Earth’s atmosphere primarily contains oxygen gas and nitrogen gas, which collectively contribute to 99% of atmospheric composition.  The remaining 1% varies considerably depending on historical land uses, nearby emissions sources, and local carbon sinks.  Despite their relative diffusion, greenhouse gases and other pollutants significantly impact atmospheric chemistry and climate conditions.  In small quantities, gases like carbon dioxide and methane provide a protective layer around the Earth, trapping heat and warming the planet to a degree suitable for life.  However, rising greenhouse gas emissions from human activities cause higher temperatures, rising sea levels, and more frequent extreme weather events, destabilizing the climate system and endangering biodiversity.  The most prevalent greenhouse gases - carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons - are emitted from agriculture, deforestation, industrial activities, transportation, and residential and commercial buildings.