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On-board measurement is a powerful method to assess vehicular exhaust gas emission, since it enables the acquisition of instantaneous raw emission values in real-world conditions. While the vehicle emissions are subject to traffic and environment fluctuations, on-board measurement is a fast and economical way to generate data for fleet emission inventories, for instance. It is part of the mandatory testing for heavy-duty vehicles in the USA, as regulated by the USEPA. In 2004, Petrobras (Brazilian Oil Company) first experienced on-board emission measurements while participating in an international joint project, whose objective was to obtain information regarding the light-duty vehicular gas emission contribution to pollutant levels in some of the major Latin-American cities.

A new on-board portable emission measurement system (PEMS) for gaseous emissions has been designed and developed to meet CFR Part 1065 requirements. The new system consists of a heated flame ionization detector (HFID) for the measurement of total hydrocarbon, a heated chemiluminescence detector (HCLD) for the measurement of NOx, and a heated non-dispersive infra-red detector (HNDIR) for the measurement of CO and CO2. The oxygen interference and relative sensitivity of several hydrocarbon components have been optimized for the HFID. The CO2 and H2O quenching effect on the HCLD have been compensated using measured CO2 and H2O concentration. The spectral overlap and molecular interaction of H2O on the HNDIR measurement has also been compensated using an independent H2O concentration measurement. The basic performance of the new on-board emission measurement system has been verified accordingly with CFR part 1065 and all of the performances have met with CFR part 1065 requirement.