relating to rules that limit what vehicles can be used, what fuels can be burned, etc., in order to reduce the amount of pollution in the air

More factories are using low-sulphur coal to comply with clean-air regulations. 越来越多的工厂正在使用低硫煤来遵守清洁空气法规。

Clean-air advocates say health costs must be weighed along with the expense to business. 清洁空气倡导者表示健康代价必须与商业成本一起权衡。

The city has been designated a clean air zone. 这个城市已被指定为清洁空气区。