Upper-air secondary pollutants downward invade to planetary boundary layer by strong turbulence at the eastern steep slope of Tibetan Plateau: results from BLMP-SCB

Abstract. The comprehensive filed campaign is essential to deeply understand the interactions between aerosol and planetary boundary layer (PBL) meteorology, and implement of the relevant campaign is difficult, and thus data is scarce at the complex terrain. The first planetary boundary layer meteorology and pollution at western SiChuan Basin (BLMP-SCB) was conducted from December 2018 to January 2019. The campaign provides good chance for revealing the poorly-known the impact of PBL turbulence on profiles of air pollutants. The primary particulate matter (PM) pollutants rapidly decline with the increasing altitude, while the secondary ultraviolet PM (UVPM_sec) reduces more slowly and even shows a peak at 1.5–2.0 km above sea level. The regional and long-range transports are comparable between the primary and secondary PM pollutants during the campaign. The more uniform UVPM_sec profiles during the nighttime are mainly modulated by thermodynamic (temperature) processes, while the secondary pollutants at PBL top downward invade into PBL by some dynamic processes, i.e., mechanical turbulence and wind shear, lending to more UVPM_sec within PBL during the daytime. This study emphasizes the importance of turbulence and wind shear for the vertical profiles of air pollutants at complex terrain, especially at the sloped terrain. The results are helpful for understanding formation mechanism of heavy air pollution at the complex terrain, and then making the targeted countermeasures.