New approaches for understanding vehicle emissions using remote sensing

Despite the intense recent focus on vehicle emissions - and especially emissions of NOx, there remains considerable uncertainty over the robustness of the underlying data. Of particular importance is the uncertainty of the source contributions of different vehicles, which has many implications for local to regional direct and indirect impacts of NOx emissions. For example, policies at the local (city) scale may be misguided, ineffective and costly if certain vehicles are wrongly targeted based on poorly characterised emissions information. Similarly, underestimates of total road transport emissions will lead to erroneous modelling of regional-scale pollutants such as ozone and secondary particulate. The primary focus of this project is therefore the development of new, flexible methodologies using an unprecedented amount of new data to generate emission factors based on remote sensing data for species including NOx, NO2, CO, HC, PM and NH3.

The project will exploit the large amount of recent remote sensing (RS) measurement data available. These data include 250,000 measurements from Ricardo (CASE partner) made over 2017/2018 and new measurements to be made at the University York using an Opus RS instrument as part of this PhD project. The Opus instrument will be available at York from June 2018 as part of NERC capital investment. Additional measurements (~50,000) made by York are also available from the use of the University of Denver instrument that York has leased over the past year. Moreover, the project partners (the ICCT and IVL) will provide access to other European campaign data from Sweden, Switzerland and Spain. The data from these other organisations will provide around an additional 1 million valid emission measurements. Together, these data sets represent the most comprehensive data on real-world emissions data available in the UK, or indeed Europe, to form a robust platform from which to derive new insights.

The comprehensiveness of RS data will allow a detailed consideration of emission factors beyond simple speed-emission curves that are commonly used. Currently, emission factors used across Europe do not account for the effects of either ambient temperature or absolute humidity, which limited analysis to date show to be important influences on emissions of NOx. These data suggest for example, that emissions from light duty diesel vehicles show a strong dependence on ambient temperature and could contribute much higher emissions under cold atmospheric conditions. The project would carefully analyse comprehensive RS data to extract the independent effects of ambient temperature (and absolute humidity) to develop practical approaches to account for these effects in emission factor development.

A recent development has been the ability to link the vehicle information with vehicle mileage based on the annual MOT test for individual vehicles measured using RS. It will be possible for the first time to understand how vehicle emissions deteriorate over time and/or with vehicle mileage, which is currently a highly uncertain and potentially important issue. It is for example important to understand the robustness of complex, newer after-treatment technologies such as Lean NOx Traps and SCR. This aspect of the project would be excepted to be highly valuable for improving emission factors across Europe because most vehicle emission measurements tend to focus on measuring new vehicles rather than older vehicles. This research would include issues such as degradation effects on NO2 production in diesel catalyst systems where emissions of NO2 are believed to reduce as a vehicle ages (but is not considered in emission factors) and effects of ammonia-slip in SCR systems.