1Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA
2Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA
3Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
4Chemical Sciences Division, Earth System Research Laboratory, National Oceanic & Atmospheric Administration, Boulder, CO, USA
5Droplet Measurement Technologies, Boulder, CO, USA
6Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA
7National Center for Atmospheric Research, Boulder, CO, USA
8Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA
*now at: Department of Chemistry, Purdue University, West Lafayette, IN, USA
Received: 14 Apr 2011 – Discussion started: 22 Jun 2011
Abstract. Biomass burning represents a major global source of aerosols impacting direct radiative forcing and cloud properties. Thus, the goal of a number of current studies involves developing a better understanding of how the chemical composition and mixing state of biomass burning aerosols evolve during atmospheric aging processes. During the Ice in Clouds Experiment-Layer Clouds (ICE-L) in the fall of 2007, smoke plumes from two small Wyoming Bureau of Land Management prescribed burns were measured by on-line aerosol instrumentation aboard a C-130 aircraft, providing a detailed chemical characterization of the particles. After ~2–4 min of aging, submicron smoke particles, produced primarily from sagebrush combustion, consisted predominantly of organics by mass, but were comprised primarily of internal mixtures of organic carbon, elemental carbon, potassium chloride, and potassium sulfate. Significantly, the fresh biomass burning particles contained minor mass fractions of nitrate and sulfate, suggesting that hygroscopic material is incorporated very near or at the point of emission. The mass fractions of ammonium, sulfate, and nitrate increased with aging up to ~81–88 min and resulted in acidic particles. Decreasing black carbon mass concentrations occurred due to dilution of the plume. Increases in the fraction of oxygenated organic carbon and the presence of dicarboxylic acids, in particular, were observed with aging. Cloud condensation nuclei measurements suggested all particles >100 nm were active at 0.5% water supersaturation in the smoke plumes, confirming the relatively high hygroscopicity of the freshly emitted particles. For immersion/condensation freezing, ice nuclei measurements at −32 °C suggested activation of ~0.03–0.07% of the particles with diameters greater than 500 nm.
Revised: 19 Nov 2011 – Accepted: 02 Dec 2011 – Published: 15 Dec 2011
Pratt, K. A., Murphy, S. M., Subramanian, R., DeMott, P. J., Kok, G. L., Campos, T., Rogers, D. C., Prenni, A. J., Heymsfield, A. J., Seinfeld, J. H., and Prather, K. A.: Flight-based chemical characterization of biomass burning aerosols within two prescribed burn smoke plumes, Atmos. Chem. Phys., 11, 12549-12565, doi:10.5194/acp-11-12549-2011, 2011.