Distribution and incidence of North American pollen aeroallergens

Using standardized aerosampling procedures, ambient pollen samples were collected at 15 locations in six regions of North America. The results provide baselines for examining human exposure to inhalant pollen allergens throughout the year on a broad geographic scale. In eastern temperate areas, pollen shed was closely linked to plant flowering seasons, with trees releasing pollen in the spring, grasses in the early summer, and weeds in the later summer and fall. Variations to this fundamental pattern were observed to the south and west; understanding these differences is essential if atopic persons suffering from allergic symptoms are to be assisted. For example, highly diverse tree pollen was found in North Carolina and Georgia for prolonged periods at high levels. These data suggest that a more sensitized population in the southeastern United States manifests allergic symptoms longer. Further south and southwest, pollen was captured throughout the year and sometimes at unexpected times. For instance, bimodal releases of grass pollen in both the spring and fall allow dual exposures of atopic persons, extending possible hypersensitivity to multiple seasons. Enhancing pollen exposure further, our data show limited overall variation in morning and afternoon levels, implying a continuous absorption of all major pollen types during daylight hours.