Measurement report: Impacts of thermodynamic and dynamic processes on the vertical distribution of carbonaceous aerosols: lessons from in-situ observations at the eastern foothills of Liupan Mountains, Loess Plateau

Abstract

The vertical distribution of carbonaceous aerosols critically influences planetary boundary layer structure and regional climate. However, high-resolution vertical data remain scarce over the Chinese Loess Plateau. To address this gap, coordinated observations of carbonaceous aerosols and meteorological variables were conducted in the Loess Plateau using tethered balloon-borne instruments during two field campaigns in July 2023 and 2024. The average near-surface concentrations of equivalent black carbon (eBC) and ultraviolet-absorbing particulate matter (UVPM) in Pingliang were 0.84 and 1.24 µg m −3 , respectively. Vertically, carbonaceous aerosol concentrations generally decreased with height. A comparison of the vertical profiles of eBC, UVPM, V TKE (mechanical turbulence), and potential temperature showed that during the early morning and nighttime, when convective activity was weak, UVPM concentrations in the upper atmosphere were higher than those of eBC. This pattern is primarily attributed to nucleation processes involving gaseous precursors during nighttime. Analysis of the roles of dynamic and thermodynamic processes indicated that thermodynamic processes dominated aerosol vertical transport in the near-surface layer, while enhanced dynamic processes at higher altitudes facilitated horizontal dispersion of pollutants. Air masses from the south of the observation site contributed significantly to UVPM levels. As air mass altitude decreased, the influence of local sources became more pronounced. Overall, this study demonstrated the regulatory mechanism of daytime and nighttime thermodynamic and dynamic impacts on the vertical distribution of air pollutants.