Evolution of Biomass Burning Aerosol Optical Properties in the Near Field

Abstract:

Biomass burning (BB) events are known to produce chemically rich environments that can impact the evolution of primary aerosols and influence secondary aerosols production rates. With their increasing in frequency, BB events are expected to exert an ever-increasing impact on climate due to aerosol radiative forcing processes. One area that is still poorly understood is the evolution of these smoke aerosols in the near field. Recent literature suggests that BB aerosols undergo a rapid evolution near their source that is then followed by a slower aging phase. During the summer of 2013, the Department of Energy-sponsored an aircraft field campaign called the Biomass Burning Observation Project (BBOP) that specifically targeted the evolution of smoke aerosols in the near field (< 2 hours). Results examining the evolution of BB optical and microphysical properties will be presented.

To probe these properties, the BBOP field campaign deployed a Single Particle Soot Photometer (SP2) to probe the mixing state of refractory black carbon (rBC) and a Soot Particle Aerosol Mass Spectrometer (SP-AMS) to investigate the composition of both non-refractory and rBC-containing particles. Aerosol optical properties were measured in situ using a 355 nm Photoacoustic spectrometer (PAS), a 532 nm photo thermal interferometer (PTI), a 630 nm cavity Attenuation Phase Shifted (CAPS) spectrometer, a 3-λ nephelometer, and a 3-λ PSAP. The BBOP study represented the maiden aircraft deployment for the SP-AMS, the 355 nm PAS and 532 nm PTI.

Discussion will be on the near-field evolution of particle mixing state and morphology, chemical composition, and microphysical processes that determine aerosol size distributions and single scattering albedo (SSA) of light absorbing aerosols. In the cases studied, increases in the coating thickness of refractive black carbon (rBC) particles, organic aerosol/rBC ratio, scattering/CO ratio, and aerosol size distributions have been observed. Results will be given from wildfires sampled in the US northwest and on controlled agricultural burns in the south-central Mississippi valley.