AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Polycyclic Aromatic Hydrocarbon Emissions in Transient Wood Combustion
Axel Eriksson, Erik, Z Nordin, Robin Nyström, Esbjörn Pettersson, Christoffer Bergvall, Roger Westerholm, Erik Swietlicki, Christoffer Boman, JOAKIM PAGELS, Lund University, Lund, Sweden
Abstract Number: 654 Working Group: Combustion
Abstract Polycyclic aromatic hydrocarbons (PAHs) have been denoted key components in particle related toxicology. Emissions of PAHs can under certain circumstances be high in residential wood combustion. However, previous attempts to identify the combustion conditions favouring high PAH emissions have typically been limited to averages over one to several combustion cycles. In this work we applied Aerosol Mass Spectrometry for highly time-resolved direct measurements of PAHs and total organics in residential biomass combustion.
Emissions from a conventional wood stove and a novel pellet reactor with possibility to control fuel and air supply were studied. The flue gas was diluted with particle free air of ambient temperature, the total dilution factor was 1:2000. A high resolution aerosol mass spectrometer (HR-TOF-AMS, Aerodyne Inc.) was used for size resolved composition of compounds vaporised at 600°C. The results were compared with off-line speciated PAH analysis using GC-MS.
In the wood stove the highest emission factors of total particle phase organics and PAHs occurred during the first 1-5 minutes after addition of new batches of logs on glowing embers, although PAHs constituted less than 1% of the total organics. Elevated PAH-emissions also occurred at hot air starved combustion in both appliances, when O2 levels in the flue gas were below 5%. In these cases, PAHs composed up to 30% of the total organics. A high burn rate under hot and air-starved combustion conditions, leads to thermal cracking of primary released oxygenated pyrolysis products (e.g. levoglucosan and methoxy-phenols). At higher temperatures mostly aromatic compounds and soot are stable enough to survive resulting in elevated PAH emissions.
It is well known that poorly insulated stoves, bad mixing and humid fuels lead to high organic emissions. This work illustrates the potential deterioration of emission levels caused by too high burn rates.