Mass Spectral Observations of Submicron Aerosol Particles and Production of Secondary Organic Aerosol at an Anthropogenically Influenced Site during the Wet Season of GoAmazon2014

Suzane S de Sá1, Brett B Palm2, Pedro Campuzano-Jost2, Doug A Day3, Weiwei Hu4, Matt K Newburn5, Joel Ferreira De Brito6, Paulo Artaxo6, John E Shilling7, Rodrigo Augusto Ferreira de Souza8, Antonio O Manzi9, M. Lizabeth L Alexander5, Jose L Jimenez10 and Scot T Martin11,12, (1)Harvard University, School of Engineering and Applied Sciences, Cambridge, MA, United States, (2)University of Colorado at Boulder, Boulder, United States, (3)University of Colorado at Boulder, Chemistry, Boulder, United States, (4)Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, (5)Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA, United States, (6)University of Sao Paulo, Sao Paulo, Brazil, (7)Pacific Northwest National Laboratory, Richland, WA, United States, (8)Universidade do Estado do Amazonas, Manaus, Brazil, (9)Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil, (10)Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, Boulder, United States, (11)Harvard University, Cambridge, MA, United States, (12)Harvard University, Earth and Planetary Sciences, Cambridge, MA, United States
Abstract:
As part of GoAmazon2014, a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed to characterize the composition, size, and spectral markers present in submicron atmospheric aerosol particles at a site downwind of Manaus, Brazil, in the central Amazon basin. The focus was on the influence of biogenic-anthropogenic interactions on the measured aerosol particles, especially as related to the formation of secondary organic aerosol (SOA). Through a combination of meteorology, emissions, and chemistry, the research site was affected by biogenic emissions from the tropical rainforest that were periodically mixed with urban outflow from the Manaus metropolitan area. Results from the first intensive operation period, from 1 February to 31 March 2014, show that for the wet season the PM1 mass concentration had typical values on order of 1 to 2 μg/m3. The organic species were dominant, followed by sulfate. The mass-diameter distribution of the particle population had a prevailing mode between 300 and 400 nm (vacuum aerodynamic diameter, dva), and at times a smaller mode at finer size was also present. Highly oxidized organic material was frequently observed, characterized by a dominant peak at m/z 44. There was a diel trend in the elemental oxygen-to-carbon (O:C) ratio peaking in the afternoon.

The analysis of the results aims at delineating the anthropogenic impact on the measurements. Multivariate statistical analysis by positive-matrix factorization (PMF) is applied to the time series of organic particle mass spectra. The factors and their loadings provide information on the relative and time-varying contributions of different sources and processes affecting the organic component of the aerosol particle phase. Relationships between AMS results and measurements from co-located instruments that provide information on anthropogenic and biogenic gas and particle tracers are investigated, toward the goal of improving the understanding of anthropogenic influences on the submicron atmospheric particle population.

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