Question

Why has the relative importance of the Pittsburgh steel industry declined? what are petrochemicals used for?

Answer 1

Andrew Carnegie, a pioneer in the industrial circles of USA, expanded the steel industry in Pittsburgh, Pennsylvania in the early part of twentieth century. But, the steel industry of this region declined gradually and by the 1970s virtually closed down, as it found it difficult to face up to foreign competition.
Petrochemicals are derived from petroleum. They are used to produce Naphtha, a vital raw material for many industries, plastics of various types, synthetic rubber, solvents of many kinds that find a wide variety of industrial uses and so on.