Complex sentence: He established his own practice in 1984, where he was principal in the firm Pennoyer Turino Architects P. C. until 1990, when he formed Peter Pennoyer Architects in New York City.
Split into simpler sentences: He established his own practice in 1984, where he was principal in the firm Pennoyer Turino Architects P. C. until 1990. He then formed Peter Pennoyer Architects in New York City.