Real-world emissions in China: A meta-study of PEMS data

Published: 2018.02.12

Liuhanzi Yang

Vehicle emissions control programs in China have made considerable progress, mainly attributed to the uptake of emissions control technologies driven by increasingly stringent standards and improved fuel quality. Nevertheless, challenges remain regarding compliance with emissions standards for vehicles under real-world driving conditions. In addition to increasing amount of evidence in Europe, recent tests in China have shown that emissions under real-world driving conditions are in some instances found to be substantially higher than laboratory-certified levels. And when the large amount of data is pooled together, the trend is clearer than ever.

By collecting and pooling existing real-world emissions data from multiple sources, the ICCT was able to perform a "meta-study" to show trends of real-world emissions from China 0 to the latest China 5/V vehicles.

For light-duty vehicles, emissions standards have played an important role in reducing vehicle emissions in China. NOx, CO, and THC emissions have declined significantly as vehicle technology has improved since China 4. However, for some modern China 4 and China 5 gasoline cars, real-world NOx emissions significantly exceed type-approval limits, which can be contributed to in-use tampering, poor durability and maintenance of three-way catalytic converters.

Results from heavy-duty vehicles are more concerning - essentially no improvement in the average ratio of NOx to CO2 emissions can be observed as the emissions standard improves. Although NOx limits decreased by 56% on paper from the China I to the China IV standard, real-world NOx emissions from modern HDVs are not following the reduction pattern set by the standards. Surprisingly, some of the best and worst bus performers are from the same model produced by the same manufacturer. This suggests widespread failure to refill urea tanks in use or the removal of selective catalytic reduction systems.

The results of our PEMS meta-study indicate that advanced emissions control technologies already exist on the market, but performance in the real world varies widely. Our study further shows end-users are tampering and disabling emission control devices. Comprehensive testing procedures and robust in-use compliance programs are required to ensure the technologies work as designed in all kinds of in-use conditions.

The Chinese environmental agencies did not have a strong in-use compliance program due to lack of authority to enforce. This has changed since the amendment to China's Clean Air Law. With the enhanced authority, environmental agencies may issue vehicle emission recalls and fines on noncompliant manufacturers, which have been adopted by the US regulators for decades.

The recently released China 6 LDV emissions standards and the proposed China VI HDV standards both introduce PEMS test procedures and comprehensive in-use compliance programs. These two regulations offer a major step towards effectively controlling real-world emissions.