Observation of nocturnal low-level wind shear and particulate matter in urban Beijing using a Doppler wind lidar

Abstract

A field experiment of nocturnal mountain wind and corresponding particulate matter (PM) evolution under weak synoptic forcing at five sites within urban Beijing was conducted using a moving Doppler wind lidar and a fixed tower. Clear wind shear and zero-horizontal-wind zones at 40–320 m above the ground with a delay of 1.5 h were found at two sites between 20 km from north to south urban Beijing. The wind speed and height of the low-level jet at the north urban Beijing site were greater than those at the east urban Beijing site. The average horizontal distribution of low-level PM at 240 m was similar to the ground-level PM at night. The PM2.5 (aerodynamic diameter ≤2.5 μm) accumulation center showed no abrupt changes with a shift in wind direction until the northerly wind jet arrived.