Nearly 78 percent of the air we breathe is nitrogen gas (N₂). Atmospheric N₂ is converted to nitrogen oxide by lightning, sunlight, and fossil fuel, and biomass combustion. Excessive nitrate discharge into the air and subsequent deposition into the water can negatively impact water quality. Atmospheric sources of biologically available forms of nitrogen have been linked to declines in lake transparency because different forms, such as nitrate and ammonium, provide nutrients for attached and free-floating algae. Nitrogen oxide can come from in-Basin sources such as car exhaust as well as from factory pollution far away. Regional programs such as increased transit and bike trails aim to reduce nitrate deposition into Lake Tahoe.