Abstract
Abstract. A series of photo-oxidation smog chamber experiments were performed to investigate the primary emissions and secondary aerosol formation from two different log wood burners and a residential pellet burner under different burning conditions: starting and flaming phase. Emissions were sampled from the chimney and injected into the smog chamber leading to primary organic aerosol (POA) concentrations comparable to ambient levels. The composition of the aerosol was measured by an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and black carbon (BC) instrumentation. The primary emissions were then exposed to xenon light to initiate photo-chemistry and subsequent secondary organic aerosol (SOA) production. After correcting for wall losses, the average increase in organic matter (OM) concentrations by SOA formation for the starting and flaming phase experiments with the two log wood burners was found to be a factor of 4.1±1.4 after five hours of aging. No SOA formation was observed for the stable burning phase of the pellet burner. The startup emissions of the pellet burner showed an increase in OM concentration by a factor of 3.3. Including the measured SOA formation potential, average emission factors of BC+POA+SOA, calculated from CO2 emission, were found to be in the range of 0.04 to 3.9 g/kg wood for the stable burning pellet burner and an old log wood burner during startup respectively. SOA contributed significantly to the ion C2H4O2+ at mass to charge ratio m/z 60, a commonly used marker for primary emissions of wood burning. This contribution at m/z 60 can overcompensate for the degradation of levoglucosan leading to an overestimation of the contribution of wood burning or biomass burning to the total OM. The primary organic emissions from the three different burners showed a wide range in O:C atomic ratio (0.19−0.60) for the starting and flaming conditions, which also increased during aging. Primary wood burning emissions have a rather low relative contribution at m/z 43 (f 43) to the total organic mass spectrum. The non-oxidized fragment C3H7+ has a considerable contribution at m/z 43 for the fresh OA with an increasing contribution of the oxygenated ion C2H3O+ during aging. After five hours of aging, the OA has a rather low C2H3O+ signal for a given CO2+ fraction, possibly indicating a higher ratio of acid to non-acid oxygenated compounds in wood burning OA compared to other oxygenated organic aerosol (OOA).
Highlights
Wood burning for domestic heating and cooking is very common in many parts of the world, and, because of its importance as a source of renewable energy, there is currently an increasing interest in its usage
We present a correlation between O:C ratio and m/z 44 obtained from unit mass resolution (UMR) mass spectra, which can be used to estimate the O:C ratio of wood burning aerosols, primary organic aerosol (POA) and secondary organic aerosol (SOA), from UMR data
Our experiments were at lower concentrations (1– 30 μg/m3 as compared to ≥40 μg/m3), which affects the partitioning of organics between the gas and particle phase (Lipsky and Robinson, 2006), and the modified combustion efficiency (MCE, defined as [CO2]/([CO2] + [Carbon monoxide (CO)])) was higher (Table 1) which has been shown to lead to lower organic matter (OM)/black carbon (BC) ratios (Grieshop et al, 2009b)
Summary
Wood burning for domestic heating and cooking is very common in many parts of the world, and, because of its importance as a source of renewable energy, there is currently an increasing interest in its usage. Three billion people use small-scale appliances (three-stone fires or cooking stoves) that are both inefficient and highly polluting (World Energy Council, 2007). Wood combustion emits a wide range of volatile organic compounds (VOC) and particulate matter (PM) which consists mainly of organics and black carbon (BC) Heringa et al.: Primary and secondary aerosol from wood combustion
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