Abstract:
As part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment (CLAIRE) 2001 campaign, separate day and nighttime aerosol samples were collected in July 2001 at a ground-based site in Amazonia, Brazil, in order to examine the composition and temporal variability of the natural "background'' aerosol. A combination of analytical techniques was used to characterize the elemental and ionic composition of the aerosol. Major particle types larger than similar to0.5 mm were identified by electron and light microscopy. Both the coarse and fine aerosol were found to consist primarily of organic matter (similar to70 and 80% by mass, respectively), with the coarse fraction containing small amounts of soil dust and sea-salt particles and the fine fraction containing some non-sea-salt sulfate. Coarse particulate mass concentrations (CPM approximate to PM10 - PM2) were found to be highest at night (average = 3.9 +/- 1.4 mg m(-3), mean night-to-day ratio = 1.9 +/- 0.4), while fine particulate mass concentrations (FPM approximate to PM2) increased during the daytime (average = 2.6 +/- 0.8 mg m(-3), mean night-to-day ratio = 0.7 +/- 0.1). The nocturnal increase in CPM coincided with an increase in primary biological particles in this size range (predominantly yeasts and other fungal spores), resulting from the trapping of surface-derived forest aerosol under a shallow nocturnal boundary layer and a lake-land breeze effect at the site, although active nocturnal sporulation may have also contributed. Associated with this, we observed elevated nighttime concentrations of biogenic elements and ions (P, S, K, Cu, Zn, NH4+) in the CPM fraction. For the FPM fraction a persistently higher daytime concentration of organic carbon was found, which indicates that photochemical production of secondary organic aerosol from biogenic volatile organic compounds may have made a significant contribution to the fine aerosol. Dust and sea-salt-associated elements/ions in the CPM fraction, and non-sea-salt sulfate in the FPM fraction, showed higher daytime concentrations, most likely due to enhanced convective downward mixing of long-range transported aerosol.

Author Keywords:
biogenic aerosol, spores, elemental composition, Amazon, bioaerosol, organic aerosol

KeyWords Plus:
LONG-RANGE TRANSPORT, ATMOSPHERIC AEROSOLS, WET SEASON, RAIN-FOREST, PARTICULATE MATTER, SIZE DISTRIBUTION, SAHARAN DUST, SOOT CARBON, DRY SEASON, PARTICLES

Addresses:
Graham B, Commonwealth Sci & Ind Res Org, Atmospher Res, Aspendale, Vic, Australia
Max Planck Inst Chem, Dept Biogeochem, D-55020 Mainz, Germany
State Univ Ghent, Inst Sci Nucl, B-9000 Ghent, Belgium
CALTECH, Div Chem & Chem Engn, Pasadena, CA 91125 USA
Tech Univ Darmstadt, Inst Mineral, D-64287 Darmstadt, Germany
Univ Fed Alagoas, Dept Meteorol, Ctr Ciencia Exatas & Nat, BR-57072970 Maceio, Alagoas, Brazil
Univ Mainz, Inst Phys Atmospher, D-55122 Mainz, Germany
Univ Antwerp, Micro & Trace Anal Ctr, B-2610 Wilrijk, Belgium
Huntington Med Res Inst, Ctr Asthma & Allergy, Pasadena, CA 91105 USA
Univ Sao Paulo, Inst Phys, BR-05315970 Sao Paulo, Brazil

Publisher:
AMER GEOPHYSICAL UNION, 2000 FLORIDA AVE NW, WASHINGTON, DC 20009 USA

IDS Number:
760WN

ISSN:
0148-0227