The Answer:

A daily count of pollen in the air has become a staple of weather forecasts. A pollen count is a count of the amount of pollen in the air, based on the average of the number of pollen grains that collect on sticky slides exposed to the air for a given period of time. It is expressed in grains of pollen per cubic meter over a 24 hour period.

With regard to this specific question, we don't know. As pollen is seasonal, statistics about it tend to focus on how high the count is at any given time of year, rather than calculating an average for the year as a whole.

With that said, a good place to start is the National Allergy Bureau of the American Academy of Allergy, Asthma and Immunology (AAAAI). They have a network of volunteers across the country who tabulate pollen data for the Bureau. You can use an interactive map on their website to pull up a table of daily pollen counts for most major U.S. cities, dating back to 1997. The organization also has publications available for sale that you might find helpful.

—The Editors