The Coalition's Heavy-Duty Diesel Initiative defines “soot-free” buses as any fuel and vehicle combination that meets emission levels for particulate matter set by Euro VI or US 2010. This can include compressed natural gas or electric-powered buses, alongside other fuel/engine types including conventional diesel engines.
The soot-free bus fleet project is technology neutral and performance-based in order to seek the maximum feasible cost-effective solutions to black carbon control in all regions.
Diesel black carbon emissions can fall dramatically through the combined use of “soot-free” engines and cleaner fuels that are readily available today.
Not all cities can immediately purchase Euro VI engines or utilize diesel particulate filters. These technologies can be damaged if currently available fuels do not meet minimum specifications. For diesel engines the most important limiting factor is fuel sulfur content.
Cities with access to diesel fuel containing no more than 50 parts per million (ppm) fuel sulfur content can allow the operation of a Euro IV or V engine that will reduce black carbon emissions by 75% compared against a baseline Euro III vehicle. But a city with access to diesel fuel containing no more than 10 ppm sulfur content can leapfrog to soot-free engine technology at the Euro VI emission level and achieve greater than a 98% reduction in black carbon emissions compared with any previously existing engine technology.
Cities can also rapidly eliminate diesel black carbon emissions by:
- Switching to engines using compressed natural gas, electricity, biodiesel or others that achieve minimum Euro VI emissions
- Selecting engines that are the cleanest allowed by currently available fuels
- Scrapping, retrofitting, and replacing existing high-emitting diesel buses with cleaner engines that meet more stringent emission standards
New opportunities to deploy soot-free engines are emerging. Today nearly one-quarter of all cities with a population greater than 1 million have access to ultra-low-sulfur fuels (less than 15ppm diesel sulfur content).
Download: Soot-free bus Euro VI fuel availability by city
Impacts & results
The Soot-Free Urban Bus Fleet project engages cities with a population of 3 million or larger to encourage shifts to soot-free engines. Seeking out cities through regional public meetings, online and other coordinated outreach activities, the project is actively targeting 20 cities in 20 countries. Eleven of these cities are in CCAC member states.
Access to fuel determines the actions expected of cities, the following three categories define the specific commitments cities are asked to make:
- Tier 1 cities: Have access over the next three years to fuels that will allow an immediate shift to soot-free engines.
- Tier 2 cities: Have access over the next three years to Euro IV fuel, such as low sulfur fuel containing 50ppm sulfur content.
- Tier 3 cities: Are not expected to have Tier 2 status within the next three years, such as cities with diesel fuel sulfur content greater than 50 ppm.
Preliminary estimate of benefits from a shift to soot-free urban bus fleets in 20 target cities
||Black carbon reduction (Kt)
|Avoided early deaths
|Tier 1 cities
|Tier 2 cities
|Tier 3 cities