| Summary: | Transboundary air pollution is one of the critical environmental problems in Southeast Asia; nevertheless the interaction between transboundary haze and local planetary boundary layer (PBL) remains unclear due to a lack of sufficient observations and sophisticated simulations. This study applied LiDAR observations and model simulations to comprehensively evaluate the interaction between transboundary haze and local PBL during a recent transboundary haze episode in Singapore in October 2023. Results show that upper-level southeasterly wind, especially the nocturnal low-level jet, created favorable conditions for aerosol transport when fire hotspot numbers increased in Indonesia. The rapid diurnal increase in PBL height facilitated the entrainment of upper-level haze into the PBL, interacting with ground-level aerosols through turbulent mixing. Model simulations further show the significant contributions of fire emissions to the transboundary haze episode in maritime Southeast Asia. The impacts extended toward the southern region of Peninsular Malaysia, driven by the persistent prevailing southeasterly wind.
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