Final answer:
Biodiesel has lower greenhouse gas emissions than petrodiesel but produces more nitrogen oxide. Its production competes with food crops for land, which can have social impacts, but it also reduces dependence on foreign oil if produced locally. The full environmental impact includes the fossil fuels used in producing the biodiesel.
Step-by-step explanation:
When comparing biodiesel to petrodiesel, biodiesel has lower greenhouse gas emissions during combustion. Biodiesel is made from plant materials such as soybeans and can also be produced from used vegetable oil. It produces less sulfur oxides, particulate matter, carbon monoxide, and unburned hydrocarbons than petrodiesel but does emit more nitrogen oxide. Still, the production of biodiesel can compete with food crops for land and resources, potentially increasing food prices and having social impacts. Using crop parts not used for food or recycled oils can mitigate this. Additionally, biodiesel production could reduce a country's dependence on foreign oil, particularly if produced locally from domestically grown crops or waste oils.
However, it's important to note that biodiesel is not entirely 'carbon neutral,' as the cultivation of the crops often involves the use of fossil fuels, and there are energy inputs required for processing the biomass into fuel. Moreover, the use of biodiesel does not deplete fossil fuel reserves directly, since it is plant-based, but the energy required for its production might partially depend on fossil fuels. Therefore, a transition to biofuels like biodiesel represents a complex trade-off between environmental benefits, such as lower carbon emissions, and potential challenges, including land use conflicts and the energetic costs associated with their production.