Effects of aging on organic aerosol from open biomass burning smoke in aircraft and laboratory studies

Abstract

Biomass burning (BB) is a large source of primary and secondary organic aerosols (POA and SOA). This study addresses the physical and chemical evolution of BB organic aerosols. Firstly, the evolution and lifetime of BB POA and SOA signatures observed with the Aerodyne Aerosol Mass Spectrometer are investigated, focusing on measurements at high-latitudes acquired during the 2008 NASA ARCTAS mission, in comparison to data from other field studies and from laboratory aging experiments. The parameter <i>f</i><sub>60</sub>, the ratio of the integrated signal at <i>m/z</i> 60 to the total signal in the organic component mass spectrum, is used as a marker to study the rate of oxidation and fate of the BB POA. A background level of <i>f</i><sub>60</sub>~0.3% ± 0.06% for SOA-dominated ambient OA is shown to be an appropriate background level for this tracer. Using also <i>f</i><sub>44</sub> as a tracer for SOA and aged POA and a surrogate of organic O:C, a novel graphical method is presented to characterise the aging of BB plumes. Similar trends of decreasing <i>f</i><sub>60</sub> and increasing <i>f</i><sub>44</sub> with aging are observed in most field and lab studies. At least some very aged BB plumes retain a clear <i>f</i><sub>60</sub> signature. A statistically significant difference in <i>f</i><sub>60</sub> between highly-oxygenated OA of BB and non-BB origin is observed using this tracer, consistent with a substantial contribution of BBOA to the springtime Arctic aerosol burden in 2008. Secondly, a summary is presented of results on the net enhancement of OA with aging of BB plumes, which shows large variability. The estimates of net OA gain range from ΔOA/ΔCO(mass) = −0.01 to ~0.05, with a mean ΔOA/POA ~19%. With these ratios and global inventories of BB CO and POA a global net OA source due to aging of BB plumes of ~8 ± 7 Tg OA yr<sup>−1</sup> is estimated, of the order of 5 % of recent total OA source estimates. Further field data following BB plume advection should be a focus of future research in order to better constrain this potentially important contribution to the OA burden

Overview of the South American biomass burning analysis (SAMBBA) field experiment

“…There is a general progression from fresh organic matter that is sampled directly above the fires, that is relatively un-oxidised, through to more aged material away from the direct source. This is consistent with previous measurements of biomass burning plumes in high latitude environments [1] and in Colorado [2]. The SAMBBA measurements fall between the slopes observed in these two environments, while the two case studies themselves exhibit different slopes closer to source.…”

Direct observation of aqueous secondary organic aerosol from biomass-burning emissions

“…2B), the guaiacol dimer signal correlates well both with BBOA (r = 0.96, P < 0.001) and with aqSOA after fog dissipation (r = 0.96, P < 0.001), suggesting that primary and secondary sources of the dimer were comparable (note that only the data collected after fog dissipation are reported here, to isolate the effects of fog processing on aqSOA formation). We further stress the link between biomass burning and aqSOA using a schematic representation of biomass-burning aging based on specific mass spectrometry features previously used in literature (32,33). Fresh biomass-burning emissions (BBOA) show a high content of anhydrosugars, like levoglucosan, which are characterized by the aforementioned signal at m/z 60 (C 2 H 4 O 2 + ) (Figs.…”

CCN closure study: Effects of aerosol chemical composition and mixing state

“…We speculate that OPOA is a mixture of both biomass burning and cooking aerosols. The BBOA is identified by the markers at m/z 60 (C 2 H 4 O + 2 ) and 73 (C 3 H 5 O + 2 ) [Aiken et al, 2009;Cubison et al, 2011]. BBOA-1 and BBOA-2 are correlated with m/z 60 (R 2 = 0.92 and 0.33, respectively) and m/z 73 (R 2 = 0.89 and 0.38, respectively).…”