Spatial-temporal patterns and multi-scale drivers of allergenic pollen Fraxinus, Platanus and Humulus in the urban and suburban area of Beijing, China

Abstract

Pollen allergy induced by allergenic plants in urban green spaces poses an escalating health risk in Beijing city during rapid expansion of urbanization. Utilizing 3-year (20162018) continuous monitoring pollen (Fraxinus, Platanus and Humulus) and meteorology data, this study analyzed spatial-temporal patterns of allergenic pollen and their influencing factors across multiple scales. Results revealed significant spatial-temporal heterogeneity in pollen seasons and pollen concentrations. Warmer pre-season and in-season temperatures accelerated pollen season start (PSS) for Platanus pollen and peak dates (PD) for Fraxinus pollen. Local vegetation abundance quantified by importance value (IV) within a 100-meter radius, was strongly correlated to seasonal pollen index (SPI) (r = 0.94–0.99, p < 0.05), emphasizing the impact of local plants on spatial patterns of pollen concentrations. SPI was also correlated with dominant wind frequency annually, except for the dominant pollen taxon of which SPI was merely associated with frequency of the wind directions aligned with local vegetation distribution. Prevailing winds were mostly responsible for high hourly pollen levels at a local scale. Low wind speeds (0–1.0 m/s) were associated with high urban hourly pollen levels, while high wind speeds (> 3.0 m/s) dominated during high-pollen hours in the suburban area. Two complementary algorithms based on the 24-h backward trajectories were performed to identify regional potential source area, such as Inner Mongolia for Platanus pollen and Hebei Province for Fraxinus pollen. Suburban Humulus pollen exhibited distinct transport pathways influenced by northerly air masses. These findings elucidate multi-scale mechanisms of pollen dispersion, and will provide further practical insights for urban greening strategies and allergy risk mitigation, including avoiding plantings of allergenic species in densely populated areas and limiting outdoor activities during peak pollen hours (particularly under low wind conditions).