Someone pls enlighten me if I am incorrect. You do not mention the time-frame involved in your study. I need a greater understanding of the source area or areas. Somehow work into your model that not all pollen grains are spheres. None of these, however, have been statistically significant occurrences, though.
Good science consists mostly of play disguised as work.
In response to Ian Spooner's query regarding particle size analysis for small samples, there are several laboratories in NY and New England that have set up laser diffraction particle size analyzers, which can analyze very small samples.