Vertical Structural Characteristics of Aerosols in the Atmospheric Boundary Layer during the Summer in Lhasa

To determine regional transport and local contribution, vertical gradient observation of air pollutants is required. Based on this, the number concentrations of aerosols in the particle size range of 0.13–3.39 μm were recorded with an optical particle counter POPS (the Printed Optical Particle Spectrometer) at ground level and in a tethered airboat in Lhasa in August 2020. The results demonstrate that (1) near-ground aerosol number concentrations in Lhasa range from 16 cm⁻³ to 870 cm⁻³, which is 2–3 orders of magnitude lower than those in northern China and the Yangtze River Delta. (2) The daily variation structure of the aerosol number concentration display two peaks and valleys. The peaks, which correlate to morning and evening peaks 1000 BJT (Beijing time) and 2100 LT, respectively, are usually dominated by small particles of 0.13–0.4 μm. (3) Furthermore, the vertical distribution of the aerosol number concentration is closely related to the evolution of the boundary layer. The aerosol in the stable boundary layer decreases with height, and the particle number concentration is 194± 94 cm⁻³. Conversely, the aerosols in the convective boundary and residual layers are uniformly distributed with the number concentrations of 165±99 cm⁻³ and 123±95 cm⁻³, respectively, which are significantly lower than that in the stable boundary layer. According to the above research results, local motor vehicle emissions are the main sources of pollution in Lhasa. Therefore, motor vehicles must be controlled and emissions must be reduced to build a highland ecotourism city.