Abundance and Group Reactivity of Intermediate Volatility Organic Compounds (IVOCs) in Urban Air Measured by TD-PTR-MS

Washington State University, Pullman WA

Investigators

Abstract

The primary objective of this proposal is to develop a method to quantify the abundance of intermediate volatility organic compounds (IVOCs) in urban air. These compounds contain 12 to 18 carbon atoms, are emitted in diesel engine exhaust, and are thought to be a significant source of reactive organic compounds that contribute to the formation of secondary organic aerosol (SOA). The abundance and atmospheric chemistry of IVOCs is very poorly understood. This proposal will establish a novel method for quantifying IVOCs in air by using thermal desorption sampling coupled to proton transfer reaction mass spectrometry (TD-PTR-MS). With this approach the total abundance of IVOC alkanes will be measured. The approach will allow a more comprehensive quantification of the IVOC carbon pool by lumping IVOC species into functional groups (i.e., alkanes, cyclic alkanes) or by their molecular weight (i.e. monocyclic aromatics, naphthalenes). The method will be used in a four week field sampling campaign to compare IVOC abundance to volatile organic compound (VOC) abundance measured by PTR-MS and gas chromatography mass spectrometry (GC-MS) to test the proposition that IVOC photooxidation is a major source of urban SOA. Laboratory experiments using a photoreaction reaction chamber will be used to photochemically age diesel fuel and diesel engine exhaust to establish IVOC group reactivity with hydroxyl radical. These experiments will aid the interpretation of field data and enhance the currently sparse knowledge of IVOC lifetimes required for chemical transport modeling. Establishing a measurement method to quantity the abundance of IVOCs in air addresses a critical gap in knowledge of urban air photochemistry and SOA formation. The research will support and train two graduate students and one undergraduate student in analysis and interpretation of organic trace gas. Results and instrumentation used will be incorporated into undergraduate classes and a senior level air quality laboratory class. Research results will be disseminated through conferences and peer reviewed journals. The results will enhance our understanding of the nature and origin of organic compounds in the atmosphere. The public benefit will be a more quantitative understanding of the levels and impacts of diesel engine exhaust in urban air.