Emission Characteristics of Organic Carbon and Elemental Carbon in Particulate Matters from Coal-Fired Boilers in Xi'an City
Coal-fired boilers are one of the important emission sources of carbonaceous aerosols in urban areas.In this study,a multifunctional portable dilution channel sampler and a Model 5L-NDIR OC/EC analyzer were used to collect the mass concentration of organic carbon(OC)and elemental carbon(EC)in PM10 and PM2.5,which were from nine coal-fired boilers in Xi'an city.Among the particulate matters emitted from coal-fired boilers,we find that the mass fraction of OC in PM2.5 was higher than that in PM10,while the counterpart of EC was higher in PM10.The mass fractions of OC,EC,and total carbon(TC)in PM10 were 4.35％±1.09％,4.25％±1.02％and 8.60％±1.87％accordingly,and were 6.91％±1.09％,2.62％±0.41％and 9.53％±1.40％,respectively,in PM2.5.The OC/EC ratios(refer to their concentration ratios)varied greatly for particulate matters from different boiler types,which were 1.50±0.96,0.89±1.06 and 12.03±8.48 in PM10,and 6.72±5.70,1.19±0.65 and 11.62±5.83 in PM2.5,respectively,from the chain-grate boiler,fluidized bed boiler and pulverized coal-fired boiler.In additional,the dominant components of carbonaceous aerosols in PM10 and PM2.5 changed significantly with different boilers,which can be used to accurately distinguish their major sources as a result.The mass proportions of TC and EC in PM10 ranked in the order of chain-grate boiler(10.64％±5.13％and 5.79％±4.78％)＞fluidized bed boiler(7.25％±2.23％and 4.15％±1.14％)＞pulverized coal-fired boiler(4.85％±1.84％and 0.50％±0.25％),and were chain-grate boiler(4.85％±2.33％)＞pulverized coal-fired boiler(4.35％±2.09％)＞fluidized bed boiler(3.10％±3.37％)for those of OC.However,the fractions of TC and OC in PM2.5 were in the order of chain-grate boiler(12.97％±5.57％and 9.25％±5.63％)＞pulverized coal-fired boiler(5.57％±1.86％and 5.02％±1.79％)＞fluidized bed boiler(4.92％±5.41％and 2.94％±3.53％),and were chain-grate boiler(3.71％±3.84％)＞fluidized bed boiler(1.97％±1.88％)＞pulverized coal-fired boiler(0.55％±0.07％)for the counterparts of EC.Different types of boilers have greater impacts on EC in PM10 and OC in PM2.5.This is mainly due to the discrepancy in coal combustion methods and combustion efficiencies of different boiler types.
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