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Soa Formation from the Irradiation of a-Pinene-NOx in the Absence and Presence of Sulfur Dioxide

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Abstract: Sulfur dioxide (SO2) is an important constituent in the polluted atmosphere. It is emitted from combustion sources using fuels that contain sulfur. Emissions of SO2 in the United States were reportedly 17 Tg in 1996 with most coming from coal and petroleum combustion. The primary removal mechanism of SO2 in the atmosphere is through reaction with the hydroxyl radical to produce sulfuric acid which will typically condense onto preexisting aerosol to form an acidic aerosol. Recent reports have suggested that prior to neutralization, these aerosols could lead to enhanced secondary organic aerosol (SOA) formation through in-situ heterogeneous reactions.

In the present study, this hypothesis was tested by producing SOA through irradiating mixtures of a-pinene/NOx in a smog chamber. The chamber was operating in a dynamic mode to allow an adequate collection of aerosol mass at reasonably moderate concentrations. Chamber conditions of 2 ppmC a-pinene, 0.25 ppm NOx, and a chamber residence time of 6 hours were set to ensure that extensive secondary gas-phase chemistry occurred. Under these conditions, nucleation of the oxidized mixture occurred producing particles for measurement. SOA yields were determined from mass measurement of the collected SOA onto Zefluor filters. These measurements used carbon-based and extractable XAD denuders to minimize filter artifacts. Organic carbon mass of the aerosol was determined using quartz filters which were corrected for the positive artifact by using a backup quartz filter. Organic aerosol collected on Zefluor filters were extracted for analysis of individual compounds using GC-MS.

Conditions in the chamber were maintained to allow the conversion of a-pinene (0.949) to remain identical for both parts of the experiment. From the Zefluor filter collections in the absence of SO2, the SOA yield was found to be 15.9%. Under the photochemical conditions in the chamber, the conversion of SO2 due to reaction with hydroxyl radicals was 4.4%, which resulted in a sulfate concentration of 45 ug m-3 associated with the predominately organic aerosol. In the presence of SO2, the SOA yield increased to 26.1%. Similarly, the yield of organic carbon was found to increase by 32% in the presence of SO2. GC-MS analysis of the aerosol showed differences in the composition of the organic aerosol under the two conditions.

This work has been funded fully, or in part, by the United States Environmental Protection Agency, under Contract Number 68-D5-0049 to ManTech Environmental Technology, Inc. It has been subjected to Agency review and approved for publication.
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Citation:Kleindienst, T. E., M. Lewandowski, E. O. Edney, M. Jaoui, and E. W. Corse. Soa Formation from the Irradiation of a-Pinene-NOx in the Absence and Presence of Sulfur Dioxide. Presented at American Association for Aerosol Research National Meeting, Anaheim, CA, October 20-24, 2003.
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Contact: Liz Hope - (919) 541-2785 or hope.elizabeth@epa.gov
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Division: Human Exposure & Atmospheric Sciences Division
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Branch: Program Operations Staff
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Product Type: Abstrct/Oral
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Presented: 10/22/2003
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Bullet Item Science Version of PM Chemistry Model
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Last Updated on Monday, October 22, 2007
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