Emission Factors Of Carbonaceous Particulate Matter And Polycyclic Aromatic Hydrocarbons From Residential Solid Fuel Combustions

Particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) are twoimportant pollutants of concern. They have significant impacts on air quality and humanhealth. To better know about the environmental behaviors and potential effects of thesepollutants, accurate emission inventory is necessarily required. Emission inventory isdeveloped by multiplying the emission factors (EFs) of a target pollutant from a givensource and total consumption of the energy. Current emission inventories often have largeuncertainties, and one main reason is lacking of credible emission factors. Among varioussources of PM and PAHs, residential solid fuel combustion, including traditional biomassand coal fuels, is a large contributor to the total emissions. Traditional solid fuels are mucheasily available and cheaper compared to that clean energy, especially in the rural area indeveloping countries. Large consumptions of these solid fuels for cooking and heating inpeople's daily lives result in high emissions of various pollutants, as well as adverse effectson human health and regional/global climate change. There were very limited studies inChina focusing on the emissions of PM and PAH from indoor solid fuel combustion, whichlimited the accurate estimation of these pollutants. Adoption of published EFs in theliterature which were mainly studied in the developed countries often biases the totalemissions, and produces high uncertainties.In this study, emission factors of PM, organic carbon (OC), elemental carbon (EC)and PAHs from indoor coal, crop residue, and wood combustion were measured under realcombustion conditions in a simulated kitchen. Main innovations of this study include:1) alarge number of EF data measured for residential solid fuel combustions under realisticcombustion conditions, which are necessary for accurate emission estimation;2) based onthe measured EFs, the influence of fuel properties and combustion conditions wereinvestigated, and several most significant factors were identified and quantified;3) theemission characterization, such as particle size distribution and PAH profiles for differentfuels were compared that can be used in source apportionment, health and climate studies;4) evaluation of retene as a unique marker for softwood combustion; and5) measurementon emissions of various pollutants from pellet burning for the first time, and analyze thepotential benefit of the pellet deployment on emission reduction.Measured EFs of PM, OC, and EC were8.19±4.27(3.41-16.8),1.38±0.70 (0.493-2.64), and1.45±0.62(0.354-2.34) g/kg, respectively. EFs of total PAHs were in therange of23.6-142mg/kg, with means and standard derivation of62.1±34.6mg/kg. EFs ofPAHs were comparable to those reported in literature for cooking stoves, but higher thanthose in open burning and EFs measured in laboratory chamber. Due to the relatively smallvolume of cooking stoves, and limited oxygen supply in the stove chamber, it was usuallydifficult to achieve complete combustion in residential fuel burning, and hence, oftenproduced high emissions of pollutants. Crop residue moisture and combustion efficiencywere two most significant factors identified (p <0.05), and about83%and60%of the totalvariations in EFs of PM and PAHs can be explained by these two factors.In residential wood combustion, brushwood produced higher emission factors of PMand PAHs than those for fuel wood. Average EFs of PM, OC, EC, and PAHs forbrushwood were3.74±0.80(3.10-4.63),0.81±0.64(0.21-1.48),1.53±1.01(0.48-2.49) g/kgand86.7±67.6(27.1-160) mg/kg, respectibely. They were2.04±1.38(0.71-6.23) g/kg,0.80±0.85(0.11-3.81) g/kg,0.50±0.36(0.06-1.19) g/kg and12.7±7.0(3.2-32.7) mg/kg,respectively for fuel wood. Total carbon mass fraction in PM for wood was61%,significantly higher than38%for crop residue. EFs of PM decreased with the increase ofcombustion efficiency, but the influence of fuel moisture was not significant. Because theinfluence of various factors often interacted with one another, and there was largevariations in measurements, the impact of a single factor on EFs may not statisticallysignificant.For the coal combustion,5coals studied included2briquettes and3raw chunks. Onehoneycomb briquette was anthracite, and the other four were bituminous. Measured EFsvaried dramatically among these five coals. EFs of PM, OC, EC and PAHs ranged in0.065-10.8g/kg,0.007-1.00g/kg,0.006-0.825g/kg and6.25-253mg/kg, respectively. Anthraciteemitted lower pollutants than bituminous, and EFs for briquette were generally lower thanthose for raw chunk. Thus, it indicated that the emission of pollutants from incomplete coalcombustion was not only influenced by the coal properties, like volatile matter content andheating values, but also related to the geometry of the coal (briquette vs. raw chunk).In comparison with parent PAHs, their derivatives have direct and usually higher toxiceffects.For the first time, EFs of PAH derivatives, including oxygenated and nitrated PAHs,from the residential coal, crop residue, and wood combustion were measured and reported.It was found that EFs of oxygenated PAHs were in the same order of magnitude of parentPAHs, but EFs of nitrated PAHs were much lower than them. PAH derivatives have moretendencies to be present in the particle phase, especially in fine PM.Size distributions of PM emitted from residential coal, crop residue and wood combustions were dominated by the fine PM. On average, PM2.5(PM with diameter lessthan2.5μm) contributed more than77.5%,81.0%and79.4%of the total PM in coal, cropresidue and wood combustion, respectively. PM from fuel wood combustion was finer thanthat from brushwood and crop residue combustion. The former was dominated by the PMwith diameter less than0.4μm, while in the latter, PM with diameter between0.7-2.1μmwas the most abundant.EFs of RET (EFRET) for crop residue, wood and coal combustion were in the range of0.012-0.45,0.042-0.47and1.1-267mg/kg, respectively. Large variations were foundamong crop residue, wood, and coal, and within the fuels of different types. EFRETfor pine(0.34±0.08mg/kg) and larch (0.29±0.22mg/kg) were significantly higher than those ofother wood types, including fir and cypress (0.081±0.058mg/kg). However, EFRETfor cropresidues were not significantly lower than those for softwood. The EFRETfor coal werevery high and ranged from2.2±1.5(anthracite briquette) to187±113mg/kg (rawbituminous chunk). These data suggest that retene is not a unique PAH marker forsoftwood combustion and that coal combustion, in particular, should be taken into accountwhen retene is used for PAH source apportionment.Emissions of CO, OC, EC, PM and PAHs from two biomass pellets made from cornstraw and pine wood, respectively were measured for the first time, and compared withthose for raw materials burned in a traditional cooking stoves. The average EFCO, EFOC,EFEC, and EFPMwere21.1±16.2,0.121±0.158,0.156±0.121, and2.62±1.20g/kg for cornstraw pellets, and4.38±2.25,0.095±0.118,0.033±0.026, and1.17±0.89g/kg for pine woodpellets, respectively. The measured values of EFPAHfor the two pellets were14.1±8.9and8.33±5.94mg/kg, respectively. In comparison with EFs for the raw pine wood and cornstraw, EFCO, EFOC, EFEC, and EFPMfor pellets were significantly lower than those for rawfuels (p <0.05). However, the differences in EFPAHwere not significant (p>0.05). Basedon the decreased EFs and relatively higher thermal efficiencies, obvious reductions in thetotal emissions of these pollutants could be achieved by replacing the raw biomass fuels intraditional cooking stoves with pellets in modern pellet burners.