Measurement and distribution characteristics of emission factors of pollutant emission in solid fuel combustion in rural areas of western China
Background,aim,and scope Solid fuels such as biomass and bulk coal are the primary energy sources for cooking and heating in rural areas of China.However,low combustion efficiency and the large amounts of pollutants emissions from solid fuels combustion cause a decline in regional air quality and damage to human health.Regional emission factors are a key factor in evaluating regional pollutant emissions which are important for regional air pollution control.In order to localize the emission factors for western China's rural areas,a portable dilution sampling system was designed and established,and the emission factors of CO2,CO,OC,EC and PM2.5 were calculated after field investigation and sampling.Materials and methods A portable dilution sampling system was used to collect the flue gas from solid fuel combustion.The concentrations of CO2 and CO were measured by in-line instruments.The filter was weighed by a high precision electronic balance,OC and EC were analyzed by a DRI model 2001A OC/EC carbon analyzer,and the emission factors were calculated following carbon balance method.Results Because coal has higher carbon content,the emission factors of CO2 and CO of coal are(2375.30±365.28)g·kg-1 and(147.11±126.92)g·kg-1,respectively,which are larger than those of firewood and straw.Firewood and straw have higher emission factors of OC,EC and PM2.5,since they burn less efficiently than coal and tend to produce more pollutants.In this study,the values of emission factors in this study are generally higher than the results measured in lab.This could be due to the fact that lab can control the fuel and combustion process more precisely,while uncontrolled combustion releases more pollutants in real life.Additionally,the type of stove has a great influence on emission factors of OC and PM2.5 of fuel wood.The emission factors for Kang were found to be about 2—3.1 times higher than those for brick stove and metal stove.Burning coal in metal stoves and firewood in brick stoves can relatively reduce emissions of solid fuel pollutants in rural areas.It is important to note that the emission factors of CO2,CO,OC,EC and PM2.5 present obviously regional difference due to differences of combustion habits in different regions.Discussion Analyzing the variations of emission factors of CO2,CO,OC,EC and PM2.5,it was found that fuel types and stove types have effect on emission factors and combustion habits cause regional distribution of emission factors.Coal has higher CO2 and CO emission factors due to its high carbon content,while straw and firewood have higher OC,EC and PM2.5 emission factors because of their relatively insufficient combustion,which tends to produce more pollutants.The type of stove had a greater impact on the OC and PM2.5 emission factors when using firewood,but had a lesser impact on the emission factors when using straw.The values in this study were slightly higher compared to the laboratory results,possibly due to the release of more pollutants from uncontrolled combustion processes in real life situations.Significant geographical differences in emission factors exist due to variations in combustion habits across different regions.The high CO2 emission factors are distributed in the regions where coal is the main fuel,and the high OC,EC and PM2.5 emission factors are distributed in the regions where biomass is the main fuel.Conclusions Emission factors are influenced by combustion habits such as the type of fuel and stove.Therefore,localization of emission factors is helpful for obtaining more accurate emission inventories.Recommendations and perspectives The findings of this study address the existing gap in regional emission factors,which can significantly reduce the variability of emission results,and provide basic data for assessing pollutant emissions from rural areas in China.Further investigation is necessary to identify specific reasons for differences between field and laboratory measurements,as the complex influences of field measurements can significantly impact emissions.