Variation Characteristics of PM2.5 Pollution and Transport in Typical Transport Channel Cities in Winter

Taking Handan，Xingtai，Hengshui，and Cangzhou，four cities in southwest Hebei Province along the Beijing-Tianjin-Hebei typical transport route，as examples，we analyzed the variation characteristics of 3a meteorological conditions and PM2. 5 concentration in winter from 2019 to 2021 and used potential source contribution analysis（PSCF）and concentration weight analysis（CWT）to identify the transport characteristics of PM2. 5 in the four cities during the study period. Based on the meteorological air quality model（WRFCMAQ）transmission matrix method and transport flux method，the contribution of PM2. 5 transport between Handan，Xingtai，Hengshui，and Cangzhou and the surrounding areas was quantitatively assessed；the vertical distribution characteristics of PM2. 5 net transport flux were revealed；and the two main transport routes of PM2. 5 pollution were further identified. The results showed that during the study period，the PM2. 5 concentration decreased by 45. 85%，49. 45%，42. 40%，and 31. 65%，respectively. The potential source contribution of Handan and Xingtai was mainly distributed in south-central Shanxi（Linfen，Changzhi，and Jinzhong），northern Henan（Xinxiang，Kaifeng，and Zhengzhou），and a small part of Inner Mongolia（PSCF > 0. 9）. The potential contribution areas of Hengshui and Cangzhou were mainly concentrated in southern Hebei（Handan and Shijiazhuang），central Shanxi （Taiyuan and Yangquan），and some Shandong regions（PSCF > 0. 7），and the CWT results were similar to those of PSCF. During the study period，the local contribution（51. 11% -62. 99%）was slightly higher than the regional contribution（37. 01%-48. 89%）during winter in the four cities. Affected by horizontal turbulence and vertical diffusion，the impact of regional transmission in 2020 was slightly higher than that in other years（0. 50%-9. 52%）. In 2021，the influence of regional transmission was slightly lower than that of other years（−2. 15% - −9. 52%）due to low PM2. 5 concentration and meteorological factors. For Handan，Xingtai，Hengshui，and Cangzhou，the total inflow（outflow）flux intensity of the four cities during winter and the surrounding areas was in 2020 > 2021 > 2019. For the total net flux，the total inflow（outflow）flux intensity of the four cities in winter was 0. 094，−0. 070，and 0. 087 kt·d-1（Xingtai：0. 212，0. 395，and 0. 544 kt·d-1；Hengshui：−0. 040，−0. 228，and 0. 185 kt·d−1；Cangzhou：0. 062，0. 126，and 0. 128 kt·d-1）. During the study，Handan，Xingtai，and Cangzhou were mostly used as transport receptors，whereas Hengshui was mostly used as a transport source. In the range of 0-1 260 m，the net transport flux intensity of PM2. 5 increased basically with the increase in height，and the maximum net flux of the various cities in different periods was different. The maximum net flux of Handan，Xingtai，and Hengshui was 252-1 261 m，817 m，and 252-817 m，respectively. The maximum net flux in Cangzhou was 252-359 m. By analyzing the transmission characteristics of the four cities，it was found that there were two main transport directions of PM2. 5，that is，the northwest-southeast direction（Shanxi → Handan → Henan and Shandong；Shijiazhuang → Xingtai → Handan and Shandong；Baoding → Cangzhou → Shandong）and the southwest-northeast direction（Shanxi → Xingtai → Hengshui → Cangzhou → Bohai Bay）. © 2024 Science Press. All rights reserved.