Greenhouse Gas Emissions (CO2)

1. Definition and Emission Characteristics

Automotive carbon dioxide (CO₂) emissions refer to greenhouse gases released into the atmosphere when carbon in fuel oxidises during the combustion process of motor vehicles. CO₂ is the most prevalent greenhouse gas in vehicle exhaust, and its emissions correlate directly and positively with fuel consumption. Unlike pollutants such as carbon monoxide and nitrogen oxides, CO₂ itself poses no direct acute toxicity to humans; however, as the primary greenhouse gas, its atmospheric accumulation is the key driver of global warming, rising sea levels, and increasingly frequent extreme weather events.

2. Emission Volume and Contribution Proportion

Vehicle CO₂ emissions are substantial. An average passenger car clocking around 15,000 km annually emits roughly 5.2 tonnes of CO₂. On a full life cycle basis (encompassing raw material extraction, vehicle manufacturing, usage, and end-of-life scrapping), a petrol passenger car sold in 2021 generates approximately 39.7 tonnes of lifetime carbon emissions, compared to around 22.4 tonnes for a battery electric vehicle (BEV)—just 56% of its petrol counterpart. On a macro level, highway motor vehicle CO₂ emissions in Kunming alone hit 2.576 million tonnes in 2021, accounting for over 98% of the area's total vehicular greenhouse gas emissions.

3. Main Factors Influencing Emissions

• Fuel Type and Consumption: CO₂ emissions are directly dictated by fuel carbon content and consumption rates. Petrol vehicles produce higher carbon intensity than equivalent diesel models, whilst fully electric vehicles boast zero tailpipe emissions during the driving phase, effectively shifting emissions upstream to power generation.

• Driving Conditions and Vehicle Speed: For passenger cars, the CO₂ emission factor is lowest (optimum fuel economy) at cruising speeds of around 80 km/h. It spikes sharply in low-speed, stop-and-go driving conditions, and climbs progressively higher as vehicle speeds exceed 80 km/h.

• Vehicle Technology and Emission Standards: Vehicles adhering to older standards like China IV were previously the primary contributors to greenhouse gas emissions. As regulatory standards advanced (e.g. China 6b), per-vehicle CO₂ reduction and emission control have progressively improved.

4. Control Technologies and Emission Reduction Strategies

• The Double-Edged Nature of Exhaust Aftertreatment: Three-way catalytic converters convert harmful CO and HC into CO₂, which mitigates toxic pollutant emissions but inherently increases direct CO₂ output.

• Deceleration Fuel Cut-Off (DFCO): Electronic fuel injection (EFI) engines automatically cut fuel delivery during off-throttle deceleration (engine speeds above ~1,500 rpm with accelerator released), instantaneously dropping CO₂ emissions to zero. Tests show that leveraging DFCO properly can reduce CO₂ emissions by around 4%.

• Electrification and Alternative Energy: Pure electric vehicles deliver significantly lower operational carbon emissions compared to internal combustion engine (ICE) vehicles, achieving a life cycle carbon reduction of over 43%.

• Life Cycle Carbon Management: China has rolled out its first automotive carbon management standards (QC/T 1248—2025 and QC/T 1249—2025), mandating full life cycle carbon footprint quantification for road vehicles and passenger cars across raw materials, manufacturing, in-use driving, and end-of-life disposal.

5. Development Trends

• Tighter Emission Regulations: A key shift in the upcoming China 7 standards under formulation is the transition from "isolated pollutant control" to "synergistic control of pollutants and greenhouse gases", bringing CO₂ into a unified regulatory framework.

• Carbon-Neutral Fuels and On-Board Carbon Capture: Automakers such as Mazda have trialled on-board CO₂ capture systems in motorsport environments, using porous materials like zeolite to adsorb exhaust CO₂ and exploring the viability of capturing carbon while driving.

• Standardised Life Cycle Auditing: International initiatives like SBTi require carmakers to report Scope 3 emissions based on a Well-to-Wheel (WTW) life cycle framework, factoring in electricity grid emissions and indirect land-use change (ILUC) from biofuels.