25 May 2023
 | 25 May 2023
Status: this preprint is currently under review for the journal AMT.

Challenges and solutions in determining dilution ratios and emission factors from chase measurements of passenger vehicles

Ville Leinonen, Miska Olin, Sampsa Martikainen, Panu Karjalainen, and Santtu Mikkonen

Abstract. Vehicle chase measurements used for studying real-world emissions apply various methods for calculating emission factors. Currently available methods are typically based on the dilution of emitted carbon dioxide (CO2) and the assumption that other emitted pollutants dilute similarly. A problem with the current methods arises when the studied vehicle is not producing CO2, e.g., during engine motoring events, such as on downhills. This problem is also encountered when studying non-exhaust emissions, e.g., from electric vehicles. In this study, we compare multiple methods previously applied for determining the dilution ratios. Additionally, we present a method applying Multivariate Adaptive Regression Splines and a new method called Near-Wake Dilution. We show that emission factors calculated with both methods are in line with the current methods with vehicles producing CO2. In downhill sections, the new methods were more robust to low CO2 concentrations than some of the current methods. The methods introduced in this study can hence be applied in chase measurements with changing driving conditions and be possibly extended to estimate non-exhaust emissions in the future.

Ville Leinonen et al.

Status: open (until 29 Jun 2023)

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Ville Leinonen et al.

Ville Leinonen et al.


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Short summary
Emission factor calculation was studied to provide models that do not use traditional CO2-based calculation in exhaust plume analysis. Two types of models, one based on physical dependency of dilution on exhaust flow rate and speed, and other two based on statistical, measured dependency of dilution on exhaust flow rate, acceleration, speed, altitude change, and/or wind, were developed. These methods could possibly be extended to calculate also non-exhaust emissions in the future.