Influence of wood-fired domestic heating on indoor PM concentration and composition

This contribute discusses the results of a study about the contribution of biomass-burning heating sources in indoor environments. Two houses were considered, both placed in a peri-urban area (near Rome, Italy) and heated by wood burning thermo-fireplace and pellet stoves, respectively. The conventional measurement of PM concentrations (sampling on membrane filters, 24-h time-resolution) did not allow to appreciate significant changes among the two heating systems, with the exception of a slight (10-15%) increase of PM concentrations during the days when the ash collection from the devices was performed. Chemical analyses showed that this increase was mainly due to organic matter and metal-rich particles. To better characterize these events of short duration, traditional sampling methods were accompanied by time-resolved measurements performed by an Optical Particle Counter (OPC) and by a Particle Into Liquid Sampler (PILS) specially modified to allow the measurement of elemental concentrations at a timeresolution of 10 minutes. A very marked increase of PM10 and PM2.5 concentrations (figure 1, upper panel) was evidenced during maintenance operations of the pellet stove (suction of ash and residues by an ash cleaner provided with abatement filter). The elemental analysis showed concentration peaks during the cleaning event, particularly significant for Li, K, Ca, Ti, Mn, Cu, As, Rb, Sr, Mo, Cd, Sn, Sb e Te (figure 1, lower panel). A similar behavior was observed during the cleaning operation of the thermo-fireplaces system, performed manually, by removing the residual ash with a brush; in this case, however, a less significant increase of PM2.5 concentration was evidenced (figure 2). The elemental analysis showed a different composition of the ash, less rich of heavy metals; the elements showing the most significant increase were Mg, K, Ca, Mn, Rb, Sr and Pb. The different size distribution and elemental composition of the produced ashes is probably due to the different quality of the combustive materials and to the different combustion conditions, less complete in the case of thermo-fireplace. The obtained results show how wood-fired domestic heating may influence PM indoor concentrations introducing potentially toxic species with high heavy metal content.