What is the difference between China 6a and China 6b standards?

[VanAustin]

The differences between China 6a and China 6b standards are as follows: 1. Carbon monoxide emissions: The China 6a standard allows no more than 700 mg per kilometer for carbon monoxide emissions, while the China 6b standard allows no more than 500 mg per kilometer; 2. Non-methane hydrocarbon content: The China 6a standard allows no more than 68 mg per kilometer for non-methane hydrocarbons, while the China 6b standard allows no more than 35 mg per kilometer; 3. Nitrogen oxide content: The China 6a standard allows no more than 60 mg per kilometer for nitrogen oxides, while the China 6b standard allows no more than 35 mg per kilometer; 4. PM particulate matter: The China 6a standard allows no more than 4.5 mg per kilometer for PM particulate matter, while the China 6b standard allows no more than 3 mg per kilometer.