Properties and evolution of biomass burning organic aerosol from Canadian boreal forest fires

Abstract

Abstract. Airborne measurements of biomass burning organic aerosol (BBOA) from boreal forest fires reveal highly contrasting properties for plumes of different ages. These measurements, performed using an Aerodyne Research Inc. compact time-of-flight aerosol mass spectrometer (C-ToF-AMS) during the BORTAS (quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites) experiment in the summer of 2011, have been used to derive normalised excess organic aerosol (OA) mass concentrations ( OA / CO), with higher average ratios observed closer to source (0.190 ± 0.010) than in the far-field (0.097 ± 0.002). The difference in OA / CO between fresh and aged plumes is influenced by a change in dominant combustion conditions throughout the campaign. Measurements at source comprised 3 plume interceptions during a single research flight and sampled largely smouldering fires. Twentythree interceptions were made across four flights in the farfield, with plumes originating from fires occurring earlier in the campaign when fire activity had been more intense, creating an underlying contrast in emissions prior to any transformations associated with aging. Changing combustion conditions also affect the vertical distribution of biomass burning emissions, as aged plumes from more flaming-dominated fires are injected to higher altitudes of up to 6000 m. Proportional contributions of the mass-to-charge ratio (m/z) 60 and 44 peaks in the AMS mass spectra to the total OA mass (denoted f 60 and f 44 ) are used as tracers for primary and oxidised BBOA, respectively. f 44 is lower on average in near-field plumes than those sampled in the far-field, in accordance with longer aging times as plumes are transported a greater distance from source. However, high levels of O 3 / CO and −log(NO x / NO y ) close to source indicate that emissions can be subject to very rapid oxidation over short timescales. Conversely, the lofting of plumes into the upper troposphere can lead to the retention of source profiles after transportation over extensive temporal and spatial scales, with f 60 also higher on average in aged plumes. Evolution of OA composition with aging is comparable to observations of BB tracers in previous studies, revealing a consistent progression from f 60 to f 44 . The elevated levels of oxygenation in aged plumes, and their association with lower average OA / CO, are consistent with OA loss through evaporation during aging due to a combination of dilution and chemical processing, while differences in combustion conditions throughout the campaign also have a significant influence on BBOA production and composition.

The role of semi-volatile organic compounds in the mesoscale evolution of biomass burning aerosol: a modeling case study of the 2010 mega-fire event in Russia

“…For example, fast (within several hours) and strong SOA formation events (associated with an increase in NEMR by a factor of 2 and more) in savannas were reported by Yokelson et al (2009) and Vakkari et al (2014). However, Akagi et al (2012) reported a net increase in the OA NEMR of only about 20 % over 4 h in the case of chaparral fires in California, and Jolleys et al (2015) observed higher NEMR values closer to the source than in aged plumes from Canadian fires. Overall, the available laboratory studies and atmospheric observations suggest that the SOA formation in the real atmosphere can be strongly influenced by the type of fuel and conditions of burning, as well as by the atmospheric conditions of BB aerosol evolution.…”

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

“…Cubison et al, 2011) (the ratio of the organic signal at m/z 60 to the total organic signal in the component mass spectrum) from oxidative decay of species such as levoglucosan. The f 60 vs. f 44 space (Cubison et al, 2011) is therefore used to characterise the evolution of biomass burning aerosols, with data from many studies exhibiting a negative correlation between f 44 and f 60 (Cubison et al, 2011;Ortega et al, 2013;Jolleys et al, 2014a). If the two SFOA factors represented different levels of processing of the same fuel type under similar conditions then SFOA1 would be expected to have higher f 44 and lower f 60 compared SFOA2.…”

Can d;PM2.5/d;CO and d;NOy/d;CO Enhancement Ratios Be Used to Characterize the Influence of Wildfire Smoke in Urban Areas?

“…Although these studies primarily characterized fresh smoke emissions, there was no clear consensus whether PM mass increases (Hobbs et al, 2003;Reid et al, 2005;Yokelson et al, 2009;Vakkari et al, 2014;Briggs et al, 2016) or stays the same (Akagi et al, 2012;Jolleys et al, 2015;May et al, 2015) (Wigder et al, 2013;Laing et al, 2016). Similar wide ranges have been observed in aged WF plume ΔOA/ΔCO (OA = organic aerosol, which makes up ~95% of PM 2.5 mass) (Jolleys et al, 2012;Sakamoto et al, 2015).…”