Shortwave absorption by wildfire smoke dominated by dark brown carbon

Area of Science:

• Atmospheric Chemistry
• Climate Science
• Aerosol Science

Background:

• Wildfires release black carbon and brown carbon, impacting Earth's radiation budget.
• Brown carbon's warming effect is uncertain due to assumed photochemical bleaching, leading to poor climate model representation.

Purpose of the Study:

• To quantify shortwave absorption by wildfire smoke aerosols.
• To investigate the properties and atmospheric processing of brown carbon in wildfire plumes.

Main Methods:

• Measurements of ensemble-scale and particle-scale shortwave absorption in western US wildfire smoke plumes.
• Analysis of brown carbon's optical properties, including water insolubility and photobleaching resistance.

Main Results:

• A specific dark brown carbon type accounts for significant short (75%) and long (50%) visible light absorption.
• This brown carbon is water insoluble, resists daytime photobleaching, and its absorptivity increases with nighttime processing.

Conclusions:

• Brown carbon's radiative impact is substantial and more persistent than previously assumed.
• Current climate model parameterizations for brown carbon require updates to accurately estimate smoke aerosol radiative forcing and warming potential.