Impacts of climate change on allergenicity

Introduction The current chapter considers the possible changes in atmospheric transport of aeroallergens that can be expected due to climate change. The main attention is given to pollen, for which dispersion is studied better than for mould spores, but the main conclusions are valid for mould spores too. The analysis starts from the pollen release from the plant, thus leaving out all processes of plant development and pollen formation (Figure 4.1). These parts of the pollen life cycle, also being vulnerable to changes in climate, are considered in different chapters of this book. The targets of this chapter are the processes related to the pollen release at local scale, its multiscale transport, and removal from the atmosphere. This chapter heavily relies on basic information on pollen behaviour in the atmosphere, which has been discussed in Chapter 5 of Sofiev and Bergmann (2013). Below, the key points from that book are summarised for the sake of completeness of the presentation. For details, the reader is referred to the main source. Pollen Features and Meteorological Parameters Controlling Its Transport in the Air There are many meteorological processes affecting pollen behaviour in the atmosphere (Di-Giovanni and Kevan, 1991; Helbig et al., 2004; Linskens and Cresti, 2000; Sofiev et al., 2013). From the point of view of the atmospheric transport, pollen and, to a large extent, mould spores are coarse but light aerosols with density around 800 kg m^-3, which makes them from 20% to five times lighter than most particles in the air. As a result, many types of bioaerosols can be transported over hundreds of kilometres or further if atmospheric conditions appear favourable. Experience with pollen dispersion modelling shows that the pollen grains of many wind-pollinated species, such as birch and olive trees, should be considered as regional- to continental-scale tracers. Coarser pollens (e.g., from many grasses) are important in regional to local scales. One of the key parameters regulating pollen release to the atmosphere is the intensity of vertical mixing. It controls two processes: Initial elevation of pollen from inflorescences upwards to the middle and upper parts of the boundary layer (where the main transport takes place), and remixing of particles during the transport, thus preventing them from settling down.