The Pollen Trap
It’s a beautiful, sunny spring day . . . but is it safe to go outside? For many, that depends on how much pollen is floating in the air. These tiny granules can make the difference between a marvelous day and a wheezy, sneezy hell. Knowing the pollen count in advance can help a lot, but how exactly does one count microscopic, wind-blown particles?
Scientists who study the movement of organisms in the atmosphere from one location to another are known as “aerobiologists,” and it’s their job to let you know exactly how itchy and unpleasant your day is likely to be. While there are many different contraptions aerobiologists use to determine pollen count, they all rely on very similar principles originating from Jim Hirst’s automatic spore trap.
Hirst, an English plant pathologist, developed his spore trap to study the dispersal of agriculturally-important fungal pathogens. The trap looks a bit like a paint can with a weathervane attached. The can part has a small slit in it through which air is drawn. The weathervane on top moves the can so that the slit is always facing into the wind. Inside the can is a metal drum, the circumference of which is wrapped in a strand of cellophane tape. The surface of the tape is smeared with a thin layer of vaseline. Pollen drawn through the slit, hits the greasy cellophane tape and sticks. The drum is also connected to a timing mechanism that turns the drum hourly or once a day so a fresh section of tape is exposed to the slit. This allows scientists to measure the amount of spores/pollen released over time.
Once the trap is finished collecting, the cellophane tape is removed, cut into sections, stained and observed under a microscope. A scientists trained to recognize different kinds of allergens must manually determine what is present and in how great a quantity for the volume of air drawn in through the slit.
Counting pollen can be tedious and requires specialized knowledge, so scientists today are trying to make the process simpler. Some labs can extract DNA from the tape and approximate the amount of pollen based on genetic markers. Other labs have tried to use AI to scan samples through a microscope and automatically detect different kinds of pollen. At the end of the day, however, the human eye remains the gold standard for pollen detection . . . second perhaps only to the human nose.
Works Cited:
Baksay, Sandra, et al. "Experimental quantification of pollen with DNA metabarcoding using ITS1 and trnL." Scientific reports 10.1 (2020): 1-9.
Kennedy, Roy, and A. J. Wakeham. "Measuring biological particles in the air using the Hirst type spore trap: aerobiology in the age of genomics." Annals of Applied Biology 166.1 (2015): 1-3.
Lacey, Maureen E., West, Jonathan S. “Using a Burkard Trap.” The Air Spora, Springer, 2006, 49-58.
Oteros, Jose, et al. "Automatic and online pollen monitoring." International archives of allergy and immunology 167.3 (2015): 158-166.
Brian Rutter, PhD, is the cofounder of Thing in a Pot Productions and a postdoctoral researcher in plant biology at Indiana University. Subscribe to our newsletter to receive our “Things About Things – Odd Facts About Plants” and video production tips in your inbox every month!