Why are forests grown in and around steel cities?

The level of pollution around steel cities is much higher than other cities. During the manufacture of steel, air emissions from the manufacturing plants emit particulate matter, sulphur oxides, nitrogen oxides, hydrocarbons and hydrogen fluoride which pollute the air. Besides these, steel plants emit significant dust levels of about 20 kilograms per metric ton of steel. Growing forests around them helps to lower the pollution as the trees act as a barrier for the dust and purify the air.