1. Identification of Secondary Organic Aerosol Compounds in Ambient PM 2.5 Samples Edward O. Edney and Tadeusz E. Kleindienst National Exposure Research Laboratory PM Model Performance Workshop Chapel Hill, North Carolina February 10, 2004

2. Secondary Organic Aerosol Reactions of aromatic and biogenic HCs with OH, O 3 and NO 3 produce SOA compounds that partition into PM 2.5 Available ambient data suggest SOA is a significant contributor to PM 2.5, especially in the southeastern US during the summer

3. Modeling Issues Temperature dependencies of SOA models are not fully characterized Questions remain surrounding extrapolation of current two-product SOA model results to complex mixtures of HCs The more explicit SOA models have yet to be evaluated Polymerization reactions, possibly acid catalyzed, in evaporating cloud water and aerosols may contribute to SOA formation SOA Measurements Contribution of SOA to PM 2.5 is based on OC/EC or source-receptor methods Relative contributions of anthropogenic and biogenic HCs to SOA are based on a combined C14 and source-receptor method

4. NERL PM Chemistry Program Conduct HC/NO x smog chamber irradiations to generate SOA from aromatic and biogenic HCs Identify possible SOA tracer compounds using derivative based GC-MS methods Conduct short-term field studies to collect ambient PM 2.5 Research Triangle Park (2000s,2001s,2003s&w) Baltimore, Philadelphia, New York City (2001s) Analyze the field samples using the same derivative based GC-MS methods

5. Derivative Based GC-MS Methods React solvent extracted PM 2.5 samples with derivatizing agents to form compounds are transferred through GC columns. Derivatization aids the identification of compounds by MS. Derivatization aids the identification of compounds by MS. Single Derivatizations Single Derivatizations PFBHA – non-acidic carbonyl groups BSTFA – OH groups CH 3 OH/BF 3 – OH groups in carboxylic acids Multiple Derivatizations Multiple DerivatizationsPFBHA/BSTFA BF 3 /PFBHA BF 3 /PFBHA/BSTFA

15. Conclusions Tracer compounds for toluene and α-pinene SOA have been identified and observed in ambient samples Based on chamber calibrations, relative contributions of α-pinene and toluene SOA have been estimated for summer samples collected in RTP, Baltimore and Philadelphia Efforts are underway to improve estimates of mass fractions of SOA tracers compounds The complexity of SOA formation is such that it is unlikely the use of tracer compounds will produce the level of results obtained for primary PM 2.5 emissions Preliminary analysis of 2003 winter RTP data shows low levels of SOA tracer compounds

16. Disclaimer Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy