Volatile Organic Compounds Emitted From Forest Plants And Its Effects On The Formation Of Secondary Pollutants

Biological processes of ecosystem have important effects on the atmosphere and the earth’s climate,volatile organic compounds(VOCs)is the key material contact biosphere and atmosphere chemical cycle.Volatile organic compounds emitted from forest vegetation accounted for more than 90%of the total volatile organic compounds,emissions as many as thousands of sorts,they have the physiological ecology function such as sterilization,air purification,but also have high reactivity,can react with atmospheric oxidation material,generate secondary organic aerosols,and have significant influence of tropospheric ozone formation,global radiation balance,the carbon cycle and the formation of atmospheric photochemical smog.Figuring out a research into emission mechanism of plant volatiles,and identifying the source of activity VOCs species were of great importance for play its role effectively in environmental purification.With the rapid development of our country economy,environmental pollution was became increasing serious,with characterized by fine particulate matter pollution of atmospheric compound pollution is growing.In the backgoround of the environment pollution,on the one hand,forest vegetation can change the forest meteorology through direct ground cover,and capture atmospheric particulate matter through the unique structure of branches and leaves,on the other hand,forest vegetation emissions of volatile organic compounds,on the other hand,secondary organic aerosols was light oxidation products of VOCs which become an important precursor of atmospheric particle pollution,the action mechanism of negative effects of SOA is still lack of comprehensive understanding.Therefore,this study selected Pinus tabuliformis,arborvitae(Platycladus orientalis),cork oak(Quercus variabilis),Populus tomentosa and black locust(Robinia pseudoacacia)five dominant forest tree species in Beijing mountainous,identifying the types and composition of volatile organic compounds systematic,calculating the emission rate of different volatile organic compounds and their response to the environmental changes,quantifying emission potential from per unit leaf area to forest stand with scale conversion.Based on the above research,adopting the combination way of the indoor simulation and the field observation,online monitoring the variation of composition and concentration of VOCs in system,dynamic monitoring the new components of particulate matter,and derived the reaction pathways of SOA nucleation.Study on the SOA nucleation mechanism by tracking the size change of ultrafine particles,and analyze time and space heterogeneity of particle size distribution,source,molecular characteristics,chemical properties of biogenic secondary organic.The main results were as follows:(1)Volatile organic compounds emitted from different forest tree species have time difference.From total volatile organic compounds point of view,the types of volatile organic compounds emitted from different tree species show some seasonal differences,summer>autumn>spring>winter.From the diurnal variation point of view,the types of VOCs emitted from conifer trees showed peak value in the period of 11:00—12:00 or 13:00—14:00,present unimodal trend with first increase then decrease.Coniferous tree species(Pinus tabulaeformis,Platycladus orientalis)and broad leaved tree species(Quercus variabilis,Populus tomentosa and Robinia pseudoacacia)release more terpene compounds.(2)The relative content of volatile organic compounds emitted from different forest tree species has time difference.From total volatile organic compounds point of view,the relative contents of volatile organic matter emitted from tree species show seasonal differences,summer>autumn>spring>winter.From the diurnal variation point of view,the relative contents of volatile organic matter emitted from Pinus tabulaeformis,Platycladus orientalis、Quercus variabilis,Populus tomentosa and Robinia pseudoacacia showed higher probability value during 13:00—14:00 and 15:00—16:00 in the spring,summer,autumn and winter,and show unimodal type change trend with first increase.In terms of specific terpene compounds,the relative content of isoprene emitted from five kinds of tree species peaked at 11:00-12:00,and show unimodal type change trend with first increase.The relative content of monoterpene emitted from five kinds of tree species showed "double peak valley" type change,peak value occurred during 11:00-12:00 and 15:00-16:00.(3)Terpene compounds emitted from different forest trees have certain differences.Coniferous tree species(Pinus tabulaeformi and Platycladus orientalis)main emit terpene,main including α-pinene(25.05%),P-pinene(13.29%)and myrcene(10.64%),parsley(5.81%),3-carene(13.91%),sabinene hydrate(10.7%).Broadleaf tree species mainly emitted isoprene,the relative content of isoprene emitted from Quercus variabilis,Populus tomentosa and Robinia pseudoacacia accounted for total volatile organic compounds 55.25%,76.47%,45.33%,respectively.(4)Isoprene emitted from broadleaf tree species is higher,the emission rate of Populus tomentosa is the biggest.Coniferous tree species(Pinus tabulaeformis,Platycladus orientalis)main emit monoterpene.The emission rate of a-pinene,myrcene and carvene of unit leaf area of pinus tabulaeformis rate is higher,the emission rate of a-pinene,limonene and phellandrene of unit leaf area is higher.The emission rate of terpenes showed a consistent variation trend wih temperature and illumination,it increases reach up to peak value with the increase of temperature and light,and decreased minimum with the decreasing of temperature and light at night.