Background: Atmospheric pollen counts are ubiquitous data, however, few guidelines exist for interpreting them. A fundamental problem involves appreciating spatial variability in atmospheric pollen concentrations, for example, differences in pollen conditions between neighborhoods within a metropolitan area. The significance of this problem is perhaps most manifest in clinical allergy where pollen counts from a single rooftop pollen sampler are often applied to an entire city.
Objectives: This review will consider experimental data concerning spatial variability in atmospheric pollen concentrations. Several guidelines for interpreting pollen counts with respect to this spatial variability will be presented.
Data sources: This review will consider three independent bodies of literature concerning spatial variability in atmospheric pollen concentrations: (1) controlled-release experiments, (2) the paleoecology literature, and (3) atmospheric surveys.
Results: Four principal results emerged. First, pollen concentrations in the atmosphere appear to be inherently heterogeneous. Differences in pollen recovery between adjacent points increase in a predictable manner as a function of distance. Second, spatial variability decreases as the distance between pollen sources and destination regions increases. Pollen recovery across a city is most similar when pollen is transported from distant source regions. Third, the size of the source area represented by a pollen sampler depends on the distance between the sampler and the nearest vegetation. Samplers located near vegetation reflect small source areas; source areas expand considerably when the distance to the nearest vegetation increases. Last, individual pollen types travel characteristic distances from their source. Heavy pollen types collected at a particular point reflect a smaller source areas than lighter types which represent much larger source areas.
Conclusions: These conclusions allow allergists to interpret their atmospheric pollen counts with greater sophistication than was previously possible. Mathematical equations presented in this review permit rough calculations concerning source areas.