Biomass-burning-derived particles from a wide variety of fuels – Part 1: Properties of primary particles

Abstract

Abstract. Relationships between various optical, physical, and chemical properties of biomass-combustion-derived particles are characterized for particles produced in the laboratory from a wide range of fuels and burn conditions. The modified combustion efficiency (MCE), commonly used to parameterize biomass particle emissions and properties, is shown to generally have weak predictive capabilities, especially for more efficient combustion conditions. There is, however, a strong relationship between many intensive optical properties (e.g., single-scatter albedo, Ångström absorption exponent, mass absorption efficiency) and the organic aerosol-to-black carbon ([OA] ∕ [BC]) mass ratio over a wider range than previously considered (0.3 to 105). The properties of brown carbon (BrC, i.e., light-absorbing organic carbon) also vary with [OA] ∕ [BC]. Coating-induced enhancements (i.e., “lensing” effects) contribute only a minor amount to BC absorption for all of the burns despite some burns producing particles having large ensemble-average coating-to-core mass ratios. The BC–OA mixing state varies strongly with [OA] ∕ [BC]; the fraction of OA that is internally mixed with BC decreases with [OA] ∕ [BC] while the relative amount of OA coated on BC increases. In contrast, there is little relationship between many OA bulk chemical properties and [OA] ∕ [BC], with the O : C and H : C atomic ratios and the relative abundance of a key marker ion (m/z=60, linked to levoglucosan) all showing no dependence on [OA] ∕ [BC]. In contrast, both the organic nitrate fraction of OA and the OA volatility do depend on the [OA] ∕ [BC]. Neither the total particle nor BC-specific size distributions exhibit any clear dependence on the burn conditions or [OA] ∕ [BC], although there is perhaps a dependence on fuel type. Overall, our results expand on existing knowledge to contribute new understanding of the properties of particles emitted from biomass combustion.

Oxygenated Aromatic Compounds are Important Precursors of Secondary Organic Aerosol in Biomass-Burning Emissions

“…An additional piece of evidence that oxygenated aromatics might be forming SOA before or close to the first aircraft transect is that, on average, the initial O:C observed in the field on the first transect was higher than the initial O:C in the chamber (and closer to the final O:C observed in the chamber; Figure S.22). This however neither agrees with the findings from the smaller chamber during FIREX 66 nor does it explain field observations of an increasing O:C of the OA with age beyond the first transect that could be linked to heterogeneous chemistry. 27,67 Several studies have hypothesized that the lack of an enhancement in OA mass in the field could be explained if the photochemistry-driven SOA formation was balanced by dilution-driven POA evaporation.…”

Biomass-burning-derived particles from a wide variety of fuels – Part 2: Effects of photochemical aging on particle optical and chemical properties

“…The Fire Influence on Regional to Global Environments and Air Quality Experiment (FIREX-AQ) lab campaign took place at the Missoula Fire Sciences Laboratory in November 2016 (NOAA, 2013). A full description of the sampling strategy and methods, including descriptions of instruments used, for our study is provided in Lim et al (2019) and McClure et al (2020). Only a short description is provided here.…”

“…The suite of instruments sampling from the mini chamber are listed in Table S2 and further details of instrument operation and uncertainties are provided in McClure et al (2020), Lim et al (2019), and Coggon et al (2019). In brief, particlephase instruments sampled alternatingly through a two-stage thermodenuder that operated at 150 and 250 • C with a residence time of ∼ 5 s. The cycle rate between ambient and thermodenuder sampling was 2 min.…”

“…The relative contribution of organic aerosol (OA) and black carbon (BC) depends on the burn conditions, which are strongly related to the fuel type and other environmental factors (McMeeking et al, 2009;McClure et al, 2020). The chemical, optical, and physical properties of freshly emitted BB particles produced from burning of various biomass fuel types under various conditions are reasonably well studied (e.g., Lewis et al, 2008;McMeeking et al, 2009;Levin et al, 2010;Cheng et al, 2016;Fortner et al, 2018;McClure et al, 2020). Such measurements have established that some fraction of the emitted OA is light absorbing, with the absorptivity dependent upon the burn conditions (Saleh et al, 2014).…”

Laboratory studies of fresh and aged biomass burning aerosol emitted from east African biomass fuels – Part 2: Chemical properties and characterization

“…Aerosols obtained from a 500 • C burn classified as BrC aerosol are spherical in morphology as seen in transmission electron microscopy (TEM) images and are yellowbrown in color due to values of the imaginary portion of the refractive index (κ) that increase sharply toward shorter visible and ultraviolet wavelengths (Bond and Bergstrom, 2006). BrC is comprised of a wide range of poorly characterized compounds exhibiting highly variable light absorption properties, with reported κ values spanning 2 orders of magnitude (Saleh et al, 2013;Chen and Bond, 2010;Kirchstetter et al, 2004;McMeeking et al, 2009). Its optical properties have been shown to change through atmospheric processing, such as oxidation and the absorption of solar radiation, leading to particle-phase reactions and aqueous-phase processing within aerosol particles (Lambe et al, 2011(Lambe et al, , 2013Sareen et al, 2013;Lee et al, 2014;Zhao et al, 2015;Nguyen et al, 2012;Laskin et al, 2015).…”