Emission estimates of selected volatile organic compounds from tropical savanna burning in northern Australia

Abstract

[1] Here we present measurements of a range of carbon-based compounds: carbon dioxide (CO 2 ), carbon monoxide (CO), methane (CH 4 ), nonmethane hydrocarbons (NMHCs), methyl halides, and dimethyl sulfide (DMS) emitted by Australian savanna fires studied as part of the Biomass Burning and Lightning Experiment (BIBLE) phase B aircraft campaign, which took place during the local late dry season (28 August to 13 September 1999). Significant enhancements of short-lived NMHCs were observed in the boundary layer (BL) over the region of intensive fires and indicate recent emissions for which the mean transport time was estimated to be about 9 hours. Emission ratios relative to CO were determined for 20 NMHCs, 3 methyl halides, DMS, and CH 4 based on the BL enhancements in the source region. Tight correlations with CO were obtained for most of those compounds, indicating the homogeneity of the local savanna source. The emission ratios were in good agreement with some previous measurements of savanna fires for stable compounds but indicated the decay of emission ratios during transport for several reactive compounds. Based on the observed emission ratios, emission factors were derived and compared to previous studies. While emission factors (g species/kg dry mole) of CO 2 varied little according to the vegetation types, those of CO and NMHCs varied significantly. Higher combustion efficiency and a lower emission factor for methane in this study, compared to forest fires, agreed well with results for savanna fires in other tropical regions. The amount of biomass burned was estimated by modeling methods using available satellite data, and showed that 1999 was an above average year for savanna burning. The gross emissions of the trace gases from Australian savanna fires were estimated.

Spatial and temporal variability in the ratio of trace gases emitted from biomass burning

“…Chem. Phys., 11, 3611-3629, 2011 www.atmos-chem-phys.net/11/3611/2011/ T. T. van Leeuwen and G. R. van der Werf: Spatio-temporal variability in emission factors (Hurst et al, 1994;Shirai et al, 2003) and tropical deforestation measurements in Brazil , (b) FTC and CH 4 EF for tropical deforestation measurements in Brazil , and (c) precipitation and CH 4 EF for extratropical forest measurements in Alaska (Laursen et al, 1992;Goode et al, 2000;Wofsy et al, 1992;Nance et al, 1993). 2002. These could account for up to about 33% (r = 0.57), 38% (r = 0.62), 19% (r = 0.43), and 34% (r = 0.58) of the variability for respectively CO, CH 4 , CO 2 , and MCE.…”

“…We focused on CO, CH 4 , and CO 2 . However, since the Modified Combustion Efficiency (MCE, defined as the amount of C released as CO 2 divided by the amount of C released as CO 2 plus CO ) has been used as an effective predictor for the emission of smoke gas composition from biomass fires (e.g., Ward et al, 1996;Sinha et al, 2003;Yokelson et al, 2003) and for certain aerosol species and characteristics (e.g., McMeeking et al, 2009;Janhäll et al, 2010), our findings on CO and CO 2 EFs can be used to better understand emissions of other trace gases and aerosols as well. We restricted our analysis to in situ measurements due to the focus on spatio-temporal variability as a result of variability in vegetation and climatic conditions; laboratory measurements of EFs were not taken into account.…”

“…For example, SAFARI campaign measurements were conducted in South Africa and Zambia, and different research groups were involved to estimate EFs. Airborne Fourier transform infrared spectroscopy (AFTIR) was used by to measure EFs, while Sinha et al (2003) used gas chromatography (GC). Both measuring techniques gave different EFs of CO, CH 4 and CO 2 , even though the location and timing of the burning event was identical.…”

“…During the last two decades biomass burning has received considerable interest, leading for example to the realization that vegetation fires impact 8 out of 14 identified radiative forcing terms (Bowman et al, 2009), contribute to interannual variability (IAV) in growth rates of many trace gases (Langenfelds et al, 2002), and influence human health and plant productivity downwind of fires through enhanced ozone and aerosol concentrations (e.g. Sitch et al, 2007).…”

“…We then expanded the database to include location-specific parameters related to vegetation type and climate of each measurement. We focused on the EFs of CO 2 , CO, and CH 4 because these gases were measured during most campaigns, and the EF of CO 2 and CO can be used to calculate the MCE, which can be used to predict EFs of other species (e.g., Ward et al, 1996;Sinha et al, 2003;Yokelson et al, 2003).…”