On-road vehicle emissions remote sensing
The ICCT commissioned this guidance document to inform policy makers of good practices in vehicle remote sensing (RS). Its purpose is to educate policy makers about RS applications, reflect upon their results, interpretation, and possible limitations, and identify the most relevant literature for further reading.
Remote sensing devices routinely measure CO2, CO, HC as propane equivalents, NO, and opacity. The latest RS devices also measure NO2, NH3 and SO2. In particular, the simultaneous measurement of NO and NO2 is highly desirable for an accurate determination of total NOx emissions from diesel vehicles with modern after-treatment devices. Black carbon emissions can be calculated based on opacity readings in the infrared and ultraviolet wavelengths.
Remote sensing is an excellent tool for monitoring average on-road fleet emissions, as its large sample volume under real-driving conditions provides very accurate results. However, results for individual vehicles are coarse and do not substitute for single vehicle tests.
On-road screening via RS can help to increase the effectiveness of an inspection and maintenance (I/M) scheme by identifying high emitters and exempting clean vehicles from mandatory inspection. In areas with no testing infrastructure, on-road testing can be at least an initial step toward encouraging maintenance and controlling high emitters.
Given the durability and low emission levels of modern vehicles, scheduled annual or biennial inspection of the whole fleet does not appear the best choice any longer. Further, it has been shown that off-cycle emissions have higher shares. Therefore more comprehensive coverage of real-world driving conditions in I/M programs and in new-vehicle certification driving cycles should be considered. Remote sensing measurements have helped to identify the relative importance of vehicle-specific power ranges for on-road emissions.
Results from RS emission testing could become more compelling with a clear mandatory status. So far, participation in voluntary repair or scrappage programs (as in California or Texas) has been low. While RS technology has proven its potential, its actual impacts on pollutant reductions strongly depend on the program set-up and implementation, as well as integration with other clean vehicle programs.
Staff contact: Cristiano Façanha