The Philippine Clean Air Act of 1999

http://www.tanggol.org/environmental_laws/cleanair.html

The methods are many different types. One is regulation and enforcement. Generally this is an administrative process that can lead to technical or engineering methods. Engineering methods are specific to a given application. For example an automobile can have a lean burn fuel system, catalytic converter and NOX control system. Another is a business that uses paint for metal, it would have an air scrubber to remove volatile organics from the paint booth. The list of engineering methods is endless.