Residential combustion of coal: Effect of the fuel and combustion stage on emissions.

Worldwide coal is still used for household heating purposes not only because it is available and cheap but also due to behavioural issues. Regional variability in fuels and combustion appliances make accurate emission estimates from this source hard to achieve. In the present study, gaseous (CO, VOCs, SO and NO) and particulate matter (TSP) emission factors (EFs) were determined for Spanish household coal combustion covering three commercial coals and distinct combustion stages and mimicking usage patterns in real households. TSP samples were analysed to determine water-soluble inorganic ions, metal(loid)s, and organic and elemental carbon (OC and EC). Additionally, the morphology of the emitted particles was also characterised. CO (3.43-169 g kg), NO (1.29-6.00 g kg) and SO (8.96-22.3 g kg) EFs showed no trend regarding the combustion stage or coal type tested. On the other hand, VOC, TSP and EC EFs were higher for the ignition/devolatilisation combustion stage, regardless of the fuel tested. TSP EFs (0.085-1.08 g kg) increased with increasing coal volatile matter while the opposite trend was recorded for VOC emissions (0.045-3.39 gC kg). TSP carbonaceous matter was dominated by EC while OC represented a small fraction of the particulate mass emitted (less than 8 %wt.). Inorganic compounds composed an important fraction of the TSP samples. Sulphate particulate mass fractions (8.66-22.9 %wt.) appeared to increase with coal S-content. Coal combustion released particles with diverse morphologies, including silicate-rich particles, ferro- and glassy-spheres. This study provides novel emission factors to update emission inventories of residential coal combustion. Additionally, detailed chemical profiles were obtained for source apportionment.