[Emission Factors of Heavy Metals in Size-resolved Particles Emitted from Residential Coal Combustion]

Based on a dilution sampling system and domestic burning tests, size-segregated particles emitted from burning of three kinds of honeycomb coals (in view of flaming and smoldering burning conditions) and four kinds of raw coals, were collected by cascade impactors (FA-3). The contents of V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Sb, and Pb were analyzed to get their emission factors (EFs) in different particle size fractions. Results indicated that:① Zn and Pb dominated the emitted mass of heavy metals from chunk (53.16%-65.76%) and honeycomb (96.08% in 0.43 μm) during the flaming combustion condition. However, the emission of Ni was increased from 30.70% to 52.36% in the smoldering condition. Thus, combustion condition may affect the composition of heavy metals in particle matters. ② In the flaming condition, both chunk and honeycomb emission factors of heavy metals were concentrated under 1.1 μm, while the larger sized particles in the range of 5.8-10 μm were distributed. So, heavy metal components may shift to the larger size of the particles at lower combustion temperatures. ③ Fine particle matters(PM) was divided into three categories based on the size distribution of 11 kinds of heavy metal emission factors. The maximum emission values of As and V fell under the PM size category of 5.8-10 μm. The fourth cycle transition metal elements, such as Cr, Mn, Cu, Ni, and Co, fell in the range of 1.1-2.1 μm and these elements represented similar emission characteristic features. Other elements, such as Pb, Sb, Cd, and Zn, were concentrated in sizes less than 0.43 μm. ④ The additive in the honeycomb during the process may import several kinds of heavy metals and may change the combustion temperature, which remodels the mechanism of heavy metal emission. Thus, honeycomb coal may emit different heavy metals under different combustion conditions.The heavy metal emission mechanism during honeycomb coal combustion needs further investigation and the emission reduction effects (especially of heavy metals) needs to be re-estimated.