The Science of the total environment | 2021
Aircraft-based observation of gaseous pollutants in the lower troposphere over the Beijing-Tianjin-Hebei region.
Abstract
To investigate the spatial and vertical distribution of atmospheric pollutants (SO2, NOx, CO and O3), aircraft-based measurements (model: Yun-12, 12 flights, 27\xa0h total flight time) were conducted from near the surface up to 2400\xa0m over the Beijing-Tianjin-Hebei (BTH) region between June 17th and July 22nd 2016. The results showed that high concentrations of primary gaseous pollutants (SO2, NOx, CO) were generally present in Beijing, Tianjin, Langfang and Tangshan areas, while high values of O3 frequently appeared in areas far from the city. The flights at noon and dusk measured higher O3 concentrations at 600\xa0m and lower O3 concentrations at higher altitudes, implying a strong influence by photochemical production. Back trajectory analysis suggested that the high levels of gaseous pollutants, especially at 600\xa0m, were associated with pollution sources transported from the southerly direction during the observation period. The first simultaneous vertical distribution measurements using aircraft and tethered balloon were conducted in Gaocun (a rural site between Beijing and Tianjin) on June 17th. The results indicated that an inversion layer at the top of the planetary boundary layer (PBL) significantly suppressed vertical exchange through the PBL and resulted in a two-layer vertical distribution of pollutants above and below the PBL. Additionally, a residual high O3 layer (79.9\xa0±\xa02.5\xa0ppb, 500-1000\xa0m) was observed above the PBL, and it contributed to the surface peak O3 level at noon through downward transport along with the opening up of the PBL. These results indicate that coupled effects of horizontal and vertical transport should be investigated in future studies to improve the chemical transport models used to study the vertical distribution and regional transport over the BTH region.