Effective emissions reduction of high-mileage fleets through a catalytic converter and oxygen sensor replacement program

Yuhan Huang; Casey K C Lee; Yat-Shing Yam; John L Zhou; Nic C Surawski; Bruce Organ; Chengwang Lei; Ho Kyong Shon

doi:10.1016/j.scitotenv.2022.158004

Effective emissions reduction of high-mileage fleets through a catalytic converter and oxygen sensor replacement program

Sci Total Environ. 2022 Dec 1:850:158004. doi: 10.1016/j.scitotenv.2022.158004. Epub 2022 Aug 12.

Authors

Yuhan Huang¹, Casey K C Lee², Yat-Shing Yam², John L Zhou³, Nic C Surawski¹, Bruce Organ⁴, Chengwang Lei⁵, Ho Kyong Shon⁶

Affiliations

¹ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW 2007, Australia.
² Environmental Protection Department, Hong Kong Special Administrative Region Government, Hong Kong.
³ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW 2007, Australia. Electronic address: junliang.zhou@uts.edu.au.
⁴ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW 2007, Australia; Jockey Club Heavy Vehicle Emissions Testing and Research Centre, Vocational Training Council, Hong Kong.
⁵ Centre for Wind, Waves and Water, School of Civil Engineering, The University of Sydney, NSW 2006, Australia.
⁶ ARC Research Hub in Nutrients in a Circular Economy, School of Civil and Environmental Engineering, University of Technology Sydney, NSW 2007, Australia.

PMID: 35970469
DOI: 10.1016/j.scitotenv.2022.158004

Abstract

High-mileage vehicles such as taxis make disproportionately large contributions to urban air pollution due to their accelerated engine deterioration rates and high operation intensities despite their small proportions of the total fleet. Controlling emissions from these high-mileage fleets is thus important for improving urban air quality. This study evaluates the effectiveness of a pilot repair program in reducing emissions from taxis in Hong Kong which account for about 2 % of the total licensed vehicles. The emission factors of a large sample of 684 in-service taxis (including 121 for an emission survey program and 563 for a pilot repair program) were measured on transient chassis dynamometers. The results showed that 63 % of the sampled taxis failed the driving cycle test before the pilot repair program. Most of failed taxis were NO related and 91 % of failed taxis exceeded the emission limits of at least two regulated pollutants simultaneously. After the pilot repair program by replacing catalytic converters and oxygen sensors, the failure rate was significantly reduced to only 7 %. In addition, the fleet average NO, HC and CO emission factors were reduced by 85 %, 82 % and 56 %, respectively. In addition, on-road remote sensing measurements confirmed the real-world emission reductions from the taxis that participated in the pilot repair program. These findings led to the implementation of a large-scale replacement program for all taxis in Hong Kong during 2013-2014, which was estimated to have reduced the total HC, CO and NO emissions by about 420, 2570 and 1000 t per year, respectively (equivalent to 5-8 % emission reductions from the whole road transport sector). Therefore, reducing emissions from the small high-mileage fleets is a highly cost-effective measure to improve urban air quality.

Keywords: Emission factors; High-mileage fleet; Inspection and maintenance; Transient chassis dynamometer; Urban air pollution.

MeSH terms

Air Pollutants* / analysis
Air Pollution*
Environmental Monitoring / methods
Motor Vehicles
Oxygen
Vehicle Emissions / analysis
Vehicle Emissions / prevention & control

Substances

Air Pollutants
Vehicle Emissions
Oxygen