Smoldering combustion during wildfires contributes significantly to emissions of pollutants, can burn for days or months, may damage roots and soil, and can transition to flaming combustion. Mitigating these hazards requires an understanding of how physical parameters control smoldering combustion, such as the chemical composition of the fuel. The main organic constituents of biomass are cellulose, hemicellulose, and lignin. Understanding how these constituents influence smoldering is an important step in further developing physics -based models and developing understanding that applies across multiple fuel sources. Previous experimental studies have investigated how varying the amount of cellulose and hemicellulose in fuel influences smoldering behavior, but have not considered the impacts of varying the lignin content. The objective of this study was to identify the influence of lignin on smoldering behavior. This objective was achieved by experimentally and numerically studying the smoldering behavior of various concentrations of lignin in mixtures of cellulose and hemicellulose. These were tested at densities of 200 and 300 kg/m 3 . An infrared camera and thermocouples were used to determine the propagation of the smoldering front in the horizontal and vertical directions, respectively. A one-dimensional reactive porous media model with global chemistry was used to simulate downward smoldering propagation. The horizontal and downward smoldering propagation velocities decrease when more lignin is present due to the slower pyrolysis rates and higher activation energy of lignin. Additionally, results from simulations match this trend for downward propagation. At higher lignin contents, the effect of the mass percentage of cellulose and hemicellulose on downward and horizontal smoldering decreases, indicating that lignin content has the largest impact on smoldering velocities of the three constituents. Increasing the density decreases both the horizontal and vertical propagation velocities due to lower oxygen diffusion and the additional mass being consumed.

PM2.5 carbonaceous particles were measured at Gosan, South Korea during 29 March-11 April 2002 which includes a pollution period (30 March-01 April) when the highest concentrations of major anthropogenic species (nss-SO4 (2-), NO3 (-), and NH4 (+)) were observed and a strong Asian dust (AD) period (08-10 April) when the highest concentrations of mainly dust-originated trace elements (Al, Ca, Mg, and Fe) were seen. The concentrations of elemental carbon (EC) measured in the pollution period were higher than those measured in the strong AD period, whereas an inverse variation in the concentrations of organic carbon (OC) was observed. Based on the OC/EC ratios, the possible source that mainly contributed to the highly elevated OC concentrations measured in the strong AD period was biomass burning. The influence of the long-range transport of smoke plumes emitted from regional biomass burning sources was evaluated by using MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data for fire locations and the potential source contribution function analysis. The most potential source regions of biomass burning were the Primorsky and Amur regions in Far Eastern Russia and southeastern and southwestern Siberia, Russia. Further discussion on the source characteristics suggested that the high OC concentrations measured in the strong AD period were significantly affected by the smoldering phase of biomass burning. In addition to biomass burning, secondary OC (SOC) formed during atmospheric long-range transport should be also considered as an important source of OC concentration measured at Gosan. Although this study dealt with the episodic case of the concurrent increase of dust and biomass burning particles, understanding the characteristics of heterogeneous mixing aerosol is essential in assessing the radiative forcing of aerosol.