A gas that is a byproduct of combustion reactions is carbon dioxide (CO2). When organic materials such as fossil fuels or biomass are burned, the combustion process typically converts carbon in the material into CO2, which is released into the atmosphere. While some combustion reactions also produce other gases, such as nitrogen oxides and particulates, carbon dioxide is the most significant in terms of its contribution to climate change. The increasing levels of CO2 from human activities are a primary concern for environmental and public health.