10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Trends in Organic Aerosol Mass and Functional Group Composition in the SouthEastern Aerosol Research and Characterization (SEARCH) Network from 2008 to 2016
ANN DILLNER, Alexandra Boris, Andrew Weakley, Bruno Debus, Eric Edgerton, Stephanie L. Shaw, Satoshi Takahama, University of California, Davis
Abstract Number: 1553 Working Group: Carbonaceous Aerosol
Abstract Organic aerosol (OA) concentrations are on the decline in the Southeastern US. This presentation covers trends in OA and its composition as described by organic functional groups at five sites in the Southeastern Aerosol Research and Characterization (SEARCH) Network over a recent 9-year period. Functional groups are estimated in particulate matter (PM) filter samples using a Fourier transform infrared spectroscopy (FT-IR) technique. The vast filter archive of SEARCH samples, stored cold since 2008, enables the application of FT-IR to nearly a decade of aerosol samples at two urban-rural paired sites and a coastal site. OA contains thousands of molecules, but typically only ~5-30% of OA mass is identified in atmospheric PM composition studies. However, in this work FT-IR functional group measurements enable the quantification of nearly all OA sample mass. In addition to describing trends in OA composition, we will estimate the ratio of organic matter to organic carbon concentration (OM/OC) in each analyzed sample to provide a metric for aerosol oxidation and to provide a tool for converting routinely measured OC concentrations to OM.
The contribution of carbonyl, carboxylic acid OH, aliphatic CH, and alcohol OH to OA mass are measured at two urban/rural pairs (i.e. Atlanta and Yorkville, GA; Birmingham and Centreville, AL) and a coastal site in Florida from 2008 to 2016. To measure functional groups, laboratory standards are made by aerosolizing compounds containing each functional group and collecting them on PTFE filters using a SEARCH sampler. The laboratory standards are analyzed by FT-IR, and the resulting infrared spectra are used to develop partial least squares calibration models. The calibration models used in this study expand upon previous work to include a broader, more atmospherically relevant selection of chemicals. This includes chemicals representing oxidation products such as multifunctional carboxylic acids and a tetrol, carboxylate salts demonstrating interaction between inorganic and organic species, levoglucosan to represent biomass burning emissions, and an amino acid to represent the contribution of reduced organic nitrogen species. This work better quantifies carbonyls in particular, as compared to prior work. This work also demonstrates the spatial and seasonal variability and trends in functional groups and OM/OC within the diverse and abundant OA collected in the SEARCH network.