Chemical evolution of the aerosol emitted by residential log wood stoves : highlight of fast oxidation processes from emission to ambient air introduction
Résumé
As it is a renewable source of energy, interest in wood burning for domestic heating has increased in Europe, notably during this last decade. Evaluation of wood combustion pollutant emission factors (EFs) is commonly achieved by measurements directly performed at the emission source. In these conditions; the results obtained are not representatives of PM concentrations and chemical composition observed in the atmosphere due to post-emission physicochemical processes: dilution, condensation and photo-oxidation of semi-volatile compounds. The main objective of the Champrobois project was to study in controlled “real” conditions the evolution of the aerosol (mass and chemical composition) emitted by two different residential log wood stoves (old and modern = 4* and 5*) from emission until its ambient air insertion. Measurements were performed directly at the emission source, at about 1 m from the stack exhaust (very close field, dilution factor about 10-20) and at 50 m from the emission exhaust (close field, dilution factor about 500). Here, the objectives were first, to evaluate the wood combustion EFs of toxic compounds such as polycyclic aromatic compounds derivatives (nitrated and oxygenated PAHs) poorly documented in literature and second, to evaluate the oxidation state of the wood combustion effluent by studying these primary/secondary compounds. The increase of equivalent EFs of PAH derivatives suggested that fast aerosol oxidation processes occurred between the emission and the close field (about 10 s after emission). This was confirmed by the study of the PAH ratio-ratio plots commonly used for source evaluation. This work was supported by ADEME (French Environment and Energy Management Agency) and the French Ministry of Ecology, Sustainable Development and Energy (MEDDE).