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BIOGENIC CONTRIBUTION TO PM-2.5 AMBIENT AEROSOL FROM RADIOCARBON MEASUREMENTS
Citation:
Lewis, C W., G. A. Klouda, AND W. D. Ellenson. BIOGENIC CONTRIBUTION TO PM-2.5 AMBIENT AEROSOL FROM RADIOCARBON MEASUREMENTS. Presented at European/American Geophysical Union Joint Assembly, Nice, France, April 6-11, 2003.
Impact/Purpose:
The analysis of ambient air samples by X-ray fluorescence is a critical component in the interpretation of complex air quality studies. The data products generated by the XRF laboratory are therefore critical to protecting human health and the environment. Analysis of particulate matter by XRF contributes to the following outcomes:
1) By characterizing emissions from different source types EPA is able to ensure timely attainment of the national ambient air quality regulations (NAAQS).
2) These analyses assist in the development of models for predicting pollutant concentrations from source emissions, apportioning sources from air concentration data, and for predicting exposures from different source types. The goal of the aforementioned models is to accurately understand risk and the ways to reduce risks to human health and the environment.
3) Datasets generated by the X-ray fluorescence laboratory cross-cut several laboratories (NERL, NHEERL, NRMRL, etc.) and represent an important collaboration effort. The XRF laboratory products are therefore crucial in the integration of varied, and sometimes wide ranging, agency goals. It is these cross-cutting relationships that enable ORD to collectively assess pollutants which pose the greatest risk to global, regional, state and local populations.
Description:
Knowledge of the relative contributions of biogenic versus anthropogenic sources to ambient aerosol is of great interest in the formulation of strategies to achieve nationally mandated air quality standards. Radiocarbon (Carbon-14) measurements provide a means to quantify the biogenic fraction of any carbon-containing sample of ambient aerosol. In the absence of an impact from biomass burning (e.g., during summertime) such measurements can provide an estimate of the contribution of biogenic secondary organic aerosol, from biogenic volatile organic compound precursors. Radiocarbon results for 11.5-h PM-2.5 samples collected near Nashville, Tennessee, USA, during summer 1999 will be presented. On average the measured biogenic fraction was surprisingly large (more than half), with the average biogenic fraction for night samples being only slightly smaller than for day samples. Discussion will include (a) description of the radiocarbon methodology, (b) use of radiocarbon measurements on local vegetation and fuel samples as calibration data, (c) concurrent measurements of organic carbon and elemental carbon ambient concentrations, (d) assessment of organic aerosol sampling artifact through use of organic vapor denuders, variable face velocities, and filter extraction, and (e) comparison with published radiocarbon results obtained in Houston, Texas in a similar study.
This work has been funded wholly or in part by the United States Environmental Protection Agency under Interagency Agreement No. 13937923 to the National Institute of Standards and Technology, and Contract No. 68-D5-0049 to ManTech Environmental Technology, Inc. It has been subjected to Agency review and approved for publication.