Organic aerosol emission ratios from the laboratory combustion of biomass fuels

Abstract

Organic aerosol (OA) emission ratios (ER) have been characterized for 67 burns during the second Fire Laboratory at Missoula Experiment. These fires involved 19 different species representing 6 major fuels, each of which forms an important contribution to the U.S. biomass burning inventory. Average normalized ΔOA/ΔCO ratios show a high degree of variability, both between and within different fuel types and species, typically exceeding differen-ces between separate plumes in ambient measurements. This variability is strongly influenced by highly contrasting ΔOA levels between burns and the increased partitioning of semivolatile organic compounds to the particle phase at high ΔOA concentrations. No correlation across all fires was observed between ΔOA/ΔCO and modified combustion efficiency (MCE), which acts as an indicator of the proportional contributions of flaming and smoldering combustion phases throughout each burn. However, a negative correlation exists with MCE for some coniferous species, most notably Douglas fir, for which there is also an influence from fuel moisture content. Changes in fire efficiency were also shown to dramatically alter emissions for fires with very similar initial conditions. Although the relationship with MCE is variable between species, there is greater consistency with the level of oxygenation in OA. The ratio of the m/z 44 fragment to total OA mass concentration (f 44 ) as measured by aerosol mass spectrometer provides an indication of oxygenation as influenced by combustion processes at source, with ΔOA/ΔCO decreasing with increasing f 44 for all fuel types. Inconsistencies in the magnitude of the effects associated with each potential influence on ΔOA/ΔCO emphasize the lack of a single dominant control on fire emissions, and a dependency on both fuel properties and combustion conditions.

Formation and evolution of Tar Balls from Northwestern US wildfires

“…This comparison supports a downwind formation mechanism. Similar observations of minimal change in the 240 ΔOA/ΔCO have been previously reported (Jolly et al, 2012;Jolleys et al, 2014;Zhou et al, 2017).…”

Investigating a two-component model of solid fuel organic aerosol in London: processes, PM<sub>1</sub> contributions, and seasonality

“…Weimer et al (2008) suggested that a low m/z 44 signal is indicative of the flaming phase whereas high signals occur during the smouldering phase. Contrastingly, Jolleys et al (2014b) found in- creased f 44 occurred more frequently during flaming combustion than smouldering burns. These opposing conclusions highlight the dependency of emissions from fires on a variety of factors, including burn conditions and fuel type.…”

“…Furthermore, BBOA evolves in the atmosphere through oxidation, whereby aged biomass burning aerosols have mass spectra similar to that of fulvic acid, used to represent highly oxidised OA with a large signal at m/z 44 (Capes et al, 2008;Grieshop et al, 2009;DeCarlo et al, 2010;Cubison et al, 2011;Lack et al, 2013). Consequently, it can sometimes be difficult to determine from the mass spectra and time series derived from PMF alone whether a factor represents primary SFOA, processed pri- mary SFOA, SOA formed from SFOA, or a mixture of SFOA and OOA which are co-emitted (e.g.…”

“…Dall'Osto et al, 2013;Zhang et al, 2014). Organic aerosols (OA) are of particular interest as they can often represent a substantial fraction, and up to 90 %, of total fine particulate mass depending on location (Kanakidou et al, 2005). In urban areas such as Paris and Cork during the winter, organic aerosols have been found to contribute 30-62 % to the total non-refractory PM 1 (NR-PM 1 , Crippa et al, 2013;Dall'Osto et al, 2013;.…”

Evolution of the chemical fingerprint of biomass burning organic aerosol during aging

“…While the influence of the fuel (hardwood for stove A and B, softwood for stove C) cannot be neglected, we highlight, from our set of experiments, the overriding importance of the MCE on both the EF of organic markers and their relative contribution to OA. Previous studies have already revealed a relationship between the MCE and characteristics of the mass spectral signature of the OA emissions (Jolleys et al, 2014;Bertrand et al, 2017) but the influence of the MCE on individual organic marker emissions is still virtually unknown. The MCE values for the log woodstoves (stove A and B) range between 0.80 and 0.91 (Table 1), indicating that the combustion in these stoves is typically smoldering (MCE < 0.9), but also highly variable.…”