Comparison Of The Application Of Various Ozone Sensitivity Analysis And Source Apportionment Technique

In recent years,with the implementation of various measures to control air pollution,the concentration of particulate matter(PM_2.5,PM₁₀)has decreased,but the problem of ozone pollution has become increasingly prominent.The formation of ozone has a complex nonlinear relationship with its precursor volatile organic compounds（VOCs）and nitrogen oxides（NO_x）.Identifying the sensitivity of ozone to precursor VOCs and NO_x,and quantifying the contribution of ozone sources,can help to accurately prevent and control ozone pollution.Currently,various ozone sensitivity analysis systems have been formed based on emission inventories and observation methods,but the results obtained by different methods differ to some extent.Therefore,exploring the differences in identifying ozone sensitivity and quantifying source contributions using different methods is conducive to improving the understanding of different methods applied in O₃ sensitivity discrimination,and providing scientific reference for developing effective O₃ emission reduction strategies using different methods.The paper takes the O₃ pollution event in the Yangtze River Delta region from July 25^th to31^st in 2017 as an example.The photochemical indicator method and the sensitivity coefficient method based on Community Multiscale Air Quality model,and the observation-based method（OBM）were used to determine the O₃-VOC-NO_x sensitivity of the Yangtze River Delta region and an observation stations in Nanjing.The similarities and differences of the three methods on temporal and spatial scales were explored.Based on the results of ozone sensitivity,the Integrated Source Apportionment Method（ISAM）and the Higher-order Decoupled Direct Method（HDDM）were used to simulate and analyze the regional and industrial sources contributions of ozone in the Yangtze River Delta region and four major cities（Nanjing,Hefei,Shanghai,and Hangzhou）,and the differences in the results of these two methods were discussed.The results of O₃ sensitivity show that:（1）The photochemical indicator method and sensitivity coefficient method have a high consistency（accounting for 63%in all cell grid）,especially in the control area dominated by a single precursor（NO_x or VOC）.For example,Shanghai dominated by VOC control with the same grid accounts for 71.5%.Hangzhou is dominated by NO_x control with the same grid accounts for 82.6%.In Nanjing and Hefei,the differences between the two methods are more significant.The sensitivity coefficient method tends to determine O₃ sensitivity as both-controlled,while the photochemical indicator method tends to determine O₃ sensitivity controlled by a single pollutant（VOC or NO_x）.（2）When using OBM to determine the O₃ sensitivity of Nanjing urban site,the impact of losing HCHO and HONO concentrations in the observation data used to constrain the model is relatively small.However,the observed concentration of NO₂ is higher than the actual concentration,which will cause OBM to underestimate the sensitivity to NO_x in the Nanjing urban site.Compared with the clean period,the differences between the methods during high pollution periods increase,and the photochemical indicator method may overestimate the sensitivity to VOC,while the results of OBM and the sensitivity coefficient method are relatively close.In practical applications,it is recommended to prioritize the use of the sensitivity coefficient method or OBM to identify the O₃ sensitivity of Nanjing urban.The results of O₃ source contribution show that:（1）ISAM and HDDM are consistent in the identification of top source categories,Therefore,when formulating emission reduction strategies and selecting source categories that need to be prioritized,the difference in the choice between the two methods is relatively small.However,there are significant differences in the absolute and relative contributions of sources categories between the two methods,mainly reflected in the negative contribution of nighttime O₃ sources in HDDM,while ISAM only considers the allocation of net O₃ generation without negative contributions.Therefore,when identifying source contributions that include O₃consumption reaction processes,HDDM can provide more accurate results.（2）For result of O₃ regional sources,ISAM tends to allocate more O₃ contribution to the transport between non-local source regions and acceptor regions,while HDDM allocates more O₃ contributions to the photochemical reaction contributions of local source regions.For industry sources,ISAM tends to allocate a portion of O₃ formation contributions to source categories with low contribution rates,such as residential sources and power sources.Therefore,ISAM is more suitable for long-term O₃ source contribution analysis,while HDDM is suitable for simulating the causes of sudden high O₃ pollution events.（3）Although the simulation startup time is set for two days,IC contribution of ISAM shows more to the generation of O₃,which is consistent with the conclusion that ISAM tends to allocate some O₃ generation contributions to source categories with lower contribution rates.Therefore,the simulation startup time of ISAM can be extended appropriately to reduce the impact of IC on the results.