They examine the numbers and types of pollen grains. RELATED: Allergy season is longer than ever. Here's why Today's "main contributors" are pine, oak, sweet gum, hackberry, and birch tree pollens.

On Tuesday, the Oregon Allergy Associates reported high levels of tree pollen in the air. The dominant pollen was Alder, but tests also picked up Birch, Cedar, Cottonwood, and Hornbeam.