Abstract
Abstract. We profile trace gas and particulate emissions from near-field airborne measurements of discrete smoke plumes in Brazil during the 2012 biomass burning season. The South American Biomass Burning Analysis (SAMBBA) Project conducted during September and October 2012 sampled across two distinct fire regimes prevalent in the Amazon Basin. Combined measurements from a Compact Time-of-Flight Aerosol Mass Spectrometer (C-ToF-AMS) and a Single Particle Soot Photometer (SP2) are reported for the first time in a tropical biomass burning environment. Emissions from a mostly smouldering tropical forest wildfire in Rondônia state and numerous smaller flaming Cerrado fires in Tocantins state are presented. While the Cerrado fires appear to be representative of typical fire conditions in the existing literature, the tropical forest wildfire likely represents a more extreme example of biomass burning with a bias towards mostly smouldering emissions. We determined fire-integrated modified combustion efficiencies, emission ratios and emission factors for trace gas and particulate components for these two fire types, alongside aerosol microphysical properties. Seven times more black carbon was emitted from the Cerrado fires per unit of fuel combustion (EFBC of 0.13 ± 0.04 g kg−1) compared to the tropical forest fire (EFBC of 0.019 ± 0.006 g kg−1), and more than 6 times the amount of organic aerosol was emitted from the tropical forest fire per unit of fuel combustion (EFOM of 8.00 ± 2.53 g kg−1, EFOC of 5.00 ± 1.58 g kg−1) compared to the Cerrado fires (EFOM of 1.31 ± 0.42 g kg−1, EFOC of 0.82 ± 0.26 g kg−1). Particulate-phase species emitted from the fires sampled are generally lower than those reported in previous studies and in emission inventories, which is likely a combination of differences in fire combustion efficiency and fuel mixture, along with different measurement techniques. Previous modelling studies focussed on the biomass burning season in tropical South America have required significant scaling up of emissions to reproduce in situ and satellite aerosol concentrations over the region. Our results do not indicate that emission factors used in inventories are biased low, which could be one potential cause of the reported underestimates in modelling studies. This study supplements and updates trace gas and particulate emission factors for fire-type-specific biomass burning in Brazil for use in weather and climate models. The study illustrates that initial fire conditions can result in substantial differences in terms of their emitted chemical components, which can potentially perturb the Earth system.
Highlights
Atmospheric aerosols represent the largest uncertainty in current understanding of radiative forcing of climate (Boucher et al, 2013), with biomass burning aerosol (BBA) aerosol– radiation interactions estimated to have a radiative forcing of 0.0 Wm−2 but with a very large uncertainty of ±0.2 Wm−2 and significant perturbations on the regional scale (Boucher et al, 2013)
The fires were sampled within the boundary layer, with out-of-plume aerosol samples dominated by biomass burning haze
Given that directly comparable measurements from fires in Brazil are more scarce for particulate emissions than trace gases and the substantial range from region to region reported in the literature (e.g. Jolleys et al, 2012), in the following text we focus on comparing with global average values and those used in emission inventories in the absence of Brazil-specific emission factors
Summary
Atmospheric aerosols represent the largest uncertainty in current understanding of radiative forcing of climate (Boucher et al, 2013), with biomass burning aerosol (BBA) aerosol– radiation interactions estimated to have a radiative forcing of 0.0 Wm−2 but with a very large uncertainty of ±0.2 Wm−2 and significant perturbations on the regional scale (Boucher et al, 2013). BBAs have both a global and a regional effect on weather and climate via perturbation of the atmospheric radiation balance and cloud microphysical properties (Ramanathan et al, 2001; Andreae et al, 2004) and visibility (Andreae et al, 1988), and they can affect human health (Cançado et al, 2006; Arbex et al, 2007; do Carmo et al, 2013). The Amazon Basin in Brazil contains approximately 4 × 106 km of evergreen tropical forest (Christian et al, 2007), and during the dry season (August–October) intense widespread burning occurs, leading to high levels of atmospheric particulate matter (Chand et al, 2006). A range of climate and fire types occurs in Brazil, with fire-impacted ecosystems including pure grassland, a gradient of wooded savannah into dry (seasonal) tropical forest and evergreen tropical forest (Ward et al, 1992; Yamasoe et al, 2000). Detailed representation of the emissions and properties of gas- and particulate-phase species from BB in Brazil are required in global climate models for their outputs to be accurate and reliable (Bowman et al, 2009)
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