Polycyclic aromatic hydrocarbon emissions from residential wood combustion

Public examination of a doctoral dissertation in the field of Environmental Science
Doctoral candidate: MSc Kati Nuutinen
Date and venue: 9.6.2016 at 12 noon, SN200, Snellmania, Kuopio campus
Language of the dissertation: English
Language of the public examination: Finnish


Wood and biomass combustion is favoured due to its expected lower climate impact compared to fossil fuels. However, incomplete combustion may produce significant emissions of pollutants that are hazardous to human health, e.g., polycyclic aromatic hydrocarbons (PAHs). Residential wood and coal combustion is one of the major sources of fine particles and PAHs in ambient European air. However, the emission factors of wood-fired appliances, particularly for PAHs, remain relatively poorly known.

In this study, new information on PAH emissions from different types of appliances, several operational practices and various combustion conditions was produced. In addition, the effect of sampling and dilution conditions on the emissions of PAHs and fine particles were studied.

Overall, the variation in particulate PAH emissions were large. Continuous combustion appliances such as small-scale pellet boilers had considerably lower PAH emissions compared to batch combustion appliances. Sauna stoves had high PAH emissions. More sophisticated and modern batch combustion devices involving the staging of combustion air had lower PAH emissions compared to conventional appliances. Poor user operation was found to cause considerably higher PAH emissions.

Novel method utilizing denuders was used for determining the partitioning of PAHs between the gas and particle phases. Sampling conditions greatly affected the partitioning. Correspondingly, due to changes in the partitioning of semivolatiles, the PM1 mass emissions measured from diluted exhaust were higher than the parallel total dust emissions from hot, undiluted exhaust.

With dilutive sampling, more atmospherically relevant sampling conditions are created, and results that better mirror exposure and combustion quality are obtained. A precise definition of acceptable sampling conditions is needed.

The results of this work show that PAH emissions from residential wood combustion can be substantially reduced by modern technologies.

The doctoral dissertation of Master of Science Kati Nuutinen, entitled Polycyclic aromatic hydrocarbon emissions from residential wood combustion will be examined at the Faculty of Science and Forestry. The opponent in the public examination will be Research Professor Hannele Hakola, Finnish Meterological Institute, and the custos will be Professor Jorma Jokiniemi, University of Eastern Finland.