Can Accurate Distance-Specific Emissions of Nitrogen Oxide Emissions from Cars Be Determined Using Remote Sensing Without Measuring Exhaust Flowrate?

Converting remote sensing NO_x/CO₂ ratios to distance-specific emission factors without exhaust flowrate measurement.

Using CO₂ type-approval and real-world fuel economy data to convert NO_x/CO₂ ratios to distance-specific emissions, at least 30 measurements are needed for ~30% accuracy compared to PEMS data, with accuracy plateauing at ~23% error beyond 300 measurements — enabling fleet screening without exhaust flowrate measurement.

Abstract

Can Accurate Distance-Specific Emissions of Nitrogen Oxide Emissions from Cars Be Determined Using Remote Sensing Without Measuring Exhaust Flowrate?

Science of the Total Environment, Vol. 816, 151500, 2022

Portable Emission Measurement Systems (PEMS) are commonly used to measure absolute (mass per unit distance) emissions of a range of pollutants from road vehicles under real driving conditions. Remote sensing devices (RSDs) can only measure emission ratios rather than absolute (distance-specific) emissions. However, distance-specific emission factors are often needed in emission inventories and transport modelling. Here we investigate whether it is possible to derive accurate distance-specific NO_x emission factors from RSDs without measuring exhaust flowrate. This is explored using CO₂ type approval data and real-world fuel economy data to convert NO_x/CO₂ emission ratios to distance-specific emissions. An analysis of the minimum number of measurements required to achieve acceptable accuracy is carried out. We show that at least 30 measurements are needed to achieve a mean absolute error of approximately 30% compared with PEMS data. The method does not introduce systematic bias and is demonstrated to be a practical approach for screening fleets of vehicles to identify those that significantly exceed air pollution standards. Accuracy plateaus at approximately 23% error when 300 or more measurements are available.

DOI