Origins and Composition of Fine Atmospheric Carbonaceous Aerosol in the Sierra Nevada Mountains, California
Abstract
We present hourly in-situ measurements of organic speciation of fine atmospheric aerosol (PM2.5) collected above a ponderosa pine plantation in the Sierra Nevada Mountains, California. The measurements were obtained using thermal desorption aerosol GC-MS (TAG) as part of the Biosphere Effects on AeRosols and Photochemistry EXperiment (BEARPEX) in late summer 2007. The early part of the campaign was characterized by hot and dry conditions and frequent influence from forest fire events. The later part was generally cooler and more humid with sporadic precipitation, which lead to significant increases in biogenic emissions. The hourly time resolution of TAG provides far greater information on diurnal variations than more traditional filter samples. We observe higher concentrations of anthropogenic marker compounds (e.g., phthalic and benzoic acids) in the early afternoon with the arrival of the pollution plume from Sacramento. Higher concentrations of biogenic oxidation marker compounds (e.g., pinonaldehyde and nopinone) are observed at night, suggesting local oxidation of primary biogenic emissions in the shallow nocturnal boundary layer. Observations via electrospray ionization high-resolution time-of-flight mass spectrometry (ESI-HR-TOFMS) of several nitrooxy-organosulfate products from terpene oxidation provides evidence for nighttime oxidation by nitrate radicals within the forest canopy. Radiocarbon (carbon-14) analysis at the site shows that >70% of the carbon present in the PM2.5 aerosol is modern indicating the importance of biogenic sources on aerosol composition at this site. We use the TAG data in conjunction with gas phase volatile organic carbon (VOC) and aerosol mass spectrometer (AMS) measurements to assign and investigate the relative contributions of different source categories (e.g., biomass burning, primary biogenic emissions, secondary biogenic oxidation, etc.) to the total observed organic aerosol mass during the BEARPEX campaign.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.A22B..04W
- Keywords:
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- 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0305 Aerosols and particles (0345;
- 4801;
- 4906);
- 0315 Biosphere/atmosphere interactions (0426;
- 1610);
- 0322 Constituent sources and sinks