(5)Contrasting the emission potential of monoterpene,Pinus tabulaeformis>Platycladus orientalis>Quercus variabilis>Populus tomentosa>Robinia pseudoacacia.From the seasonal emission potential point of view,summer>autumn>spring>winter,potential emissions of summer is eight times higher than in winter.From emission potential of different months in different point of view,the biggest emission potential of Pinus tabulaeformis,Platycladus orientalis,Quercus variabilis,Populus tomentosa and Robinia pseudoacacia community slightly were in July(1.32 mg·m-2·h-1,1.19 mg·m-2·h-1,0.87 mg·m-2.h-1,0.73 mg·m-2·h-1,0.69 mg·m-2·h-1),the minimum was in January(0.12 mg·m-2·h-1,0.08 mg·m-2·h-1,0.1 mg·m-2·h-1,0.06 mg·m-2·h-1).(6)The terpenes emitted from coniferous tree species(Pinus tabulaeformis,Platycladus orientalis,)and broad leaved tree species(Quercus variabilis,Populus tomentosa and Robinia pseudoacacia)were positively correlated with temperature and illumination,and negatively correlated with relative humidity.The emission rate of terpene exponentialy increase wih temperature at a certain range.The emission rate of terpene showed nonlinear increase with illumination at a certain range,and reach smooth in the light to a certain extent.The emission rate of terpenes emitted from different tree species showed significantly positively correlation with net photosynthetic rate(Pn)and transpiration rate(Tr).The emission rate of monoterpenes showed significantly positively correlation with net photosynthetic rate(Pn),stomatal conductance(gs)and transpiration rate(Tr),and negatively correlated to the intercellular carbon dioxide concentration(Ci).(7)The contribution of terpenes for the formation and growth of secondary organic aerosols was higher by react with O3.When the concentration of O3 increases from 100 ppbv to 400 ppbv,the particle number concentration increased 3.76×103 particles·cm-3,and the particle size increased from 9.8 nm to 25.53 nm.When the concentration of O3 increases from 200 ppbv to 400 ppbv,the particle size increase obviously,however O3 concentrations for 100 ppbv,the particle number concentration was low,particle size change is not obvious.(8)The concentration of photochemical product of isoprene(3-MeTHF-3,4-diols(tra ns-3-methyltetrahydrofuran-3,4-diol and cis-3-methyltetrahydrofuran-3,4-diol),2-methy glyceric acid,C5-alkene,2-methylterols)was 0.87 ± 0.33 μg·m-3,6.13±2.36 μg·m-3,17.64±1.82 μg·m-3 and 8.12±2.14 μg·m-3;The concentration of photochemical p roduct of α-/β-pinene(cis-pinonic acid,3-hydorxyglutaric acid,3-methyl-1,2,3-butanet ricarboxylic acid)was 7.25 ± 1.87 μg·m-3、4.64 ± 1.52 μg·m-3 and 3.12±1.14 μg·m-3;The concentration of photochemical product of β-caryophyllene β-caryophyllinic a cid)was 3.44 ± 1.53 μg·m-3.The concentration of secondary organic aerosol was p ositively correlated with atmospheric temperature and negatively correlated with atm ospheric relative humidity.(9)The concentration of secondary organic aerosols in fine particle modal was larg er.The concentration of 3-MeTHF-3,4-diols,C5-alkene,2-methylterols(photochemica 1 product of isoprene)reach peak value at 0.4 nm、0.7 nm and 0.8 nm,respectivel y,however 2-methyglyceric acid reached peak value at 0.7 nm and 0.8 nm,respec tively.The concentration of cis-pinonic(photochemical product of α/β-pinene)reach ed peak value at 0.8 nm and 3.3 nm,respectively,however 3-hydorxyglutaric acid and 3-methyl-1,2,3-butanetricarboxylic acid(MBTCA)present unimodal distribution,reached peak value at 0.4 nm and 3.3 nm,respectively.The concentration of β-cary ophyllinic acid(photochemical product of p-caryophyllene)reached peak value from 0.4 nm-3.3 nm.The concentration of succinic acid,glutaric acid and o-phthalic a cid present bimodal distribution,reached peak value from 0.5 nm-4.7 nm;howeve r malic acid,m-phthalic and p-phthalic unimodal distribution,reach peak value at 0.8 nm、1.1 nm and 1.1 nm,respectively.(10)Olefin substance emission from the conifer and broadleaf species had the biggest contribution rate for the formation of secondary fine particulate matter.The volatiles compounds emitted form P.tabuliformis generates SFPM with 7.43 μg/m3(spring),12.56μg/m3(summer),7.43 μg/m3(fall)and 1.55 μg/m3 in winter.Pinus tabulaeformis and α-pinene and β-pinene of olefin emitted from P.tabuliformis and P.orientalis had the highest contribution to the formation SFPM.The volatiles compounds emitted form P.orientalis generates SFPM with 6.46 μg/m3(spring),9.27 μg/m3(summer),8.56 μg/m3(fall)and 1.33 μg/m3 in winter.The Volatiles compounds emitted form Q.s variabilis generates SFPM with 5.19 μg/m3(spring),11.09 μg/m3 mu(summer),and 5.69 μg/m3(fall).The volatiles compounds emitted form P.tomentosa generates SFPM with 6.94 μg/m3(spring),9.86 μg/m3(summer),and 7.85 μg/m3 SFPM(fall).The volatiles compounds emitted form R.pseudoacacia generates SFPM with 7.82 μg/m3(spring),9.26 μg/m3(summer),and 5.69μg/m3(fall).Olefin had the highterst contribution to the formation of SFPM among volatile organic compounds emitted from five tree species in different seasons.α-pinene,β-pinene 3-carene,β-caryophyllene and longifolene on the contrition of SFPM formation were highest among broadleaved tree species.