Non-target Screening Of VOCs And Its Ozone Formation Potential

Volatile organic compounds（VOCs）widely exist in the air,which have an important impact on the atmospheric environment and can generate ozone and secondary organic aerosols.It can provide support for the prevention and control of VOCs and O₃pollution by studying the concentration level,pollution characteristics and atmospheric chemical reactivity of VOCs.At present,researches mostly focus on the analysis of VOCs emissions from anthropogenic source such as industrial areas,while there are relatively few studies on BVOCs in urban ambient air.VOCs have diverse components and complex structures.When using target analysis to monitor VOCs,it may not be possible to fully understand the pollution characteristics of VOCs.Non-target screening is a new analytical method to identify unknown substances in complex environmental media based on high-resolution mass spectrometry technology,which can conduct a more comprehensive analysis of sample data without taking a specific target as a preset research object.In this paper,a non-target screening method was established taking VOCs in ambient air as the object.The method was used to qualitatively analyze Dalian ambient air samples,and quantitatively analyze the identified VOCs.The pollution characteristics and atmospheric chemical reactions of VOCs were studied.In order to more comprehensively identify VOCs in the atmosphere,a non-target screening method for VOCs was constructed using GC-Orbitrap/MS.By establishing a high-resolution spectral library of VOCs,the qualitative efficiency of VOCs is improved;the matching index thresholds of search score（SI）and high-resolution filter score（HRF）are selected to be 700 and 80,respectively,to reduce the probability of false positive results and improve the screening efficiency of unknown compounds;EI and CI modes were comprehensively used to obtain molecular and fragment ion information of compounds;a retention index prediction model was established to solve the problem of missing RI information in the NIST spectral library.Based on the constructed non-target screening method,ambient air samples in Dalian City characterized by traffic and plant emissions were collected and analyzed.The results showed that a total of 253 compounds were identified in the two types of ambient air samples from plant source and traffic source in Dalian,of which 154 were qualitatively at level 1 or 2a.Quantitative and semi-quantitative analysis of the identified VOCs showed that the average values ofφ（TVOCs）at the sampling points of traffic source and plant source were（22.5±10.4）×10^-9and（16.7±6.06）×10^-9,respectively.The propylene-equivalent concentration method（PEC）and the maximum incremental reactivity method were used to evaluate the reactivity and ozone formation potential（OFP）of VOCs,and identify key active components of VOCs that affect the generation of O₃in Dalian.The result shows that aromatic hydrocarbons and OVOCs have higher PEC and OFP contributions.In this study,the estimated OFP can be increased by more than 11%after including these screened out VOCs which received less attention in the past.This study established a non-target screening method for VOCs with GC-Orbitrap/MS as the main instrument.The pollution characteristics of VOCs from traffic source and plant source in Dalian and their effects on ozone formation were analyzed based on this method.It provides a scientific basis for the prevention and control of VOCs and O₃pollution in Dalian.