Characterization of a large biogenic secondary organic aerosol event from eastern Canadian forests

Abstract

Abstract. Measurements of aerosol composition, volatile organic compounds, and CO are used to determine biogenic secondary organic aerosol (SOA) concentrations at a rural site 70 km north of Toronto. These biogenic SOA levels are many times higher than past observations and occur during a period of increasing temperatures and outflow from Northern Ontario and Quebec forests in early summer. A regional chemical transport model approximately predicts the event timing and accurately predicts the aerosol loading, identifying the precursors as monoterpene emissions from the coniferous forest. The agreement between the measured and modeled biogenic aerosol concentrations contrasts with model underpredictions for polluted regions. Correlations of the oxygenated organic aerosol mass with tracers such as CO support a secondary aerosol source and distinguish biogenic, pollution, and biomass burning periods during the field campaign. Using the Master Chemical Mechanism, it is shown that the levels of CO observed during the biogenic event are consistent with a photochemical source arising from monoterpene oxidation. The biogenic aerosol mass correlates with satellite measurements of regional aerosol optical depth, indicating that the event extends across the eastern Canadian forest. This regional event correlates with increased temperatures, indicating that temperature-dependent forest emissions can significantly affect climate through enhanced direct optical scattering and higher cloud condensation nuclei numbers.

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

“…These trends, which diverge from the expected characteristics for emissions of this origin, are further compounded by high O 3 / CO (> 0.2), indicative of an elevated level of oxygenation and photochemical activity (Mason et al, 2001;Parrington et al, 2013). Formation of SOA from biogenic precursors has previously been observed in the forests of Ontario (Slowik et al, 2010). These SOA events were also characterised by OA / CO levels far in excess of those derived for BB emissions during the same study.…”

“…In accordance with this trend, OA / CO within the low altitude plumes in B621 and B622 were consistently above the average for aged emissions (0.097), reaching as high as ∼ 0.4. There is subsequently considerable evidence to support biogenic SOA as a potential contributor to the OA burden during BORTAS, which could provide further enhancement of OA / CO as demonstrated by the Slowik et al (2010) Ontario study. Whilst the further properties of aged plumes discussed here would suggest this effect is isolated and limited in its overall impact, it presents a further source of uncertainty for any attempts to develop parameterisations for the contribution of forest fires to regional and global OA budgets.…”

Interannual variability of ozone and carbon monoxide at the Whistler high elevation site: 2002–2006

“…CO is not only a good tracer for pollution and biomass burning, it also increases as a result of the oxidation of biogenic NMHCs (e.g. Hudman et al, 2008;Slowik et al, 2010) which may contribute to this secondary peak. In summer, the average maximum diurnal changes in CO and O 3 during JJA are 6 ppbv and 3.5 ppbv respectively (Fig.…”

Analysis of cloud condensation nuclei composition and growth kinetics using a pumped counterflow virtual impactor and aerosol mass spectrometer

“…(Vlasenko et al, 2009;Chan et al, 2010;Shantz et al, 2010;Slowik et al, 2010). Egbert is located in a rural area approximately 70 km north of Toronto.…”