Why did the steam engines contribute to the air pollution in the 19th century?

The steam engine and steam locomotive evidently had major consequences on European society. Positive and negative effects are apparent, as these major technological breakthroughs transformed European society. Even today, many aspects of society and economics are present due to the profound impact these inventions had, which is why they are such big turning points in history. 

1. the spread of reform movements aimed at perfecting american society