Rapid economic growth, growing mobility, increasing purchasing power, and rising demand for goods have made China one of the fastest growing—and one of the largest—auto markets in the world. From 1990 to 2007, the total number of registered civil-use vehicles in China grew from 5.5 million to 57 million (not including motorcycles). The majority of these vehicles are used in populous metropolitan areas. Consequently, vehicle emissions have become an increasingly conspicuous contributor to air pollution in Chinese urban areas.

Despite the fact that China has made much progress in setting up standards regulating new vehicle emissions and fuel quality, the understanding of environmental performance of in-use vehicles has been rather poor.

Characteristics of the Tianjin fleet found by the team’s vehicle activity study included:

• The total distance traveled by all vehicles in Tianjin was about 38 million kilometers (23.6 million miles) per day. Light-duty vehicles together contributed to 82% of all distance traveled (passenger cars, 64%; taxis, 18 %), buses and trucks contributed to 11% and 8% of total distance traveled respectively.

• Most of the passenger cars were very new (less than 4 years old) and about half of them had engines with displacements of less than 1.5 liters. Most of the light-duty vehicles were equipped with multi-point fuel injection systems and three-way catalytic converters. 13% of passenger cars and 35% of taxis were still using carburetors.

• Most of the trucks and buses ran on diesel fuel and had already accumulated high mileage. Fourteen percent buses used gasoline, were equipped with carburetors, and had no any end-of-pipe emission control devices.

• The average speeds on highway, arterial, and residential roads were about 28, 22, and 15 km/h (17.4, 13.7 and 9.3 mph). Urban traffic was not smooth in the daytime, but it was particularly slow during the morning rush hours. The speed also decreased around noon and in the early evenings.

The team used remote sensing devices and on-board portable emissions measurement systems to gather data. Relying on the International Vehicle Emissions model, the researchers modified base emission factors based on their emissions testing and established vehicle emissions inventories for Tianjin:

• The Tianjin fleet generated 690 tons of CO, 84 tons of VOC, 158 tons of NO_x, 2 tons of SO_x, 6 tons of PM, and about 13.4 thousand tons of CO₂ on a typical spring day.

• Light-duty gasoline vehicles were the major contributors to CO and VOC emissions. Passenger cars accounted for 60% and 54%, and taxis accounted for 21% and 28% of all mobile VOC and CO emissions.

• Carbureted gasoline vehicles contributed to disproportionally high share of CO and VOC emissions. Carbureted light-duty vehicles accounted for only 15% of the total distance traveled, but they contributed to about one third and one half of the total mobile CO and VOC emissions. Carbureted buses accounted for only 2% of total distance traveled, but they contributed to about 16% and 12% of the total mobile CO and VOC emissions.

• Diesel trucks and buses accounted for most of the mobile PM and NO_x emissions (trucks: 44% and 27%; buses: 54% and 56%), despite that they only accounted for 8% and 11% of total distance traveled respectively.

The study yielded some important insights regarding vehicle emissions control in China, according to the study’s authors.

The most powerful policy instrument for reducing emissions from new vehicles is tightened standards. Although the rigorousness of Chinese emission standards lags considerably behind that of developed countries, China is still ahead of many of its developing country peers.

Low-end auto products in China, even newer models, often suffer from poor environmental performance. Although low-end auto products satisfy the demands of many consumers, the national government could enhance its enforcement of the product approval and certification process.

Scrapping carbureted light-duty vehicles can be an effective way to reduce CO and VOC emissions from mobile sources. Replacing carbureted taxis and personal vehicles with vehicles of similar size that are in compliance with the currant emission standards could reduce roughly a quarter of all mobile VOC emissions and one seventh of all mobile CO emissions in Tianjin. Accelerating fleet turnover rate (especially taxis and buses) will likely help improving air quality in most cities.

Replacing gasoline buses with cleaner diesel buses will lead to considerable reductions of VOC and CO levels, while replacing or retrofitting dirty, high-mileage diesel buses will lead to significant reductions of PM and NO_x emissions. To help taxi and bus companies shoulder the costs, the government may consider providing financial incentives such as subsides or tax breaks for the early retirement (or retrofitting) of dirty taxis and buses.

Inspection and Maintenance programs for in-use vehicles are weak. A considerable percentage of the light-duty vehicles made in the early 2000s could not meet their certified emission standards at the time of the study (2005), which suggests that Tianjin lacked an effective I/M program to ensure that in-use vehicles are in consistent compliance with emission standards. Questions linger as to what extent emissions tests are carried out honestly and rigorously and about how local environmental protection agencies can better supervise inspection stations.

Resources

• Oliver, Hongyan He. “In-Use Vehicle Emissions in China — Tianjin Study”. Discussion Paper 2008-08, Cambridge, Mass.: Energy Technology Innovation Policy research group, Belfer Center for Science and International Affairs, October 2008.