Comprehensive analysis of factors influencing temporal changes in airborne grass pollen

Abstract

Grass pollen is considered a primary allergenic source worldwide and constitutes an important global public health concern. This is due to several characteristics, including massive pollen production for wind pollination and the abundance of grass-dominated vegetation near densely populated areas. Temporal changes in factors affecting any of these characteristics could considerably impact the allergenic rates of grasses in the long term. The main aim of this study was to analyse grass pollen trends for stations in the Madrid Autonomous Region (central Spain) during the 1996–2025 period and to identify the factors influencing temporal changes in airborne grass pollen. Three main factors were analysed, namely, the abundance of sources identified as major contributors to airborne grass pollen, seasonal meteorological influence, and remotely-sensed vegetation productivity. The distribution and abundance of natural and semi-natural grasslands were significantly related to airborne grass pollen amounts. The results did not reveal any generalisable trends in grass pollen incidence, although specific stations in the north and south showed an increased pattern. While global warming is evident, most relevant meteorological variables influencing pollen incidence did not exhibit any consistent long-term climate trend throughout the entire study area. Consequently, climate change does not appear to considerably affect airborne grass pollen amounts. Furthermore, a compensation effect could be occurring in the short term where anthropogenic land-use transformations have reduced the abundance of pollen sources. On the other hand, the vegetation productivity of the pollen sources was also related to airborne pollen production, which confirms an important link between vegetative and reproductive productive rates. Years with the highest pollen incidence coincided with maximum vegetation productivity rates and favourable meteorological conditions for pollen production and dispersal. Beyond general trends, extreme pollen episodes must be considered as atypical environmental conditions that may cause unexpected high-exposure events that deviate from the average.