<p>Major ionic constituents (Cl^–, Na⁺, K⁺, Mg²⁺, Ca²⁺, NH₄⁺, NO₃^–, SO₄^2–) and dissolved organic nitrogen were determined, from September 2009 to January 2010, in bulk atmospheric deposition in the lower course of Cachoeira River, southern Bahia, Brazil, where studies on this theme are still absent. The high fluxes of Na+, Mg2+ and Cl– observed in the innermost sampling site evidence the continuity of marine influence in the atmosphere of the city of Itabuna. Concentrations of H⁺, Ca²⁺, SO₄^2– and NO₃^– denoted non-marine anthropogenic sources. The contributions of dissolved organic and inorganic nitrogen were different between the evaluated sites. This region is still subject to little impact by anthropogenic emissions compared to other urban areas in Brazil, according to estimates of atmospheric fluxes of SO₄^2–, NO₃^– and NH₄⁺.</p>

Nitrous oxide (N2O) emissions were measured monthly from January to June 2010 in the aeration tank of a wastewater treatment plant (WWTP) in Southeast Brazil. Emissions were lower in summer than winter and were positively related with influent ammonium (NH4+) concentration. The average N2O emission was 1.11 kg N day-1 corresponding to 0.02% of the influent total nitrogen load. The average emission factor calculated for the population served was 2.5 lower than that proposed by the Intergovernmental Panel on Climate Change (IPCC) for inventories of N2O emissions from WWTPs with controlled nitrification and denitrification processes.

This study investigated the emission of N2O during the sequential aerated (60-min) and non-aerated (30-min) stages of an intermittent aeration cycle in an activated sludge wastewater treatment plant (WWTP). N2O emission occurred during both stages; however, emission was much higher during aeration. Air stripping is the major factor controlling transfer of N2O from the sewage to the atmosphere. The N2O emissions exclusively from the aeration tank represented 0.10% of the influent total nitrogen load and the per capita emission factor was almost 3 times higher than that suggested by the IPCC for inventories of N2O emission from WWTPs.

Rainwater samples (bulk deposition samples) were collected in Pinheiro and Viana. Rainwater pHs were higher than the range usually expected for unpolluted rain (5.0-5.6). The highest values were found in the beginning of the rainy season. High concentrations of ammonium found in the rainwater samples could probably explain the high pHs. Grazing animals and other human activities, combined with soil characteristics and climatic conditions can be the potential factors controlling the rainwater concentrations of ammonium in Baixada Maranhense.