The difference in the boundary layer height between urban and suburban areas in Beijing and its implications for air pollution

Serious regional pollution often erupts in clean areas, and the impact of boundary layer structure evolution on heavy pollution in clean areas urgently needs to be studied. During the period from November 3rd to December 31st, 2014, ceilometers were used to observe the boundary layer height (BLH) of urban and suburban areas in Beijing. During the observation period, there was no significant difference in the average BLH between the urban and suburban areas of Beijing, both of which had BLHs of approximately 600 m. However, there were significant differences in the diurnal changes in the boundary layer between the urban and suburban areas. During the day, the urban area BLH was 112 m higher than the suburban area BLH, and at night, the urban area BLH was 144 m lower than the suburban area BLH. Under the background of rapid urbanization in Beijing, the variation in the underlying surface and the large amount of anthropogenic heat emissions were the main reasons for the differences between the urban and suburban boundary layers. Combined with an analysis of particulate matter concentrations, it was found that the insufficient development of the boundary layer in the suburbs at noon limited the diffusion of pollutants and caused the accumulation of pollutants, resulting in a clean, low-emission area that was heavily polluted. This research has important guiding significance for clarifying the cause of heavy regional pollution.