1. Reasons for Higher AQI in Beijing and Tianjin In the testing 5 major cities in China, only the average AQI in Beijing and Tianjin is over 120. The main reason is that these two cities are in Northern region which is near the heavy industrial region Northeast Provinces (Jilin, Liaoning & Heilongjiang). In the Northeast Provinces, the major industries are some high polluting industries such as energy, chemical engineering and mechanical industries. As Beijing and Tianjin are near to the Northeast Provinces, they are easily to be polluted when there are southerly winds. Another two reasons lead to their higher air pollution are the geographical situation and soil qualities in these two cities. The western area of Beijing and Tianjin are surrounded by mountain. As a result, when there are easterly winds, the air pollutants will be probably trapped in the Jing-Jin-Ji region. Furthermore, there are usually alkaline soils in Northern area which are easier to trap and scatter air pollutants. Therefore, the Northern major cities, Beijing and Tianjin, have more severe air pollution problems. Between these two cities, the air quality in Tianjin is a bit better than Beijing. The main reason is that Tianjin is nearer to the coastline than Beijing. The air pollutants will be easier to scatter with the sea-wind in Tianjin. Also, there are less temperature inversion effect which will lead to more severe air pollution problem 2. Reasons for Better Air Qualities in Shenzhen The better air qualities in Shenzhen should be mainly based on Guangdong economic transition and Shenzhen stricter Environment policies. As Guangdong and Shenzhen are the earliest region to develop after the announcement of Chinese Economy Reform, the heavily-polluted industries in Guangdong Province are mostly moved to other Province. Shenzhen is now mainly developing in Computer Program industry and financial industry. Therefore, the surrounding industries in Shenzhen are cleaner than other five major cities. Another reason is that Shenzhen has stricter environmental protec