Environmental & Climate Sciences Department Seminar
"Emission and Aging of Organic Aerosols from Wildfires in the Western US: Insights from the BBOP campaign"
Presented by Qi Zhang, University of California, Davis
Thursday, August 17, 2017, 11:00 am — Conference Room Bldg 815E
Biomass burning (BB) is one of the most important contributors to atmospheric aerosols on a global scale and the environmental impacts of BB aerosols are strongly correlated with their chemical, optical, and microphysical properties. In this study, we investigated the properties and atmospheric aging of BB aerosols from wildfires in the Western US from the Mt. Bachelor Observatory (MBO; ~ 2700 m a.s.l.) in Central Oregon, as part of the DOE Biomass Burning Observation Project (BBOP) campaign in summer 2013. Plumes transported from forest fires in N California and SW Oregon were frequently observed. Organic aerosol (OA) dominated aerosol composition in BB plumes and three types of BBOA was identified: a less oxidized (O/C = 0.35), semivolatile BBOA-1 (~ 20% of OA mass) and two more oxidized BBOAs (BBOA-2 and BBOA-3). BBOA-1 was enriched of levoglucosan and was chemically similar to POA in fresh BB emissions. BBOA-3 was highly oxidized (O/C = 1.06; 31% of OA mass), contained no levoglucosan, showed very low volatility with only ~ 40% mass loss at 200°C, and had a similar mass spectrum as low-volatility oxygenated OA (LV-OOA) commonly observed in regional airmass. This finding highlights the possibility that the influence of BB emission could be significantly underestimated in regional air masses where highly oxidized BBOA (e.g., BBOA-3) might be a significant aerosol component. Increasing oxidation of BBOA was observed in more aged BB plumes but the enhancement ratios of BBOA relative to CO were nearly constant independent of plume aging. The chemical evolution of BBOA was examined for a BB plume event where fire plumes originated from a single fire source were sampled continuously for 36 hours. The average oxidation state of BBOA and the mass fraction of aged BBOA (= BBOA-2 + BBOA-3) in fire smoke increased with the increase of cumulative solar irradiance during transport, but the OA/CO ratios remained constant in the plumes. A possible explanation is that SOA f
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