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.

Oxygen Production and Carbon Sequestration in an Upwelling Coastal Margin

We examined high-resolution cross-shelf distributions of particulate organic carbon (POC) and dissolved O(2) during the upwelling season off the Oregon coast. Oxygen concentrations were supersaturated in surface waters, and hypoxic in near-bottom waters, with greatly expanded hypoxic conditions late in the season. Simplified time-dependent mass balances on cross-shelf integrated concentrations of these two parameters, found the following: ( 1) The average net rate of photosynthesis generated 2.1 mmol O(2) m(-3) d(-1) and ( 2) essentially none of the corresponding net carbon fixation of 1.4 mmol m(-3) d(-1) could be accounted for in the observed standing stocks of POC. After examining other possible sinks for carbon, we conclude that most of the net production is being exported to the adjacent deep ocean. A simplified POC budget suggests that about a quarter of the export is via alongshore advection, and the remainder is due to some other process. We propose a simplistic conceptual model of across-shelf transport in which POC sinks to the bottom boundary layer where it comes into contact with mineral ballast material but is kept in suspension by high turbulence. When upwelling conditions ease, the BBL waters move seaward, carrying the suspended, ballasted POC with it where it sinks rapidly into the deep ocean at the shelf break. This suggests a mechanism whereby the duration and frequency of upwelling events and relaxations can determine the extent to which new carbon produced by photosynthesis in the coastal ocean is exported to depth rather than being respired on the shelf.