Pollution Characteristics And Source Apportionment Of Volatile Organic Compounds(VOCs)in Atmospheric Environment In Lanzhou

Volatile Organic Compounds(VOCs)play an important role in the formation of Ozone(03)and Secondary Organic Aerosols(SOA).As a typical industrial city in western China,Lanzhou was the first field evidence of photochemical smog in China in the 1970s,which becomes a milestone of China’s modern air pollution research.Recently,the high emissions of petrochemical industry and the rapid growth of motor vehicles as well as special terrain conditions of "natural smoke box" have made the composite pollution of particle and ozone raised more attention in Lanzhou.As one of important precursors of photochemical smog and ozone,VOCs have attract more and more attentions.The industrial structure of heavy chemical industry makes the industrial emissions the most important source of VOCs in Lanzhou.The heavy industry-based industrial structure makes the emissions of industrial the most important source of VOCs.However,the VOCs sources of local industrial have not been thoroughly studied recently in Lanzhou,especially VOC source profiles of key industries.On the basis of practical investigation,we selected three typical enterprises of petrochemical,ethylene and paint plant as well as four processes of petroleum plant.The characteristic of emission sources were analyzed through sampling with SUMMA tank.Also we investigated the characteristics and chemical behaviors of atmospheric VOCs in Lanzhou.And based on the local VOC source profiles of industrial,the source of VOCs in Lanzhou was discussed.The main conclusions:(1)During the observation period,the overall level of atmospheric VOCs in Lanzhou was 54.9±48.3ppbv with high volatility,and the concentration ranged from 9.5 to 184.2ppbv;There are some significant differences between two observations,the concentration of VOCs during the observation period in May(76.3 ppbv)was 2.3 times that in June;the daily variation of VOCs was not alike in different sampling point.Due to the instability of source emissions in Xigu District,the daily variation was extremely irregular and abnormal increase occurs frequently.However the non-industrial areas showed better photochemical characteristics,which revealed the influence of traffic sources.The spatial distribution of VOCs showed the characteristics of low center and high periphery,with the specific performance of Lanyuan Hotel>Anning District Committee>Environmental Protection Bureau>Qilihe River;the alkane was the most contribution to Lanzhou with more than 50%in different sites,but the contribution of olefins and aromatic hydrocarbons was slightly different in two observations;Although the high-frequency static wind in Lanzhou have little effect on the transmission of pollutants,for long time scales,the small winds under special terrain conditions make the distribution of VOCs at each site affected by petrochemical industrial zone.(2)In terms of emission sources of VOCs,the concentration of VOCs in unorganized emissions of various enterprises is quite different,ranging from 20.8 to 6520.3 ppbv,of which the coating plant has the highest concentration,followed by petrochemical plants.There are obvious differences in the composition of VOCs between different industries.The alkane in petrochemical plants and ethylene plants is the highest,accounted for 82.1%and 51.2%respectively.Due to the production process,the aromatic hydrocarbons of painting plants accounted for 92.2%.It was worth noting that the concentration of high-carbon alkanes is also relatively high;the diesel process was the greatest distributor to petrochemical plant,and there was a good coherence of species between gasoline,kerosene,and diesel process;the main components of VOCs are similar,especially the processes of gasoline and kerosene;Isopentane,ethylene,n-butane and toluene are typical species of petrochemical enterprises.(3)The OH radical reactivity methods(LOH)、the maximum incremental reaction method(MIR)and Principal component analysis method(PCA)were used to analyze the potential formation of O3 and SOA.The results showed that:①Lanyuan Hotel contributed the most to the OFP in Lanzhou with the order of Lanyuan Hotel>Environmental Protection Bureau>Anning District Committee>Qilihe,and OFP was between 61.3～754.9ppbv.Olefins and aromatic hydrocarbons are the key active components of Lanzhou VOCs contributing to OFP.Toluene,isopentane,propylene,n-pentane and all are the major contributors in Lanzhou.②VOCs of Lanzhou contributed a lot to SOA generation with the value of 9.89 μg/m3,especially the Lanyuan Hotel(15.6 μ g/m3).And aromatic hydrocarbons and high carbon alkanes are major contributors to SOAp of Lanzhou,such as dodecane,undecane,n-tanane,m-xylene,toluene,benzene and ethylbenzene.Controlling and emission reduction of dominant species in precedence are key to reducing ozone and particulate matter pollution in Lanzhou.(4)The results of VOCs source in Lanzhou based on the analysis of VOC source profiles of local industrial indicated that local emissions are mainly source of VOCs,and petrochemical industry has a great influence on the distribution of VOCs in the whole region.Petrochemical industry,vehicle emission,solvent usage and combustion sources are major sources of VOCs in the city,which contributed to 33.9%,31.6%,19.2%and 7.9%of the total monitored VOCs,respectively.Besides,the Lanyuan Hotel area is greatly affected by the emissions from surrounding industrial areas,while the Qilihe and Environmental protection bureau are significantly affected by traffic sources.