Unburned hydrocarbons are organic compounds that are not fully combusted during the burning of fossil fuels, such as gasoline or diesel. These compounds can be released into the atmosphere from vehicles, industrial processes, and other sources. They contribute to air pollution and can have harmful effects on human health and the environment. The presence of unburned hydrocarbons is often measured to assess the efficiency of combustion engines and to develop cleaner technologies. Reducing these emissions is important for improving air quality and meeting environmental regulations, such as those set by the Environmental Protection Agency (EPA).