Validation and comparison of methods of measurement of the condensable fraction of aerosols emitted by residential wood combustion appliances and boilers
Résumé
The 20/20/20 target for Europe, i.e. to decrease the emissions of greenhouse gases by 20 % and to increase the use of renewable energy to 20% by the year 2020, will lead to an increased use of biomass combustion, e.g. using wood logs and wood pellets. On the other hand, the Air Quality Directive (2008/50/EC) lies down stringent requirements on maximum levels of particulate matter in the ambient air. Solid fuel burning appliances and boilers produce particulate matter emissions which are of concern to authorities and the public. More particularly, the soot and organic components of these emissions are of most concern because they include compounds known for their potential impact on the human health and the environment. Moreover, part of ambient air particles is initially emitted as semi-volatiles (SVOCs), also named condensable fraction, and volatile organic compounds (VOCs) that form primary organic aerosols (POA) by condensation as the flue gas cools down, or secondary organic aerosols (SOA) due to photochemical oxidation into the atmosphere. Ambient measurements establish particle bound organic carbon as the largest carbonaceous fraction from wood burning emissions. It is important to note that the contribution of the condensable fraction to the emission depends on the quality of the combustion; the poorest the quality of the combustion, the highest its contribution to the emissions. Different particle sampling procedures can be used to characterize emission from residential wood combustion, depending on the sampling method chosen, the condensable fraction will be taken into account or not. Two methods of measurements including the condensable fractions have been adapted from existing ones and compared to existing standards (US EPA 5H, Dilution tunnel, EN 13284-1, EN ISO 23210) and to each other. The first one consists of collecting the condensable fraction using cold impingers filled in with isopropanol and placed after a heated filter collecting the solid fraction. The second one consists of diluting the aerosol using a portable dilution device and combine it to online mass measurements using a tempered oscillating mass balance (TEOM) initially designed for ambient air mass measurements. The present paper will describe the adaptation and validation steps of the methods, the correlations obtained against existing standards as well as applications and perspectives of use in terms of emission factors determination, combustion characterization, and reduction techniques evaluation.