Temporal And Spatial Variation Of NO₂ In Beijing-Tianjin-Hebei Region And Its Impact On Emission Reduction And Meteorolog

As an important atmospheric pollutant,the spatial and temporal variations of NO₂in the Beijing-Tianjin-Hebei（BTH）region and its influencing factors is a regional atmospheric environmental change problem that needs to be understood in depth and can provide a scientific basis for air pollution prevention and control.In this study,we use the multi-source environmental-meteorological observation data over 2014-2022 to systematically understand the changes of NO₂concentrations in BTH region and their connection to meteorological and environmental elements;and to characterize the high-resolution regional variations of NO₂in BTH region with fusion data of the TROPOMI satellite remote sensing-ground observation;and analyze the interannual changes in NO_xemissions and meteorological conditions in the BTH region from 2014 to 2022,by using the MEIC anthropogenic emission source inventory and the EMI environmental meteorological assessment index of air pollutants in China,and quantitatively assess the contributions of anthropogenic pollutant emissions and regional meteorological conditions to the long-term changes of NO₂concentration.The main research contents of this paper are summarized as follows:（1）Spatial and temporal variations of NO₂concentrations connecting with meteorological and environmental changes in Beijing-Tianjin-Hebei regionTo characterize atmospheric environmental changes in recent years,this study used near-surface NO₂concentration data from the BTH region between 2014 and 2022,combining with meteorological and other pollutant observation data,to investigate the spatial and temporal variations of NO₂concentrations in the region and the correlations with meteorological factors and other pollutants such as O₃,PM_2.5,PM₁₀,SO₂,and CO.The results showed that the NO₂concentrations in the BTH region decreased in recent years.At the seasonal scale,air pollution was most severe in winter,and the NO₂concentration in most cities exceeded the second-level standard for ambient air quality.The diurnal variation of NO₂concentration presented the bimodal pattern with lower concentrations during the day than at night,and the difference in NO₂concentration between day and night increased from year to year.In terms of spatial distribution,NO₂concentration exhibited a northwest-to-southeast gradient with higher NO₂concentrations in the BTH urban agglomeration and in areas such as Baoding,Shijiazhuang,Xingtai,and Handan than in surrounding areas.The NO₂concentration in the BTH region was negatively correlated with air temperature,relative humidity,wind speed,and precipitation,meaning that NO₂is more likely to be diluted,dispersed,and wet-deposited with the high air temperature and relative humidity,strong wind speed,and precipitation,resulting in decreases in NO₂concentration.NO₂change was positively correlated with PM_2.5,PM₁₀,SO₂,and CO,reflecting the dominant role of anthropogenic pollutant emissions on air pollutants such as NO₂.As the precursors of O₃,NO₂showed a negative correlation with O₃.（2）Fine regional distribution of NO₂based on TROPOMI remote sensing and ground observation fusion and meteorological impactsTo investigate the fine spatioal distribution of NO₂and the meteorological impacts in the BTH region,we combine satellite remote sensing and ground observation data by using the variational method to obtain the high-resolution distribution of NO₂concentrations.The environmental meteorological evaluation index（EMI）is used to analyze the impact of meteorological conditions on NO₂concentration changes.The meteorological conditions are poor in autumn and winter,and good in spring and summer.There are also significant spatial differences in meteorological conditions,as the semi-enclosed terrain formed by the Yanshan Mountains in the north and the Taihang Mountains in the west hinders the diffusion of atmospheric pollutants in the plains of the BTH region,creating unfavorable meteorological conditions,while higher elevations have better atmospheric diffusion conditions.Meteorological conditions have a significant impact on the NO₂concentration in spring and summer,while the impact is smaller in autumn and winter.The effects of meteorological conditions on different concentration ranges of NO₂differ,with more significant effects observed for low and high concentrations.During both air pollution episodes and the pandemic lockdown with significantly reduced emissions,changes in meteorological conditions dominate changes in NO₂concentration.（3）Contribution of anthropogenic emissions and meteorological conditions to the changes of NO₂in the Beijing-Tianjin-Hebei during the past 8 years of emission reductionTo fully understand the influencing factors of the interannual variations of NO₂concentration in the BTH region,this chapter selects the MEIC emission inventory data from2014 to 2017 and linearly interpolates it to 2014-2022 to study the temporal and spatial distribution characteristics of NO_xemissions during the reduction process in recent years.The NO_xemissions in the BTH region have decreased year by year,with the lowest NO_xemissions in spring and high amounts in summer and winter.The NO_xemissions in BTH region have decreased.The NO_xemission reduction rates in cities with high population density and high urbanization level was slightly higher than those in other cities.Environmental meteorological conditions in the BTH region have tended to get better year by year over the past eight years.Based on the MEIC emission sata and the Environmental Meteorology Index（EMI）from 2014 to 2022,the relative contributions of anthropogenic pollutant emissions and regional meteorological conditions to the interannual changes of NO₂concentrations were quantitatively analyzed.The results show that the interannual variations in NO₂concentrations in the BTH regional average over the last eight years is contributed by meteorological conditions at 50.73%,comparable to the contribution of anthropogenic pollution reductions（49.27%）;the contribution of meteorological conditions to the variations in NO₂concentrations in the major source area cities of Beijing（28.67%）is significantly smaller than the contribution of anthropogenic emission changes（71.33%）,highlighting an importance of the emission reductions in improving urban air quality.