The Role of Atmospheric Boundary Layer Wind and Turbulence on Surface Pollen Levels

The atmospheric boundary layer (ABL) is the lowest layer of the atmosphere, where most of the interactions between the atmosphere and the Earth’s surface occur. Within this layer, the air movements and the turbulent processes facilitate the dispersion and transport of particles. This work quantifies the effect of ABL-dynamics related variables on the surface pollen concentrations in the city of Granada, southeastern Spain. The Main Pollen Season (MPS) of two pollen types (Olea and Cupressaceae) and Doppler lidar data for different height ranges and ABL regimes were used for the period 2017-2022 and statistically analyzed based on Spearman correlations and Generalized Linear Model (GLM). Olea pollen concentrations, mainly originating from sources in the outskirts of the city, were significantly influenced by daytime wind direction, transporting high concentrations into the urban area, explaining up to 28% of the variability of the Olea pollen concentrations in the ABL of the city. At night, surface Olea pollen concentrations were affected by vertical wind, which explain the 5% of the variability, leading to fluctuations associated with its vertical transport. For Cupressaceae pollen concentrations, however, the pollen sources are located within the city and surface concentrations of Cupressaceae pollen are predominantly influenced by the urban ABL. The variability in surface concentrations is partly determined by diverse phenomena and conditions occurring across different regimes of ABL dynamics. Katabatic flows significantly contributed to Cupressaceae pollen concentrations at night, while high turbulence produced by the convective boundary layer (CBL) played a key role in their dispersion during daytime, explaining up to 10% of the variability of the Cupressaceae pollen concentrations near to surface. The difference in the results between both pollen types can be attributed to several interrelated factors such as location of sources, local weather conditions, different ABL regimes, intrinsic characteristics of pollen, and the flowering phenology and interactions with other environmental factors. The overall results demonstrate the substantial influence of ABL dynamics on surface pollen concentrations (explain up to 29% of the variability for Olea pollen concentrations and 37% for Cupressaceae ones), highlighting its crucial role in the particle transport, dispersion and distribution in the atmosphere. These findings emphasize the need for a better understanding of the ABL to adequately address air quality and public health challenges in urban environments.