Identification of Secondary Organic Identification of Secondary Organic Aerosol Compounds in Ambient PMAerosol Compounds in Ambient PM2.52.5

SamplesSamples

Edward O. Edney and Tadeusz E. KleindienstEdward O. Edney and Tadeusz E. KleindienstNational Exposure Research LaboratoryNational Exposure Research Laboratory

PM Model Performance WorkshopPM Model Performance WorkshopChapel Hill, North CarolinaChapel Hill, North Carolina

February 10, 2004February 10, 2004

Secondary Organic AerosolSecondary Organic Aerosol

Reactions of aromatic and biogenic HCs with Reactions of aromatic and biogenic HCs with OH, OOH, O33 and NO and NO33 produce SOA compounds that produce SOA compounds that partition into PMpartition into PM2.52.5

Available ambient data suggest SOA is a Available ambient data suggest SOA is a significant contributor to PMsignificant contributor to PM2.52.5, especially in the , especially in the southeastern US during the summer southeastern US during the summer

Modeling IssuesModeling Issues

Temperature dependencies of SOA models are not fully characterizedTemperature dependencies of SOA models are not fully characterized

Questions remain surrounding extrapolation of current two-product SOA Questions remain surrounding extrapolation of current two-product SOA model results to complex mixtures of HCsmodel results to complex mixtures of HCs

The more explicit SOA models have yet to be evaluatedThe more explicit SOA models have yet to be evaluated

Polymerization reactions, possibly acid catalyzed, in evaporating cloud Polymerization reactions, possibly acid catalyzed, in evaporating cloud water and aerosols may contribute to SOA formationwater and aerosols may contribute to SOA formation

SOA MeasurementsSOA Measurements

Contribution of SOA to PMContribution of SOA to PM2.52.5 is based on OC/EC or source-receptor is based on OC/EC or source-receptor methodsmethods

Relative contributions of anthropogenic and biogenic HCs to SOA are Relative contributions of anthropogenic and biogenic HCs to SOA are based on a combined C14 and source-receptor method based on a combined C14 and source-receptor method

NERL PM Chemistry ProgramNERL PM Chemistry Program

Conduct HC/NOConduct HC/NOxx smog chamber irradiations to generate smog chamber irradiations to generate SOA from aromatic and biogenic HCsSOA from aromatic and biogenic HCs

Identify possible SOA tracer compounds using derivative Identify possible SOA tracer compounds using derivative based GC-MS methodsbased GC-MS methods

Conduct short-term field studies to collect ambient PMConduct short-term field studies to collect ambient PM2.52.5

Research Triangle Park (2000s,2001s,2003s&w)Research Triangle Park (2000s,2001s,2003s&w)Baltimore, Philadelphia, New York City (2001s)Baltimore, Philadelphia, New York City (2001s)

Analyze the field samples using the same derivative based Analyze the field samples using the same derivative based

GC-MS methodsGC-MS methods

Derivative Based GC-MS MethodsDerivative Based GC-MS Methods

React solvent extracted PMReact solvent extracted PM2.52.5 samples with derivatizing samples with derivatizing agents to form compounds are transferred through GC agents to form compounds are transferred through GC columns.columns.

Derivatization aids the identification of compounds by Derivatization aids the identification of compounds by MS.MS. Single DerivatizationsSingle Derivatizations

PFBHA – non-acidic carbonyl groupsPFBHA – non-acidic carbonyl groupsBSTFA – OH groupsBSTFA – OH groupsCHCH33OH/BFOH/BF33 – OH groups in carboxylic acids – OH groups in carboxylic acids

Multiple DerivatizationsMultiple Derivatizations

PFBHA/BSTFAPFBHA/BSTFABFBF33/PFBHA/PFBHABFBF33/PFBHA/BSTFA/PFBHA/BSTFA

OHCH3

OHO

OH O

OHHO

OOO

ConclusionsConclusions

Tracer compounds for toluene and Tracer compounds for toluene and αα-pinene SOA have -pinene SOA have been identified and observed in ambient samplesbeen identified and observed in ambient samples

Based on chamber calibrations, relative contributions of Based on chamber calibrations, relative contributions of αα-pinene and toluene SOA have been estimated for-pinene and toluene SOA have been estimated forsummer samples collected in RTP, Baltimore and summer samples collected in RTP, Baltimore and PhiladelphiaPhiladelphia

Efforts are underway to improve estimates of mass Efforts are underway to improve estimates of mass fractions of SOA tracers compoundsfractions of SOA tracers compounds The complexity of SOA formation is such that it is unlikely The complexity of SOA formation is such that it is unlikely the use of tracer compounds will produce the level of the use of tracer compounds will produce the level of results obtained for primary PMresults obtained for primary PM2.52.5 emissions emissions

Preliminary analysis of 2003 winter RTP data shows low Preliminary analysis of 2003 winter RTP data shows low levels of SOA tracer compounds levels of SOA tracer compounds

DisclaimerDisclaimer

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