What are good things about mercury (gas), sulfur dioxide, and nitrogen oxide?
Mercury vapor is widely used in lighting applications. Fluorescent lamps and ultraviolet lamps rely on mercury vapor. Sulfur dioxide is an important precursor to sulfuric acid, the most widely produced industrial chemical. Sulfur dioxide is also used as a food preservative. Finally, sulfur-oxidizing and -reducing bacteria use sulfur dioxide as an intermediate between sulfate and sulfur or sulfide. Nitrogen oxides are an important form of fixed nitrogen in the environment. In addition to human sources, they are produced by lightning. Nitrogen oxides react with water and oxygen to form nitric and nitrous acid, which dissolve in rain. This introduces fixed nitrogen into ecosystems. Nitric oxide is also an important signaling molecule in many organisms, including humans. The drug Viagra works by boosting production of this molecule. Nitrous oxide is used as a propellant in aerosol cans, especially whipped cream, and is also used as a sedative in medicine and dentistry.
