Fine particulate matter and gas emissions at different burn phases from household coal-fired heating stoves

Household coal burning contributes a large proportion of fine particulate matter (PM_2.5), black carbon (BC), organic carbon (OC), and CO emissions in China. Previous lab or field investigations generally measured short-term emissions from heating coal stoves, and only covered the high power phase or the flaming combustion processes, and did not consider smoldering combustion condition, which does not provide full characterization of the actual conditions in most cases. In this study, we investigated air pollutant emissions during the different burn phases of seven types of coal burned in a typical household coal-fired heating stove in the lab with a hood sampling system. We proposed a method to estimate coal consumption at the different burn phases, and thus quantify emission factors (EFs) at different burn phases. The concentrations of CO₂, CO, SO₂, NO_x, and PM_2.5 fluctuated over 1 to 4 orders of magnitude during the whole burn cycle. The air pollutant concentration peaks, such as CO and PM_2.5, were generally associated with coal addition. EFs of CO₂, SO₂, total water soluble inorganic ions (TWSIIs) followed the trend: high power phase > low power phase > banked fire phase. However, CO EFs followed the opposite trend, i.e., banked fire phase > low power phase > high power phase. EFs of NO_x and EC in high power phase and low power phase were higher than those in banked fire phase. The variation in EFs of PM_2.5 and OC in different burn phases across seven types of coal burned in this study is complicated. When using EFs from high power phase or flaming phase to represent EFs from the whole process, CO₂, SO₂, NOx, EC and TWSIIs emissions will be overestimated, CO emissions will be underestimated, PM_2.5 and OC emissions may be overestimated or underestimated, depending on coal types.