Examination of Combustion-Generated Smoke Particles from Biomass at Source: Relation to Atmospheric Light Absorption

Abstract

The formation of carbonaceous aerosols from biomass combustion are associated with a high degree of uncertainty in global climate models. In this work, soot samples were generated from the combustion of pine wood, wheat straw and barley straw in a fixed bed stove; as well as from the combustion of biomass pyrolysis model compounds. Samples were collected on filters, which were used for the determination of Absorption Angstrom Exponent (AAE). In addition, the content and composition of elemental carbon (EC) and organic carbon (OC) were determined, and the interrelationships between these and the AAE were examined. It was found that the spectroscopic signature of samples with high 'brown carbon' emissions was comparable to that of many PAH and polyphenols, with AAE ranging from 1.0-1.2 for model compounds to 0.5-5.7 for biomass. In addition to the filter samples, particles were collected directly onto microscopy grids and analysed by transmission electron microscopyelectron energy loss spectroscopy (TEM-EELS) in order to determine structural characteristics. This was used to examine the impact of combustion conditions and flue gas dilution on particle structure. Smouldering phase and diluted particles were found to be less graphitic and twice as oxygenated as undiluted flaming phase particles. The results are interpreted to better understand the impact of combustion processes on soot formation from biomass combustion.

Structural effects of C3 oxygenated fuels on soot formation in ethylene coflow diffusion flames

“…Even though alternative fuels can be sustainablysourced, the combustion of most fuels has the side effect of releasing particulate matter (commonly known as soot) into the atmosphere and causes harm to our health [16,17] and environment [18][19][20][21]. Therefore, it is essential to understand how alternative fuels affect the generation of such particulate matter.…”

The Impact of Fuelwood Moisture Content on the Emission of Gaseous and Particulate Pollutants from a Wood Stove

“…These conditions lead to the formation of a higher OC fraction. On average, the ratio of EC/TC for the low moisture fuel is 0.84 while for high It is interesting to compare the results obtained previously using a total soot sample analyzer (Jones et al (2020)). Of note is the fact that for this <1 µm sample the colors are black or brown.…”

“…This color change from black to brown was as result of a higher tar-phase formation on the soot surface resulting in a higher organic fraction. Similarly, Jones et al (2020) identified a change in the visible color of soot samples collected during different phases of combustion -also a result of the variation in EC/TC. Crudely, darker and black soot is representative of periods of higher temperature and higher efficiency combustion while lighter brown, tan, yellow and gray soot samples are indicative of reduced combustion efficiency and fuel smoldering.…”

“…Black is (0,0,0) while light brown is (150,75,0). This allows the soot samples which are black, brown or tan-like to be characterized qualitatively (Jones et al (2020)).…”

“…In previous work (Jones et al (2020)) examined soot properties for samples where the full range of particulate sizes was captured on filter papers. In the current work, the soot was captured in four size fractions using a Dekati Impinger.…”