Newer Generation of Scooters: Polychlorinated Dibenzo-p-dioxin and Dibenzofuran and Polychlorinated Biphenyl Reductions

Jheng-Hong Chen,Lin-Chi Wang,Jau-Huai Lu,Chia-Fon Lee,Yun-Hwei Shen,Yen-Kung Hsieh,Sheng-Lun Lin,Hsi-Hsien Yang

doi:10.4209/aaqr.2020.04.0138

Abstract

ABSTRACT Scooter emissions have attracted attention in recent years because of human exposure to their direct effects in urban areas. Trace toxics, such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) have thus become important in scooter emissions. In this work, ten Tier 5 and 6 scooters were tested using a 100-second model to analyze their PCDD/F and PCB emissions and compare the results with previous Tier 3 studies. Tier 5 and 6 scooters emitted 1.86–2.91 and 0.133–0.298 pg WHO-TEQ Nm-3 of PCDD/Fs and PCBs, respectively. It was interesting to find that the PCDD/Fs were reduced by 94.6–97.4% and 99.4–99.6% in Tier 5 and 6 motors, respectively. The congener profiles of PCDD/Fs were affected by improving the emission control. The domination of highly chlorinated congeners shown in Tier 3 was reduced in Tier 5 with increases in low chlorinated PCDFs. This showed that de novo synthesis occurred and could be inhibited by the OBD system in Tier 6. The tailpipe renews reduced 60.0–93.8% of PCDD/Fs and 85.3–97.7% of PCB emissions, but several cases would still exhibit a delay for stable operation of a catalytic converter. The annual emissions of PCDD/F TEQ was calculated based on the statistics in 2019 and tested as 1.63 g WHO-TEQ. It could be 99.7% reduced to 3.55 mg by replacing all scooters with Tier 6. Consequently, the improvement of electronic fuel injection and on-board diagnostics systems from a carburetor without feedback control not only reduced the regulated pollutants but effectively reduced PCDD/F emissions.

Highlights

The rapid economic development and increasing population leads to more environmental impact by human activities
The production of carbon monoxide (CO) and HC are generally caused by incomplete combustion with unsteady air-fuel control (Yang et al, 2007; Chiang et al, 2014), while the oxidation rate of CO to CO2 was sensitively affected by the local temperature in the combustion zone (Chang et al, 2014)
There were seven Tier 5 and three Tier 6 scooters tested with a 100-second transient model to analyze the PCDD/F and polychlorinated biphenyls (PCBs) emission and compare with those from the Tier 3 motors reported in the previous study

Summary

Introduction

The rapid economic development and increasing population leads to more environmental impact by human activities. The relative health risks are in terms of pollutant emission especially in the urban area (Goel and Guttikunda, 2015; Grivas et al, 2018; Wu et al, 2020). The volatile organic carbons (VOCs) emissions are concerned in the densely populated urban area (Tsai et al, 2018b). They could be contributed by both human life activity (Que et al, 2019) and locally traffic emission, when the secondary pollutants subsequently occurs from the atmospheric chemical reactions.

Methods

Results

Conclusion