This paper presents a comprehensive and validated inventory of road transport emissions worldwide. The bottom-up calculation correlates within 2% and 10% with fuel sales data in Organisation for Economic Co-operation and Development (OECD) and non-OECD regions, respectively; this adds credibility to the results. The inventory covers eight exhaust compounds emitted by five vehicle categories and five fuel types each. For many non-OECD countries, road transport exhaust emissions have been calculated for the first time at this level of detail. Furthermore, this paper provides a conservative estimate of primary particulate matter emissions from diesel and gasoline vehicles. The Group of Seven countries (Canada, France, Germany, Italy, Japan, the United Kingdom, and the United States) together with Brazil, China, India, Mexico, and Russia account for more than three-quarters of all considered exhaust emissions, followed by major countries in the Middle East and Southeast Asia. Action in these 15 countries could reduce emissions for the whole region significantly. Exhaust control and maintenance can focus on motorized two-wheelers, buses, and heavy-duty trucks. The inventory is particularly suited for comparisons across countries and regions. Data uncertainties in transport volumes and real-world emissions, notably of hydrocarbon and particulate matter, should be reduced.

To improve the accuracy, reliability, and representativeness of emission factors, 10 European laboratories worked together to study the influence of 20 parameters on the measurement of light-vehicle emission factors on chassis dynamometer of 4 main categories: driving patterns, vehicle-related parameters, vehicle sampling, and laboratory-related parameters. The results are based on (1) literature synthesis, (2) approximately 2700 specific tests with 183 vehicles, and (3) the reprocessing of more than 900 tests. These tests concern the regulated atmospheric pollutants and pre-Euro to Euro 4 vehicles. Of the 20 parameters analyzed, 7 seemed to have no effect, 7 were qualitatively influential, and 6 were highly influential (gearshift strategy, vehicle mileage, ambient temperature, humidity, dilution ratio, and driving cycle). The first four of the six were able to have correction factors developed for them. The results allow for the design of recommendations or guidelines for the emission factor measurement method.

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