The Texas Supreme Court has ruled that a Clean Air Ordinance enacted by the city of Houston in 2007 is preempted by the Texas Clean Air Act. Petrochemical, energy and business interests had been challenging the law for years.

ExxonMobil Corp. was among the companies that sued in 2008 after the city of Houston broke ties with the Texas Commission on Environmental Quality (TCEQ) and said it would sue industrial polluters under a city nuisance ordinance. The city at the time had said TCEQ was not doing enough to regulate polluters.

The Houston measure targeted small businesses, such as dry cleaners and auto repair shops, all the way up to large facilities, such as the petrochemical plants along the Houston Ship Channel.

Three years ago the state Supreme Court reviewed an aspect of the law and sided with business interests against the city. Later, a lower court found that the Texas Clean Air Act does not prevent a city from taking on enforcement of of its own air pollution abatement efforts.

That ruling was appealed by companies such as ExxonMobil, Dow Chemical and others, and the state Supreme Court ruled in their favor, saying the city law would wrongly circumvent state regulators.