| In Jing-Jin-Ji area,particle pollution has caused a series of problems,such as environmental deterioration,climate change,health issues,etc.The burning of biomass can emit a large amount of gaseous pollutants,VOCs,PAHs,and dioxins,and contributes a lot of global atmospheric particulates.According to previous researches,in Beijing,the annual contribution of PM2.5 from the biomass burning is about 11%and up to 44%.Inoder to control the PM2 5 pollution from biomass buring,the vegetation can be applied which have an effct of absorbtion,interception of PM2.5.By now,there are little study about the evaluation of the vegetation,and the invetistion or simution study is needed to reveal the effect of vegetation on surface air PM2.5 removal.To study the secondary pollution caused by biomass burning pollutants,we designs and processes biomass burning simulator cabin and small outdoor smog chamber independently.Based on these equipment,a natural process of atmospheric photochemical reaction from corn straw burning was simulated.This study tested the burning cabin and the smog chamber first.On the basis of guaranteeing the reliability and stability of the experimental system,the characteristics of primary pollutants emitted directly from the burning process were examined.According to the results,the emission factor of NOx is 12.76±44.11 g/kg,the emission factor of PM2.5 is 4.89±3.30 g/kg.After determining the parameters of the smog chamber through characterization experiments,photochemical simulations were carried out in autumn,winter and spring.The results showed that,with the accumulation of O3 and the increase of PM2.5 concentration,the typical photochemical reaction occured in each experiment.98 kinds of VOCs in biomass burning smoke were measured.The average concentration of total VOCs collected in the dark chamber was 158.980±24.852 ppb.During the reaction,the substance which increased most was acetaldehyde,and the major reductions were ethylene and propylene.The conversion of olefins to OVOCs occurred.41 kinds of organic compounds in particle were detected.Levoglucosan,the markers of biomass burning has the highest concentration of organic compounds in primary particles,which accounted for 58.28%.After the photochemical reaction the saccharides decreased nearly 44.17%on average,aliphatic acid decreased 0.64%.However,PAHs got 4.40%increase on average,n-alkanes got 19.54%increase,and aromatic ester got 20.01%increase.Typical photochemical reactions occurred in all experiments,and secondary pollutants were detected and analyzed.It is showed that although the ultraviolet radiation is relatively weak in winter,it is enough to cause photochemical reactions of pollutants emitted from biomass burning.The invesgitation and simulation of PM2 5 depostion by vegetation were carried out.The results showed that vetigation can absorb and remove the PM2 5 efficiently,and the size distributions and quality concentrations of PM2.5 were changed obviously.The simulation results show that the amount of particulate matter adsorbed by Sophora japonica and Buxus megistophylla was nearly saturated after 11 h.Plants have the most significant effect on the 50-2500 nm particles.In the range of 10-10000 nm,the average adsorption rates of the five plants were 65.14%(Sophora japonica),59.10%(Hosta plantaginea),55.81%(Rosa chinensis),49.59%(Spiraea Salicifolia),and 43.74%(Buxus megistophylla).The average adorption rate of Sophora japonica was higher than other plants,probably because of the rich foliage structure of trees,which played an effective role in adsorption and interception.By calculating the deposition flux and velocity of eight water-soluble inorganic ions(sodium,ammonium,potassium,magnesium,calcium,chloride,nitrate,and sulfate)in PM2.5 during different time periods,the deposition characteristics of these ions above the forestry system were determined.In general,the total deposition flux of the eight ions measured in the JNFP was greater than that in the OFP.This can be explained by the difference in tree species at the sampling sites,and the different meteorological conditions.The total deposition flux during the day was higher than that at night.Sulfate showed the largest deposition flux in both the JNFP and OFP,whereas other ions showed different characteristics at these two sampling sites.Similar to deposition flux,the deposition velocities of all eight ions were higher in the JNFP than in the OFP and were higher in the day than at night.We also demonstrated that deposition velocity was affected by friction velocity,tree species and meteorological conditions(wind speed,temperature,and humidity).Both in the two investigation sites(JNFP and OFP),the concentration of NO3-,Ca2+,SO42-were higher than other inorganic ions.The conifers had higher ablility to remove PM2.5 than the broad-leaved trees. |
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