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

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.

Re-evaluating effectiveness of vehicle emission control programmes targeting high-emitters

“…Roadside pollutant concentrations are exceeding air quality standards in many cities worldwide 1,2 . Motor vehicles, especially diesel vehicles, are the major source of air pollution in urban areas.…”

Statistical evaluation of on-road vehicle emissions measurement using a dual remote sensing technique

“…The above studies observed opposite NO emission trends due to the different fuel types concerned, i.e. gasoline and LPG vehicles in Bishop and Haugen (2018); Organ et al (2019) vs diesel vehicles in Huang et al (2018c); Pujadas et al (2017). RS studies showed that gasoline NOx reduced obviously in the past 15-20 years but diesel NOx did not reduce over the same period including those vehicles equipped with exhaust after-treatment systems for NOx control (Carslaw and Rhys-Tyler, 2013;Chen and Borken-Kleefeld, 2014).…”

“…They found that NO/CO2 of diesel vehicles did not reduce with the introduction of increasingly stringent emission standards and this trend differed greatly among various brands and engine models. Huang et al (2018c) further investigated the emission trends of the dominant diesel vehicle models in Hong Kong. They observed a significant increase of NO emissions (g/kg fuel) from one dominant model during 2005 to 2011, which was caused by the change of fuel supply system from indirect to direct fuel injection.…”

Effects of direct injection timing associated with spark timing on a small spark ignition engine equipped with ethanol dual-injection

“…The combination of nitric oxide (NO) and nitrogen dioxide (NO2) forms the nitrogen oxides (NOX) emissions which are one of the major pollutants produced by combustion [44]. In this 301 study, only NO is measured.…”