Tackling nitric oxide emissions from dominant diesel vehicle models using on-road remote sensing technology

Yuhan Huang,Yat Shing Yam,Casey K.C Lee,Bruce Organ,John L Zhou,Nic C Surawski,Edward F.C Chan,Guang Hong

doi:10.1016/j.envpol.2018.09.088

Abstract

Remote sensing provides a rapid detection of vehicle emissions under real driving condition. Remote sensing studies showed that diesel nitrogen oxides emissions changed little or were even increasing in recent years despite the tightened emission standards. To more accurately and fairly evaluate the emission trends, it is hypothesized that analysis should be detailed for individual vehicle models as each model adopted different emissions control technologies and retrofitted the engine/vehicle at different time. Therefore, this study was aimed to investigate the recent nitric oxide (NO) emission trends of the dominant diesel vehicle models using a large remote sensing dataset collected in Hong Kong. The results showed that the diesel vehicle fleet was dominated by only seven models, accounting for 78% of the total remote sensing records. Although each model had different emission levels and trends, generally all the dominant models showed a steady decrease or stable level in the fuel based NO emission factors (g/kg fuel) over the period studied except for BaM1 and BdM2. A significant increase was observed for the BaM1 2.49 L and early 2.98 L models during 2005–2011, which we attribute to the change in the diesel fuel injection technology. However, the overall mean NO emission factor of all the vehicles was stable during 1991–2006 and then decreased steadily during 2006–2016, in which the emission trends of individual models were averaged out and thus masked. Nevertheless, the latest small, medium and heavy diesel vehicles achieved similar NO emission factors due to the converging of operation windows of the engine and emission control devices. The findings suggested that the increasingly stringent European emission standards were not very effective in reducing the NO emissions of some diesel vehicle models in the real world.

Highlights

Nitrogen oxides (NOx) emissions, which refer to the combination of nitric oxide (NO) and nitrogen dioxide (NO2), are one of the major pollutants in the ambient air
For light commercial diesel vehicles, the dominant models are BaM1†, BcM1 and BeM1, with 108559, 21573 and 12290 records, respectively. Their engine sizes are usually smaller than 3 L and the gross weight is within 3.5 t. These models are mostly used as light goods vehicles (LGV) in Hong Kong
This study has evaluated the NO emission factors of diesel vehicles in Hong Kong using a large remote sensing database collected in a three-year measurement program from April 2014 to April 2017

Summary

Introduction

Nitrogen oxides (NOx) emissions, which refer to the combination of nitric oxide (NO) and nitrogen dioxide (NO2), are one of the major pollutants in the ambient air. NOx emissions are usually produced from the combustion of fossil fuels via the thermal NO (or Zeldovich) mechanisms under high-temperature rich-oxygen conditions (Huang et al, 2015). Especially diesel vehicles, are the main source of NOx emissions (Anenberg et al., 2017; Font and Fuller, 2016; Suarez-Bertoa and Astorga, 2018). The majority of NOx emissions (~ 90%) from uncontrolled diesel engines are emitted as NO which will later be oxidized into secondary NO2 (Gentner and Xiong, 2017). Exposure to NOx emissions has serious adverse health effects on human respiratory systems, including increased morbidity and mortality (Amster et al, 2014). NOx emissions are strictly regulated in both air quality and automotive emission standards

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