Background : Grass pollen is a potent outdoor aeroallergen, responsible for allergic rhinitis and asthma exacerbation. Whilst there are known variations in sensitivity to pollen from different grass species, these species cannot be distinguished by established methods for monitoring of airborne pollen concentrations. As such, the modelling of changes in aerial- dispersion of pollen from individual grass species is currently not possible and it is not known whether temporal turnover in species composition of air-borne pollen matches terrestrial flowering patterns. The aim of this study was to use DNA metabarcoding of trapped pollen grains to obtain species- level discrimination of grass pollen across a network of UK sampling sites.

Method : We used two complementary DNA barcode marker genes (rbcL and ITS2) to identify how the taxonomic composition of grass pollen exposure changes across the summers of 2016/17. This involved establishment of a UK- wide network of Burkard Multivial Cyclone Samplers for daily sampling and development of DNA metabarcoding methods to identify the trapped pollen grains.

Results : We found that UK grass species display discrete, temporally restricted peaks of pollen incidence which vary with latitude and longitude across the UK. Grass pollen comprised the majority (ca . 60%) of airborne pollen during the summer months, dominated by Lolium and Holcus spp. Significant amounts of Agrostis capillaris, Poa trivialis, Dactylis glomerata and Arrhenatherum elatius (ca . 5% of all grass pollen each) were also detected. Thus the taxonomic composition of airborne grass pollen changes substantially across the grass allergy season and changes in total grass pollen concentration. We also demonstrate that flowering and anthesis (pollen release) events may be useful for predicting the incidence of particular species of grass pollen in the air. 
Conclusion : Our results demonstrate how targeted, high- throughput sequencing of eDNA can be used to understand the biodiversity of airborne pollen communities and fill a substantial knowledge gap that has persisted over the past 50 years of aerobiology research. By developing more refined aeroallergen profiling, we anticipate that our findings will facilitate the exploration of links between taxon-specific exposure of harmful grass pollen and disease, with concomitant socio-economic benefits.