It is a system designed to eliminate NOx generated in car and industrial emission and known to consist of NO and NO2 and be the primary cause of global warming, impacting human health and growth of animals/plants.

- SCR Process (Selective Catalytic Reduction System)
- SNCR Process (Selective Non-Catalytic Reduction System)

- Industrial boiler
- Industrial waste incinerator
- Refuse incinerator plant, Resource Recovery Facility
- Power plant, Steel mill, Nitric acid factory
- HRSG boiler