Characterization of in-stack particulate emissions from residential wood hydronic heater appliances under different combustion conditions

In the current work, we provide measurements of size-resolved particle number concentration (PNC), particle mass concentration (PMC), lung-deposited surface area (LDSA), and black carbon (BC) concentration for three biomass fired hydronic heaters during operation in four different combustion conditions. The appliances include one woodchip-fueled hydronic heater and two outdoor cordwood-fueled hydronic heaters. The operating conditions included startup, low output, high output, and burnout. Measurements were made using a custom dilution sampling system and a suite of commercially available, time-resolved, ambient aerosol measurement instrumentation. The PNC, as measured using an Dekati Electrical Low Pressure Impactor+ (ELPI), had operating condition mean values ranging between 4.1 and 52 million particles per cubic centimeter (#/cm(3)). The highest reported PNC occurred during the startup condition in all cases. Calculating the particle size distribution measured across each operating phase for the same instrument gave geometric mean diameters (d(g) ) in the range of 0.080-0.256 mu m. The largest d(g) per appliance was nearly always attributable to the startup condition (for hydronic heater 1, startup d(g) ranked second). We did not observe the same trends when we transformed the ELPI PNC to PMC and particle surface area concentration estimates across operating conditions, suggesting PNC and d(g) are highly variable. Furthermore, simultaneous measurements of PNC, PMC, and PSAC using instrumentation with different working principles gave varying results, potentially suggesting that particles of different composition and morphology are produced under different combustion conditions.Implications: In this work we compare the results from testing of 3 biomass fired hydronic heaters including one chip-fired appliance and two cordwood-fired appliances. The emissions from these appliances were made across four operating conditions and using three different non-regulatory emissions metrics. This work: describes the difference between chip and cordwood fired units and the effect of operating condition on emissions across the three emissions metrics.