The Shades of Smoke

Last month, hundreds acres of mesic flatwoods were maintained during a prescribed burn at the Buffer Preserve in Port St. Joe. Teams from the Gulf Corps, Apalachicola National Estuarine Research Reserve, The Nature Conservancy & Bald Point State Park were there to help ensure burn went as efficiently as possible. While fire crews maintained the fire, Sandra Chafin taught Caitlin McCauley how to accurately record weather data and deliver hourly updates to crews. As the sweeping flames crawled across the saw palmettos and wiregrass, a striking display of smoke filled the canopies of the slash pine and longleaf pine that dotted the horizon. “I wonder why some smoke is black and some smoke is white” pondered Caitlin, and so the investigation began!  

“During a fire, lighter smoke usually indicates a higher moisture content of the fuel, meaning it could possibly still be green, or the relative humidity and relative fuel moisture contents of the day were high” explained Ronald Henderson, one of the fire crew members who assisted with that Thursday's burn. “Dark smoke in other cases can indicate certain chemicals being burned off, but we mostly see dark smoke on prescribed burns because of how intense the combustion is from the cured wood.” 

In other words, white smoke can indicate high moisture content in the vegetation, meaning it could possibly still be green or the relative fuel moisture contents of that day were high. On the other hand, darker smoke mostly comes from cured wood. The more dead fuel, the more intense the combustion.