Increased rupture of cypress pollen type due to atmospheric water in central and southeastern Spain.

This study aims to investigate the meteorological variables determining Cupressaceae pollen grain disruption in the environment. A parallel sampling of pollen grains and disrupted Cupressaceae pollen grains was performed in six cities using two Spanish aerobiological networks. The pollen concentrations, disrupted pollen concentrations, percentage of disrupted pollen and number of days when the percentage of disrupted pollen was above or equal to 50 % were quantified during two pollen seasons. The concentrations were determined following the standardised method EN 16868. Results show that the concentrations of pollen grains and disrupted pollen grains were not determined by geographical features and rarely by bioclimatic variables or indexes but by the ornamental use of the specimens in the vicinity of the pollen sampler, highlighting the possibility of using management practices to reduce exposure to allergens in the cities. African dust outbreaks coincided with higher concentrations of pollen grains and disrupted pollen grains, but the reduced percentage of disrupted pollen grains pointed to a non-causal relationship with long-distance transport. The effect of wind and maximum gusts remained negligible. The triggering factor for pollen disruption was the amount of water in the atmosphere, mainly reported as relative humidity. Rainfall increased the effect of disruption due to pollen grain swelling caused by its wash-out effect. The higher the relative humidity, the higher the disrupted pollen concentrations. This aligns with the mechanism of Cupressaceae reproduction since the family needs a water medium in the form of pollination droplets for the pollination tube to develop and the pollen grain to perform its biological function. Therefore, people that develop allergic symptoms to Cupresaceae pollen should avoid exposure during days with high relative humidity in the main pollen season.