Chemistry and processing of aerosols at Mt. Bachelor during BBOP: influences from regional transport and wildfire plumes

 

Authors

Shan Zhou — University of California, Davis
Sonya Collier — University of California
Jonathan Hee — University of Washington, Seattle
Nicole Briggs — Gradient Corp
Daniel Jaffe — University of Washington
Larry Kleinman — Brookhaven National Laboratory
Arthur J Sedlacek — Brookhaven National Laboratory
Qi Zhang — University of California, Davis

Category

Absorbing Aerosol

Description

An Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) was deployed at the Mt. Bachelor Observatory (MBO), which is located at the summit of Mt. Bachelor in Oregon (43.9794° N, 121.6885° W, 2,763 m asl), to study the chemical characteristics and atmospheric processing of biomass burning (BB) aerosols, as part of the DOE sponsored Biomass Burning Observation Project (BBOP). MBO, which has been used for 10 years to study wildfire impacts on CO, O3, and other pollutants in the free troposphere, is an ideal location for studying remote and high elevation aerosol as well as the evolution of trace species in air coming from the boundary layer during daytime. Our surface measurements are also complimentary to simultaneous aircraft BB plume measurements. Our observations indicate a dynamic variation in the chemical composition and physical properties of aerosols with repeatable diurnal patterns. Periods of low particulate matter (PM) loading show distinctly 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 loading and markedly different characteristics have been observed due to effects from injection of wildfire plumes into air masses transported to MBO. Observations during the affected periods show elevated OA loading of up to 60 µg/m3 and an overall organic mass fraction of 90% while correlating with elevated aerosol light scattering and gas-phase CO concentration. OA from these events have shown an enhancement in the BB characteristic ion (C2H4O2+) at m/z = 60 and with O/C ratios ranging from 0.4-0.6, suggesting these BB aerosols are intermediately oxidized. Inorganic nitrates and amines also appear to be important components of these detected BB events. More detailed analyses, such as back trajectory analysis and factor analysis of the HR-ToF-AMS spectra, will be performed to unravel the significance of these sampled events and how the transport affects fresh BB plumes. These analyses may also shed light on the importance of BB emissions as precursors to secondary organic aerosol and their overall effect on regional air quality in the Pacific Northwest.

Lead PI

Qi Zhang — University of California, Davis