Comprehensive characterisation of PM emissions from old and modern boilers using wood and fossil fuels

• Modern boilers reduce PM2.5 emissions by up to 99.96 % compared to old designs. • Significant CO-OGC emission correlation (R² = 0.98) in coal combustion identified. • Ultrafine particles (PM0.1) dominate emissions, especially during coal combustion. • Fuel moisture strongly impacts PM emissions, with wet wood increasing emissions. • Advanced boilers show greater sensitivity to fuel quality and combustion conditions. In light of the increasing number of decommissioned old small-scale combustion appliances, there is great anticipation for a significant improvement in local air quality. However, even modern appliances emit harmful pollutants, necessitating monitoring and reduction to mitigate their impact on the environment. The study compares particulate matter number and mass concentrations in the flue gas from commonly used boiler types. Low-Pressure Cascade Impactor (DLPI) to determine the mass concentration of individual dust fractions was used, as well as an Electrical Low-Pressure Cascade Impactor (ELPI) and a particle mobility sizer SMPS 3936 (TSI). Beyond appliance design, the type and quality of fuel emerged as significant factors influencing flue gas composition. In addition to particulate matter characteristics, measurements of CO, organic gaseous compounds (OGC), and PMx mass concentrations allowed for the determination of correlations among these pollutants. The highest correlation was observed between CO and OGC, with a coefficient of determination (R²) value of 0.98 for coal combustion. The feasibility of replacing older stationary combustion appliances with new ones was demonstrated across several parameters, including specific emissions for the PM2.5 and PM0.1. The reduction between overfire and automatic boilers reached 99.96 % and 93 %, respectively.