What do China III and China IV mean for vehicles?

[AlexandraRose]

China III and China IV refer to the emission standards for vehicle exhaust. The China IV emission standard is stricter than China III. The National Third Stage Motor Vehicle Pollutant Emission Standard, abbreviated as China III, is equivalent to the Euro 1 emission standard, meaning the pollutant content in the exhaust is similar to Euro 1. The difference is that new vehicles must be equipped with an OBD (On-Board Diagnostics) system. The OBD system features an increased number of detection points and monitoring systems, with oxygen sensors installed at both the inlet and outlet of the three-way catalytic converter to ensure compliance by real-time monitoring of vehicle emissions. The National Fourth Stage Motor Vehicle Pollutant Emission Standard, abbreviated as China IV, targets major vehicle pollutants such as hydrocarbons, nitrogen oxides, carbon monoxide, and particulate matter. The China IV standard controls and reduces vehicle emissions below specified limits through technologies like the active layer of the catalytic converter, secondary air injection, and exhaust gas recirculation systems with cooling devices.

[DelAurora]

I've been driving for ten years, and emission standards like China III and China IV directly affect us car owners. Simply put, they are national exhaust emission tiers - the higher the number, the stricter the requirements. China III was implemented nationwide in 2008, while China IV was introduced in 2011. Nowadays, China III vehicles are banned from entering urban areas in many places. For example, China III diesel trucks have been prohibited from operating 24/7 in our city since last year. When buying used cars, you must check carefully - the same model with different emission standards could be 20,000-30,000 yuan cheaper. Especially for diesel vehicles, China IV models started installing exhaust treatment devices, which are much more expensive to repair than China III models. Annual inspections are also troublesome - Old Zhang in our neighborhood had to test his China III pickup truck three times this year before it passed.

[JeremiahRose]

Anyone in auto repair knows that emission standard upgrades mean major changes in vehicle technology. During the China III era, engines switched to electronic fuel injection systems, and China IV directly added aftertreatment devices. The most noticeable example is the urea tank system – China IV diesel trucks immediately experience torque limitation if urea fluid isn’t added. Catalytic converters were also upgraded: China III used standard three-way catalysts, while China IV introduced advanced units with oxygen storage capacity. Back in 2010, repair shops constantly modified diagnostic interfaces on China III vehicles just to make OBD systems read China IV-standard oxygen sensor data. Nowadays, if a diagnostic tool isn’t compatible with China IV protocols, it can’t even retrieve trouble codes.

[DeVivian]

Simply put, it's about environmental thresholds. I've checked the data: China IV standards are 60% stricter than China III, with CO emissions dropping from 2.3 to 1.0, and HC+NOx reduced from 0.5 to 0.3. When Beijing implemented China IV ahead of schedule in 2008, the sulfur content in 93-octane gasoline decreased from 150ppm to 50. The most drastic change was the PM2.5 limit - China IV diesel vehicles saw an 80% reduction compared to China III. Nowadays, most black-smoke vehicles on the road are outdated China III models that exceed standards.