What are the environmental standards for automobiles?
2 Answers
Automobile emission standards refer to regulations on the content of harmful gases such as CO (carbon monoxide), HC+NOx (hydrocarbons and nitrogen oxides), and PM (particulate matter, soot) emitted from vehicle exhaust. Automobile emissions refer to harmful gases discharged from exhaust. These gases are produced during the combustion process in the engine. The causes of these harmful gases vary: CO is an intermediate product of incomplete fuel oxidation and is produced when oxygen is insufficient. A rich air-fuel mixture or uneven mixture distribution can increase CO emissions. HC represents unburned fuel components, resulting from uneven mixture distribution or cold combustion chamber walls causing some fuel to be discharged without complete combustion. NOx is a substance produced during the combustion of fuel (gasoline). PM is also a substance generated when fuel burns under oxygen-deficient conditions, most notably in diesel engines. Since diesel engines use compression ignition, diesel fuel is more prone to cracking under high temperature and pressure, producing large amounts of visible soot.
As someone who commutes by car every day, I've actually looked into the environmental standards. Basically, it's the threshold set by the government for vehicle exhaust emissions. The current mainstream China 6 standard is particularly strict, mainly controlling tailpipe pollutants like carbon monoxide, hydrocarbons, and nitrogen oxides. I remember all new cars must pass environmental certification before leaving the factory—those green labels from the DMV marked with China 5 or China 6 indicate the emission level. Older vehicles also get their exhaust tested during annual inspections; my neighbor's car recently failed and was required to undergo repairs due to excessive emissions. If you buy a new energy vehicle, there are basically no emission issues, but for traditional fuel vehicles, you'd better make sure it meets China 6 standards to be safe.
