Towards the Integrated Assessment of Human Exposure to Grass Pollen in Urban Environments

Pollen allergy affects a substantial proportion of the European population, and in many European countries the greatest rates of sensitisation are found for grass pollen allergen. Pollen allergy incidence rates tend to be greater in urban than in rural areas, likely due in part to the effects of urban air pollution on the allergy-causing potential of pollen grains. Background pollen concentrations
measured at roof level monitoring stations are typically used as a proxy for exposure, but may differ considerably from the exposure experienced by allergy sufferers. In a 2003 report on phenology, the World Health Organisation
highlighted the need for an improved understanding of the relationship between pollen monitoring station data and actual personal exposure.

Four studies are presented in this thesis. Three of these address three different aspects of urban exposure to grass pollen, whilst the fourth supporting study concerns pollen sampler effciency. In Study A, the relative efficiency
relationships between three models of pollen sampler were established under field conditions, and effciency correction factors derived. These factors enable
the quantitative comparison of data collected with different samplers, as is often necessary during exposure assessment. The results contribute to Study B, in which background grass pollen concentrations measured at roof
level were compared with those at street level within an urban canyon. A tendency for lower concentrations within the canyon was observed, consistent with the deposition of pollen from the recycling component of within-canyon
air, and indicating that monitoring station data typically overestimates exposure in the canyon environment. In Study C, grass pollen dose rates estimated
through personal sampling were compared with monitoring station data, and dose rate/background concentration ratios determined. These ratios, which as far as the author is aware have not been reported previously, may be used
to estimate inhaled pollen dose from monitoring station data. In Study D, diurnal grass pollen concentration profiles were shown to vary systematically
throughout the pollen season, with this variation apparently associated with a succession of different grass species with different flowering patterns dominating
pollen emission as the season progresses. Profles averaged over entire seasons are commonly used to advise allergy sufferers on avoidance strategies, however such systematic intra-seasonal variation is not thought to have previously
been demonstrated.
As far as the author is aware, each of these four studies represents a novel contribution to the area of pollen exposure assessment. As a body of work, this thesis furthermore lays foundations for the development of a human exposure model for grass pollen, an important constituent of an integrated pollen exposure assessment strategy.