Highly controlled, reproducible measurements of aerosol emissions from combustion of a common African biofuel source

Abstract

Abstract. Particulate emissions from biomass burning can both alter the atmosphere's radiative balance and cause significant harm to human health. However, due to the large effect on emissions caused by even small alterations to the way in which a fuel burns, it is difficult to study particulate production of biomass combustion mechanistically and in a repeatable manner. In order to address this gap, in this study, small wood samples sourced from Côte D'Ivoire in West Africa were burned in a highly controlled laboratory environment. The shape and mass of samples, available airflow and surrounding thermal environment were carefully regulated. Organic aerosol and refractory black carbon emissions were measured in real time using an Aerosol Mass Spectrometer and a Single Particle Soot Photometer, respectively. This methodology produced remarkably repeatable results, allowing aerosol emissions to be mapped directly onto different phases of combustion. Emissions from pyrolysis were visible as a distinct phase before flaming was established. After flaming combustion was initiated, a black-carbon-dominant flame was observed during which very little organic aerosol was produced, followed by a period that was dominated by organic-carbon-producing smouldering combustion, despite the presence of residual flaming. During pyrolysis and smouldering, the two phases producing organic aerosol, distinct mass spectral signatures that correspond to previously reported variations in biofuel emissions measured in the atmosphere are found. Organic aerosol emission factors averaged over an entire combustion event were found to be representative of the time spent in the pyrolysis and smouldering phases, rather than reflecting a coupling between emissions and the mass loss of the sample. Further exploration of aerosol yields from similarly carefully controlled fires and a careful comparison with data from macroscopic fires and real-world emissions will help to deliver greater constraints on the variability of particulate emissions in atmospheric systems.

High- and low-temperature pyrolysis profiles describe volatile organic compound emissions from western US wildfire fuels

“…Such a comparison would help define the relationship between VOCs and characteristics of primary organic aerosol. We note that the primary aerosols have also been shown to have distinct profiles that correlate with different pyrolysis and combustion processes in the fire (Reece et al, 2017;Haslett et al, 2018).…”

“…VOCs emitted from biomass burning can be generally organized into major structural groups: furans, aromatics, oxygenated aromatics, aliphatic compounds, and so on. Within each structural category, compounds can have various functionalities, such as alcohol or alkene substituents (Hatch et al, 2015). VOC composition, classified by 11 structures and 17 functionalities, is shown in Figs.…”

Production of particulate brown carbon during atmospheric aging of residential wood-burning emissions

“…It may also be related to the fact that OA and BC are emitted during separate phases of combustion. OA-rich particles are emitted during the pre-flaming pyrolysis stage of combustion, whereas most BC is emitted during flaming combustion (Heringa et al, 2011;Corbin et al, 2015a, b;Haslett et al, 2018). These two stages of combustion may coexist in different regions of the stove, particularly during simulated real-world usage.…”

“…Biomass burning OA, which contributes two-thirds of the global budget of directly emitted primary OA (POA), is expected to be a considerable source of BrC (Chakrabarty et al, 2010;Hecobian et al, 2010;Lack and Langridge, 2013;Liu et al, 2014). The variability in reported light absorption properties of biomass burning OA with fuel type and burn conditions remains a major obstacle complicating its treatment in climate models (Saleh et al, 2013;Lu et al, 2015).…”

Optical Properties of Laboratory and Ambient Biomass Burning Aerosols: Elucidating Black, Brown, and Organic Carbon Components and Mixing Regimes

“…In addition to fuel characteristics and fuel variability, SSA and AAE depend on combustion conditions (S. Liu, Aiken, et al, 2014;Pokhrel et al, 2016). Recent work has characterized three combustion phases with distinct emissions: (1) pyrolysis generating predominantly OA, (2) flaming combustion producing the majority of rBC and BrC, and (3) smoldering combustion producing primarily OA (Haslett et al, 2018;Saleh et al, 2018). This source variability in properties from combustion phase should be averaged at larger spatial scales and aging times potentially simplifying their representation in models.…”