Characteristics Of VOCs In The Northern Suburbs Of Nanjing And Their Impact On Ozon

In recent years,air pollution problems were highlighted,and the hazards of volatile organic compounds（VOCs）in photochemical pollution and human health problems cannot be ignored.Meanwhile,as the main precursors of ozone（O₃）,VOCs play an important role in O₃ pollution.In this paper,we explored the basic characteristics of the above pollutants using the observed data from 2014 to 2016 in the northern suburbs of Nanjing,including VOCs and other pollutants(NO,NO₂,CO,SO₂,O₃ and PM_2.5).Then,the positive matrix factorization（PMF）source resolution method,combined with backward trajectory and concentration weighted trajectory（CWT）methods,was used to investigate the influence of VOCs sources and long-range transport.Finally,the characteristics of pollutants such as VOCs on O₃ pollution days and clean days were discussed,and the sensitivity of O₃ generation on O₃ pollution days and clean days,and the abatement measures for pollutants such as VOCs were explored using the NCAR Master Mechanism（NCAR mm）model.The results indicate that:From 2014 to 2016,the volume fraction of TVOC（alkanes,alkenes,alkynes,and aromatic hydrocarbons）decreased from（39.4±23.1）×10^-9 in 2014 to（36.2±20.5）×10^-9 in 2016.There was a significant seasonal variation in TVOC between 2014 and 2016,with its volume fraction being highest in winter and the lowest in spring.In contrast,both ozone formation potential（OFP）and secondary organic aerosols potential（SOAP）showed high values in summer.BTESX（benzene,toluene,ethylbenzene,m/p-xylene,o-xylene and styrene）as important species of VOCs.Meanwhile,there were seasonal differences in BTESX,whose volume fraction was highest in summer,and also,more attention should be paid to the hazards of BTESX in summer.From 2014 to 2016,there were seven sources of VOCs,of which LPG/NG（26.1%～39.1%）and industrial emission sources（27.6%～35.1%）were the main sources of VOCs.While LPG/NG and petrochemical industrial sources-alkenes contribute the most to OFP,with the sum of their contributions approaching or exceeding 50%,the contribution of steel industrial sources（15.0%～15.6%）and solvent use（6.10%～22.2%）to OFP cannot be ignored.In 2014and 2015,the contribution of LPG/NG in the western direction was greater than that in the east,while in 2016,the contribution of LPG/NG in the west was less than that in the east.from 2014to 2016,the contribution of steel industrial sources,vehicle emissions and petrochemical industrial source-benzene were much lower in the west than in the east.in 2014 and 2015,the high value areas of LPG/NG and solvent use were concentrated in Nanjing local and surrounding cities;the high value areas of each industrial emission source were mainly distributed in the eastward direction of the observation point.Due to the rapid development of urbanization and industrialization in recent years,the high value areas of solvent use,vehicle emissions and steel industrial sources shifted to Zhejiang and Anhui provinces in 2016.The volume fraction of TVOC was（42.1±22.4）×10^-9 on the O₃ pollution day,which was lower than that of the O₃ clean day[（46.0±15.1）×10^-9].O₃ generation was mainly controlled by VOCs on O₃ pollution days.It was recommended to reduce VOCs from solvent use,vehicle emissions,and petrochemical industrial-benzene.However,to more effectively improve O₃pollution,the reduction proportion of NO_x was also crucial.For example,when reducing VOCs from steel industry,the reduction proportion of NO_x should be below 40%or above 80%;when reducing VOCs from petrochemical industrial-alkenes,the reduction proportion of NO_x should be above 40%.On O₃ clean days,both VOCs and NO_x contribute to the control of O₃ generation.It was essential to consider the reduction proportion of NO_x when reducing TVOC to prevent an increase in O₃.In this case,when controlling the VOCs emitted from steel industrial,the reduction proportion of NO_x should be between 60%and 80%;when controlling VOCs from petrochemical industrial-benzene and bio-emissions,the reduction proportion of NO_x should be below 80%.