China I/China II/China III/China IV/China V/China VI Emission Standards

1. Definition and Evolution Background

Vehicle emission standards are mandatory technical specifications established by national authorities to regulate harmful tailpipe emissions from motor vehicles. Since introducing the China I standard around 2000 based on European regulatory benchmarks to the nationwide enforcement of China 6b in 2023, China has compressed nearly 30 years of European and American regulatory evolution into just over two decades, establishing one of the world's most stringent emission control frameworks.

2. Standards by Phase and Key Technical Upgrades

Each regulatory phase reflects a progressive step-up across implementation timelines, emission thresholds, and core engineering technologies.

Phase	Nationwide Implementation Date	Core Thresholds and Technical Changes
China I	1 July 2001	Initial baseline standard, primarily setting basic CO and HC limits for carburettor-equipped models
China II	1 July 2004	CO reduced by 30%, HC reduced by 55%, accelerating the widespread adoption of electronic fuel injection (EFI)
China III	1 July 2007	Mandated On-Board Diagnostics (OBD) and upgraded three-way catalytic converters; total emissions cut by 40% compared to China II
China IV	1 July 2010	Introduced Selective Catalytic Reduction (SCR) technology for diesel vehicles, reducing NOx by 30% versus China III; upgraded three-way catalytic converters for petrol vehicles
China V	1 January 2018	Added Particle Number (PN) limits; diesel NOx emissions reduced by 25% compared to China IV
China 6a	From 1 July 2020 (Light-Duty Vehicles)	Transitional phase with limits roughly 30% stricter than China V; RDE testing conducted for "monitoring and reporting only"
China 6b	Fully implemented on 1 July 2023	CO reduced by 50% compared to China V, with mandatory Real Driving Emissions (RDE) compliance thresholds introduced

3. Core Technological Evolution

From China I to China VI, automotive emission control has transitioned from purely in-engine combustion optimisation to an integrated system combining in-engine management with advanced exhaust aftertreatment. The introduction of On-Board Diagnostics (OBD) during the China III phase enabled real-time emission monitoring, marking a crucial shift from static limit compliance to active in-use monitoring. Subsequently, the adoption of SCR technology (using aqueous urea solution to reduce NOx) under China IV and Particle Number (PN) limits under China V expanded regulatory oversight from gaseous pollutants to solid particulate matter. The China VI phase adopted the Worldwide Harmonised Light Vehicles Test Cycle (WLTC) and introduced on-road Real Driving Emissions (RDE) testing, requiring vehicles to stay within emission limits under actual driving conditions and marking a decisive transition from laboratory test cycles to real-world, all-scenario compliance.

4. Future Outlook

China 6b represents the definitive benchmark of the current regulatory framework. Ongoing revisions to the China VI standard are currently underway, focusing on refining test procedures for specialised applications—such as three-axle, six-wheel vehicles—and tightening in-use emission compliance monitoring. Future standard revisions will place greater emphasis on integrated pollutant and greenhouse gas (GHG) mitigation and full life-cycle carbon footprint accounting, driving the automotive industry to transition toward low-carbon and zero-emission vehicle technologies while supporting clean air initiatives.