What are the differences between China 6a and China 6b?

[KatherineDella]

The differences between China 6A and China 6B lie in more stringent emission requirements and different implementation timelines. "China 6A" serves as a transitional phase between China 5 and China 6. For light-duty vehicle emission limits, the government has established two levels of requirements: the "China 6A" phase and the "China 6B" phase, with "China 6B" representing the true "China 6" emission standard. Additionally, "China 6" adopts a fuel-neutral principle, meaning the same emission limits apply regardless of the fuel type. In contrast, during the previous "China 5" phase, diesel and gasoline vehicles had different emission standards. Implementation Timeline: China 6a and 6b are two stages of the national implementation of the China 6 standard, with different effective dates. China 6a was implemented from July 1, 2019, to July 1, 2020, while China 6b was implemented from July 1, 2020, to July 1, 2023. After July 1, 2019, most newly purchased vehicles adhered to the China 6 emission standard. However, the vehicle compliance certificate does not specify whether the vehicle meets China 6a or China 6b standards. Currently, most China 6-compliant vehicles are China 6a models, as the full implementation of China 6b requires a transitional period of several years. China's China 6 emission standard was officially released on June 28, 2018, as part of the sixth-phase vehicle pollutant emission regulation. Pilot implementation began on July 1, 2019, initially targeting heavy-duty diesel and fuel-powered vehicles. The emission standard for light-duty vehicles took effect on July 1, 2019, with nationwide implementation for all vehicles starting July 1, 2020. Specific Requirements: China 6A Emission Standard: Carbon monoxide (CO) emissions must not exceed 700mg/km; non-methane hydrocarbons (NMHC) must not exceed 68mg/km; nitrogen oxides (NOx) must not exceed 60mg/km; particulate matter (PM) must not exceed 45mg/km; and particulate number (PN) must not exceed 6×10^11mg/km. China 6B Emission Standard: For gasoline vehicles, CO emissions must not exceed 500mg/km; NMHC must not exceed 35mg/km; NOx must not exceed 35mg/km; PM must not exceed 3mg/km; and PN must not exceed 6×10^11mg/km. Data shows that China 6B significantly reduces emissions for CO, NMHC, NOx, and PM, making it the strictest emission standard to date. The China 6A emission standard is largely similar to China 5: The China 6A emission standard is essentially the same as China 5, merely adopting the strictest values from China 5's requirements. For example, China 5 limits CO emissions for gasoline vehicles to 1g/km and diesel vehicles to 0.5g/km, while China 6A sets a uniform limit of 0.5g/km for both. However, China 6a requires a 30% reduction in CO emissions compared to China 5. China 6B Standard: The "China 6B" emission standard will be mandatory from January 1, 2023. China 6b reduces CO emissions by 20% compared to China 6a, while hydrocarbons (HC) and NOx are reduced by 50% compared to China 5, and PM by 30%. Overall, except for CO and PN, which remain unchanged, China 6B's emission limits for other gases are nearly twice as strict as China 6A and significantly more stringent than China 5. The most notable change is for diesel vehicle NOx emissions: China 5's limit was 180mg/km, while China 6B's is 35mg/km—less than 20% of the former. Additionally, China 6 introduces a new limit for nitrous oxide (N2O) emissions.