A snapshot of suspended sediment and fluid mud occurrence in a mixed-energy embayment, Tijucas Bay, Brazil

Along the southern Brazilian coast, Tijucas Bay is known for its unique muddy tidal flats associated with chenier plains. Previous field observations pointed to very high suspended sediment concentrations (SSCs) in the inner parts of the bay, and in the estuary of the Tijucas River, suggesting the presence of fluid mud. In this study, the occurrences of suspended sediments and fluid mud were examined during a larger-scale, high-resolution 2-day field campaign on 1-2 May 2007, encompassing survey lines spanning nearly 80 km, 75 water sampling stations for near-bottom density estimates, and ten sediment sampling stations. Wave refraction modeling provided qualitative wave energy estimates as a function of different incidence directions. The results show that SSC increases toward the inner bay near the water surface, but seaward near the bottom. This suggests that suspended sediment is supplied by the local rivers, in particular the Tijucas. Near-surface SSCs were of the order of 50 mg l(-1) close to the shore, but exceeded 100 mg l(-1) near the bottom in the deeper parts of the bay. Fluid mud thickness and location given by densimetry and echo-sounding agreed in some places, although being mostly discordant. The best agreement was observed where wave energy was high during the campaign. The discrepancy between the two methods may be an indication for the existence of fluid mud, which is recorded by one method but not the other. Agreement is considered to be an indication of fluidization, whereas disagreement indicates more consolidation. Wave modeling suggests that waves from the ENE and SE are the most effective in supplying energy to the inner bay, which may induce the liquefaction of mud deposits to form fluid mud. Nearshore mud resuspension and weak horizontal currents result in sediment-laden offshore flow, which explains the higher SSCs measured in the deeper parts of the bay, besides providing a mechanism for fine-sediment export to the inner shelf.

Use of levoglucosan, potassium, and water-soluble organic carbon to characterize the origins of biomass-burning aerosols

Three chemical species related to biomass burning, levoglucosan, potassium and water-soluble organic carbon (WSOC), were measured in aerosol samples collected in a rural area on the outskirts of the municipality of Ourinhos (Sao Paulo State, Brazil). This region is representative of the rural interior of the State, where the economy is based on agro-industrial production, and the most important crop is sugar cane. The manual harvesting process requires that the cane be first burned to remove excess foliage, leading to large emissions of particulate materials to the atmosphere. Most of the levoglucosan (68-89%) was present in small particles (<1.5 mu m), and its concentration in total aerosol ranged from 25 to 1186 ng m(-3). The highest values were found at night, when most of the biomass burning occurs. In contrast, WSOC showed no diurnal pattern, with an average concentration of 5.38 +/- 2.97 mu g m(-3) (n = 27). A significant linear correlation between levoglucosan and WSOC (r = 0.54; n = 26; p < 0.0001) confirmed that biomass burning was in fact an important source of WSOC in the study region. A moderate (but significant) linear correlation between levoglucosan and potassium concentrations (r = 0.62; n = 40; p < 0.0001) was indicative of the influence of other sources of potassium in the study region, such as soil resuspension and fertilizers. When only the fine particles (<1.5 pm; typical of biomass burning) were considered, the linear coefficient increased to 0.91 (n = 9). In this case, the average levoglucosan/K+ ratio was 0.24, which may be typical of biomass burning in the study region. This ratio is about 5 times lower than that previously found for Amazon aerosol collected during the day, when flaming combustion prevails. This suggests that the levoglucosan/K+ ratio may be especially helpful for characterization of the type of vegetation burned (such as crops or forest), when biomass-burning is the dominant source of potassium. The relatively high concentrations of WSOC (and inorganic ions) suggest an important influence on the formation of cloud condensation nuclei, which is likely to affect cloud formation and precipitation patterns. (C) 2012 Elsevier Ltd. All rights reserved.

Urban air pollution: a representative survey of PM2.5 mass concentrations in six Brazilian cities

In urban areas of Brazil, vehicle emissions are the principal source of fine particulate matter (PM2.5). The World Health Organization air quality guidelines state that the annual mean concentration of PM2.5 should be below 10 mu g m(-3). In a collaboration of Brazilian institutions, coordinated by the University of Sao Paulo School of Medicine and conducted from June 2007 to August 2008, PM2.5 mass was monitored at sites with high traffic volumes in six Brazilian state capitals. We employed gravimetry to determine PM2.5 mass concentrations, reflectance to quantify black carbon concentrations, X-ray fluorescence to characterize elemental composition, and ion chromatography to determine the composition and concentrations of anions and cations. Mean PM2.5 concentrations and proportions of black carbon (BC) in the cities of Sao Paulo, Rio de Janeiro, Belo Horizonte, Curitiba, Recife, and Porto Alegre were 28.1 +/- 13.6 mu g m(-3) (38% BC), 17.2 +/- 11.2 mu g m(-3) (20% BC), 14.7 +/- 7.7 mu g m(-3) (31% BC), 14.4 +/- 9.5 mu g m(-3) (30% BC), 7.3 +/- 3.1 mu g m(-3) (26% BC), and 13.4 +/- 9.9 mu g m(-3) (26% BC), respectively. Sulfur and minerals (Al, Si, Ca, and Fe), derived from fuel combustion and soil resuspension, respectively, were the principal elements of the PM2.5 mass. We discuss the long-term health effects for each metropolitan region in terms of excess mortality risk, which translates to greater health care expenditures. This information could prove useful to decision makers at local environmental agencies.