1 PM2.5 Pollution Characteristics of Key Cities in Beijing-Tianjin-Hebei Region 1.1 Overview 1.2 Sampling program 1.2.1 Sampling sites 1.2.2 Sampling method and equipment 1.2.3 Chemical analysis and methods 1.3 PM2.5 and its component characteristics in different city of region 1.3.1 The characteristics of elements and water soluble ions 1.3.2 OC and EC pollution characteristics 1.3.3 PM2.5 chemical balance 1.4 PM2.5 chemical composition analysis in different functional subdivisions in Tangshan 1.4.1 The variations of PM2.5 mass concentration 1.4.2 Characterization of inorganic elements in PM2.5 1.4.3 Secondary water soluble ions (SWSI) 1.4.4 Carbon species in PM2.5 samples 1.4.5 PM2.5 mass balance 1.5 Conclusions 2 The Combination Source Apportionment Approaches of Air Pollution Based on Monitoring and Numerical Simulation 2.1 Overview 2.2 Source apportionment of PM2.5 in Beijing by usual methods 2.2.1 Source apportionment of carbon components in PM2.5 by principal component analysis (PCA) and CTM model 2.2.2 Source apportionment of PM2.5 by PMF model 2.2.3 Source apportionment of PM2.5 and O3 by CTM model 2.3 Source apportionment of PM2.5 by a new couple of hybrid modeling approaches 2.3.1 The hybrid PMF-EI approach for primary species 2.3.2 The hybrid CAMx-PSAT-CP approach for secondary species 2.3.3 Source apportionment results of PM2.5 in Tangshan 2.4 Conclusions 3 The Impact of Meteorological Conditions on the Air Pollution Source and Regional Transportation 3.1 Overview 3.2 Methodology and simulated data verification 3.2.1 Methodology 3.2.2 Simulated data verification 3.3 The response of PM2.5 to meteorological variability 3.3.1 Meteorological and emission changes in Beijing 3.3.2 Meteorological impact on air quality simulation data 3.3.3 Meteorological impact on source apportionment results between 2015 and 2017 3.4 Regional transport contributions of primary and secondary PM2.5 components 3.4.1 Study the regional transport of primary and secondary PM2.5 components by CAMx model 3.4.2 The trajectory clustering analyzed by HYSPLIT 3.4.3 Trajectory clustering combine with the potential source contribution function 3.5 Conclusions 4 The Aerosol-radiation Interactions Effect on Air Pollution Control 4.1 Overview 4.2 Materials and methods 4.2.1 Model description 4.2.2 Model performance 4.3 ARI impacts on meteorological variables and air quality 4.3.1 Impacts on meteorological variables 4.3.2 Impacts on air quality 4.4 ARI impacts of different PM2.5 component 4.4.1 ARI impact on meteorological variables 4.4.2 ARIs of different BC sources 4.5 Conclusions 5 Evaluation of Emission Reduction Effects on Air Quality and Oxidative Potential Characterization 5.1 Overview 5.2 Methodology 5.2.1 Modeling description 5.2.2 Sampling program 5.2.3 Oxidative potential analysis 5.3 The effect of emission control assessment 5.3.1 Emission reduction in different control strategies 5.3.2 Characterization of PM2.5 and its components 5.3.3 The effect of emission reduction 5.4 Oxidative potential characterization of different PM2.5 sources and components 5.4.1 PM2.5 characterization and the source 5.4.2 Oxidative potential analysis and health risk assessment 5.4.3 Multiple regression analysis 5.5 Conclusions References