Aerosol and precipitation chemistry in a remote site in Central Amazonia: the role of biogenic contribution

A long-term (2–3 years) measurement of aerosol and precipitation chemistry was carried out in a remote site in Central Amazonia, Balbina, (1 • 55 ′ S, 59 • 29 ′ W, 174 m above sea level), about 200 km north of Manaus city. Aerosols were sampled using stacked filter units (SFU), which separate fine (d<2.5 µm) and coarse mode 5 (2.5 µm<d<10.0 µm). Filters were analyzed for particulate mass (PM), black carbon (BC) and elemental composition by Particle Induced X-Ray Emission (PIXE). Rain-water samples were collected using a wet-only sampler and samples were analyzed for pH and ionic composition, which was determined using ionic chromatography (IC). Aerosol mass was predominantly of biogenic origin and concentrated in coarse mode, 10 comprising up to 81% of PM 10 concentration during the wet season. Natural biogenic aerosol also dominates the fine mode in the wet season, with very low concentrations (average 2.2 µg/m 3). Large-scale transport of smoke from biomass burning was the second most important contribution, reaching 77% of fine mode particulate mass during the dry season. Soil dust was responsible by a minor fraction of the aerosol mass 15 (less than 17%). Rainwater chemistry was controlled by biogenic emissions. The volume-weighted mean (VWM) pH was 4.90. The most important contribution to acidity was weak organic acids. The organic acidity was predominantly associated with the presence of acetic acid, instead of formic acid which is more often observed in pristine tropical areas. Deposition rates for major species did not differ significantly between dry 20 and wet season, except for NH + 4 and acetate, which had smaller deposition rates during dry season. While biomass burning emissions were clearly identified in the aerosol component, it was not possible to discern any presence of biomass burning emissions in rainwater chemistry. The long-range transport of sea salt and biogenic particles was observed both in aerosols and rainwater composition. The results showed here 25 indicate that in Amazonia it is still possible to observe pristine atmospheric conditions, relatively free of anthropogenic influences. Aerosol and precipitation chemistry in Central Amazonia T. Pauliquevis et al.