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