Emission ratio determination from road vehicles using a range of remote emission sensing techniques

Naomi J Farren; Christina Schmidt; Hannes Juchem; Denis Pöhler; Shona E Wilde; Rebecca L Wagner; Samuel Wilson; Marvin D Shaw; David C Carslaw

doi:10.1016/j.scitotenv.2023.162621

Emission ratio determination from road vehicles using a range of remote emission sensing techniques

Sci Total Environ. 2023 Jun 1:875:162621. doi: 10.1016/j.scitotenv.2023.162621. Epub 2023 Mar 5.

Authors

Naomi J Farren¹, Christina Schmidt², Hannes Juchem³, Denis Pöhler⁴, Shona E Wilde⁵, Rebecca L Wagner⁵, Samuel Wilson⁵, Marvin D Shaw⁶, David C Carslaw⁵

Affiliations

¹ Wolfson Atmospheric Chemistry Laboratories, University of York, YO10 5DD, UK. Electronic address: naomi.farren@york.ac.uk.
² Airyx GmbH, Justus-von-Liebig-Str. 14, 69214 Eppelheim, Germany; Institute of Environmental Physics, University of Heidelberg, INF 229, 69120 Heidelberg, Germany.
³ Institute of Environmental Physics, University of Heidelberg, INF 229, 69120 Heidelberg, Germany.
⁴ Airyx GmbH, Justus-von-Liebig-Str. 14, 69214 Eppelheim, Germany.
⁵ Wolfson Atmospheric Chemistry Laboratories, University of York, YO10 5DD, UK.
⁶ Wolfson Atmospheric Chemistry Laboratories, University of York, YO10 5DD, UK; National Centre for Atmospheric Science, University of York, YO10 5DD, UK.

PMID: 36878292
DOI: 10.1016/j.scitotenv.2023.162621

Abstract

The development of remote emission sensing techniques such as plume chasing and point sampling has progressed significantly and is providing new insight into vehicle emissions behaviour. However, the analysis of remote emission sensing data can be highly challenging and there is currently no standardised method available. In this study we present a single data processing approach to quantify vehicle exhaust emissions measured using a range of remote emission sensing techniques. The method uses rolling regression calculated over short time intervals to derive the characteristics of diluting plumes. We apply the method to high time-resolution plume chasing and point sampling data to quantify gaseous exhaust emission ratios from individual vehicles. Data from a series of vehicle emission characterisation experiments conducted under controlled conditions is used to demonstrate the potential of this approach. First, the method is validated through comparison with on-board emission measurements. Second, the ability of this approach to detect changes in NO_x / CO₂ ratios associated with aftertreatment system tampering and different engine operating conditions is shown. Third, the flexibility of the approach is demonstrated by varying the pollutants used as regression variables and quantifying the NO₂ / NO_x ratios for different vehicle types. A higher proportion of total NO_x is emitted as NO₂ when the selective catalytic reduction system of the measured heavy duty truck is tampered. In addition, the applicability of this approach to urban environments is illustrated using mobile measurements conducted in Milan, Italy in 2021. Emissions from local combustion sources are distinguished from a complex urban background and the spatiotemporal variability in emissions is shown. The mean NO_x / CO₂ ratio of 1.61 ppb/ppm is considered representative of the local vehicle fleet. It is envisaged that this approach can be used to quantify emissions from a range of mobile and stationary fuel combustion sources, including non-road vehicles, ships, trains, boilers and incinerators.

Keywords: Plume chasing; Point sampling; Regression; Remote sensing; Vehicle emissions.