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23.
Size-Resolved Chemical Composition of Biomass Burning Aerosols
in the Brazilian Amazon: Carbonaceous Aerosols and Water-Soluble
Ions
Dianna
L. Ortiz(1), L. L. Soto-García(1), O.
L. Mayol-Bracero(1), S. González(1),
M. O. Andreae(2), T. W. Andreae(2), P. Artaxo(3),
W. Elbert(2), W. Maenhaut(4), I. Trebs(2)
(1)
Institute for Tropical Ecosystem Studies and Department of Chemistry,
University of Puerto Rico, San Juan, PR
(2) Department of Biogeochemistry, Max Planck Institute for Chemistry,
Mainz, Germany
(3) Institute for Physics, University of São Paulo, São
Paulo, Brazil
(4) Institute for Nuclear Sciences, Ghent University,
Ghent, Belgium
Atmospheric particles emitted in biomass burning
increase the number of cloud condensation nuclei reducing the
cloud droplet size and, therefore, modifying rainfall location
and intensity. To have a better understanding of these processes,
information is needed on the chemical and physical properties
of these aerosols. As part of the project Smoke Aerosols, Clouds,
Rainfall and Climate: Aerosols from Biomass Burning Perturb Global
and Regional Climate (LBA-SMOCC), size-resolved chemical characterization
was performed on aerosol samples collected in a pasture site in
the Brazilian Amazon during the period that includes the burning
season and the beginning of the wet season (September-November
2002). A Dekati low-pressure impactor with 13 stages was used
to collect particles with diameters in the range of 0.03 to 10
?m. The mass collected on the substrates was determined by gravimetric
analyses. Evolved gas analyses were performed to determine the
mass concentrations of the carbonaceous aerosol (total carbon
(TC), elemental carbon (EC) and organic carbon (OC)). Ion chromatography
was used for the determination of the mass concentrations of water-soluble
ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3-, SO42-). Online measurements
of total aerosol particle number and aerosol light scattering
coefficients were also performed. Results show that aerosol TC
comprised more than 85% of the total aerosol mass during the three
sampling periods (dry, transition, wet). Particle number and mass
concentrations during the dry season were higher during nighttime
(daytime vs nighttime: 6800 N cm-3 vs 11600 N cm-3 and 25 mg m-3
vs 120 mg m-3) mainly due to the decrease in the height of the
boundary layer. The fine fraction (mainly pyrogenic aerosols,
TC, SO42- > NO3- > NH4+ > K+) was higher during the dry
season (fine: 67.4 mg m-3; coarse: 5.0 mg m-3). The coarse fraction
(mainly biogenic and dust particles, NO3- > Na+ > SO42-
> NH4+) started to increase as we approached the wet season
(less fires, more rain). A mass scattering efficiency of ~4.8
m2 g-1 was observed for the fine aerosol during the dry/transition
period.
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