This is a past event.

Improving our Understanding of Light Absorbing Aerosols from Biomass Burning

Aerosols emitted from open biomass burning (BB), including wildfires and agricultural burns, are recognized to perturb Earth’s climate through the direct effect (both scattering and absorption of incoming shortwave radiation), the semi-direct effect (evaporation of cloud drops due to absorbing aerosols), and indirect effects (by influencing cloud formation and precipitation).  The overall effect of these BB emissions on the atmospheric radiation balance, either forcing the atmosphere to heat or cool, depends on the abundance, cloud forming activity, and refractive index (specifically the absorption) of emitted primary particles and secondary aerosol species.  Global climate modeling has recently highlighted the potential radiative forcing impacts of absorbing organic compounds (“brown” carbon or BrC) and report that in some locations BrC radiative forcing could be of order +0.04 to +0.11 W/m².  The BB emission inventory inputs necessary for these modeling calculations are often based upon laboratory experiments due to the severe paucity of field measurements.  However, a growing body of available field measurement data is beginning to indicate that BB aerosols undergo very rapid changes in their chemical, microphysical, and optical properties that may not be captured in laboratory studies. 

During the summer and fall of 2013, the Department of Energy’s Atmospheric Radiation Measurement (ARM) program sponsored an aircraft study to investigate the near-field evolution (< 5 hrs) of biomass-burning (BB) aerosol particles. This field campaign, known as BBOP (Biomass Burning Observation Project), represents the first time that the near-field evolution of BB aerosol particles has been exclusively targeted with research aircraft.  For the wildfire flights, a Lagrangian sampling protocol was employed in which flight transects orthogonal to the plume direction were conducted at selected distances downwind of the source.  The plume age was calculated using prevailing wind speed/direction and the assumption of a constant emission source during the sampling period.  In this way, plume samples of a specific age could be acquired.  I will present recent findings on the formation and evolution of tar balls – type of BrC particle, the near field changes in BB aerosol chemical, microphysical, and optical properties, and on measurements from the Mt. Bachelor Observatory (MBO, ~ 2700k) in Central Oregon which provide complementary information on regional characteristics of wildfire plumes to the BBOP flight results.