Abstract
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.
Highlights
Biomass burning emissions produce a considerable amount of greenhouse gases and are estimated to contribute ∼34– 38 % of global carbonaceous aerosol (Forster et al, 2007)
The RF03 burn was characterized as a flaming fire, a smoldering component was observed to be associated with the dormant mountain mahogany (Cercocarpus)
During in Clouds Experiment-Layer Clouds (ICE-L), the smoke plumes of two Wyoming Bureau of Land Management (BLM) prescribed burns were intercepted aboard the NCAR/NSF C-130 aircraft
Summary
Biomass burning emissions produce a considerable amount of greenhouse gases and are estimated to contribute ∼34– 38 % of global carbonaceous aerosol (Forster et al, 2007). Fresh dry smoke particles, primarily in the submicron size range, have been found to consist of ∼80 % OC, ∼5–9 % black carbon (BC), and ∼12–15 % trace inorganics, such as potassium, sulfate, chloride, and nitrate (Reid et al, 2005b). A secondary recommendation by Reid et al (2005b) was to investigate further the aging of smoke particles immediately following emission with high time resolution to bridge the gap between fresh and aged biomass burning aerosols, the physical and chemical properties of which impacts optical properties and cloud-forming potentials. The young smoke plumes were investigated in detail utilizing a unique suite of real-time aerosol instrumentation, measuring single-particle chemical composition, non-refractory aerosol mass concentrations, and black carbon mass concentrations. Concurrent measurements of CCN and IN were obtained and provide a basis for discussing aerosol cloud activation properties
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