| In recent years,Zhengzhou has faced a complex air pollution problem of ozone?O3?and haze.As the important precursor of O3 and secondary organic aerosol?SOA?,volatile organic compounds?VOCs?have attracted wide attention.This study took VOCs as the object,and carried out offline observation of VOCs in an urban area of Zhengzhou in May 2018 and January 2019,respectively.The changes of concentration,composition characteristic and sources of VOCs during O3 pollution period and haze pollution period were studied,and the regional transmission sources of VOCs were analyzed.We also evaluated the potential contribution of components and sources of VOCs to the formation of O3 and SOA and potential risks to human health.Meanwhile,the characteristics of the two pollution periods were also compared and analyzed.First,based on the laboratory analysis,the average mixing ratios of VOCs during O3 and haze pollution periods were?29.11±15.33?×10-9 and?44.51±25.12?×10-9,respectively.Oxygenated VOCs was the main component,ethyl acetate and acetone were the most abundant species.The mixing ratio of VOCs during haze pollution period was higher than that of O3 pollution period.During the O3 episode,the mixing ratio of VOCs decreased by 11.7%compared with the non-O3 episode,and other components except sulfide showed the downward trend,with the largest decrease in aromatics.With the increase of pollution level of particulate matter during haze pollution period,the mixing ratios of VOCs and most components continued to increase,and aromatics,halocarbons and sulfide might play important roles in the evolution of pollution.Then,based on the positive matrix factorization model,five VOCs sources were identified in this study.During O3 pollution period,they were solvent utilization?33.7%?,industrial emission?21.8%?,long-lived and secondary species?17.8%?,vehicular emission?17.7%?,and biogenic emission?9.0%?.There were significant differences in the source contributions of solvent utilization and industrial emission during non-O3 and O3 episode.The five sources obtained during haze pollution period were vehicular emission?29.3%?,industrial emission?20.4%?,solvent utilization?17.8%?,combustion source?17.4%?,and LPG utilization?15.1%?.There were significant differences in the source contribution at different pollution levels,and the control measures of industrial emission and solvent utilization should be strengthened in winter.Affected by seasonal emission characteristics,there were differences in the sources of VOCs in two seasons,but industrial emission always occupied an important position.Meanwhile,the mixing ratios of VOCs were closely related to changes in meteorological conditions such as humidity,temperature and wind speed,and the correlations between VOCs and humidity and wind speed in O3 pollution period were weaker than those in haze pollution period.In addition to local pollution source emissions,the observation site during O3 and haze pollution periods were greatly affected by pollution transmission in local areas such as the east and northeast directions and the southwest and northeast directions,respectively.Finally,the effects of VOCs on environment and human health were analyzed.The stabilities of chemical composition of VOCs in the air masses were both good during O3 and haze pollution periods,and the chemical reactivity of VOCs was at a medium level.Alkanes and aromatics had greater impacts on the formation of O3,and aromatics also played a key role in the formation of SOA.In the O3 pollution period,the solvent utilization and vehicular emission had greater impacts on the formation of O3,and the solvent utilization also had a largest impact on the formation of SOA in haze pollution period.Long-term exposure to species such as chloroform,1,2-dichloroethane,hexachloro-1,3-butadiene,benzene,and naphthalene may pose carcinogenic risks to the health of residents in the study area,and acrolein may pose a great non-carcinogenic risk during haze pollution period.Industrial emission posed greater risks to human health during O3 pollution period while solvent utilization and industrial emission posed higher risks during haze pollution period. |
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