Effective Density and Morphology of Particles Emitted from Small-Scale Combustion of Various Wood Fuels

The effective density of fine particles emitted from small-scale wood combustion of various fuels were determined with a system consisting of an aerosol particle mass analyzer and a scanning mobility particle sizer (APM-SMPS). A novel sampling chamber was combined to the system to enable measurements of highly fluctuating combustion processes. In addition, mass-mobility exponents (relates mass and mobility size) were determined from the density data to describe the shape of the particles. Particle size, type of fuel, combustion phase, and combustion conditions were found to have an effect on the effective density and the particle shape. For example, steady combustion phase produced agglomerates with effective density of roughly 1 g cm^–3 for small particles, decreasing to 0.25 g cm^–3 for 400 nm particles. The effective density was higher for particles emitted from glowing embers phase (ca. 1–2 g cm^–3), and a clear size dependency was not observed as the particles were nearly spherical in shape. This study shows that a single value cannot be used for the effective density of particles emitted from wood combustion

Photochemical Aging Induces Changes in the Effective Densities, Morphologies, and Optical Properties of Combustion Aerosol Particles

Effective density (ρeff) is an important property describing particle transportation in the atmosphere and in the human respiratory tract. In this study, the particle size dependency of ρeff was determined for fresh and photochemically aged particles from residential combustion of wood logs and brown coal, as well as from an aerosol standard (CAST) burner. ρeff increased considerably due to photochemical aging, especially for soot agglomerates larger than 100 nm in mobility diameter. The increase depends on the presence of condensable vapors and agglomerate size and can be explained by collapsing of chain-like agglomerates and filling of their voids and formation of secondary coating. The measured and modeled particle optical properties suggest that while light absorption, scattering, and the single-scattering albedo of soot particle increase during photochemical processing, their radiative forcing remains positive until the amount of nonabsorbing coating exceeds approximately 90% of the particle mass

Photochemical Aging Induces Changes in the Effective Densities, Morphologies, and Optical Properties of Combustion Aerosol Particles

Effective density (ρeff) is an important property describing particle transportation in the atmosphere and in the human respiratory tract. In this study, the particle size dependency of ρeff was determined for fresh and photochemically aged particles from residential combustion of wood logs and brown coal, as well as from an aerosol standard (CAST) burner. ρeff increased considerably due to photochemical aging, especially for soot agglomerates larger than 100 nm in mobility diameter. The increase depends on the presence of condensable vapors and agglomerate size and can be explained by collapsing of chain-like agglomerates and filling of their voids and formation of secondary coating. The measured and modeled particle optical properties suggest that while light absorption, scattering, and the single-scattering albedo of soot particle increase during photochemical processing, their radiative forcing remains positive until the amount of nonabsorbing coating exceeds approximately 90% of the particle mass

Real-Time Chemical Composition Analysis of Particulate Emissions from Woodchip Combustion

Residential wood combustion is one of the major sources of fine particles. The chemical composition of the particles plays a key role in both adverse health and environmental effects. It is important to understand how chemical composition of particulate emissions varies during different combustion processes and conditions. In this work, combustion of wood chips was studied in a moving step-grate burner in different combustion conditions (efficient, intermediate, and smoldering) in the laboratory. The particulate emissions were measured with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS). It was found that two phases were occurring frequently in the intermediate and smoldering combustion. Phase 1 took place when gaseous carbon monoxide (CO) was rapidly increasing after the new fuel addition. Phase 2 was a stable, burn-out period with low CO emissions until the new fuel addition and automatic removal of fuel leftovers from the grate. The analysis on the organic aerosol by positive matrix factorization (PMF) extracted out five factors: hydrocarbon-like organic aerosol (HOA), low-volatile-oxidized organic aerosol (LV-OOA), biomass burning organic aerosol (BBOA), and two additional factors of “polycyclic aromatic hydrocarbon (PAH) factor” and “aromatic factor”. PAH and LV-OOA were found to be forming mainly during phase 1. HOA showed similar behavior as a PAH factor and LV-OOA in a time series. BBOA was consistent with levoglucosan formation during the combustion and became higher during phase 2. The aromatic factor was mainly composed of fragment ions of <i>n</i>-butyl benzenesulfonamide compound, which was observed in both phases. To our knowledge, this is the first work to report the particulate organics of combustion aerosols and PAH distinguished by PMF. The results prove that the particulate organic emissions can be reduced efficiently when keeping combustion efficiency high. This may help in targeting the efforts on emission reduction better in the future