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Buses, despite being known for being a 'green' way to travel, run on one of the most polluting and dangerous fuels we use: Diesel. There is a movement in the United States to convert buses to cleaner fuels to reduce greenhouse gas emissions. these are some examples of clean alternative fuels that can be used in one of the most popular forms of public transit.

Diesel
Currently 90% of buses in the United States run on Diesel fuel. Diesel produces high amounts of some of the most dangerous air pollutants, nitrogen oxides and particulate matter. These are extremely hazardous to people's respiratory health Vehicles that run on Diesel in the United States are required to run on Ultra-low sulfur diesel, but they still are producing hazardous amounts of air pollutants. Because biodiesel produces fewer pollutants than petroleum based diesel, if these buses were converted to the alternative fuel Biodiesel, the pollutants they would create would be significantly reduced.

Types of Diesel Fuels
Biodiesel is essentially Diesel produced by renewable sources rather than non-renewable fossil fuels. There are several plants that can be used to create Biodiesel, but the most popular is rapeseed, which is also used to make canola oil. There are two popular blends of Biodiesel, the first being B100 (100% Biodiesel) and the second being B20 (20% Biodiesel). B100 is cleaner than B20, but it requires modifications to replace tubing and other parts with ones that can handle the corrosiveness of Biodiesel. B20 does not require any modifications to the car, but it may cause parts to become corroded quicker, at which point it would be advisable to replace them with parts that resist corrosion.

Cleanliness of Biodiesel
While ULSD Vehicles produce between 10 and 15 parts per million (ppm) of sulfur oxides, a study done by the EPA has shown that B100 produces only extremely minute amounts. Biodiesel also produces also about 2/3 fewer Hydrocarbon emissions, and 1/2 less particulate matter and carbon monoxide compared to regular Diesel.

Natural Gas
Natural Gas is one of the most popular alternative fuels. It produces 75% fewer pollutants and 35% fewer Greenhouse Gas emissions. As many as 90,000 buses in the United States run on natural gas. Not only is it cleaner than gasoline, 87% of it comes from the US. Since so much of the natural gas we use does not have to be imported from other countries, it costs around $1.78 per gallon.

Ethanol
Ethanol is another popular alternative fuel because of its relative ease of production, and also because of the attention it has received from the media. It is produced by fermenting corn. The alcohol made is called Ethanol. Several American cars have been designed with the option of running on E85 (a blend of 85% ethanol and 15% gasoline). Along with Natural Gas, Ethanol is the most popular alternative fuel option for buses.

Ethanol has received lots of praise, but it has also received plenty of criticism. The amount of corn that would be needed to make enough ethanol to power every car in the United States alone would use almost all the corn produced in America. This is why, despite being touted as the solution to America's fuel crisis, Ethanol has fallen off in popularity as of late.

Electricity
There are two types of electricity as a fuel. One is battery power, such as that used by the Toyota Prius, which is not used by buses due to the lack of power and endurance. The more popular one is electricity produced by Hydrogen Fuel Cells. These fuel cells produce electricity to power the vehicle's motor without creating any pollution. In fact, the only emission given off by a hydrogen fuel cell is water.