## 2 Economic Development and Air Pollution in the Beijing-Tianjin-Hebei Region
### Air Pollution and Urban Industrial Structure in the Beijing-Tianjin-Hebei Region  
The existing industrial structure in the Beijing-Tianjin-Hebei region has gradually highlighted the constraints on the environmental carrying capacity of major cities. In recent years, with the continuous increase of urban population and the continuous expansion of urban areas, natural resources pollution, such as of air and water sources, has intensified, and the improvement of the socio-economic level has been severely restricted [25; 26]. The high-end and low-end industries in urban manufacturing are unevenly distributed. The long-term existence of \"two high-end and one low-end\" industries is an important cause of air pollution in the Beijing-Tianjin-Hebei region. Since 2012, the excessive particulate matter and reduced visibility in the air has appeared in many places in China. Among them, it is most prominent in the three regions of Beijing, Tianjin and Hebei. Of the 74 cities that apply the new air standard, 8 out of 10 cities with relatively poor air quality are located in the Beijing-Tianjin-Hebei region. In 2015, the average air quality compliance days in Beijing-Tianjin-Hebei region accounted for 52.4%, far lower than the 71.2% of compliance days in 74 key cities nationwide. Among them, Hengshui, Baoding, Xingtai, Handan, Tangshan and Shijiazhuang accounted for less than 50% of the air quality compliance days, with PM2.5 as the primary pollutant accounting for 68.4% of the over-standard days. Air pollution in the Beijing-Tianjin-Hebei region is closely related to its industrial structure. The industrial structure of Beijing has changed rapidly, and the proportion of the three industries has changed from 5:71:24 in 1978 to 0.4: 18.6: 81.0 in 2018. At present, the proportion of primary industry is relatively low, and the focus of the industry is shifting from secondary industry to tertiary industry. The overall development trend of the industrial structure in Tianjin is similar to that of Beijing. The proportion of primary industry in Tianjin is relatively low. The center of the industry has shifted from the secondary industry to tertiary industry, but the transfer rate is significantly slower than that of Beijing. In 2014, the proportion of tertiary industry in Tianjin surpassed that of secondary industry, which was about 20 years later than in Beijing. The proportion of the three industries changed from 6: 70: 24 in 1978 to 0.9: 40.5: 58.6 in 2018. Secondary industry is still predominant in Hebei Province. Until 2018, the proportion of service industry surpassed secondary industry, and the ratio of the structure of the three industries changed from 29: 50: 21 in 1978 to 9.3: 44.5: 46.2 in 2018. Compared with the overall structure of the country, secondary industries in Tianjin and Hebei account for a relatively high proportion, resulting in serious air pollution in this region. Figure 1 shows the air quality and industrial development of the Beijing-Tianjin-Hebei region during the study period. There are obvious spatial differences in the industrial structure of the Beijing-Tianjin-Hebei region. The cities transformation to the \"tertiary industry-secondary industry-primary industry\" type and the \"secondary industry-tertiary industry-primary industry\" type is also a manifestation of advanced industrial structure. Industrial structure adjustment is an effective means to promote pollution reduction, but due to the previous air pollution prevention and control policy, it is difficult to clarify the task requirements of industrial structure optimization and adjustment, especially the pollution reduction goals that the work in this field needs to strive to achieve, leading to inter-regional industrial structure adjustment. The intensity varies greatly, and the effects of pollution reduction have not been fully exerted.