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Chemical Signatures of Fire and Urban Influenced Secondary Aerosol Formation in the Central Amazon
EMILY FRANKLIN, Lindsay Yee, Rebecca Wernis, Gabriel Isaacman-VanWertz, Nathan Kreisberg, Robert Weber, Brett Palm, Weiwei Hu, Pedro Campuzano-Jost, Douglas Day, Paulo Artaxo, Rodrigo Souza, Jose-Luis Jimenez, Scot T. Martin, Allen Goldstein, University of California, Berkeley
Abstract Number: 141
Working Group: Remote and Regional Atmospheric Aerosol
Abstract
Biogenic secondary organic aerosol (SOA) plays a critical role in atmospheric chemistry and climate in the tropics, a region where increasing anthropogenic activities (urbanization and fires) perturb natural processes of oxidation chemistry. While SOA formation in the tropics has been observed and modeled to increase in the presence of anthropogenic pollutants, the mechanisms by which these enhancements occur and implications for particle chemistry remain unclear. During the Green Ocean Amazon (GoAmazon) field campaign of 2014/5, over 200 submicron aerosol samples were collected over periods spanning both the wet and dry seasons of 2014 at the “T3” Manacapuru rural site, located 70km downwind of urban Manaus. Utilizing TD-GCxGC-EI-HRToFMS (thermal desorption two-dimensional gas chromatography with electron ionization time-of-flight mass spectrometry), ~1500 unique organic compounds from these samples are separated, cataloged, and traced. Using dynamic time warping hierarchical clustering and time series correlation with established tracers of biomass burning and urban influence, the chemical signatures of anthropogenically influenced SOA formation are extracted from background measurements representing a range of natural conditions. These chemical signatures reveal that biomass burning activity accounts for ~50% of dry season organic signal and ~10% of wet season organic signal. Urban plume influence, consisting of both primary emissions from the city as well as products that are uniquely produced when biogenic precursors are exposed to anthropogenic oxidants, accounts for approximately one quarter of wet season organic signal and less than one fifth of dry season organic signal. Mass spectral comparisons to compounds in the NIST/EPA/NIH mass spectral database and those in samples collected from single precursor oxidation experiments conducted under a variety of oxidizing conditions reveal the presence of previously unpublished monoterpene oxidation products which are observed in the field exclusively under urban plume influenced conditions. These new tracers provide mechanistic insights into how human activity alters biogenic secondary aerosol formation.