Sentinel-2 satellite shows that local cereal harvesting substantially contributes to peak Alternaria spore concentrations in Central-Northern Europe

Alternaria is a plant and animal pathogen and human aeroallergen. Cereal harvesting emits large amount of Alternaria spores into the atmosphere. However, estimating the peak spore periods from large areas is often a challenge because of insufficient observation stations. The purpose of this study was to examine, using remote sensing, the contribution of cereal harvesting to peak Alternaria spore concentrations for the period 2016-2018. Sentinel-2 satellite imagery alongside corine land cover 2018 (CLC2018) and Eurostat data on cereal production were integrated to map the potential sources contributing to the peak of Alternaria spore concentrations at 12 central-northern European sites. Ground truth cereal harvesting at Worcester and meteorological data for all sites were examined for their effect on daily Alternaria spore concentrations. Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) backward trajectory and dispersion modelling was used to simulate the dispersion and deposition of the spores from the air masses. The results showed that minimum NDVI values of agricultural areas were detected at a time when intensive harvesting happened and this coincided with a rapid increase of Alternaria spore concentrations. Furthermore, local agricultural areas cultivated with cereals were the main sources of the peak Alternaria spore concentrations in all the study sites. Remote sources also potentially contributed to the peak Alternaria spore concentrations. Natural sources, e.g. pastures, grasslands and green urban areas, to a lesser extent, also contributed to the peak spore concentrations at some sites, e.g. Borstel, Leicester and Worcester. Temperature and precipitation during the harvesting periods (Jul and Aug) were found to significantly contribute to the peak spore concentrations. Overall, the study showed that it is possible to estimate periods of peak Alternaria spore concentrations over large areas using Sentinel-2 satellites. This approach can be replicated for other bioaerosols that affect health, agriculture and forestry.