PM2.5 and Pollen

What is PM2.5?

Have you ever wondered what fine particle pollution is, or why we forecast a PM2.5 AQI? Fine particle pollution is made of tiny particulates smaller than the width of a human hair! It can contain dust, smoke particles, pollen, mold, byproducts of combustion, etc. At high concentrations, fine particle pollution can cause adverse health effects, particularly for sensitive groups such as the elderly, young children, and those who are cardiovascularly compromised.

PM2.5 is specifically particles that are less than 2.5 micrometers in diameter, and is what we forecast for every day across the state of North Carolina. This is actually smaller than the pollen particles that have been covering your cars and outdoor surfaces for the last few weeks now that spring is in full bloom. With that in mind, pollen concentrations are not a part of our PM2.5 forecast due to the larger size of pollen particles.

A diagram shows the relative size of a human hair, beach sand, PM10, and PM2.5. The width of a grain of beach sand is roughly 90 µm in diameter, the width of a human hair is 50-70 µm in diameter, PM10 includes particulates less than 10 µm in diameter (dust, pollen, mold, etc), and PM2.5 includes particulates less than 2.5 µm in diameter (combustion particles, organic compounds, metals, etc).
PM2.5 is 20-30x smaller than the width of a human hair

Code Yellow, but Not Pollen

The widespread Code Yellow AQI conditions seen in recent weeks was driven by transported smoke from seasonal burning – not pollen (although the pollen all over the place may make everything seem “code yellow” for a few weeks!).

Please check our forecast page for more details regarding what’s happening with North Carolina’s day-to-day air quality, including a written discussion with the details that inform our forecast.

For information regarding pollen monitoring, please see the NCDAQ pollen monitoring page (

Is there something you’re wondering about with regards to Air Quality that you would like to see in future posts? Let us know in the comments!