Properties of aerosols from sugar-cane burning emissions in Southeastern Brazil

Abstract

The influences of biomass burning emissions in the composition of aerosol have been studied during 1 year around the city of Piracicaba (Southeastern Brazil). Inhalable particles, separated in PM_2.5 and coarse particulate mode (CPM, with size in the range (2.5<d_p<10 μm)), were sampled from April 1997 to March 1998 and analyzed for BC, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Rb, Sr, Zr, Pb. The average concentrations of PM_2.5, CPM, BC and chemical elements were statistically higher in the dry season than in the wet season. The results of absolute principal component analysis showed four and three different sources for PM_2.5 and CPM, respectively. Sugar-cane burning is the main source of PM_2.5 representing 60% of PM_2.5, soil dust accounted for 14%, and industries and oil combustion contributed with 12% each one. Resuspended soil is the main source of CPM followed by industrial emissions and sugar-cane burning. The sampling and analytical procedures applied in this study showed that sugar-cane burning and agricultural practices are the main sources of inhalable particles, possibly altering the aerosol composition around the city of Piracicaba.

Introduction

In the Northern Hemisphere the main source of aerosols is linked to fossil fuel burning, whose emissions have been well documented, while in tropical areas biomass burning may be one of the most important global source of atmospheric particles (Crutzen and Andreae, 1990; Oglesby et al., 1999). Aerosol particles from biomass burning are important in the radiative balance of the atmosphere, through a complex microphysical process, possibly affecting the ground-based radiation budget (Oglesby et al., 1999; Ramanathan et al., 2001). The carbonaceous aerosols (black carbon and organic aerosol) are identified as playing a major role in the absorption of solar radiation. These aerosols, together with the resulting reflection of solar radiation to space, lead to large changes (global mean radiative aerosol forcing range from −0.5 to +0.2 W m⁻²) in the solar radiation absorbed on the surface (Ramanathan et al., 2001; Streets et al., 2001). Additionally, the particles emitted by biomass burning can affect the concentration of cloud condensation nuclei, probably changing the hydrological cycles and cloud albedo (Roberts et al., 2001; Rosenfeld, 1999).

Due to the large fire catastrophes of anthropogenic origin in recent years and the intensive scientific efforts over the last decade, the general public as well as the scientific community are now aware that emissions from biomass burning represent a large perturbation to global atmospheric chemistry, particularly in the tropics. Biomass burning includes the burning of forests, savannas, and agricultural lands. Brazil plays an important role in biomass burning emissions, with the detection by AVHRR of about 235,000 fire spots in 2004 (www.cptec.inpe.br/queimadas). Most of these fires occurred in the southern part of the Amazon basin during the dry season (from August to November). Emissions from these fires have significant impacts on the concentration of trace gases and aerosols over a large area (Artaxo et al., 2002; Yamasoe et al., 2000). From Southeastern through Northeastern Brazil sugar-cane burnings are also key contributors in terms of emissions, as already highlighted a decade ago by Crutzen and Andreae (1990). Brazil owns 25% of the global sugar-cane areas, and is the major sugar-cane producer in the world. Currently, it has 4,500,000 ha of sugar-cane crops and more than 1,100,000 rural workers are involved in the sugar-cane industry (Zamperlini et al., 2000). The area cultivated with sugar-cane in the state of São Paulo in Southeastern Brazil, reaches approximately 24,000 km². In order to facilitate harvesting, which also occurs in others places such as Hawaii and Africa, the sugar-cane is burned and most fires occur every year during the dry season (from May to November). About 20 t of sugar-cane dry matter per hectare is burned, contributing to a global emission with approximately 0.48 Tg of carbon per year. As a result, aerosol and trace gases emitted from sugar-cane fires have significant effects on the composition and acidity of rainwater over large areas of Southern Brazil (Lara et al., 2001). Despite its importance, little information is available about the effects of sugar-cane burnings on aerosol particles (Azevedo et al., 2002; Martinelli et al. 2002).

The focus of this paper was the investigation of the chemical and physical characteristics of sugar-cane burning aerosol emissions, looking especially at the elemental composition, and source apportionment of fine and coarse mode aerosols. The use of real-time aerosol monitors (TEOM and Aethalometer) allowed obtaining of diurnal patterns, while stacked filter units (SFU) separated fine and coarse mode aerosol.