Study On Biogenic Volatile Organic Compounds Emission From Forest Plants In Beijing

Volatile organic compounds（VOCs）are important precursors in atmospheric chemistry and photochemistry.They can produce ozone（O₃）and secondary organic aerosol（SOA）that are harmful to the environment.The ozone pollution in Beijing’s summer atmosphere is serious,and Biogenic Volatile Organic Compounds（BVOCs）play a key role in the formation of ozone pollution.This paper takes Beijing forest plants as the research object,based on the national forest resource second-level survey results.Screens the dominant forest plants and calculates the forest plants leaf biomass.Using dynamic heasspace sampling monitor the BVOCs emission rates of forest plants in Beijing.Using the G95 model,simulated the BVOCs emissions of Beijing forest plants in 2017.The BVOCs emission distribution and characteristics of forest plants in Beijing were analyzed.The results are as follows:BVOCs emissions rates from 24 dominant plants in Bejing were monitored in this study.Isoprene and monoterpenes are most common components of BVOCs emitted by plants.Generally,deciduous tree species have a higher emission rate of isoprene and evergreen tree species have a higher rate of monoterpenes.The three plants with the highest rate of isoprene were Platanus occidentalis(21.36μg g^-1 h^-1),Robinia pseudoacacia(11.55μg g^-1 h^-1),Lonicera maackii(9.17μg g^-1 h^-1),but there are also evergreen plants that emit isoprene at a higher rate.For example,the emission rate of isoprene from Taxus cuspidata is 5.86μg g^-1 h^-1.The three forest plants with the highest monoterpenes emission rates are Platycladus orientalis(27.18μg g^-1 h^-1),Pinus armandii(23.11μg g^-1 h^-1)and Buxus megistophylla(13.07μg g^-1 h^-1);In 2017,the total amount of BVOCs emissions from forest plants in Beijing was 43,601.91 tons.Among them,Miyun,Yanqing and Changping were the three districts with the largest BVOCs emissions.Their total BVOCs emissions amount were 5805.71 tons,4942.62 tons and 4639.99 tons.The remaining eight districts are ranked by the largest to the smallest:Huairou 4102.82 tons,Chengliuqu 4004.24 tons,Fangshan 3964.94 tons,Tongzhou 3788.11 tons,Daxing 3635.36 tons,Mentougou 3375.51 tons,Shunyi 3275.23 tons and Pinggu 2153.38 tons.Monoterpene and isoprene are the main components of BVOCs emission in Beijing,with a contribution rate of 33.86%and 29.12%.Shrubs,hardwood and arborvitae are the main emission plants of BVOCs,accounting for 45.88%,16.53%and 11.84%of the total emissions of volatile organic compounds in Beijing,respectively.July is the month with the highest forest plants BVOCs emissions of the year,with an emission of 9634.06 tons.Summer is the season with the highest BVOCs emissions in Beijing.Among the 24 dominant plants selected in this study,volatile organic compounds emitted by Platanus occidentalis,Robinia pseudoacacia,Lonicera maackii,Phyllostachys propinqua and Platycladus orientalis had the highest OH reactivity.Compared with other BVOCs,isoprene,α-pinene,β-pinene,γ-terpinene and limonene have higher OH reactivity.And isoprene and monoterpenes are the two types of BVOCs with the highest emissions.Therefore,in Beijing,shrubs,arborvitae,oak trees,and Chinese pine all have important effects on atmospheric photochemical processes due to the emission of large amounts of high-OH reactivity BVOCs.At the same time,this study estimatedt the isoprene and monoterpenes OFP emissions from Beijing’s forest plants in 2017 were 134,800 tons and 76,600 tons,.As the OFP emissions of plants increase with the increase of their isoprene and monoterpene emissions,several plants that contribute more to the forest plant OFP in Beijing are shrubs,oak trees,hardwood and arborvitae.