Airborne pollen has a predominantly even distribution up to 300cm height
Where atmospheric pollen counts are reported, a single rooftop-mounted volumetric sampler (e.g.: Burkard Trap) ordinarily serves an entire city or region. While efforts are underway to better understand the regional variation in pollen distribution, nothing is known of its variation in the 0-300cm height range, i.e.: that which is relevant to human exposure outdoors.
We constructed an apparatus of 23cm diameter airfoil-shaped horizontal disks in a vertical series, 25cm apart, each carrying microscope slides to collect pollen by aerial fallout. We deployed this apparatus outdoors but away from tree canopy, in a suburban setting of lower New York State for 3 days at the end of May 2013. This interval incorporates end of the spring tree season and the early summer grass season.
Because the taxonomic composition of pollen was limited to 5 major types, the late May sampling served a second purpose. As such, microscopic analysis was suitable for several summer undergraduate research projects. Normally, the protracted learning/training time for pollen analysis makes this work impractical for summer students without previous experience. Each student analyzed a unique subsample of the pollen of every slide. Subsamples were identified as horizontal transects using the microscope stage numerical scales.
Hickory, Pine, Oak, Walnut and Grass dominated the pollen spectrum at all levels. The remaining types comprised all other taxa, including unidentified, or unidentifiable pollen. For the purposes of our analysis all were grouped together as “Other”. There was a generally even distribution of pollen of all types throughout the height range, and this was most particularly so with Grass pollen. However, we found a moderate but significant difference among the tree pollen types, which showed a slightly higher rate of deposition at 125cm and 150cm height.
The proximity of buildings may account for the observed higher deposition rate for tree pollen 125-150cm. Our apparatus was situated midway between houses to the east and west, approximately 10 meters apart, but with an open porch only on the west side. Hickory, pine, oak and walnut are all growing within 100 meters to the west of the sampling location. By allowing air currents from the west, this particular architecture may have caused tree pollen of these species to become more concentrated toward the middle of our sampling range. However, grass pollen, which is ordinarily released closer to the ground appears to have become more evenly dispersed up to 300cm height.