AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Aerosol Chemistry and Processing at Mt. Bachelor Summit: Influences from Wildfire Plumes
SHAN ZHOU, Sonya Collier, Jon Hee, Nicole Wigder, Dan Jaffe, Lawrence Kleinman, Arthur J. Sedlacek, Qi Zhang, University of California, Davis
Abstract Number: 417 Working Group: Biomass Burning Aerosol: From Emissions to Impacts
Abstract In the summer of 2013, an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) was deployed continuously for 4 weeks at the Mt. Bachelor Observatory (MBO), located at the summit of Mt. Bachelor in Oregon (43.9794° N, 121.6885° W, 2,763 m a.s.l), to study the chemical characteristics and atmospheric processing of biomass burning (BB) aerosols, as part of the US Department of Energy (DOE) sponsored Biomass Burning Observation Project (BBOP). Our surface measurements were compared to simultaneous aircraft measurements. Observations at MBO indicated a dynamic variation in the chemical composition and physical properties of aerosols. Periods of low particulate matter (PM) loading (average = 2.9 micro-gram/m$^3) showed highly oxidized organic aerosol (OA) with oxygen-to-carbon atomic ratios (O/C) reaching above 1, as well as containing an ammonium sulfate fraction of up to 50% of submicron aerosol mass. Contrasting periods of higher PM loading (up to 120 micro-gram/m$^3) with markedly different characteristics have been frequently observed due to effects from injection of wildfire plumes into air masses transported to MBO. OA (> 90%) dominated aerosol composition during these BB periods, with elevated aerosol light scattering, elemental carbon, and gas-phase CO. OA from these plumes also showed an enhancement of the AMS BB tracer ion (C$_2H$_4O$_2$^+) at m/z = 60 and with O/C ratios ranging from 0.3 – 0.6. BB plumes showed variable Modified Combustion Efficiency (MCE) where the enhancement of aerosol light scattering and OA relative to CO$_2 decreased with increasing MCE. An increase of PM enhancement relative to CO 1-2 days downwind of fire sources at MBO compared to observations near the source indicates secondary organic aerosol (SOA) formation. These analyses shed light on the overall impact of wildfires on regional air quality in the Pacific Northwest of the USA. Future analysis comparing ground site and aircraft measurements will be performed to investigate the importance of BB emissions as SOA precursors.