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Chemical Speciation of Secondary Organic Aerosols

EPA Grant Number: FP916349
Title: Chemical Speciation of Secondary Organic Aerosols
Investigators: Surratt, Jason D.
Institution: California Institute of Technology
EPA Project Officer: Boddie, Georgette
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $111,688
RFA: STAR Graduate Fellowships (2004)
Research Category: Academic Fellowships , Fellowship - Atmospheric Sciences , Air Quality and Air Toxics

Description:

Objective:

The purpose of this research is to conduct a detailed investigation of the chemical speciation within secondary organic aerosol (SOA). The chemical species that exist in SOA are typically formed by homogeneous gas reactions of volatile organic compounds (VOCs) with atmospheric oxidants such as ozone (O3), nitrate radical (NO3), and hydroxy radical (OH). Polar products (such as dicarboxylic acids) that are produced from these reactions will partition from the gas phase to the aerosol phase as a result of their relatively low vapor pressures. Polar organic products are typically responsible for a major fraction of organic composition found within aerosol. More recently, it has been found that heterogeneous reactions occurring on the aerosol particles may also affect chemical speciation within SOA. These heterogeneous reactions have been found to produce polymeric products, possibly via acid-catalyzed reactions. The mechanism and detailed product information of polymerization within SOA still remains under debate throughout the atmospheric chemistry community. The specific objectives of this research are to: (1) describe the chemical speciation of different SOA systems formed by common anthropogenic and biogenic precursor hydrocarbons (i.e., mainly from aromatics and alkenes); (2) use chemical speciation information to provide detailed reaction mechanisms responsible for products found; and (3) try to connect the whole spectrum of products formed via homogeneous and heterogeneous reactions because of the importance of polymerization within SOA. The overall goal of this research is to understand the mechanisms in which SOA forms in the atmosphere.

Approach:

SOA will be generated in the California Institute of Technology indoor smog chamber and will be collected on Teflon filters (PALL Life Sciences, 47 mm diameter, 1.0 μm pore size). SOA will be generated under varying ambient atmospheric conditions: (1) light versus dark; (2) humid versus dry; (3) acidic versus nonacidic; and (4) the use of different seed aerosol. Conditions within the chamber will be varied to study the different products formed and elucidate different possible reaction mechanisms. Chemical speciation of low molecular weight (MW < 250 m/z) products will be conducted with liquid chromatography–mass spectroscopy (HPLC-MS) using the electrospray ionization (ESI) mode. Chemical speciation of large molecular weight species (MW > 250 m/z) will be analyzed with ion trap mass spectroscopy (ITMS). Filter samples collected from smog chamber experiments will be prepped for HPLC-MS and ITMS analysis by extraction in 5 ml of HPLC-grade methanol followed by sonication. The extracted solution will be dried with a stream of N2 gas. The left over sample then will be reconstituted with 0.1 percent acetic acid in water solution with 50 percent methanol and subsequently run through the HPLC-MS and ITMS for analysis. A Nova-Pak C18 column (300 × 3.9 mm, Waters) will be used for the HPLC-MS runs.

Supplemental Keywords:

fellowship, chemical speciation, secondary organic aerosol, volatile organic compounds, VOCs, aerosol formation, atmosphere, atmospheric oxidants, ozone, nitrate radical, hydroxy radical, dicarboxylic acids, atmospheric chemistry , POLLUTANTS/TOXICS, Air, Scientific Discipline, PHYSICAL ASPECTS, Engineering, Chemistry, & Physics, State of Matter, Chemicals, Environmental Chemistry, Ecology and Ecosystems, aerosol, Volatile Organic Compounds (VOCs), chemical detection techniques, chemical composition, ozone, aerosol particles, atmospheric aerosols, hydroxyl radical, secondary organic aerosol
Relevant Websites:

2004 STAR Graduate Fellowship Conference Poster (PDF, 1p., 274KB, about PDF)

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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