The Emission Factors And Components Of PM_2.5 From Combustion Of Main Tree Species In Fujian

The release of large amounts of particles from biomass combustion has an important impact on the atmosphere,ecosystem and human health.About one billion tons of biomass combustion and emissions of particulate pollutants to the atmosphere in the world every year,in which forest fires in the biomass burning particles in the emission contribution of up to 42%.In addition,the frequency of future forest fires is still increasing with global climate change.Previous studies of forest fire emissions focused on pollutant emission inventory,emission characteristics of flue gas,migration and movement of flue gas and estimation of flue gas emission the analysis of emission characteristics and composition of particulate matter in flue gas is not thorough enough.Studies have shown that forest fires release particulate matter,especially fine particulate matter PM2.5(the proportion of PM2.5 in the particles is more than 90%),it can enrich many harmful substances,such as organic matter and ion,and can float in the ecosystem for a long time.This has a profound effect on forest ecosystem,atmospheric environment and human health.Fujian province is located in the subtropical area,the forest fire occours frequently due to the influence of natural factors and human activities.In addition,the forest production and management behavior such as slash burning will lead to a large number of forest fuel combustion.Which further increases the emissions of particulate matter from flue gas.Therefore,it is of great significance to explore the emission characteristics and chemical composition of PM2.5 from the main tree branches in Fujian Province,and to reveal the relationship between the smoke released from forest fires and the regional environment.However,there are few studies on forest fire emissions in Fujian,and there are few reports on PM2.5 emissions and composition analysis.The branches and leaves of four dominant tree species(Cunninghamia lanceolata Hook,Pinus massoniana,Eucalyptus robusta Smith,Cinnamomum camphora L.,Keteleeria fortunei(Murr.)Carr and Phoebe bournei)were burned based on independent-designed biomass combustion system for analyzing the variation of emission factor of PM2.5 and chemical composition between tree species under different combustion conditions.Comparison and analysis of different PM2.5 emission characteristics and components under different tree organs(branches,leaves)and different burning stage(smoldering,flaming),and provide basic data for impact assessment of forest fires in Fujian province on regional environment.The main results are as follows:1.There are significant differences in PM2.5 emission factors between different tree branches and leaves during smoldering and flaming.The mean PM2.5 emission factors of leaf smoldering and flaming are 28.61±4.90 g/kg,10.91±3.32 g/kg,respectively,and the mean value of PM2.5 emission factor of branches are 21.09±2.86 g/kg,9.74±2.76 g/kg,respectively.Leaves and branches are significantly higher than that of smoldering stage,and the same burning stage,PM2.5 emission factor of leaves is greater than the tree branches.The results show that the contribution of fine particles emitted from coniferous trees is more than that of broad-leaved trees leaf tree.2.The average range of TC content in PM2.5 released from branches and leaves burning was 51.3%-61.9%,of which,OC was about 40.2%-50.7%and EC was 7.7%-21.7%.Smoldering stage accelerates the release of OC;however,the release of EC is promoted by flaming stage.The ratio between OC,EC and PM2.5 can be used to distinguish the different combustion conditions.3.The content of water-soluble ions in PM2.5 released by branches and leaves burning varied between different tree species and also being affected by the burning stage.The total content range of 10 ions is 2.9912.74%,K+and Cl’ are two main water-soluble ions.The emission factors of same water-soluble ion under smoldering is greater than that under flaming stage.The correlation between anions and cations varies greatly with different combustion states,so the binding modes of water-soluble anions in particulate matter will be different with different combustion states.4.Sixteen kinds of water-soluble inorganic elements are detected in PM2.5 from different tree branches and leaves,among which K,Ca,Na,Mg and P elements as plant growth elements are the main elements in PM2.5 of branches and leaves burning.For heavy metal elements,the contents of Zn and Cu in PM2.5 were relatively high.The element emission was higher than flaming during smoldering state.The content of inorganic elements in PM2.5 of Chinese fir,camphor and Phoebe leaves was higher than that of tree branches,but the difference of other tree species was not significant.5.There are significant differences in 16 kinds of polycyclic aromatic hydrocarbons(PAHs)between smoldering and flaming in PM2.5 from different tree branches and leaves.The total concentrations of PAHs in PM2.5 emitted from leaves during smoldering and flaming are 0.49-6.63 mg/g,0.48-4.13 mg/g,respectively,and the branches are 2.68-38.31 mg/g,0.87-23.78 mg/g,respectively.Under different burning stage,the PAHs in PM2.5 emissions from different tree branches under smoldering are higher than flaming stage;and Under the same burning stage,the PAHs in PM2.5 emitted from tree branches is higher than that in leaves.6.The carbon number distribution of 23 n-alkanes detected in PM2.5 from different tree branches and leaves under different burning stage is C8-C40.The burning of leaves and branches showed a single peak distribution with C18 as the main peak.The total of n-alkanes in PM2.5 from different tree leaves are 3.10-13.34 mg/g,1.78-15.29 mg/g,respectively,and 4.73-13.75 mg/g,1.45-17.19 mg/g of branches during smoldering and flaming stage,respectively.Under different burning stage the n-alkane in the PM2.5 emitted from the tree species under smoldering is higher than that in the flaming except Masson pine.Under the same burning stage,the n-alkane in the PM2.5 burning by tree branches was not significantly different from that in the leaves.