Seasonal variation of local atmospheric circulations and boundary layer structure in the Beijing‐Tianjin‐Hebei region and implications for air quality

Abstract

The Beijing-Tianjin-Hebei (BTH) region experiences frequent heavy haze pollution in fall and winter. Pollution was often exacerbated by unfavorable atmospheric boundary layer (BL) conditions. The topography in this region impacts the BL processes in complex ways. Such impacts and implications on air quality are not yet clearly understood. The BL processes in all four seasons in BTH are thus investigated in this study using idealized simulations with the WRF-Chem model. Results suggest that seasonal variation of thermal conditions and synoptic patterns significantly modulates BL processes. In fall, with a relatively weak northwesterly synoptic forcing, thermal contrast between the mountains and the plain leads to a prominent mountain-plain breeze circulation (MPC). In the afternoon, the downward branch of the MPC, in addition to northwesterly warm advection, suppresses BL development over the western side of BTH. In the eastern coastal area, a sea-breeze circulation develops late in the morning and intensifies during the afternoon. In summer, southeasterly BL winds allow the see-breeze front to penetrate farther inland (150 km from the coast), and the MPC is less prominent. In spring and winter, with strong northwesterly synoptic winds, the sea-breeze circulation is confined in the coastal area, and the MPC is suppressed. The BL height is low in winter due to strong near-surface stability, while BL heights are large in spring due to strong mechanical forcing. The relatively low BL height in fall and winter may have exacerbated the air pollution, thus contributing to the frequent severe haze events in the BTH region.

Understanding meteorological influences on PM<sub>2.5</sub> concentrations across China: a temporal and spatial perspective

“…According to this pattern, when a regional PM 2.5 -induced air pollution episode occurs in winter, the regional air quality is more likely to be simultaneously improved by the same meteorological factor. This is consistent with the common scene in winter that regional air pollution episodes in the BeijingTianjin-Hebei region can be considerably mitigated by strong northwesterly synoptic winds, which are produced by the presence of high air pressure in northwestern Beijing (NW-High; Tie et al, 2015;Miao et al, 2015). On the other hand, regional air pollution in summer can hardly be solved simultaneously through one specific meteorological factor.…”

“…According to this research given the diversity of dominant meteorological factors on local PM 2.5 concentrations in different regions and seasons, it is more efficient to design meteorological means accordingly. For the heavily polluted North China region, especially the Beijing-Tianjin-Hebei region, the northwesterly synoptic wind (Tie et al, 2015;Miao et al, 2015) is much stronger in winter than winds in summer and exerts a dominant influence on PM 2.5 concentrations . Furthermore, in North China, the PM 2.5 concentration is much more sensitive to the change in wind speed than that of other meteorological factors .…”

Characterization of atmospheric trace gases and particulate matter in Hangzhou, China

“…Also, dry/wet deposition should have strong seasonal variations because high precipitation favors wet deposition and high soil humidity, and the growth of deciduous plants may also favor the dry deposition of particulate matter in warm seasons ). The relatively low concentrations of PM 2.5 and PM 10 in summer may also be partly due to an increased vertical mixing (i.e., a higher boundary layer height) and more convection (Ding et al, 2013;Miao et al, 2015b). PM 2.5 mass concentration also shows strong month-to-month variations.…”

Investigation of the Air Pollution Event in Beijing-Tianjin-Hebei Region in December 2016 Using WRF-Chem

“…Beijing-Tianjin-Hebei (BTH) is a super urban agglomeration on the North China Plain, with an area of 21,600 kilometers and more than 100 million people [1]. BTH has become one of the most heavily polluted areas in the world because of extensive industrialization and urbanization in the past few decades [2,3].…”

“…erefore, numerous studies in recent years have focused on the formation of air pollution episodes in BTH [1,[8][9][10][11][12][13][14]. e air pollution is composed of multiple pollutants, which are mainly attributed to power plants, domestic pollutants, industry, and vehicle exhaust [9,[15][16][17].…”