基于集合卡尔曼滤波的NOx同化方法研究及其在华北地区的应用

NOx is one of the most important atmospheric pollutants and also the precursor of nitrate aerosol in fine particulate matters. It has been recognized as the major contribution towards the heavy haze pollution over North China in recent years, while air quality forecast and pollution control is rather limited due to the uncertainty in emission inventory. Data assimilation is used in atmospheric chemistry models to improve air quality forecasts, construct re-analyses of three-dimensional chemical (including aerosol) concentrations and perform inverse modeling of input variables or model parameters (e.g., emissions), and the development of data assimilation in atmospheric chemistry is more recent compared to meteorological assimilation. Motivated by the question of whether and how data assimilation can facilitate fine-scale characterization of NOx, the transformation process as well as the influence of various uncertainty, the Ensemble Kalman Filter is introduced and applied to a regional atmospheric chemistry transport model CMAQ to study NOx over North China. This project intends to (1) develop NOx assimilation scheme through assimilation of initial fields and assimilation of emissions, (2) discuss the differences of concentration and emissions spatial-temporal distribution before and after assimilation, explore the impacts of emission pattern changes during the continuous development of urbanization, (3) and investigate the effect on nitrate aerosol before and after assimilation to gain insight into the behavior of the assimilation system for the strongly related species (i.e. NOx and nitrate). This project has important theoretical significance in the development of atmospheric chemistry data assimilation and efficient utilization of observational data.

NOx是重要的大气污染物，也是细颗粒物中硝酸盐气溶胶的前体物。近年来华北地区灰霾污染严重，NOx贡献突出，但排放源的不确定性在很大程度上影响着空气质量预报和污染调控。资料同化是一种重要的手段，在大气化学领域中主要用于改进数值预报效果、反演污染物排放源、和重建污染物浓度三维分析场，华北地区监测资料丰富，所以本项目拟开展NOx浓度和排放源同化研究，并深入探讨NOx同化对细粒子生成的影响。主要内容包括：（1）发展NOx浓度初值和排放同时同化方案，考察冬夏季典型污染过程中NOx预报效果的改进情况；（2）针对突发性污染事件、减排情形等开展NOx排放源反演研究，探讨华北地区同化前后源排放的时空分布特征变化；（3）研究NOx在向硝酸盐转化过程中同化的效应，考察前体物NOx同化对硝酸盐转化的影响。本项目研究结果将对大气化学资料同化的发展及观测数据的科学有效应用提供重要的科学基础。

NOx是重要的大气污染物，也是细颗粒物中硝酸盐气溶胶的前体物。近年来华北地区NOx贡献突出，但排放源的不确定性在很大程度上影响着空气质量预报和污染调控。资料同化是一种重要的手段，在大气化学领域中主要用于改进数值预报效果、反演污染物排放源、和重建污染物浓度三维分析场，华北地区监测资料丰富，所以本项目开展了NOx浓度和排放源同化研究。主要内容包括：（1）发展完善了NOx浓度初值和排放协同同化方案，通过同化技术改进NO2数值预报效果，探讨了NOx与O3同化的关系及其可能的影响因素；（2）开展了NOx排放源反演方案优化研究，通过对比同化前后NOx排放源的时空分布特征变化揭示了华北地区NOx源的变化，分析了不同情形下排放源分布动态格局的变化；（3）针对基于上述协同同化方案的中国地区PM2.5再分析数据集，通过整理分析PM2.5四年的再分析场（2016−2019），利用天气分型的方法评估了气象场的作用，结果表明在中国减排的大背景下，气象条件对这几年空气质量变好起到了积极作用。本项目研究结果将对大气化学资料同化的发展及观测数据的科学有效应用提供重要的科学基础。