Preliminary estimation of the rainfall chemical composition evaluated through the scavenging modeling for north-eastern Amazonian region (Amapá state, Brazil).

Numerical modeling of scavenging processes has been compared with data obtained for rainwater and aerosol chemistry at Serra do Navio, in the state of Amapá in the Brazilian Amazon region. Sulfate, nitrate and ammonium concentrations were determined in rainwater samples collected from May 1995 until June 1997. The levels of these same chemicals were also determined in aerosols for the same period and region. Scavenging processes have been evaluated on a rainfall event basis, via numerical modeling, in order to simulate the rainwater concentrations and compare them with the observed data. RAMS (Regional Atmospheric Modeling System) was used to simulate cloud structures. A model of below-cloud scavenging was evaluated, as well. The determinations made from the results of the scavenging model are the following: a) aerosol vertical profiles are quite important to rainwater concentrations; b) modeled sulfate in rainwater is a better fit to the observed data values than ammonium and nitrate; c) the obtained sulfate aerosol concentrations samples are similar to ones found in the literature, although the sulfate concentrations in rainwater are much lower than other studies in the literature; d) the in-cloud scavenging process dominates, e) our modeled results, using an input gas vertical profile extracted from the ABLE2B experimental data set, present a smaller ratio between gas and aerosol scavenging than found in other studies in the literature, other studies may have had larger rainfall times, which increase the importance of gas phase scavenging.

Mercury fluxes in a natural forested Amazonian catchment (Serra do Navio, Amapá State, Brazil).

Mercury (Hg total) fluxes were calculated for rainwater, throughfall and stream water in a small catchment located in the northeastern region of the Brazilian Amazon (Serra do Navio, Amapá State), whose upper part is covered by a natural rainforest and lower part was altered due to deforestation and activities related to manganese mining. The catchment area is 200 km from the nearest gold mining (garimpo). Minimum and maximum Hg concentrations were measured monthly from October 1996 to September 1997 and were 3.5-23.4 ng l(-1) for rainwater, 16.5-82.7 ng l(-1) for throughfall (March-August 1997) and 1.2-6.1 and 4.2-18.8 ng l(-1) for stream water, in natural and disturbed areas, respectively. In the natural area, the inputs were 18.2 microg m 2 year(-1) in rainwater and 72 microg m(-2) year(-1) in throughfall. This enrichment was attributed to dry deposition. The stream output of 2.9 microg m(-2) year(-1) indicates that Hg is being recycled within the forest as other chemical species or is being retained by the soil system, as confirmed by the cumulative Hg burden in the 0-10 cm surface layer, which was 36480 microg m(-2). When the disturbed area of the catchment was included, the stream output was 9.3 microg m(-2), clearly indicating the impact of the deforestation of the lower part of the basin on the release of mercury. The Hg burden in the disturbed area was 7560 microg m(-2) for the 0-10 cm surface layer.