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Science Rendezvous > Posters
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A new approach to chemically-speciated aerosol fluxes over tropical and temperate forests.
D.K.Farmer (1), J.R. Kimmel (1,2), E. Nemitz (3), G. Phillips (3), K. Docherty (1), S. Martin (4), Q. Chen (4), M. Cubison91), J.-L. Jimenez (1,5)
(1) CIRES, (2)Aerodyne Research, Inc., (3) CEH, UK, (4) School of Engineering and Applied Sciences, Harvard University, (5) Chemistry, University of Colorado-Boulder
Aerosols play an important role in the planet’s radiation balance; however, their sources and sinks remain highly uncertain. In particular, due to instrumental limitations, there are few measurements of particle fluxes over the Earth’s surface. Particles are expected to deposit over forests, leading not only to an aerosol sink, but also to an ecosystem source of nutrients and acids. However, forests emit volatile organic compounds (VOCs) that are known to produce secondary organic aerosol, thus also acting as aerosol sources.
We have developed a new approach to measure biosphere-atmosphere exchange of chemically-speciated aerosol using a High Resolution-Time of Flight-Aerosol Mass Spectrometer (HR-ToF-AMS; DeCarlo et al., Anal. Chem., 2006) in a new Eddy Covariance Flux mode (at 10 Hz). This approach allows us to directly measure fluxes of non-refractory organic, sulphate, nitrate and ammonium in submicron particles.
Measurements have been carried out over two forests: a temperate ponderosa pine plantation at Blodgett Forest (BEARPEX-I campaign, 2007) and a tropical rain forest in the Brazilian Amazon during the wet season (AMAZE campaign, 2008). Data collected at these sites allows us to demonstrate that the flux mode of the HR-ToF-AMS meets the rigorous instrumental requirements of the eddy covariance approach and that fluxes of different chemical species can be quantified. Aerosol fluxes under clean and anthropogenically-impacted conditions are compared. These measurements allow us to better constrain dry deposition over forested environments and to understand the potential of flux measurements to constrain the biogenic SOA budget.
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