These fuels include coal, petroleum products such as gasoline, and natural gas. The use of these fuels has a number of harmful effects on health and the environment. According to the World Health Organization, outdoor air pollution, largely due to the burning of fossil fuels, including coal, kills at least 800,000 people each year and causes health problems for dozens of people. millions more. Technologies exist to reduce this air pollution, but their use is expensive and results in higher fuel consumption.