HR: 13:40h
AN: B43D-01    [Abstracts]
TI: The NH$_{4}$$^{-}$-NO$_{3}$$^{-}$-Cl$^{-}$-SO$_{4}$$^{2-}$-H$_{2}$O Aerosol System and its Gas Phase Precursors at a Rural Site in the Amazon Basin: How Relevant are Mineral Cations and Soluble Organic Acids?
AU: Helas, G
EM: gth@mpch-mainz.mpg.de
AF: Max Planck Institute for Chemistry, J.J. v. Becherweg 28, Mainz, 55128 Germany
AU: * Trebs, I
EM: ivonne@mpch-mainz.mpg.de
AF: Max Planck Institute for Chemistry, J.J. v. Becherweg 28, Mainz, 55128 Germany
AU: Metzger, S
EM: metzger@mpch-mainz.mpg.de
AF: Max Planck Institute for Chemistry, J.J. v. Becherweg 28, Mainz, 55128 Germany
AU: Meixner, F X
EM: meixner@mpch-mainz.mpg.de
AF: Max Planck Institute for Chemistry, J.J. v. Becherweg 28, Mainz, 55128 Germany
AU: Hoffer, A
EM: ahoffer@mpch-mainz.mpg.de
AF: Max Planck Institute for Chemistry, J.J. v. Becherweg 28, Mainz, 55128 Germany
AU: Moura, M A
EM: malm@ccen.ufal.br
AF: Universidad Federal de Alagoas, CCEN-Depto. de Meteorologia, Campus A. C. Simoes BR 104 - km 14, Tabuleiro do Martins, Maceio, 57072-970 Brazil
AU: da Silva, R S
EM: rosibertojunior@bol.com.br
AF: Universidad Federal de Alagoas, CCEN-Depto. de Meteorologia, Campus A. C. Simoes BR 104 - km 14, Tabuleiro do Martins, Maceio, 57072-970 Brazil
AU: Rudich, Y
EM: Yinon.Rudich@weizmann.ac.il
AF: Weizmann Institute, Departement of Environmental Sciences, Rehovot, 76100 Israel
AU: Falkovich, A
EM: alla@wisemail.weizmann.ac.il
AF: Weizmann Institute, Departement of Environmental Sciences, Rehovot, 76100 Israel
AU: Artaxo, P
EM: artaxo@if.usp.br
AF: Universidade de Sao Paulo, Instituto de Fˇsica, Rua do Matao, Travessa R, 187, Sao Paulo, 05508-900 Brazil
AU: Slanina, J
EM: Sjaak@slanina.com
AF: University of Wageningen, Department of Environmental Sciences, Duivendaal 2, Wageningen, 6701 Netherlands
AU: Andreae, M O
EM: andreae@mpch-mainz.mpg.de
AF: Max Planck Institute for Chemistry, J.J. v. Becherweg 28, Mainz, 55128 Germany
AB: We performed real-time measurements of ammonia (NH$_{3}$), nitric acid (HNO$_{3}$), hydrochloric acid (HCl), sulfur dioxide (SO$_{2}$) and the water-soluble inorganic aerosol species, ammonium (NH$_{4}$$^{+}$), nitrate (NO$_{3}$$^{-}$), chloride (Cl$^{-}$), and sulfate (SO$_{4}$$^{2-}$) at a pasture site in the Amazon Basin (Rond“nia, Brazil). The measurements were made during the closing of the dry season (biomass burning), the transition period, and the onset of the wet season (clean conditions) (12 Sep. to 14 Nov. 2002, LBA-SMOCC*), using a wet-annular denuder (WAD) in combination with a Steam-Jet Aerosol Collector (SJAC). Real-time data were combined with measurements of mineral cations (K$^{+}$ , Ca$^{2+}$ , Mg$^{2+}$) and low-molecular weight (LMW) polar organic acids on 12-, 24- and 48-hours integrated filter samples. The contribution of inorganic species to the fine particulate mass (D$_{p}$ $<$ 2.5 um)was frequently below 20 % by mass, indicating the preponderance of organic matter. The high abundance of NH$_{3}$ at the sampling site substantially influenced gas/aerosol partitioning processes, being responsible for complete acid neutralization through the aerosol phase forming aerosol NH$_{4}$$^{+}$. Balances of aerosol fine mode inorganic ionic charges indicated the role of dissociated low-molecular weight (LMW) polar organic acids, which were apparently neutralized by excess NH$_{3}$. The measured concentration products of NH$_{3}$ x HNO$_{3}$ and NH$_{3}$ x HCl persistently remained below the theoretical equilibrium dissociation constants of the NH$_{3}$/HNO$_{3}$/NH$_{4}$NO$_{3}$ and NH$_{3}$/HCl/NH$_{4}$Cl systems during daytime (RH $<$ 90 %). The application of thermodynamic equilibrium models (EQMs), namely EQSAM, ISORROPIA, GEFMN and SCAPE2 indicated that balancing of aerosol NO$_{3}$$^{-}$, Cl$^{-}$ and SO$_{4}$$^{2-}$ preferentially proceeded via mineral cations (particularly pyrogenic K$^{+}$) during daytime. At nighttime (RH $>$ 90 %) NH$_{4}$NO$_{3}$ and NH$_{4}$Cl were predicted to be formed in the aqueous aerosol phase. Cl$^{-}$ was largely driven out of the aerosol phase by reaction of KCl with HNO$_{3}$ and H$_{2}$SO$_{4}$. As shown by an updated version of EQSAM, which incorporates mineral aerosol species and lumped LMW polar organic acids, daytime aerosol NH$_{4}$$^{+}$ was mainly balanced by organic compounds. *Large Scale Biosphere Atmosphere Experiment in Amazonia Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate).
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0365 Troposphere--composition and chemistry
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting