stationarity due to motion on time scales that are slightly greater than turbulence (Mahrt 2010) when the large-scale flow is weak. To obtain the actual turbulent quantities and quantify the strength of the local turbulent intermittency, an automated algorithm (Ren et al 2019a), which is based on arbitrary-order HSA method (Huang et al 2008;Wei et al 2016), is used. The automated algorithm can identify the spectral gap and has been applied in turbulence analysis in the SBL (Ren et al 2019a, b).…”

Roles of Atmospheric Turbulence and Stratification in a Regional Pollution Transport Event in the Middle Reaches of the Yangtze River

“…Therefore, Ren et al. (2019a) proposed an index to represent the intensity of turbulence intermittency and noted that turbulence intermittency was strongest during the accumulation stage, less strong in the transport stage, and weakest in the dissipation stage (Ren et al., 2019b).…”