In-situ investigation of real-world emissions from 111 measurements on solid fuel household boilers

Over the years, emissions from significant stationary and mobile sources have significantly reduced, while solid fuel household combustion appliances have substantially contributed to air pollution. Growing evidence links residential solid fuel combustion to air pollution, prompting extensive studies on emissions. Field-based emission measurements provide more accurate characterisation of real-world emissions. A mobile emissions laboratory and measurement procedure was constructed to measure emissions from domestic boilers in the field, in residential settings, during real-world operation by homeowners using typical fuels. Emissions of total suspended particulate matter (TSP), organic gaseous compounds (OGC), carbon monoxide (CO) and overall thermal efficiency during three-hour operating tests were measured. Data were collected from 111 measurements of boilers, including overfire, downdraft, gasification, and automatic boilers that combust wood pellets, wood chips, wood logs, and coals, covering different brands, constructions, and emissions certification standards. The results show that the investigated newer boilers had lower emissions of CO, OGC, and TSP (approximately half) compared to older boiler technology, resulting in a substantial improvement. The emissions from most of the new boilers were substantially higher (about five times) than their strict applicable limit values due to improper operation. In many cases, fuel size, composition, wood moisture content, boiler installation and maintenance, operating procedure, and operator technical knowledge were considered substandard, with some observations of excessive wear and tampering. The findings confirm the importance of real-world local heating emissions measurements and suggest that relatively fast, inexpensive, and substantial emissions reductions may be achieved by improving the maintenance and education of operators.