The Causes of “Vulnerable Regions” to Air Pollution in Winter in the Beijing-Tianjin-Hebei Region: A Topographic–Meteorological Impact Model Based on Adaptive Emission Constraint Technique

Abstract

The Beijing-Tianjin-Hebei (BTH) region, with its complex terrain, has serious issues with air pollution. The northern and western parts of the BTH region are surrounded by the Yan Mountains and Loess Plateau (LP), and the south-central part of that region is a large open plain. Such special geographic configuration is prone to result in a concentrated pollution belt along the north-to-south direction on the eastern margin of the plateau, in addition to the influence of pollutant-emission sources and population distribution. In this study, based on an original adaptive nudging constraint method, we quantitatively analyzed the differences in the influence of emission sources under different dynamic and thermal conditions in the BTH region, which is impacted by a special large-scale leeward slope terrain. The mechanism of air pollution vulnerability and the comprehensive effects of terrain–meteorological conditions on air pollution in the BTH region were also discussed. The results indicated that the atmospheric diffusion conditions on the eastern side of the plateau were poor, and a sub-synoptic-scale “vortex sequence”, which was composed of a series of linked vortices, was identified. The corresponding atmospheric pollution convergence line stretched from Beijing to Hebei to Northern Henan in the lower atmosphere. On the eastern edge of the plateau, a “warm cover” formed by a temperature anomaly and a downdraft impeded the vertical diffusion of pollutants. Therefore, pollutants tended to converge at the eastern edge of the plateau, and the pollution belts would move longitudinally north and south along the topography of the eastern slope when south-westerly and north-easterly winds alternated. The movement generated a “train” of pollutants that were transported on the eastern edge of the plateau, which then caused air pollution to persist there. Such terrain–meteorological conditions amplified the effects of emissions by an average of 50% to 150% in the region, leading the eastern side of the LP to become a “naturally vulnerable region” to haze pollution.

Atmospheric Boundary Layer—Free Troposphere Air Exchange in the North China Plain and its Impact on PM2.5 Pollution

“…The horizontal convergence implies the adverse condition leading to air pollutant accumulation. Although the wind convergence belt and the topographic low pressure trough over the NCP have long been known (Meng et al., 2019; Su et al., 2004), Figure 5 presents quantitatively the climatological convergence feature of ABL in this region, and relates the convergence to the ABL‐FT exchange at the first time, as the authors know.…”

Multiple Land-Use Fugacity Model to Assess the Environmental Fate of PAHs – A Mega-City Under COVID-19 Pandemic

“…Besides, Beijing typically has a warm, temperate, sub-humid continental monsoon climate, and it is surrounded by the Yan Mountains and Loess Plateau on three sides. Pollution easily becomes trapped and accumulates in this area due to weak atmospheric ventilation24 . The geographical impact, industrialization, and urbanization are the important causes of the pollution in Beijing and its adjacent areas.…”