Pollen fragments amplify cross-boundary impacts on air quality

Pollen grains are recognized drivers of respiratory diseases, yet their fragments pose an even greater public health risk. However, the persistence, variability, and sources of these fragments remain largely unknown, hindering effective risk mitigation. Here we integrate real-time bioaerosol observations, DNA sequencing, a new data-driven framework, and atmospheric transport modelling to provide the first evidence of sustained cross-boundary transport of pollen fragments from the Asian continent to Japan. Pollen fragments dominated local exposures, exceeding intact grains by over sixfold, with continental sources contributing more than 30% from February to April and surpassing 70% in February. Such unaccounted-for episodes persisted for months, revealing a hidden health burden that current pollen alert systems fail to capture. This blind spot undermines Japan’s pollen risk mitigation strategies and highlights parallel gaps in international policy frameworks. Ignoring pollen fragments leads to systematic underestimation of health burdens, underscoring the urgent need for next-generation monitoring and coordinated cross-boundary policies to address this overlooked dimension of atmospheric bioaerosols.