Chemical speciation and phase fractionation of N, S and Cl compounds in the atmosphere of Reconcavo, Bahia, Brazil

Abstract

Studies of chemical speciation and phase fractionation of atmospheric inorganic compounds of N, S and Cl have been undertaken in the atmosphere of the Reconcavo Baiano. The objectives were to determine the enrichment of the clean air masses coming from the Atlantic by different chemical species resulting from NO2 SO2, HCl and NH3 emissions from the industrial areas at the Reconcavo and to estimate the changes in air quality regarding between 2008 and 2010. The following sampling devices were used: passive samplers (PS) and continuous analyzers for NO2 and SO2; diffusion tubes coated with citric acid for ammonia and NaF for strong acids (HCl, HNO3 and H2SO4), the latter in a thermodiffusion system with a back-up filter for collection of the thermically stable (140 °C) ammonium salts and other particles < 2 μm. In parallel, Cl−, NO3−, SO42− and NH4+ suspended particles fractionated by size on Nuclepore membrane with a Berner cascade impactor (0.06 to > 14.9 μm). The analytical methodology for the discontinuous measures included ion chromatography (SO2 as SO42− in the PS, anions of the PM and as representants of the acids in the gas phase) and molecular spectrophotometry using the Griess–Saltzman method (λ = 540 nm) and indophenol method (λ = 630 nm) for determination of NO2 and NH3, respectively. Clean air masses from the Atlantic (13 nmol m− 3 HCl, 2.9 nmol m− 3 HNO3, 1.6 nmol m− 3 H2SO4, 9.8 nmol m− 3 SO2, 16 nmol m− 3 NO2 and 84 nmol m− 3 NH3) are slighted enriched in the gas and particulate phase with respect to HNO3 and H2SO4, respectively, by emissions of the industrial complex. However, enrichment occurs for HCl, SO2, NO2 and NH3. In the area of industrial complex influence hydrochloric acid predominates over the other two strong acids, as expected, due to its direct emission from the petrochemical waste incinerator. Ammonium chloride is the predominant gas to particle transformations. During the period of 2008–2010 a decrease varying between 18 and 49% is observed on the levels of almost all compounds in Lamarão do Passé, downwind from an oil refinery but not in Camaçari, downwind from the industrial complex, where all other compounds presented an increased in their concentrations with the exception of HNO3 and HCl.