Study On Quantitative Analysis Method Of Regional PM_2.5 Transport Based On Three-Dimensional Assimilation Of Lidar Network

The rapid development of industrialization and urbanization has exacerbated atmospheric environmental problems,with fine particulate matter(PM2.5)as the primary pollutant.Frequent air pollution events not only degrade the quality of the air,but also risk people’s health.With atmospheric movement,high concentrations of PM2.5 can be transported over long distances,resulting in regional pollution events.However,due to a lack of stereoscopic observation data,the characteristics of PM2.5 transport in three-dimensional space that quantified by air quality model are highly uncertain,limiting our understanding of the charactristics of the pollution transport in pollution events.The air quality model can simulate the generation,transformation,and deposition of atmospheric pollutants in three-dimensional space,and it can also be used in conjunction with pollution source analysis technology to quantify the pollution transportation process between cities.The results of model simulations and pollution transport quantification have a lot of uncertainty.With the advent of data assimilation technology,it is now possible to combine observation and simulation,and improve simulation accuracy by correcting the model’s initial conditions using observation data.Currently,the concentrations of PM2.5 from the near ground or from the satellite were absorbed for data forecasting research.However,by absorbing the stereo observations with high temporal and spatial resolution to build a three-dimensional data assimilation system and coupling it with the pollution source analysis technology to achieve quantitative analysis of pollution transport is still lacking.The spatial and temporal distribution of atmospheric particles can be obtained using lidar detection technology,and the research on the characteristics of pollution distribution in a region can be realized by establishing a lidar network.The PM2.5 concentration fields of multi-source atmospheric particulate matter monitoring equipment(nationally monitoring stations,lidar network)are combined in the same observation period to compensate for each other’s blind spots in space,forming a range from the ground to the boundary layer.The open-source GSI data assimilation system created a binary background field based on the simulation results of the CMAQ model,and solved the problem of incompatibility between the CMAQ model’s input interface and the GSI assimilation system,resulting in the LIDAR-CMAQ-GSI threedimensional stereo assimilation system,as well as the error evaluation of each module of the system.The three-dimensional PM2.5 concentration field after assimilation of the three-dimensional data is used to quantify the characteristics of pollution transport in the Beijing-Tianj in-Hebei region,and summarize the PM2.5 transport sources,transport height range characteristics and hourly average contribution during the cleaning period and the pollution period,by coupling the three-dimensional assimilation system with the pollution source analysis technology.The results show that the correlation between the PM2.5 simulation and observation after data assimilation has increased from 0.75 to 0.88,and the RMSE was improved from the range of-2.03～33.78 μg/m3 to 0.89～22.85 μg/m3,the accuracy and reliability of the three-dimensional stereo assimilation system were confirmed.The characteristics of pollution transport in the Beijing-Tianj in-Hebei region were quantified in this paper for three cleaning periods(E0,E4,E6)and four pollution periods(E1,E2,E3,E5)during the study period from January 9 to 31 in winter 2018.The results showed that:during the cleaning period,local emissions from Beijing were mainly concentrated from near the ground to 0.1 kilometers,with an hourly average contribution of 8.56 μg/m3 near the ground and a contribution rate of 60.26%.The regional transport were primarily from the northwest region(Zhangjiakou and Inner Mongolia);the pollutant transport height were mainly concentrated from near the ground to 1.0 kilometers;the maximum hourly average contribution is 2.49 μg/m3.During the pollution period,the local emissions primarily concentrated from near the ground to 0.2 kilometers.The near-surface layer contributed the most,with contribution rates of 47.76%(E1),65.37%(E2),46.90%(E3),and 60.11%(E5).There are more source regions compared with the clean period.Baoding,Shanxi,Tianjin,Langfang,Zhangjiakou,Inner Mongolia,and Shandong are the main source regions in each pollution period.And the main source regions also include Cangzhou,Tangshan,Shijiazhuang,Hengshui,Chengde,and Qinhuangdao.The main height of foreign transportation was between 0.2 and 0.8 kilometers,with a total hourly average contribution of 5.34 to 20.42 μg/m3,which could be 1.0 to 9.3 times greater than that of Beijing(1.35 to 9.32 μg/m3).From 0.8 to 2.0 kilometers,the contribution from local emissions and regional transport were decresed rapidly.It is important to joint air pollution control of the cities,especially during the pollution episodes.