Introduce the English composition about the weather in Lanzhou hometown.

Lanzhou is located in the temperate zone, with a semi-arid climate (K? It is hot in summer and cold and dry in winter. The average annual rainfall is 315mm (12.4 inches), and almost all the rainfall occurs from May to1October. Winter is very dry, so snow is very rare.

In terms of air pollution, Lanzhou is one of the cities with the worst air quality in China. According to the data of Blacksmith Institute, Lanzhou is one of the 30 most polluted cities in the world, and its TSP (Total Suspended Particles) is 247% higher than that recommended by Gansu Province. The air quality is poor, and sometimes people can't see Lanshan, which stands upright along the south of the city. On one occasion, someone put forward a controversial proposal to level a mountain in a neighboring city in order to let fresh air into the bowl where Lanzhou is located. The premise of this proposal is that the surrounding mountains hinder the free flow of air in the city. The city is located in a narrow valley, and an unfortunate bend causes it to be surrounded by an environment without free air flow. Lanzhou is also home to many factories, including some involved in oil processing, and suffers from sandstorms from the Gobi desert, especially in winter and spring.

The Yellow River carries a lot of sediment in the reach of Lanzhou, which gives the river a unique muddy appearance. However, the water quality in this section is better than "the foul effluent, which barely qualified after two hours downstream".