pollen count

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A measure of the amount of pollen in the air, usually calculated as the average number of pollen grains in a cubic meter or other standard volume over a 24-hour period.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun the measurement of the number of grains of pollen in a cubic meter of air

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the number of pollen grains (usually ragweed) in a standard volume of air over a twenty-four hour period and a specified time and place