Ground Level Ozone Concentration Characteristics And Formation Sensitivity In China's Three Agglomerations

In recent years,with the rapid development of industrialization and urbanization in China,high-concentration ozone?O₃?pollution incidents have occurred frequently.The environmental pollution problems brought by O₃ pollution have been paid more and more attention by the public and relevant government departments,becoming the primary pollutants in some urban agglomerations,such as Beijing-Tianjin-Hebei?BTH?and Yangtze River Delta?YRD?.Studies have shown that ozone pollution may continue to deteriorate in the future,which will seriously endanger the health of urban residents and damage the ecological environment.However,due to the non-linear relationship between ozone and its precursors,ozone pollution in developed urban agglomerations in China is still one of the most crucial and difficult issues in atmospheric pollution control.Therefore,studying the ozone generation mechanism in different urban agglomerations and determining ozone sensitivity are scientifically significant in prevention and control of ozone pollution.Based on the proportion of “city and building area” pixels,this paper classify the land use types?including developed areas,comparatively developed areas and less-developed areas?of three major urban agglomerations with the data product MODIS MCD12Q1.The classification results are in good correlation with the location information from Guangdong-Hong Kong-Macao Pearl River Delta Regional Air Quality Monitoring Network.It is found that the number of developed areas in the three major urban agglomerations is much larger than the national average.The developed areas of the BTH are mainly concentrated in Beijing and Tianjin,and there is also a clear distribution along the Beijing-Baoding-Shijiazhuang area;The developed areas of the YRD are mainly concentrated in the four cities of Jiaxing,Suzhou,Shanghai and Wuxi;the proportion of developed areas in the Pearl River Delta?PRD?,which mainly concentrated in the central cities,is highest among these three agglomerations.Combined with the land use type distribution,it is found that in the same urban agglomeration,the average concentration of surface O₃ in descending order are developed areas,comparatively developed areas and less-developed areas,but different agglomerations exhibit different characteristics:The ozone pollution problem of BTH is the most serious among the three major urban agglomerations.The ozone episodes are more concentrated?April-August?;the ozone pollution in the YRD is less severe than Beijing-Tianjin,and the ozone episodes happen in April to October;the average ozone concentration in PRD is lowest among the three major urban agglomerations,and the highest ozone concentration is not in June,but in October.The ozone episodes there occur between March and October.In addition to the characteristics of ozone concentration,studying ozone sensitivity is an effective way to understand the complex generation mechanism of ozone.FNR?the ratio of HCHO and NO₂?is one of the scientific indicators to study ozone sensitivity.In order to calculate the FNR,we need to clearly understand the change characteristics of the precursor of the indicator:from 2005 to 2016,the average column concentration of the tropospheric HCHO in the BTH showed a fluctuating upward trend,and the concentration of the tropospheric NO₂ column increased in early years and then decreased;the tropospheric HCHO column concentration in the YRD did not show clear annual trend,and the tropospheric NO₂ column concentration has a relatively clear upward trend;the tropospheric HCHO and NO₂ column concentrations in the PRD have significantly decreased.The study about FNR indicator found that from 2005 to 2016,the area of VOCs-limited area is in a process of increasing first and then decreasing in the BTH and YRD,while the area of VOCs-limited area in the PRD is always cut back.The VOCs-limited area in the BTH is mainly concentrated in the Beijing-Tianjin-Tangshan and Baoding-Shijiazhuang-Handan areas.Chengde and Zhangjiakou in the northern part of this agglomeration are mainly influenced by NO_x;the core area of Shanghai,Suzhou to Nanjing in the YRD are covered by the VOCs-limited area,the peripheral cities are dominated by NO_x-limited areas;in the PRD,the areas where the ozone formation is controlled by VOCs are mainly concentrated in the central part of the agglomeration,including southern Guangzhou,Foshan,Zhongshan,Shenzhen and parts of Jiangmen.The sensitivity of different land use types was analyzed,too.The results showed that the developed areas are mainly in VOCs/transitional regimes;the comparatively developed areas are mainly in transitional regimes;the less developed areas are in NO_x regimes.