Numerical modelling of allergenic
Large-scale dispersion of pollen grains has been known since middle of previous century but attracted significant attention comparatively recently. It has two consequences: (i) short-term changes in the pollen concentrations over (possibly, large) receptor regions and (ii) rapid large-scale redistribution of genetic material along the atmospheric pathways. Recently, a substantial progress has been achieved in understanding the short-term component, which leads to sharp and irregular modifications in the allergenic seasons over large areas.
Different taxa exhibit varying significance of long-range transport for their concentration patterns. This is related to the aerodynamic features of the grains but is also influenced by the typical atmospheric conditions during flowering. One of the most-important species in Europe is birch, with approximately 15% of the population being sensitized to its allergens. According to model simulations supported by the observations, birch pollen is frequently transported over the whole continent significantly contributing to the concentrations thousands of kilometres away from the source areas. Conversely, large-scale transport of grass pollen is much more limited, owing to substantially larger pollen size and lower height of the plants.
One of popular explanations of the rising pollen-related allergy prevalence is a negative impact of “conventional” pollutants, i.e. the chemical atmospheric constituents. The interaction with chemicals can occur along several lines: chemicals and aerosols may affect the production of pollen and/or its allergen; they can affect the pollen dispersion and transformation in the atmosphere; they can also affect the way human organism reacts to allergenic exposure. This is highly uncertain area but the evidence is mounting that all three lines are real. For instance, high concentrations of nitrogen oxides and ozone can damage the pollen grains and provoke the release of allergen.
A key tool for analysing and forecasting the pollen distribution and its interactions with chemicals is atmospheric dispersion modelling. Integrated approaches based on models covering main parts of the pollen life cycle and its atmospheric transport are under development in several countries. The European-scale integrated system SILAM is operational in Europe since 2005. It performs short-tern (up to 120 hours) forecasting of development of the birch, grass, olive, ragweed, mugwort, and alder pollen seasons, evaluates the release of the grains, and their dispersion around Europe. The model takes into account the main processes responsible for the season development including the short-term meteorological factors (rain, humidity, wind, temperature). The model has shown the capability to predict early peaks of the pollen concentrations attributed to the LRT but showed necessity of high-resolution local simulations for mountain regions. Pollen-related applications of SILAM can be combined with the conventional air quality assessments, thus revealing the potential for interaction of chemical and biological species. It has been demonstrated that at least in some cases the meteorological conditions are capable of synchronising the anthropogenic and biogenic species, which would enforce their interactions.