KATHMANDU: The government is preparing to introduce new emission standards for vehicles already in operation, aiming to curb rising air pollution caused by older vehicles. The proposed rules will replace the current system, under which all vehicles are tested against the same emission limits, with standards based on a vehicle’s registration year and fuel type.
The Ministry of Forests and Environment has drafted the “Emission Standards for In-Use Vehicles, 2083” and has published the proposal for public feedback. The ministry said the draft will be finalized after incorporating suitable suggestions and will come into effect 91 days after its publication in the Nepal Gazette.
Vehicles divided into four categories
Under the proposed standard, vehicles will be classified into four groups based on their registration year:
- Registered before December 24, 1999
- Registered between December 24, 1999 and October 15, 2012
- Registered between October 15, 2012 and June 23, 2025
- Registered after June 23, 2025
Each category will have different emission limits depending on the age of the vehicle.
Different testing methods for different fuel types
The draft also introduces separate testing procedures for petrol, diesel, and CNG/LPG-powered vehicles.
Emission tests will be conducted under both idle speed and high idle speed, where the engine operates at approximately twice the normal idle RPM.
For petrol vehicles, inspectors will measure:
- Carbon monoxide (CO)
- Hydrocarbon (HC)
- Lambda (air-fuel ratio) for modern fuel-injected vehicles equipped with catalytic converters
For diesel vehicles, testing will focus on smoke opacity, measured using:
- Light absorption coefficient
- Hartridge Smoke Unit (HSU)
For CNG/LPG vehicles, the proposal replaces conventional hydrocarbon measurement with Non-Methane Hydrocarbon (NMHC) and Reactive Hydrocarbon (RHC) testing.
Emission limits tighten for newer vehicles
The proposed standards become progressively stricter for newer vehicles.
Vehicles registered before December 24, 1999
- Petrol two- and three-wheelers: CO limit of 4.5% and HC limit of 7,800 ppm
- Petrol four-wheelers: CO limit of 3.5% and HC limit of 100 ppm
- Diesel vehicles: Smoke opacity limit of 3.23 m⁻¹ or 75% HSU
Vehicles registered between December 24, 1999 and October 15, 2012
- Petrol two- and three-wheelers: CO limit of 3.5% and HC limit of 7,800 ppm
- Petrol four-wheelers: CO limit of 3.5% and HC limit of 1,000 ppm
- Diesel vehicles: Smoke opacity limit of 2.45 m⁻¹ or 65% HSU
Vehicles registered between October 15, 2012 and June 23, 2025
- Petrol two-wheelers: CO limit of 3.0%, HC 3,000 ppm
- Petrol three-wheelers: CO limit of 3.5%, HC 4,500 ppm
- Petrol four-wheelers: CO limit of 0.5%, HC 750 ppm
- Diesel vehicles: Smoke opacity limit of 2.45 m⁻¹ or 65% HSU
Vehicles registered after June 23, 2025
- Petrol two- and three-wheelers: CO limit of 0.5%
- Petrol four-wheelers: CO limit of 0.3%
- HC limits: 500 ppm for two- and three-wheelers and 200 ppm for four-wheelers
- Modern petrol vehicles with fuel injection and catalytic converters will also undergo lambda testing
- Diesel vehicles: Smoke opacity limit of 1.62 m⁻¹ or 50% HSU
Scope of the new standard
The proposed standard will apply to all vehicles currently in use, except tractors, power tillers, bulldozers, cranes, rollers, excavators, other construction equipment, and special military vehicles imported on the recommendation of the Ministry of Defence.
For petrol, CNG, LPG and other non-diesel vehicles, the standards will apply nationwide. For diesel-powered vehicles, the new limits will be enforced within Kathmandu Valley, metropolitan cities and sub-metropolitan cities.
