In which areas are the air pollution sources in Lanzhou mainly concentrated?

It is mainly concentrated in Xigu District. In 216, the number of days when the air in Lanzhou reached the standard was the most delayed. In fact, there are pollution sources in all districts. However, due to the large number of factories in Xigu District, the pollution sources are more complicated and the treatment is the most difficult. In addition, the terrain of Lanzhou belongs to the basin effect, and the polluted gas is covered over Lanzhou like a pot cover, so it can't be dispersed without strong winds and rain and snow. Winter prevention (prevention and control of air pollution in winter) is also mainly aimed at measures such as people not burning bituminous coal for heating, straw garbage for burning in rural areas, and forced closure of barbecue stalls. All these measures are tinkering around the edges, but the real big pollution sources are not closed, because leaders still don't want to sacrifice economic indicators in exchange for air quality. We should know that economic indicators can best reflect leadership achievements, and all aspects have led to more serious pollution in Lanzhou. (pure hand, hope to adopt)