Emission emissions
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Emission Emissions: A Comprehensive Overview
Global Emission Projections of Particulate Matter (PM) from On-Road Vehicles
Introduction to PM Emissions
Particulate matter (PM) emissions from on-road vehicles are a significant concern for global air quality. Projections indicate that PM emissions will vary based on vehicle type, age, and regional economic conditions. The SPEW-Trend model, which incorporates detailed technology stock and superemitters, provides a comprehensive framework for these projections1.
Key Findings
- Emission Trends: Global PM emissions are projected to range from 1100 Gg to 1360 Gg by 2030, with a decrease expected until 2035 due to stricter emission standards and the phasing out of older engines1.
- Regional Variations: Emissions are expected to increase significantly in Africa due to delayed implementation of emission standards, while Asian regions will see a decreasing contribution to global totals1.
- Superemitters: Vehicles with very high emissions, or superemitters, could contribute more than 50% of global emissions around 2020, highlighting the need for targeted mitigation policies1.
Comparison of Diesel and Compressed Natural Gas (CNG) Emissions
Emission Profiles
A comparison of emissions from vehicles fueled with diesel and CNG reveals significant differences in pollutant levels. Diesel buses without after-treatment have the highest emissions of particulate matter and polycyclic aromatic hydrocarbons (PAHs), while untreated CNG buses emit higher levels of carbon monoxide, hydrocarbons, and volatile organic compounds2.
Impact of After-Treatment
Exhaust after-treatments significantly reduce emissions for both diesel and CNG buses, bringing them to similar levels. However, diesel buses equipped with traps have higher nitrogen dioxide emissions, and CNG vehicles with three-way catalysts exhibit lower nitrogen oxides (NOx) emissions2.
Emissions from Hydrogen-Powered Vehicles
Emission Analysis
Hydrogen-powered vehicles, including internal combustion engine, hybrid, and fuel cell vehicles, show varying emission profiles based on the form of hydrogen used. Gaseous hydrogen (GH2) powered fuel cell vehicles (FCVs) are the best option for reducing emissions, while liquid hydrogen (LH2) powered spark ignition internal combustion engine vehicles (SI ICEVs) have the highest emissions3.
Future Projections
By 2050, GH2 powered FCVs are expected to have the lowest CO2 emissions at 81 g/km, whereas LH2 powered SI ICEVs had the highest emissions at 416 g/km in 20103.
In-Use Emissions from Heavy-Duty Diesel Vehicles
Measurement Techniques
Emissions from heavy-duty diesel vehicles have been measured using chassis dynamometer, remote sensing, and tunnel studies. While there is reasonable agreement for NOx emissions, other pollutants show qualitative differences across measurement methods4.
Emission Trends
Over the past two decades, average emissions of particulate matter, carbon monoxide, and hydrocarbons have decreased, but NOx emissions have remained unchanged. This indicates that while PM regulations have been somewhat effective, further efforts are needed to address NOx emissions4.
Impact of Fuel Composition on Emissions
Fuel Blends and Emissions
Changes in fuel composition, such as the addition of ethanol and biodiesel to diesel, can significantly impact emissions. For instance, diesel/ethanol blends show higher reductions in NOx emissions compared to pure diesel, while ternary blends containing vegetable oil tend to increase emissions of high-weight carbonyl compounds5.
Emission Reductions
The use of oxygenate fuels like ethanol and biodiesel enhances combustion efficiency, leading to more complete combustion and reduced NOx emissions. However, CO2 emissions show varied reductions depending on the specific blend and engine load5.
Regulatory Impact on Diesel Engine Emissions
Evolution of Emission Standards
The introduction of EURO 5 and EURO 6 standards has led to significant reductions in particle emissions from diesel engines. However, increased temperatures required for these reductions have resulted in higher NOx emissions, leading to the "Diesel scandal" where some manufacturers used illegal software to manipulate test results6.
Future Outlook
Despite the challenges, diesel engines remain more energy-efficient than gasoline engines, resulting in lower CO2 emissions. Continued regulatory efforts and advancements in emission control technologies are essential for further reducing emissions from diesel engines6.
Conclusion
The research highlights the complexity and variability of vehicle emissions based on fuel type, vehicle technology, and regional factors. While advancements in emission standards and fuel compositions have led to significant reductions in certain pollutants, ongoing efforts are needed to address remaining challenges, particularly with superemitters and NOx emissions. The future of vehicle emissions will depend on continued innovation and stringent regulatory measures to ensure cleaner and more sustainable transportation.
Sources and full results
Most relevant research papers on this topic
Global emission projections of particulate matter (PM): I. Exhaust emissions from on-road vehicles
Superemitters could contribute over 50% of global emissions by 2020, highlighting the need for targeted mitigation policies.
Highly CitedA comparison of emissions from vehicles fueled with diesel or compressed natural gas.
CNG buses with after-treatment have lower emissions than diesel buses, but diesel school buses have higher CO2 emissions.
Highly CitedAn emission analysis study of hydrogen powered vehicles
Gaseous hydrogen-powered fuel cell vehicles are the best option for total emissions reduction, while liquid hydrogen-powered spark ignition internal combustion engine vehicles are the worst.
In-Use Emissions from Heavy-Duty Diesel Vehicles
Heavy-duty diesel vehicles have reduced average emissions of particulate matter, carbon monoxide, and hydrocarbons over the past two decades, but NOx emissions have not changed.
Highly CitedEmission profile of 18 carbonyl compounds, CO, CO2, and NOx emitted by a diesel engine fuelled with diesel and ternary blends containing diesel, ethanol and biodiesel or vegetable oils
Diesel/ethanol fuel blends can significantly reduce NOx emissions and CO2 emissions in diesel engines, offering a more rapid and effective alternative to fuel consumption and pollution reduction.
Highly CitedDiesel engine emissions: are they no longer tolerable?
Diesel engine emissions have significantly reduced, but air concentrations near high traffic areas still exceed limit values, causing debate on whether they are no longer tolerable.
Review of the studies on emission evaluation approaches for operating vehicles
Different measurement methods and considering influencing factors significantly impact the assessment of vehicle emissions, with new technology vehicles benefiting from multiple analysis methods.
Literature ReviewAtmospheric emissions from road transportation in India
Comprehensive inspection and maintenance of commercial vehicles is crucial to limit atmospheric pollutants from India's road transportation sector.
Highly CitedRoad vehicle emission factors development: A review
Road vehicle emission factors can be accurately estimated using various measurement techniques, but real-world data is crucial for accurate emissions inventories.
Literature ReviewHighly Cited