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The aim of this study is to develop an experimental approach and statistical methodology to assess the effectiveness of technological measures to improve vehicle emissions in real world use. The ultimate purpose is to provide a tool to support decisions made by public administrators and transit authorities, and assess the costs/benefits of environment-oriented investments. In this paper we report some results from the application of the proposed approach within a research project carried out by the Istituto Motori of the National Research Council of Italy, funded by the Ministry of the Environment, in cooperation with urban and extra-urban public transit companies and other public agencies. Our research focused on measuring particulate emissions in real use with and without an after-treatment device. Tests were performed in three Italian cities (Naples, Palermo and Lecce) using seven buses (homologation class EURO 0, 1 and 2) from three public local transit companies.

A 1.2 l instrumented car, equipped with an on-board acquisition system capable of detecting and recording car speed, gear, engine and catalyst operating parameters, has been tested in designed trips all over Naples urban area with different drivers. Driving cycles statistically representative of car operation under different traffic conditions in urban and expressway trips, have been determined by multivariate statistical analysis of speed and gear. Emission tests have been performed in the laboratory with car on the dynamometer chassis using defined driving cycles and engine/catalyst conditions to define emission factors for this type of car for a wide and significant spectrum of road performance.