Fossil fuels are the primary source of energy for most of the world, however they are also one of the biggest sources of pollution. Coal, oil and natural gas are the three main fossil fuels, and their combustion is responsible for the majority of air pollutant emissions. Coal is the most polluting, releasing more carbon dioxide, sulfur dioxide and nitrogen oxides than oil or natural gas. Other pollutants associated with fossil fuel use include mercury, lead, and particulate matter. Efforts to reduce emissions from fossil fuels will be critical to reducing air pollution and achieving a sustainable energy future.
An ecosystem is a community of living organisms and the nonliving components that interact with one another. Interaction in an ecosystem is the process by which organisms of the same or different species interact with each other and their environment. Examples of interactions in an ecosystem include competition for resources, predation, parasitism, mutualism and commensalism. Interactions can also occur between organisms and their abiotic environment, such as climate, soil, and water. Understanding the interactions of species in an ecosystem is critical for conserving and managing the environment.