城市人口多，密度大，而且高层建筑较多，危险。还有就是建筑分布密度大，不利于烟雾扩散，一般郊外就可以放，最好河边或者海边。最重要的一点，For everyone's health!
The city has a large density of population, and a large number of high-rise buildings. Also, the density of the building is so dense that it is not conducive to the spread of smoke. Generally, it can be put on the outskirts of the city, preferably by the river or by the sea.
