Urban motorcycle exhaust emissions in Vietnam: Status and technical solutions

Abstract

Vietnam's major cities experience severe air pollution with Hanoi recording PM2.5 concentration of approximately 45 µg/m³, nearly 9 times higher than the WHO guideline value. This situation is driven by 77 million motorcycles, of which 70% are over 10 years old and 94% lack emission control systems. Motorcycles account for about 76% of urban CO, 68% of HC, and 54% of NOx. The transition toward electric vehicles faces critical challenges, including 10 - 15 years of infrastructure development versus an 18-month policy deadline, battery production emissions (60 - 100 kg CO2/kWh), and coal-thermal electricity transferring pollution. This paper analyzes emission control technologies and reveals that electronic fuel injection and E10 achieve only 30 - 40% reductions while increasing NOx, whereas three- way catalytic converters demonstrate more than 85% reduction across all pollutants at significantly lower cost than immediate electric vehicle conversion. A two-phase framework is proposed: i) immediate retrofitting (2025 - 2028) supported by clean fuel supply and gas power expansion, and ii) a systematic transition (2028 - 2040) enabled by diversified clean energy infrastructure, metro networks, and green hydrogen ecosystem. Throughout both phases, coordination with the petroleum sector is emphasized to ensure energy security during the transformation.