We present measurements of a large suite of gas and particle phase carboxylic acid containing compounds made with a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to a high resolution time of flight chemical ionization mass spectrometer (HR-ToF-CIMS) developed at the University of Washington. The instrument was deployed on environmental simulation chambers, at the SMEAR II boreal forest station in Hyyti�l�, Finland, and at the Centreville, AL site during the Southern Oxidant and Aerosol Study. In all locations, hundreds of organic acid compounds were observed in the gas and particle phases. Particulate organics detected by FIGAERO are highly correlated with and explain at least 25 � 50% of the organic aerosol mass measured by an AMS. The detailed structure in the thermograms reveals a significant contribution (~50%) from large molecular weight organics and/or oligomers that either thermally desorb directly or thermally decompose into fragments which then desorb. These compounds, many containing acid functionalities, have effective vapour pressures 3 or more orders of magnitude lower than commonly measured monoterpene or isoprene oxidation products. This contribution to SOA time varies at the both field sites, and is shown to be dependent upon specific monoterpene oxidation pathways probed in the environmental chamber. Specifically, a significant fraction of these low volatility compounds have 16 to 20 carbons and 6 � 9 oxygens, and importantly, are observed in the gas-phase in both chamber and field studies. We present evidence that these are formed from RO2 radical cross reactions, and that they help to both reconcile the source of low volatility organic acids detected in the particle phase and the observed phase partitioning of smaller (C8 � C10) compounds. We discuss the implications of these findings for measurements of gas-particle partitioning and the sources of biogenic SOA.

Field and chamber measurements of low volatility gas-phase organic acids from monoterpene oxidation: Gas-phase organic peroxy radical chemistry and implications for SOA

248th National Meeting (2014)

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