Chemical evolution of the aerosol emitted by domestic wood stoves : evidence of fast oxidation processes from emission to ambient air introduction
Résumé
As it is a renewable source of energy, wood burning for domestic heating is increasing interest in its usage, notably during this last decade in Europe. Evaluation of wood combustion pollutant emission factors (EFs) is commonly achieved by measurements directly performed at the emission source (chimney). Results obtained in these conditions are not representatives of PM concentrations and chemical composition observed in the atmosphere due postemission physical-chemical processes: dilution, photooxidation and condensation 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 domestic log wood burners (old and modern = 4* and 5*) from emission until its ambient air introduction. Measurements were performed directly at the emission source, at about 1 m from the chimney exhaust (very close vicinity, dilution factor about 10-20) and at 50 m from the emission exhaust (close vicinity, dilution factor about 500). Our specific objectives were first, to evaluate the wood combustion EFs of toxic compounds such as polycyclic aromatic compounds derivatives (nitrated and oxygenated PAHs, NPAHs and OPAHs) poorly documented in the literature (Figure 1) and second, to evaluate the oxidation state of the wood combustion effluent studying these primary/secondary compounds. Results obtained showed clearly that fast aerosol oxidation processes occurred between the emission and the close vicinity (about 10 s after emission) (increase of equivalent EFs of PAH derivatives). This was confirmed by the study of the PAH ratio-ratio plots commonly used for source evaluation.